Intraspecific Variation in the Information Content of an Ornament: Why Relative Dewlap Size Signals Bite Force in Some, But Not All Island Populations of Anolis sagrei

Intraspecific Variation in the Information Content of an Ornament: Why Relative Dewlap Size... Abstract In many animals, male secondary sexual traits advertise reliable information on fighting capacity in a male–male context. The iconic sexual signaling device of anole lizards, the dewlap, has been extensively studied in this respect. For several territorial anole species (experiencing strong intrasexual selection), there is evidence for a positive association between dewlap size and bite capacity, which is an important determinant of combat outcome in lizards. Intriguingly, earlier studies did not find this expected correlation (relative dewlap size–relative bite force) in the highly territorial brown anole lizard, Anolis sagrei. We hypothesize that the dewlap size–bite force relationship can differ among populations of the same species due to interpopulation variation in the degree of male–male competition. In line with this thought, we expect dewlap size to serve as a reliable predictor of bite performance only in those populations where the level of intrasexual selection is high. To tackle this hypothesis, we examined the relationship between male dewlap size and bite force on the intraspecific level in A. sagrei, using an extensive dataset encompassing information from 17 island populations distributed throughout the Caribbean. First, we assessed and compared the relationship between both variables in the 17 populations under study. Second, we linked the relative dewlap size–bite force relationship within each population to variation in the degree of intrasexual selection among populations, using sexual size dimorphism and dewlap display intensity as surrogate measures. Our results showed that absolute dewlap size is an excellent predictor of maximum bite force in nearly all A. sagrei populations. However, relative dewlap size is only an honest signal of bite performance in 4 out of the 17 populations. Surprisingly, the level of signal honesty did not correlate with the strength of intrasexual selection. We offer a number of conceptual and methodological explanations for this unexpected finding. Introduction The evolution of male secondary sexual traits, such as the colossal antlers in deer or the giant horns in rhinoceros beetles, has fascinated biologists ever since Darwin (1871; Andersson 1982; Bradbury and Vehrencamp 1998; Emlen 2008). These elaborate sexual traits can function as real weapons to overpower or even kill male opponents (e.g., mandibles of male fig wasps; Bean and Cook 2001), but also as reliable signals advertising “fighting capacity” without playing a role during actual physical combats (e.g., red coloration in male mandrills; Setchell and Wickings 2005). Traits that honestly signal fighting capacity seem highly beneficial to predict contest outcomes and thereby avoid the costly interactions physical combats may impose (Andersson 1994). This is especially true for species where actual fights between males can result in serious body damage and even in death (e.g., wasps, Bean and Cook 2001; Abe et al. 2003; spiders, Leimar et al. 1991). The idea that male secondary sexual signals communicate reliable information about quality in an intrasexual context has been evidenced by a variety of studies showing a direct link between variation in signal design (especially size and color) and the ability to win male contests (e.g., Jennions and Backwell 1996; Panhuis and Wilkinson 1999; Alonso-Alvarez et al. 2004). In many cases, the size of these sexual traits correlates strongly with overall body size (arguably the most important predictor of contest outcome (e.g., Clutton-Brock et al. 1979; Hughes 1996; Karsten et al. 2009; Hardy and Briffa 2013), and as such acts as a redundant or back-up signal (Zuk et al. 1992; Johnstone 1996; Candolin 2003) when advertising fighting capacity. However, in at least some cases, the size of secondary sexual traits reveals more than just the carrier’s overall body size during agonistic interactions. Here, sexual signal size contains information on fighting capacity independent of overall body size (i.e., relative size), and can therefore be considered as a reliable signal in itself. In dung beetles, for example, relative male horn size accurately predicts pulling force and maximal exertion, two ecologically relevant performance measures associated with fighting success in beetles (Lailvaux et al. 2005). Also in lizards, male signals can act as size-free indices of fighting capacity, quantified by endurance or bite force (e.g., Perry et al. 2004; Lappin and Husak 2005; Vanhooydonck et al. 2005a). Anole lizards in particular have received considerable attention in this respect (e.g., Lailvaux et al. 2004; Vanhooydonck et al. 2005b; Lailvaux and Irschick 2007). They typically have an extendible throat fan, called a dewlap. This sexually selected trait is generally far more elaborated in the male sex and is exceptional for its high degree of interspecific variation in design (Nicholson et al. 2007; Johnson and Wade 2010). Besides, anoles exhibit varying degrees of territoriality and male–male competition (Losos 2009; Johnson et al. 2009; Kamath and Losos 2017), also reflected by their remarkable diversity in sexual size dimorphism (SSD; i.e., predominantly male-biased SSD) (Stamps et al. 1997; Ord et al. 2001; Butler et al. 2007). One obvious question that arises is whether dewlap size indicates fighting capacity in Anolis lizards? The evidence is rather mixed. In highly territorial, sexually dimorphic (high-SSD) species (i.e., A. carolinensis, A. cristatellus, A. evermanni, A. gundlachi, and A. lineatopus), relative dewlap size predicts bite force and thus seems to contain detailed information on fighting capacity (Vanhooydonck et al. 2005a; Lailvaux and Irschick 2007). However, no such relationship was found in less dimorphic (low-SSD) species (i.e., A. angusticeps, A. distichus, and A. valencienni; Vanhooydonck et al. 2005a; Lailvaux and Irschick 2007). The authors explain the lack of this relation in less dimorphic species preliminary by a low degree of territoriality. Bite performance, in particular, might be far less important for males of species that do not actively defend territories or that do not experience a high degree of male–male competition associated with vigorous fights. Lailvaux and Irschick (2007) further corroborated this idea by showing that bite force predicted male combat success only in the high-SSD species and that the incidence of biting increased with SSD. Intriguingly, one species in their dataset defied this putative principle: Anolis sagrei, albeit clearly sexually dimorphic, did not show the expected positive correlation between relative dewlap size and bite performance (although a significant relationship was found between absolute dewlap size and bite force). In accordance, Driessens et al. (2015) also failed to find such a relationship in wild-caught males from Florida, when looking at relative indices. Because of these unexpected results, we aimed to further explore the dewlap size–bite force relationship in this polygynous and highly territorial species (Schoener and Schoener 1980; Tokarz 1998, 2002). Direct physical combats are commonly observed among brown anole males and primarily involve biting, jaw sparring, and interlocking (Scott 1984; Tokarz 1985, 1987; McMann 2000; Steffen and Guyer 2014; Driessens et al. 2014). Anolis sagrei has a yellow-to-reddish dewlap that can show dramatic intraspecific variation in size, color, pattern, and even use (Vanhooydonck et al. 2009; Edwards and Lailvaux 2012; Driessens et al. 2017). Adult males primarily use dewlap displays in combination with push-ups and head-bobs for territorial defense and/or for access to females (e.g., Scott 1984; Simon 2011; Driessens et al. 2014). Recently, display behavior and dewlap color have been reported to predict the outcome of staged contests between size-matched males (Steffen and Guyer 2014), further demonstrating the role of the A. sagrei dewlap in signaling quality to opponents (but see Tokarz et al. 2003). Close-proximity contest experiments additionally revealed that A. sagrei males with enhanced biting capacities are at a competitive advantage for winning fights (Lailvaux and Irschick 2007), highlighting the importance of signaling bite capacity too, during agonistic interactions. The main goal of this study is to look in more detail at the relationship between male dewlap size and bite force, explicitly for A. sagrei. Therefore, we took an intraspecific comparative approach, documenting and comparing this specific relationship in 17 A. sagrei island populations distributed across the Caribbean. We looked at the relationship between dewlap size and bite force, using absolute as well as relative indices. Consistent with previous studies, we expected absolute dewlap size to be a good predictor of absolute bite force for each study population (Lailvaux and Irschick 2007; Cox et al. 2009; Driessens et al. 2015). However, we hypothesize that the relative dewlap size–bite force relationship will differ among populations due to interpopulation variation in the degree of male–male competition. In line with this thought, we expect dewlap size to serve as a reliable predictor of bite performance only in those populations where the level of intrasexual selection is high (following Lailvaux and Irschick 2007). To do so, we linked the dewlap size–bite force relationship within each population to both SSD and display intensity (DI) among populations, taking into account phylogenetic relationships. Materials and methods Animals We sampled a total of 639 adult A. sagrei males from 17 populations distributed across the Caribbean (Fig. 1). Sampling localities included Acklins, Andros, Chub Cay, Crooked Island, Grand Bahama, Pidgeon Cay, Staniel Cay (data collection for these seven populations occurred in April–May 2003), Jamaica (March 2012), Cuba (Santa Clara, Soroa 1, Soroa 2; April–May 2012), San Salvador (January 2013), Cayman Islands (Cayman Brac, Grand Cayman, Little Cayman; March 2013), South Abaco, and South Bimini (March 2015). Since previous studies on A. carolinensis have reported a significant effect of seasonality on dewlap size, bite force, and display behavior (Jenssen et al. 1995, 2001; Irschick et al. 2006; Lailvaux et al. 2015), data were collected during the A. sagrei breeding season (March–September, Lee et al. 1989), apart from one population (i.e., San Salvador) that was sampled in January. We caught 404 A. sagrei males by noose and kept them individually in plastic bags for maximum 48 h, before releasing them back at the location of capture. For these individuals, we measured morphology, quantified dewlap size, and carried out standard bite force measurements. Another 235 male individuals (but only for ten populations) were video-recorded while behaving in their natural habitat. Fig. 1 View largeDownload slide (a) Phylogenetic relationships among the 17 Anolis sagrei study populations presented with corresponding sampling sites (b) distributed across the Caribbean. Circle size represents the mean dewlap size (red) and bite force (blue) of a population. Photograph (c) showing the large dewlap of a male A. sagrei lizard. Fig. 1 View largeDownload slide (a) Phylogenetic relationships among the 17 Anolis sagrei study populations presented with corresponding sampling sites (b) distributed across the Caribbean. Circle size represents the mean dewlap size (red) and bite force (blue) of a population. Photograph (c) showing the large dewlap of a male A. sagrei lizard. Morphology We measured the lizards’ snout–vent length (SVL) and head length (HL; from the tip of the snout to the posterior edge of the parietal scale) using digital calipers (Mitutoyo CD-15DC, accuracy 0.01 mm). For measuring dewlap size, lizards were first positioned on their left side against a 1-cm2 gridded paper. We then gently pulled the base of the ceratobranchial forward with a pair of forceps until the dewlap was fully extended parallel to the grid (Bels 1990). Next, we photographed the dewlap, using a Nikon D70 camera mounted on a tripod. Last, Adobe Photoshop CS3 extended software (AP CS3, version 10.0) was used to trace the outer edge of the dewlap on the digital images and to calculate absolute dewlap area. This standard method for measuring dewlap dimensions has produced highly repeatable results in a previous study (Vanhooydonck et al. 2005a). Bite force Standard methods were used to measure maximum bite force. Briefly, we encouraged lizards to bite on two metal plates connected to an isometric Kistler force transducer (type 9203) and charge amplifier (type 5995); for detailed descriptions of setup and biting procedure, see Herrel et al. (1999a) and Vanhooydonck et al. (2005b). Each individual was subjected to a total of five bite trials with approximately 30 min in between (as in e.g., Herrel et al. 2001; Lailvaux et al. 2004; Irschick et al. 2006; Lailvaux and Irschick 2007). The highest of the five bite force measurements was then used as the maximal bite force capacity in each individual. The applied methodology has been widely used and shown to be effective for obtaining maximal bite forces in lizards (e.g., Herrel et al. 2001; Lailvaux et al. 2004; Vanhooydonck et al. 2005b; Lailvaux and Irschick 2007; Baeckens et al. 2017). Since temperature is known to affect bite performance (Bennett 1985; Herrel et al. 1999b; Anderson et al. 2008), we made sure every lizard had a body temperature between 29°C and 31°C prior to every bite trial (the average field-active body temperature of A. sagrei is 30.6°C; Losos 2009). Body temperature was verified using a cloacal thermometer (APPA51, K-type). Sexual size dimorphism Consistent with Lailvaux and Irschick (2007, and references therein), we calculated SSD as mean SVL in males divided by mean SVL in females. Values of SSD were calculated for each population, and only SVLs of mature males and females were included. Display intensity As in Driessens et al. (2017), we recorded the natural behavior of 20–30 males per population (ten study populations) for a timespan of 10 min, using a high-definition camera (Sony, HDR-CX260VE). First, we located lizards by walking slowly through their natural habitat until an apparently undisturbed individual was spotted. Next, we started filming the lizard’s behavior from approximately 5–15 m using the camera zoom function (30× optical zoom), in order to minimize disturbances caused by our presence. Video recordings were only made during sunny or partly cloudy conditions to avoid possible confounding effects of weather on the lizard’s activity level (Huey 1982; Hertz et al. 1993). All behavioral recordings were scored offline, using JWatcher event-recorder software (Blumstein and Daniel 2007). For each focal individual, we noted the number and duration of three main display types: head-nods (up-and-down movement of the head), push-ups (up-and-down movement of the body and tail caused by flexion of the legs), and dewlap extensions (pulsing of the dewlap). These displays can function in species recognition (e.g., Rand and Williams 1970; Losos 1985), in predator deterrence (e.g., Leal and Rodríguez-Robles 1995, 1997), but most often in social and sexual communication (e.g., Greenberg and Noble 1944; Jenssen 1970; Crews 1975; Carpenter 1978; Driessens et al. 2014; Baeckens et al. 2016). Moreover, DI is typically inter-correlated in the sense that males that frequently perform one display type also exhibit the other types at a high rate (e.g., Scott 1984; McMann 2000; Driessens et al. 2014; Steffen and Guyer 2014). In the remaining, “DI” refers to the proportion of time that individuals spent displaying in their natural setting during the 10 min observation period (averaged per population). Statistical analyses Prior to statistical analyses, data on HL, dewlap size, bite force, and SSD were log10-transformed. Proportion data (i.e., DI) were normalized via arcsin-square root transformation (Sokal and Rohlf 1995). In all cases, assumptions of normality were confirmed using Shapiro–Wilk tests, and probabilities (P) lower than 0.05 were considered significant. All statistical tests involving dewlap size and bite force were done with absolute as well as relative (i.e., size-corrected) data. Consistent with Vanhooydonck et al. (2005a) and Lailvaux and Irschick (2007), we used HL for removing effects of overall size. This metric strongly correlated with dewlap size and bite force, and has previously proven to be most appropriate for calculating relative indices of these two variables (Vanhooydonck et al. 2005a; Herrel and O’Reilly 2006). Relative bite force and dewlap size were calculated by regressing log10 bite force and log10 dewlap size against log10 HL and, subsequently, by extracting the residual values for all individuals. We first ran a univariate general linear model (GLM) to test whether the relationship between dewlap size and bite force (independent and dependent variable, respectively) differed among our study populations. HL was then added to the model as a covariate, to assess the same effects after size correction. Both GLM analyses revealed significant dewlap size * population interaction effects on bite force, which impelled us to subsequently examine this relationship separately within populations. We therefore carried out linear regressions per population with dewlap size as independent and bite force as dependent variable. Following Lailvaux and Irschick (2007), we obtained relative indices by regressing dewlap size and bite force against HL and calculating the residuals for all individuals per population. We then ran a second set of linear regressions, this time with relative bite force against relative dewlap size (i.e., residuals; consistent with Vanhooydonck et al. 2005a; Lailvaux and Irschick 2007). Among-population analyses were performed in an explicit phylogenetic context in order to account for the non-independency of our data points (Felsenstein 1985; Harvey and Pagel 1991). We used the phylogenetic tree proposed by Driessens et al. (2017) in all phylogenetic comparative analyses. Driessens’ tree was created using the exact same populations sampled in this study. To test the idea that reliable information content of the dewlap in itself depends on the local intensity of intrasexual selection, we regressed the slope of the relative “dewlap size–bite force” regression line for each population (i.e., coefficient b) against SSD and DI, respectively. We here employed phylogenetic generalized least squares (pgls) regressions with incorporation of phylogenetic relationships on population level (caper package R, Orme et al. [2013]; for a detailed description of the used phylogenetic tree, see Driessens et al. 2017). This method uses maximum likelihood to simultaneously estimate the regression model and phylogenetic signal (Pagel’s λ) of the residual error (Garland and Ives 2000; Revell 2010), and has shown to do better than a priori tests of phylogenetic signal; especially when sample sizes are smaller than 20 (Blomberg et al. 2003; Revell 2010; Kamilar and Cooper 2013). Because data from one population (i.e., San Salvador) could only be collected outside the breeding season, we ran an additional set of the same pgls regression analyses excluding these particular data. Results Population means and standard deviations for tested variables are provided in Table 1. The relationship between dewlap size and bite force differed significantly among populations (F16,381 = 14.93, P < 0.0001), also after correcting for body size (F16, 380 = 9.36, P < 0.0001). Within-population regression analyses revealed that absolute dewlap size is an excellent predictor of absolute bite force in nearly all study populations (R > 0.65, P < 0.005, Table 2); only for the population of Santa Clara the relationship failed to reach the conventional level of statistical significance (R = 0.38, P = 0.054). However, after correcting for body size, in only 4 out of the 17 tested populations, relative dewlap size still exhibited a significant positive relationship with bite force (Table 2 and Fig. 2). We additionally observed that these results based on relative indices varied widely across populations with estimated slopes ranging from −0.353 in Little Cayman to +0.729 in South Abaco (Table 2). Overall, results of the population sampled outside the breeding season (i.e., San Salvador) did not deviate from the other study populations sampled during the reproductive cycle in A. sagrei (both absolute and relative indices, Tables 1 and 2 and Fig. 1). Table 1 Descriptive statistics of the tested variables Populations  HL (mm)  SVL (mm)  Dewlap size (cm2)  Bite force (N)  SSD  DI  Acklins  15.09 ± 1.06 (10)  56.36 ± 5.24 (10)  2.58 ± 0.68 (10)  5.75 ± 1.45 (10)  1.43 (10, 12)  —  Andros  12.81 ± 0.87 (23)  46.37 ± 3.25 (23)  1.21 ± 0.33 (23)  1.90 ± 0.51 (23)  1.23 (23, 18)  —  Cayman Brac  15.19 ± 1.03 (28)  55.07 ± 4.30 (28)  1.53 ± 0.39 (28)  5.22 ± 1.65 (28)  1.33 (28, 29)  0.01 ± 0.03 (23)  Chub Cay  13.92 ± 0.88 (20)  47.87 ± 3.62 (20)  1.67 ± 0.49 (20)  3.36 ± 0.92 (20)  1.32 (20, 16)  —  Crooked Island  13.68 ± 1.04 (23)  49.86 ± 4.61 (23)  1.81 ± 0.61 (23)  3.66 ± 1.34 (23)  1.25 (23, 20)  —  Grand Bahama  12.82 ± 1.43 (24)  46.78 ± 6.34 (24)  1.59 ± 0.41 (21)  2.26 ± 1.39 (24)  1.33 (24, 11)  —  Grand Cayman  14.47 ± 1.21 (27)  51.74 ± 4.57 (27)  1.64 ± 0.41 (27)  6.11 ± 2.19 (27)  1.28 (27, 29)  0.07 ± 0.11 (24)  Jamaica  13.92 ± 1.00 (32)  48.60 ± 3.98 (32)  1.17 ± 0.27 (32)  6.90 ± 2.17 (32)  1.24 (32, 23)  0.02 ± 0.03 (22)  Little Cayman  15.17 ± 1.06 (28)  53.46 ± 4.35 (28)  2.00 ± 0.56 (28)  5.22 ± 1.57 (27)  1.29 (28, 27)  0.01 ± 0.01 (23)  Pidgeon Cay  14.15 ± 0.80 (16)  48.19 ± 3.28 (16)  1.56 ± 0.39 (16)  2.82 ± 0.79 (16)  1.21 (16, 8)  —  San Salvador  16.27 ± 1.52 (27)  58.13 ± 5.85 (27)  1.96 ± 0.75 (27)  7.99 ± 2.24 (27)  1.35 (27, 14)  0.02 ± 0.02 (24)  Santa Clara  15.80 ± 0.82 (27)  55.21 ± 2.97 (27)  2.06 ± 0.36 (27)  7.68 ± 1.78 (27)  1.33 (27, 24)  0.18 ± 0.13 (24)  Soroa 1  14.84 ± 1.35 (23)  51.10 ± 4.44 (23)  1.91 ± 0.45 (23)  6.63 ± 1.94 (23)  1.24 (23, 21)  0.11 ± 0.11 (24)  Soroa 2  15.50 ± 1.03 (22)  55.45 ± 4.46 (22)  2.27 ± 0.46 (22)  7.53 ± 2.00 (22)  1.32 (22, 24)  0.17 ± 0.14 (30)  South Abaco  13.07 ± 1.16 (26)  46.59 ± 4.15 (26)  1.35 ± 0.48 (26)  2.27 ± 0.96 (25)  1.28 (26, 21)  0.02 ± 0.04 (21)  South Bimini  14.91 ± 1.38 (24)  53.66 ± 4.60 (27)  1.62 ± 0.45 (26)  4.04 ± 1.13 (24)  1.30 (27, 23)  0.02 ± 0.02 (20)  Staniel Cay  13.86 ± 1.16 (26)  51.82 ± 5.41 (26)  1.91 ± 0.69 (26)  3.14 ± 1.05 (26)  1.32 (26, 20)  —  Populations  HL (mm)  SVL (mm)  Dewlap size (cm2)  Bite force (N)  SSD  DI  Acklins  15.09 ± 1.06 (10)  56.36 ± 5.24 (10)  2.58 ± 0.68 (10)  5.75 ± 1.45 (10)  1.43 (10, 12)  —  Andros  12.81 ± 0.87 (23)  46.37 ± 3.25 (23)  1.21 ± 0.33 (23)  1.90 ± 0.51 (23)  1.23 (23, 18)  —  Cayman Brac  15.19 ± 1.03 (28)  55.07 ± 4.30 (28)  1.53 ± 0.39 (28)  5.22 ± 1.65 (28)  1.33 (28, 29)  0.01 ± 0.03 (23)  Chub Cay  13.92 ± 0.88 (20)  47.87 ± 3.62 (20)  1.67 ± 0.49 (20)  3.36 ± 0.92 (20)  1.32 (20, 16)  —  Crooked Island  13.68 ± 1.04 (23)  49.86 ± 4.61 (23)  1.81 ± 0.61 (23)  3.66 ± 1.34 (23)  1.25 (23, 20)  —  Grand Bahama  12.82 ± 1.43 (24)  46.78 ± 6.34 (24)  1.59 ± 0.41 (21)  2.26 ± 1.39 (24)  1.33 (24, 11)  —  Grand Cayman  14.47 ± 1.21 (27)  51.74 ± 4.57 (27)  1.64 ± 0.41 (27)  6.11 ± 2.19 (27)  1.28 (27, 29)  0.07 ± 0.11 (24)  Jamaica  13.92 ± 1.00 (32)  48.60 ± 3.98 (32)  1.17 ± 0.27 (32)  6.90 ± 2.17 (32)  1.24 (32, 23)  0.02 ± 0.03 (22)  Little Cayman  15.17 ± 1.06 (28)  53.46 ± 4.35 (28)  2.00 ± 0.56 (28)  5.22 ± 1.57 (27)  1.29 (28, 27)  0.01 ± 0.01 (23)  Pidgeon Cay  14.15 ± 0.80 (16)  48.19 ± 3.28 (16)  1.56 ± 0.39 (16)  2.82 ± 0.79 (16)  1.21 (16, 8)  —  San Salvador  16.27 ± 1.52 (27)  58.13 ± 5.85 (27)  1.96 ± 0.75 (27)  7.99 ± 2.24 (27)  1.35 (27, 14)  0.02 ± 0.02 (24)  Santa Clara  15.80 ± 0.82 (27)  55.21 ± 2.97 (27)  2.06 ± 0.36 (27)  7.68 ± 1.78 (27)  1.33 (27, 24)  0.18 ± 0.13 (24)  Soroa 1  14.84 ± 1.35 (23)  51.10 ± 4.44 (23)  1.91 ± 0.45 (23)  6.63 ± 1.94 (23)  1.24 (23, 21)  0.11 ± 0.11 (24)  Soroa 2  15.50 ± 1.03 (22)  55.45 ± 4.46 (22)  2.27 ± 0.46 (22)  7.53 ± 2.00 (22)  1.32 (22, 24)  0.17 ± 0.14 (30)  South Abaco  13.07 ± 1.16 (26)  46.59 ± 4.15 (26)  1.35 ± 0.48 (26)  2.27 ± 0.96 (25)  1.28 (26, 21)  0.02 ± 0.04 (21)  South Bimini  14.91 ± 1.38 (24)  53.66 ± 4.60 (27)  1.62 ± 0.45 (26)  4.04 ± 1.13 (24)  1.30 (27, 23)  0.02 ± 0.02 (20)  Staniel Cay  13.86 ± 1.16 (26)  51.82 ± 5.41 (26)  1.91 ± 0.69 (26)  3.14 ± 1.05 (26)  1.32 (26, 20)  —  Notes: Population means ± standard deviations are presented for each population, with the exception of SSD (i.e., mean SVL males divided by mean SVL females). Sample sizes are provided between brackets for each variable separately; for SSD the number of implemented males and females is shown (left and right, respectively). HL, head length; SVL, snout-to-vent length; SSD, sexual size dimorphism; DI, display intensity, as the proportion of time that individuals spent displaying. Table 1 Descriptive statistics of the tested variables Populations  HL (mm)  SVL (mm)  Dewlap size (cm2)  Bite force (N)  SSD  DI  Acklins  15.09 ± 1.06 (10)  56.36 ± 5.24 (10)  2.58 ± 0.68 (10)  5.75 ± 1.45 (10)  1.43 (10, 12)  —  Andros  12.81 ± 0.87 (23)  46.37 ± 3.25 (23)  1.21 ± 0.33 (23)  1.90 ± 0.51 (23)  1.23 (23, 18)  —  Cayman Brac  15.19 ± 1.03 (28)  55.07 ± 4.30 (28)  1.53 ± 0.39 (28)  5.22 ± 1.65 (28)  1.33 (28, 29)  0.01 ± 0.03 (23)  Chub Cay  13.92 ± 0.88 (20)  47.87 ± 3.62 (20)  1.67 ± 0.49 (20)  3.36 ± 0.92 (20)  1.32 (20, 16)  —  Crooked Island  13.68 ± 1.04 (23)  49.86 ± 4.61 (23)  1.81 ± 0.61 (23)  3.66 ± 1.34 (23)  1.25 (23, 20)  —  Grand Bahama  12.82 ± 1.43 (24)  46.78 ± 6.34 (24)  1.59 ± 0.41 (21)  2.26 ± 1.39 (24)  1.33 (24, 11)  —  Grand Cayman  14.47 ± 1.21 (27)  51.74 ± 4.57 (27)  1.64 ± 0.41 (27)  6.11 ± 2.19 (27)  1.28 (27, 29)  0.07 ± 0.11 (24)  Jamaica  13.92 ± 1.00 (32)  48.60 ± 3.98 (32)  1.17 ± 0.27 (32)  6.90 ± 2.17 (32)  1.24 (32, 23)  0.02 ± 0.03 (22)  Little Cayman  15.17 ± 1.06 (28)  53.46 ± 4.35 (28)  2.00 ± 0.56 (28)  5.22 ± 1.57 (27)  1.29 (28, 27)  0.01 ± 0.01 (23)  Pidgeon Cay  14.15 ± 0.80 (16)  48.19 ± 3.28 (16)  1.56 ± 0.39 (16)  2.82 ± 0.79 (16)  1.21 (16, 8)  —  San Salvador  16.27 ± 1.52 (27)  58.13 ± 5.85 (27)  1.96 ± 0.75 (27)  7.99 ± 2.24 (27)  1.35 (27, 14)  0.02 ± 0.02 (24)  Santa Clara  15.80 ± 0.82 (27)  55.21 ± 2.97 (27)  2.06 ± 0.36 (27)  7.68 ± 1.78 (27)  1.33 (27, 24)  0.18 ± 0.13 (24)  Soroa 1  14.84 ± 1.35 (23)  51.10 ± 4.44 (23)  1.91 ± 0.45 (23)  6.63 ± 1.94 (23)  1.24 (23, 21)  0.11 ± 0.11 (24)  Soroa 2  15.50 ± 1.03 (22)  55.45 ± 4.46 (22)  2.27 ± 0.46 (22)  7.53 ± 2.00 (22)  1.32 (22, 24)  0.17 ± 0.14 (30)  South Abaco  13.07 ± 1.16 (26)  46.59 ± 4.15 (26)  1.35 ± 0.48 (26)  2.27 ± 0.96 (25)  1.28 (26, 21)  0.02 ± 0.04 (21)  South Bimini  14.91 ± 1.38 (24)  53.66 ± 4.60 (27)  1.62 ± 0.45 (26)  4.04 ± 1.13 (24)  1.30 (27, 23)  0.02 ± 0.02 (20)  Staniel Cay  13.86 ± 1.16 (26)  51.82 ± 5.41 (26)  1.91 ± 0.69 (26)  3.14 ± 1.05 (26)  1.32 (26, 20)  —  Populations  HL (mm)  SVL (mm)  Dewlap size (cm2)  Bite force (N)  SSD  DI  Acklins  15.09 ± 1.06 (10)  56.36 ± 5.24 (10)  2.58 ± 0.68 (10)  5.75 ± 1.45 (10)  1.43 (10, 12)  —  Andros  12.81 ± 0.87 (23)  46.37 ± 3.25 (23)  1.21 ± 0.33 (23)  1.90 ± 0.51 (23)  1.23 (23, 18)  —  Cayman Brac  15.19 ± 1.03 (28)  55.07 ± 4.30 (28)  1.53 ± 0.39 (28)  5.22 ± 1.65 (28)  1.33 (28, 29)  0.01 ± 0.03 (23)  Chub Cay  13.92 ± 0.88 (20)  47.87 ± 3.62 (20)  1.67 ± 0.49 (20)  3.36 ± 0.92 (20)  1.32 (20, 16)  —  Crooked Island  13.68 ± 1.04 (23)  49.86 ± 4.61 (23)  1.81 ± 0.61 (23)  3.66 ± 1.34 (23)  1.25 (23, 20)  —  Grand Bahama  12.82 ± 1.43 (24)  46.78 ± 6.34 (24)  1.59 ± 0.41 (21)  2.26 ± 1.39 (24)  1.33 (24, 11)  —  Grand Cayman  14.47 ± 1.21 (27)  51.74 ± 4.57 (27)  1.64 ± 0.41 (27)  6.11 ± 2.19 (27)  1.28 (27, 29)  0.07 ± 0.11 (24)  Jamaica  13.92 ± 1.00 (32)  48.60 ± 3.98 (32)  1.17 ± 0.27 (32)  6.90 ± 2.17 (32)  1.24 (32, 23)  0.02 ± 0.03 (22)  Little Cayman  15.17 ± 1.06 (28)  53.46 ± 4.35 (28)  2.00 ± 0.56 (28)  5.22 ± 1.57 (27)  1.29 (28, 27)  0.01 ± 0.01 (23)  Pidgeon Cay  14.15 ± 0.80 (16)  48.19 ± 3.28 (16)  1.56 ± 0.39 (16)  2.82 ± 0.79 (16)  1.21 (16, 8)  —  San Salvador  16.27 ± 1.52 (27)  58.13 ± 5.85 (27)  1.96 ± 0.75 (27)  7.99 ± 2.24 (27)  1.35 (27, 14)  0.02 ± 0.02 (24)  Santa Clara  15.80 ± 0.82 (27)  55.21 ± 2.97 (27)  2.06 ± 0.36 (27)  7.68 ± 1.78 (27)  1.33 (27, 24)  0.18 ± 0.13 (24)  Soroa 1  14.84 ± 1.35 (23)  51.10 ± 4.44 (23)  1.91 ± 0.45 (23)  6.63 ± 1.94 (23)  1.24 (23, 21)  0.11 ± 0.11 (24)  Soroa 2  15.50 ± 1.03 (22)  55.45 ± 4.46 (22)  2.27 ± 0.46 (22)  7.53 ± 2.00 (22)  1.32 (22, 24)  0.17 ± 0.14 (30)  South Abaco  13.07 ± 1.16 (26)  46.59 ± 4.15 (26)  1.35 ± 0.48 (26)  2.27 ± 0.96 (25)  1.28 (26, 21)  0.02 ± 0.04 (21)  South Bimini  14.91 ± 1.38 (24)  53.66 ± 4.60 (27)  1.62 ± 0.45 (26)  4.04 ± 1.13 (24)  1.30 (27, 23)  0.02 ± 0.02 (20)  Staniel Cay  13.86 ± 1.16 (26)  51.82 ± 5.41 (26)  1.91 ± 0.69 (26)  3.14 ± 1.05 (26)  1.32 (26, 20)  —  Notes: Population means ± standard deviations are presented for each population, with the exception of SSD (i.e., mean SVL males divided by mean SVL females). Sample sizes are provided between brackets for each variable separately; for SSD the number of implemented males and females is shown (left and right, respectively). HL, head length; SVL, snout-to-vent length; SSD, sexual size dimorphism; DI, display intensity, as the proportion of time that individuals spent displaying. Table 2 Univariate linear regression analyses of bite force (dependent variable) against dewlap size (independent variable) within population Population  R  F  df  Coefficient b ± SE  P-value  Absolute bite force against dewlap size          Acklins  0.819  16.28  9  0.761 ± 0.189  0.004  Andros  0.806  38.81  22  0.758 ± 0.122  <0.001  Cayman Brac  0.652  19.28  27  0.792 ± 0.180  <0.001  Chub Cay  0.909  85.16  19  0.948 ± 0.102  <0.001  Crooked Island  0.810  40.09  22  0.828 ± 0.131  <0.001  Grand Bahama  0.723  20.82  20  1.503 ± 0.329  <0.001  Grand Cayman  0.784  39.87  26  0.156 ± 0.183  <0.001  Jamaica  0.740  36.31  31  0.933 ± 0.155  <0.001  Little Cayman  0.704  23.55  25  0.682 ± 0.141  <0.001  Pidgeon Cay  0.708  14.03  15  0.622 ± 0.166  0.002  San Salvador  0.904  112.0  26  0.637 ± 0.060  <0.001  Santa Clara  0.375  4.093  26  0.471 ± 0.233  0.054  Soroa 1  0.870  65.69  22  1.078 ± 0.133  <0.001  Soroa 2  0.795  34.45  21  1.254 ± 0.214  <0.001  South Abaco  0.762  31.89  24  0.936 ± 0.166  <0.001  South Bimini  0.729  23.77  22  0.670 ± 0.137  <0.001  Staniel Cay  0.799  42.48  25  0.651 ± 0.100  <0.001  Relative bite force against relative dewlap size        Acklins  0.380  1.352  9  0.214 ± 0.184  0.278  Andros  0.413  4.328  22  0.420 ± 0.202  0.050  Cayman Brac  0.266  1.972  27  −0.303 ± 0.216  0.172  Chub Cay  0.490  5.679  19  0.635 ± 0.267  0.028  Crooked Island  0.108  0.249  22  0.089 ± 0.178  0.623  Grand Bahama  0.305  1.955  20  0.345 ± 0.246  0.178  Grand Cayman  0.153  0.603  26  0.185 ± 0.239  0.445  Jamaica  0.312  3.230  31  0.306 ± 0.170  0.082  Little Cayman  0.273  1.937  25  −0.353 ± 0.254  0.177  Pidgeon Cay  0.221  0.720  15  0.186 ± 0.219  0.411  San Salvador  0.166  0.707  26  0.112 ± 0.134  0.411  Santa Clara  0.212  1.177  26  0.251 ± 0.232  0.288  Soroa 1  0.623  13.36  22  0.639 ± 0.175  0.001  Soroa 2  0.335  2.523  21  0.451 ± 0.284  0.128  South Abaco  0.495  7.460  24  0.729 ± 0.267  0.012  South Bimini  0.243  1.318  22  0.301 ± 0.262  0.264  Staniel Cay  0.271  1.907  25  0.198 ± 0.144  0.180  Population  R  F  df  Coefficient b ± SE  P-value  Absolute bite force against dewlap size          Acklins  0.819  16.28  9  0.761 ± 0.189  0.004  Andros  0.806  38.81  22  0.758 ± 0.122  <0.001  Cayman Brac  0.652  19.28  27  0.792 ± 0.180  <0.001  Chub Cay  0.909  85.16  19  0.948 ± 0.102  <0.001  Crooked Island  0.810  40.09  22  0.828 ± 0.131  <0.001  Grand Bahama  0.723  20.82  20  1.503 ± 0.329  <0.001  Grand Cayman  0.784  39.87  26  0.156 ± 0.183  <0.001  Jamaica  0.740  36.31  31  0.933 ± 0.155  <0.001  Little Cayman  0.704  23.55  25  0.682 ± 0.141  <0.001  Pidgeon Cay  0.708  14.03  15  0.622 ± 0.166  0.002  San Salvador  0.904  112.0  26  0.637 ± 0.060  <0.001  Santa Clara  0.375  4.093  26  0.471 ± 0.233  0.054  Soroa 1  0.870  65.69  22  1.078 ± 0.133  <0.001  Soroa 2  0.795  34.45  21  1.254 ± 0.214  <0.001  South Abaco  0.762  31.89  24  0.936 ± 0.166  <0.001  South Bimini  0.729  23.77  22  0.670 ± 0.137  <0.001  Staniel Cay  0.799  42.48  25  0.651 ± 0.100  <0.001  Relative bite force against relative dewlap size        Acklins  0.380  1.352  9  0.214 ± 0.184  0.278  Andros  0.413  4.328  22  0.420 ± 0.202  0.050  Cayman Brac  0.266  1.972  27  −0.303 ± 0.216  0.172  Chub Cay  0.490  5.679  19  0.635 ± 0.267  0.028  Crooked Island  0.108  0.249  22  0.089 ± 0.178  0.623  Grand Bahama  0.305  1.955  20  0.345 ± 0.246  0.178  Grand Cayman  0.153  0.603  26  0.185 ± 0.239  0.445  Jamaica  0.312  3.230  31  0.306 ± 0.170  0.082  Little Cayman  0.273  1.937  25  −0.353 ± 0.254  0.177  Pidgeon Cay  0.221  0.720  15  0.186 ± 0.219  0.411  San Salvador  0.166  0.707  26  0.112 ± 0.134  0.411  Santa Clara  0.212  1.177  26  0.251 ± 0.232  0.288  Soroa 1  0.623  13.36  22  0.639 ± 0.175  0.001  Soroa 2  0.335  2.523  21  0.451 ± 0.284  0.128  South Abaco  0.495  7.460  24  0.729 ± 0.267  0.012  South Bimini  0.243  1.318  22  0.301 ± 0.262  0.264  Staniel Cay  0.271  1.907  25  0.198 ± 0.144  0.180  Notes: Results are shown for regressions with absolute and relative variables, respectively. Significant results (P < 0.05) are shown in bold font. Table 2 Univariate linear regression analyses of bite force (dependent variable) against dewlap size (independent variable) within population Population  R  F  df  Coefficient b ± SE  P-value  Absolute bite force against dewlap size          Acklins  0.819  16.28  9  0.761 ± 0.189  0.004  Andros  0.806  38.81  22  0.758 ± 0.122  <0.001  Cayman Brac  0.652  19.28  27  0.792 ± 0.180  <0.001  Chub Cay  0.909  85.16  19  0.948 ± 0.102  <0.001  Crooked Island  0.810  40.09  22  0.828 ± 0.131  <0.001  Grand Bahama  0.723  20.82  20  1.503 ± 0.329  <0.001  Grand Cayman  0.784  39.87  26  0.156 ± 0.183  <0.001  Jamaica  0.740  36.31  31  0.933 ± 0.155  <0.001  Little Cayman  0.704  23.55  25  0.682 ± 0.141  <0.001  Pidgeon Cay  0.708  14.03  15  0.622 ± 0.166  0.002  San Salvador  0.904  112.0  26  0.637 ± 0.060  <0.001  Santa Clara  0.375  4.093  26  0.471 ± 0.233  0.054  Soroa 1  0.870  65.69  22  1.078 ± 0.133  <0.001  Soroa 2  0.795  34.45  21  1.254 ± 0.214  <0.001  South Abaco  0.762  31.89  24  0.936 ± 0.166  <0.001  South Bimini  0.729  23.77  22  0.670 ± 0.137  <0.001  Staniel Cay  0.799  42.48  25  0.651 ± 0.100  <0.001  Relative bite force against relative dewlap size        Acklins  0.380  1.352  9  0.214 ± 0.184  0.278  Andros  0.413  4.328  22  0.420 ± 0.202  0.050  Cayman Brac  0.266  1.972  27  −0.303 ± 0.216  0.172  Chub Cay  0.490  5.679  19  0.635 ± 0.267  0.028  Crooked Island  0.108  0.249  22  0.089 ± 0.178  0.623  Grand Bahama  0.305  1.955  20  0.345 ± 0.246  0.178  Grand Cayman  0.153  0.603  26  0.185 ± 0.239  0.445  Jamaica  0.312  3.230  31  0.306 ± 0.170  0.082  Little Cayman  0.273  1.937  25  −0.353 ± 0.254  0.177  Pidgeon Cay  0.221  0.720  15  0.186 ± 0.219  0.411  San Salvador  0.166  0.707  26  0.112 ± 0.134  0.411  Santa Clara  0.212  1.177  26  0.251 ± 0.232  0.288  Soroa 1  0.623  13.36  22  0.639 ± 0.175  0.001  Soroa 2  0.335  2.523  21  0.451 ± 0.284  0.128  South Abaco  0.495  7.460  24  0.729 ± 0.267  0.012  South Bimini  0.243  1.318  22  0.301 ± 0.262  0.264  Staniel Cay  0.271  1.907  25  0.198 ± 0.144  0.180  Population  R  F  df  Coefficient b ± SE  P-value  Absolute bite force against dewlap size          Acklins  0.819  16.28  9  0.761 ± 0.189  0.004  Andros  0.806  38.81  22  0.758 ± 0.122  <0.001  Cayman Brac  0.652  19.28  27  0.792 ± 0.180  <0.001  Chub Cay  0.909  85.16  19  0.948 ± 0.102  <0.001  Crooked Island  0.810  40.09  22  0.828 ± 0.131  <0.001  Grand Bahama  0.723  20.82  20  1.503 ± 0.329  <0.001  Grand Cayman  0.784  39.87  26  0.156 ± 0.183  <0.001  Jamaica  0.740  36.31  31  0.933 ± 0.155  <0.001  Little Cayman  0.704  23.55  25  0.682 ± 0.141  <0.001  Pidgeon Cay  0.708  14.03  15  0.622 ± 0.166  0.002  San Salvador  0.904  112.0  26  0.637 ± 0.060  <0.001  Santa Clara  0.375  4.093  26  0.471 ± 0.233  0.054  Soroa 1  0.870  65.69  22  1.078 ± 0.133  <0.001  Soroa 2  0.795  34.45  21  1.254 ± 0.214  <0.001  South Abaco  0.762  31.89  24  0.936 ± 0.166  <0.001  South Bimini  0.729  23.77  22  0.670 ± 0.137  <0.001  Staniel Cay  0.799  42.48  25  0.651 ± 0.100  <0.001  Relative bite force against relative dewlap size        Acklins  0.380  1.352  9  0.214 ± 0.184  0.278  Andros  0.413  4.328  22  0.420 ± 0.202  0.050  Cayman Brac  0.266  1.972  27  −0.303 ± 0.216  0.172  Chub Cay  0.490  5.679  19  0.635 ± 0.267  0.028  Crooked Island  0.108  0.249  22  0.089 ± 0.178  0.623  Grand Bahama  0.305  1.955  20  0.345 ± 0.246  0.178  Grand Cayman  0.153  0.603  26  0.185 ± 0.239  0.445  Jamaica  0.312  3.230  31  0.306 ± 0.170  0.082  Little Cayman  0.273  1.937  25  −0.353 ± 0.254  0.177  Pidgeon Cay  0.221  0.720  15  0.186 ± 0.219  0.411  San Salvador  0.166  0.707  26  0.112 ± 0.134  0.411  Santa Clara  0.212  1.177  26  0.251 ± 0.232  0.288  Soroa 1  0.623  13.36  22  0.639 ± 0.175  0.001  Soroa 2  0.335  2.523  21  0.451 ± 0.284  0.128  South Abaco  0.495  7.460  24  0.729 ± 0.267  0.012  South Bimini  0.243  1.318  22  0.301 ± 0.262  0.264  Staniel Cay  0.271  1.907  25  0.198 ± 0.144  0.180  Notes: Results are shown for regressions with absolute and relative variables, respectively. Significant results (P < 0.05) are shown in bold font. Fig. 2 View largeDownload slide Relative bite force regressed against relative dewlap size for each A. sagrei population, separately. Straight regression lines represent a significant correlation between both variables, i.e., Andros, Chub Cay, Soroa 1, and South Abaco. Dotted regression lines represent no significant relationship between relative dewlap size and bite force. Detailed statistics are provided in Table 2. The illustration (right, below) visualizes a male brown anole biting on a purpose-built force plate. Fig. 2 View largeDownload slide Relative bite force regressed against relative dewlap size for each A. sagrei population, separately. Straight regression lines represent a significant correlation between both variables, i.e., Andros, Chub Cay, Soroa 1, and South Abaco. Dotted regression lines represent no significant relationship between relative dewlap size and bite force. Detailed statistics are provided in Table 2. The illustration (right, below) visualizes a male brown anole biting on a purpose-built force plate. An among-population regression analysis (pgls) failed to find a significant association between the relative dewlap size–bite force relationship (i.e., slope coefficient b) and SSD (R = 0.11, df = 16, P = 0.662). Thus, in populations characterized by larger SSD, dewlap size in itself was not a more reliable signal of bite force than in populations characterized by lower SSD. The same applies to DI, as no significant correlation was found between the relative dewlap size–bite force relationship and DI (R = 0.23, df = 9, P = 0.532). Excluding the population of San Salvador from the pgls regressions did not alter any of our results (results remained non-significant, SSD: R = 0.12, df = 15, P = 0.657 and DI: R = 0.13, df = 8, P = 0.747). Discussion By studying a series of island populations, we here present our findings on the reliability of dewlap size as a predictor for bite performance in a territorial Caribbean anole, and how this dewlap size–bite force relationship varies so drastically among populations. We used absolute and relative indices to assess the link between dewlap size and bite force, as both indices can differ in the messages they convey (Lailvaux and Irschick 2007). Absolute dewlap size–bite force relationship Our results revealed that dewlap size is an excellent predictor of bite force capacity in nearly all study populations. A strong association between absolute dewlap size and bite force in A. sagrei males has also been reported in all previous studies (Lailvaux and Irschick 2007; Cox et al. 2009; Driessens et al. 2015), emphasizing the generality of this finding. In many animal species, including A. sagrei, body size is the key predictor in determining combat outcome, with larger individuals having a substantial advantage over smaller ones (e.g., Tokarz 1985; Hughes 1996; Hardy and Briffa 2013). Gathering accurate information on the opponent’s body size (assessment game) seems thus crucial to avoid costs associated with escalated fights (Andersson 1994; Emlen 2008). Yet, in reality, the accurate transmission of information is often impeded by ambient noise (e.g., precipitation, low light levels, and windblown vegetation), and particularly when only one signal component is involved (e.g., Fleishman 1992; Lengagne and Slater 2002; Peters and Evans 2003; Leonard and Horn 2005). A commonly adopted signaling strategy to cope with such impeding factors is to repeat the same message in different ways by using redundant signal components (e.g., Zuk et al. 1992; Møller and Pomiankowski 1993; Johnstone 1996). Within all our study populations, absolute dewlap size correlated strongly with overall body size and might as such, serve as a redundant signal for body size to increase signal accuracy during mate assessment. Characterized by a brown to grayish body color, A. sagrei is well camouflaged in the microhabitats it usually occupies (trunk-ground ecomorph; Schoener and Schoener 1982; Losos 2009). In contrast, its bright yellow to reddish dewlap is highly conspicuous, due to high color and pattern contrasts with background vegetation (Endler 1992, 1993, 2012). Thus, by using the combination of a more cryptic body together with a conspicuous dewlap, males can transmit more accurate information on size and consequently, fighting capacity to opponents. The potential role of the A. sagrei dewlap as redundant signal for body size might be most prominent during the early stages of opponent assessment, when signaling still occurs over relatively long distances (more ambient noise), or perhaps during territorial advertisement in order to discourage unseen rival males from intruding (McMann 1998; Orrell and Jenssen 2003). Accordingly, Henningsen and Irschick (2012) showed in their study that surgically reducing the size of the dewlap did not change the outcome of staged close-proximity interactions between size-matched A. carolinensis males; bite force capacity in itself appeared to be more important in determining the outcome of these staged interactions. Based on their results, the authors suggested that dewlap size functions as a signal of bite force primarily during non-directed, long-distance territorial displays, whereas more direct means of assessing one another (e.g., jaw size, head size, body condition, push-ups) may be of higher importance during close-proximity aggressive interaction. In this respect, future behavioral experiments on A. sagrei testing the importance of absolute dewlap size as a redundant signal for size during long-distance versus short-distance male interactions might be a valuable addition. Relative dewlap size–bite force relationship In addition to conveying information on body size, a sexual trait can function as direct, honest signal for advertising fighting capacity (e.g., Panhuis and Wilkinson 1999; Lailvaux et al. 2005). Evidence for a positive link between relative male dewlap size and bite force during the breeding season has been shown for several territorial anole species (Vanhooydonck et al. 2005a; Lailvaux and Irschick 2007). Surprisingly, earlier studies did not observe this correlation in the highly territorial brown anole lizard, A. sagrei (Lailvaux and Irschick 2007; Cox et al. 2009; Driessens et al. 2015). By examining a large set of island populations, we now also found support for a significant relationship between relative dewlap size and bite force within A. sagrei, though, only in 4 out of the 17 tested populations. In contrast to our expectations, the degree of SSD and DI could not explain the observed variation in the relative dewlap size–bite force relationship found among our populations. Thus, populations where relative dewlap size appeared to be an honest signal of bite force were not per se characterized by a higher degree of intrasexual selection, which is inconsistent to earlier findings from Lailvaux and Irschick (2007) (at the species level). Standard errors of the estimated slopes for the relative dewlap size–bite force relationships fell within a relatively narrow range (0.134–0.284, Table 2), and we therefore believe that our failure to find an association between the slopes and SSD or DI is due to the low among-population differences in variance. Another potential reason why we fail to find an association might be due to relative low sample sizes. While the majority of regression analyses showed a high statistical power (power > 0.99), hence, adequate sample sizes, analyses on the populations where relative bite force was not significantly correlated with relative dewlap size were characterized by a relative low statistical power (power < 0.5). Although our sample sizes and statistical power were similar to those of other studies that correlated relative bite force with relative dewlap size (i.e., Vanhooydonck et al. 2005a; Lailvaux and Irschick 2007; Cox et al. 2009), an increase in sample size would have increased the power of our analyses, hence, might have affected our results on an association between the slopes and SSD or DI. Moreover, one can also question the validity of SSD as a measure of the intensity of intrasexual selection. Indeed, it has long been pointed out that SSD may also arise as a consequence of natural selection for reduction of food competition (Darwin 1871) or on clutch size in females (Tinkle et al. 1970). Reassuringly, several studies have found that among-species variation in SSD correlates positively with other aspects of sexual dimorphism (such as dichromatism: Pérez I de Lanuza et al. 2013; Chen et al. 2012; Dale et al. 2015), indicating that SSD is at least to some extent under sexual selection. In a comparative analysis of almost 500 lizard species, Cox et al. (2003) did find significant correlations between SSD and female home range ratio and female home range size, two widely accepted proxies for the strength of intrasexual selection. In Anolis, the use of SSD as an indirect measure of sexual selection intensity has a long tradition (e.g., Trivers 1976; Stamps 1983), although several studies have suggested that variation in SSD may be driven by natural selection as well (e.g., Rand 1967; Losos et al. 2003). In a recent study on our study species A. sagrei, for example, Bonneaud et al. (2016) reported that resource availability can highly influence the degree of SSD among insular populations distributed across the Bahamas. Furthermore, paternity studies on A. sagrei proved that sexual selection is not uniformly directional with respect to male size and, therefore, fails to fully explain the observed male-biased SSD (Calsbeek and Sinervo 2004; Cox et al. 2007). Thus, the use of SSD here as metric for sexual selection is disputable. Besides, DI may be a rather “gross” proxy for the degree of intrasexual selection on each island population, because A. sagrei males may exhibit displays in various contexts (Driessens et al. 2014). Clearly, data on reliable estimates of the intensity of sexual selection are required. Some authors have advocated the use of sex ratios (e.g., Stamps 1983; Muralidhar and Johnson 2017), but others have warned that it is unsure to what extent observed sex ratio reflects operational sex ratio (the ratio of breeding males to breeding females, Cox et al. 2003). Other options include behavioral observations (e.g., number or duration of male–male aggressive interactions) and distributional data (territory size, overlap, number of females per territory, encounter rates; Johnson et al. 2009; Kamath and Losos 2018), but obtaining such data for many populations requires substantial time and effort, which probably explains why, after 50 years of research on anoles, such data remain largely unavailable (Losos et al. 2003). SSD and DI cannot explain differences in the relationship between relative dewlap size and bite force among populations, but what other factors potentially can? One possible explanatory factor may involve intrapopulational variation in body size and the idea that relative indices become particularly important in populations where opponents match more often in body size. Transferring information on body size is likely the first and most crucial step in the assessment game (e.g., Tokarz 1985; Hardy and Briffa 2013), as we already stated in the previous paragraph. However, when males of similar body size encounter each other, dewlap size might become the major signal for advertising fighting capacity. In support of this idea, we would expect relative dewlap size to become a more reliable signal of bite force when variation in body size decreases across populations. We could simply test this prediction with available data by regressing the slope of the relative dewlap size–bite force relationship against variance in body size across populations. Our data did not support the proposed idea (pgls regression: coefficient b variance SVL, R = 0.26, df = 16, P = 0.317), perhaps because encounters between size-matched opponents may not occur that frequently. Moreover, previous studies have shown that when opponents are more similar in size, fights are more likely to escalate (as opposed to merely opponent assessment) and the outcomes harder to predict (Rand 1967; Molina-Borja et al. 1998; Panhuis and Wilkinson 1999). This might challenge the view that honest signals play a major role in the advertisement of fighting capacity during agonistic encounters between size-matched males. Another factor that has recently been reported to affect the relationship between relative dewlap size and bite force is resource availability. Particularly, Lailvaux et al. (2012) showed that under limiting resource conditions, the honest dewlap size–bite force relationship in A. carolinensis gets disrupted. To put this idea to the test, we assessed whether variation in body condition (an estimate for resource availability) could explain the variation in the relative dewlap size–bite force relationship observed within A. sagrei. Indeed, we obtained a significant association with body condition (pgls regression: coefficient b ∼ body mass normalized for SVL, R = 0.62, df = 16, P = 0.009). However, the correlation was negative and, therefore, opposes the findings reported by Lailvaux et al. (2012). We found that for A. sagrei males, dewlap size in itself becomes a more reliable signal of bite force in populations where males are in worse body condition (the relationship with body condition was not significant when using the absolute dewlap size–bite force relationships, P = 0.575). Overall, we suggest that body size remains, independent of resource availability, the key predictor during opponent assessment. Yet, when males of similar body size encounter each other, the use of dewlap size to honestly signal fighting capacity might be particularly important for A. sagrei males in poor body condition. We believe that males in poor body condition will suffer more from the exhaustion and injuries related to physical fights than A. sagrei males in normal or good body condition. Accordingly, in populations where males have a low body condition, the strong need to avoid escalated fights and thus, to precisely assess a size-matched opponent, might be higher (Andersson 1994; Maynard-Smith and Harper 2003). This may explain why dewlap size becomes a more reliable predictor of bite force in such populations. In contrast, males under high resource conditions might directly engage in physical fights when encountering a size-matched opponent (Rand 1967; Molina-Borja et al. 1998). Of course, future experiments are needed to confirm our suggestions and to provide additional evidence that resource availability, indeed, influences the correlation between relative dewlap size and bite force in A. sagrei. Last, several other factors have been found to explain variation only in dewlap size and can as such, also affect the relation between signal size and performance trait. For example, Vanhooydonck et al. (2009) revealed that A. sagrei males had relatively larger dewlaps in populations where curly-tailed lizards (Leiocephalus carinatus), known to predate on anoles, are present. In that same study was also reported that relative dewlap size increased with SSD. Also hormone levels (i.e., testosterone) are proven to change dewlap size in A. sagrei males (Cox et al. 2009) and can, due to fluctuating levels, affect the relationship between dewlap size and bite force throughout seasons. In accordance, a previous study on A. carolinensis has shown that dewlap size is only a reliable signal of bite force during the breeding season, and not during winter (Irschick et al. 2006). Following Lailvaux and Irschick (2007), we sampled our A. sagrei populations during the breeding season, with the exception of one (i.e., population from San Salvador). Results from that latter population did not markedly deviate from the other study populations, indicating that the dewlap–bite force relationship in A. sagrei might not be significantly affected by season. Yet, experiments assessing the link between dewlap size and bite force in the same A. sagrei individuals throughout the year are needed to accurately assess seasonal effects. Conclusion To our knowledge, this is the first study showing evidence for a link between relative dewlap size and bite force within A. sagrei populations, during the breeding season. Based on our results, we suggest that dewlap size in A. sagrei males is in general a redundant signal for body size in the advertisement of fighting capacity (absolute indices), but only in particular cases a direct signal of bite force (relative indices). Our study makes an important contribution by showing that the relationship between signal size and performance trait can differ substantially within one species. We therefore suggest that the use of only one population is not sufficient to draw general conclusions for a whole species, in this respect. Several factors (e.g., degree of territoriality, resource availability, season) are already known to affect the correlation between dewlap size and bite force; however, additional research is needed to shed more light on how these factors exactly affect this relationship. Acknowledgments We acknowledge S. De Decker, J. Harvey, A. Herrel, J. Husak, P. Maillis, J. Mertens, J.J. Meyers, D. Norris, V. Rivalta, L. Schettino, E. Schramme, B. Scott-Edwards, M. Valley, and L. Vandervorst for help during data collection. We further thank G. Reynolds for his useful advice regarding phylogenetic analyses, S. Van Dongen for statistical assistance, and two anonymous reviewers for significantly improving drafts of this manuscript. Funding This work was supported by the Belgian American Education Foundation (BAEF) [to S.B. a postdoctoral fellow]. This study was financed by an FWO-FL research grant [to T.D., an aspirant doctoral fellowship]. K.H. is a postdoctoral fellow of FWO-FL. Additional expenses for field missions were provided by Leopold III fund and the University of Antwerp (DOCOP). All work was carried out in accordance with the local Environmental Agencies and the University of Antwerp animal welfare standard and protocols (ECD 2011-64). References Abe J, Kamimura Y, Kondo N, Shimada M. 2003. Extremely female-biased sex ratio and lethal male–male combat in a parasitoid wasp, Melittobia australica (Eulophidae). Behav Ecol  14: 34– 9. Alonso-Alvarez C, Bertrand S, Devevey G, Gaillard M, Prost J, Faivre B, Sorci G. 2004. An experimental test of the dose-dependent effect of carotenoids and immune activation on sexual signals and antioxidant activity. Am Nat  164: 651– 9. Anderson RA, McBrayer LD, Herrel A. 2008. Bite force in vertebrates: opportunities and caveats for use of a nonpareil whole-animal performance measure. Biol J Linn Soc  93: 709– 20. Andersson M. 1982. Female choice selects for extreme tail length in a widowbird. Nature  299: 529– 34. Andersson M. 1994. Sexual selection . Princeton (NJ): Princeton University Press. 624 p. Baeckens S, Driessens T, Van Damme R. 2016. Intersexual chemo-sensation in a “visually-oriented” lizard, Anolis sagrei. PeerJ  4: e1874. Baeckens S, García-Roa R, Martín J, Ortega J, Huyghe K, Van Damme R. 2017. Fossorial and durophagous: implications of molluscivory for head size and bite capacity in a burrowing worm lizard. J Zool  301: 193– 205. Bean D, Cook JM. 2001. Male mating tactics and lethal combat in the nonpollinating fig wasp Sycoscapter australis. Anim Behav  62: 535– 42. Bels V. 1990. The mechanism of dewlap extension in Anolis carolinensis (Reptilia: iguanidae) with histological analysis of the hyoid apparatus. J Morphol  206: 225– 44. Bennett AF. 1985. Temperature and muscle. J Exp Biol  155: 333– 44. Blomberg SP, Garland T, Ives AR. 2003. Testing for phylogenetic signal in comparative data: behavioral traits are more labile. Evolution  57: 717– 45. Blumstein DT, Daniel JC. 2007. Quantifying behavior the JWatcher way . Sunderland (MA): Sinauer Associates. 211 p. Bonneaud C, Marnocha E, Herrel A, Vanhooydonck B, Irschick DJ, Smith TB. 2016. Developmental plasticity affects sexual size dimorphism in an anole lizard. Funct Ecol  30: 235– 43. Bradbury JW, Vehrencamp SL. 1998. The principles of animal communication . Sunderland (MA): Sinauer Associates. 697 p. Butler MA, Sawyer SA, Losos JB. 2007. Sexual dimorphism and adaptive radiation in Anolis lizards. Nature  447: 202– 5. Calsbeek R, Sinervo B. 2004. Progeny sex is determined by relative male body size within polyandrous females’ clutches: cryptic mate choice in the wild. J Evol Biol  17: 464– 70. Candolin U. 2003. The use of multiple cues in mate choice. Biol Rev  78: 575– 95. Carpenter CC. 1978. Ritualistic social behaviors in lizards. In: Greenberg N, MacLean PD, editors. Behavior and neurology of lizards.  Rockville (MD): NIMH. p. 253– 67. Chen IP, Stuart-Fox D, Hugall AF, Symonds MRE. 2012. Sexual selection and the evolution of complex color patterns in dragon lizards. Evolution  66: 3605– 14. Clutton-Brock TH, Albon SD, Gibson RM, Guinness FE. 1979. The logical stag: adaptive aspects of fighting in red deer (Cervus elaphus L.) Anim Behav  27: 211– 25. Cox RM, Skelly SL, John-Alder HB. 2003. A comparative test of adaptive hypotheses for sexual size dimorphism in lizards. Evolution  57: 1653– 69. Cox RM, Butler MA, John-Alder HB. 2007. The evolution of sexual size dimorphism in reptiles. In: Fairbairn DJ, Blanckenhorn WU, Szekely T, editors. Sex, size & gender roles: evolutionary studies of sexual size dimorphism . Oxford: Oxford University Press. p. 38– 49. Cox RM, Stenquist DS, Henningsen JP, Calsbeek R. 2009. Manipulating testosterone to assess links between behavior, morphology, and performance in the brown anole Anolis sagrei. Physiol Biochem Zool  82: 686– 98. Crews D. 1975. Effects of different components of male courtship behavior on environmentally induced ovarian recrudescence and mating preferences in the lizard Anolis carolinensis. Anim Behav  23: 349– 56. Dale J, Dey CJ, Delhey K, Kempenaers B, Valcu M. 2015. The effects of life history and sexual selection on male and female plumage colouration. Nature  527: 367– 70. Darwin CR. 1871. The descent of man, and selection in relation to sex . London: John Murray. 745 p. Driessens T, Vanhooydonck B, Damme R. 2014. Deterring predators, daunting opponents or drawing partners? Signaling rates across diverse contexts in the lizard Anolis sagrei. Behav Ecol Sociobiol  68: 173– 84. Driessens T, Huyghe K, Vanhooydonck B, Van Damme R. 2015. Messages conveyed by assorted facets of the dewlap, in both sexes of Anolis sagrei. Behav Ecol Sociobiol  69: 1251– 64. Driessens T, Baeckens S, Balzarolo M, Vanhooydonck B, Huyghe K, Van Damme R. 2017. Climate-related environmental variation in a visual signalling device: the male and female dewlap in Anolis sagrei lizards. J Evol Biol  30: 1846– 61. Edwards JR, Lailvaux SP. 2012. Display behavior and habitat use in single and mixed populations of Anolis carolinensis and Anolis sagrei lizards. Ethology  118: 494– 502. Emlen DJ. 2008. The evolution of animal weapons. Annu Rev Ecol Evol  39: 387– 413. Endler JA. 1992. Signals, signal conditions, and the direction of evolution. Am Nat  139: 125– 53. Endler JA. 1993. The color of light in forests and its implications. Ecol Monogr  63: 1– 27. Endler JA. 2012. A framework for analysing colour pattern geometry: adjacent colours. Biol J Linn Soc  107: 233– 53. Felsenstein LJ. 1985. Phylogenies and the comparative method. Am Nat  125: 1– 15. Fleishman LJ. 1992. The influence of the sensory system and the environment on motion patterns in the visual displays of anoline lizards and other vertebrates. Am Nat  139: 36– 61. Garland T, Ives AR. 2000. Using the past to predict the present: confidence intervals for regression equations in phylogenetic comparative methods. Am Nat  155: 346– 64. Greenberg G, Noble GK. 1944. Social behavior of the American chameleon (Anolis carolinensis Voigt). Physiol Zool  17: 392– 439. Hardy ICW, Briffa M. 2013. Animal contests . Cambridge (MA): Cambridge University Press. 379 p. Harvey PH, Pagel MD. 1991. The comparative method in evolutionary biology . Oxford: Oxford University Press. 248 p. Henningsen JP, Irschick DJ. 2012. An experimental test of the effect of signal size and performance capacity on dominance in the green anole lizard. Funct Ecol  26: 3– 10. Herrel A, O’Reilly JC. 2006. Ontogenetic scaling of bite force in lizards and turtles. Physiol Biochem Zool  79: 31– 42. Herrel A, Spithoven L, Van Damme R, De Vree F. 1999. Sexual dimorphism of head size in Gallotia galloti: testing the niche divergence hypothesis by functional analyses. Funct Ecol  13: 289– 97. Herrel A, Aerts P, Fret J, De Vree F. 1999. Morphology of the feeding system in agamid lizards: ecological correlates. Anat Rec  254: 496– 507. Herrel A, Van Damme R, Vanhooydonck B, De Vree F. 2001. The implications of bite performance for diet in two species of lacertid lizards. Can J Zool  79: 662– 70. Hertz PE, Huey RB, Stevenson RD. 1993. Evaluating temperature regulation by field-active ectotherms: the fallacy of the inappropriate question. Am Nat  142: 796– 818. Huey RB. 1982. Temperature, physiology, and the ecology of reptiles. In: Gans C, Pough FH, editors. Biology of the reptilia.  New York (NY): Academic Press. p. 25– 91. Hughes M. 1996. Size assessment via a visual signal in snapping shrimp. Behav Ecol Sociobiol  38: 51– 7. Irschick DJ, Ramos M, Buckley C, Elstrott J, Carlisle E, Lailvaux SP, Bloch N, Herrel A, Vanhooydonck B. 2006. Are morphology–performance relationships invariant across different seasons? A test with the green anole lizard (Anolis carolinensis). Oikos  114: 49– 59. Jennions MD, Backwell PRY. 1996. Residency and size affect fight duration and outcome in the fiddler crab Uca annulipes. Biol J Linn Soc  57: 293– 306. Jenssen TA. 1970. The ethoecology of Anolis nebulosus. J Herpetol  4: 1– 38. Jenssen TA, Greenberg N, Hovde KA. 1995. Behavioral profile of free-ranging male lizards, Anolis carolinensis, across breeding and post-breeding seasons. Herpetol Monogr  9: 41– 62. Jenssen TA, Lovern M, Congdon JD. 2001. Fieldtesting the protandry-based mating system for the lizard Anolis carolinensis: does the model organism have the right model? Behav Ecol Sociobiol  50: 162– 72. Johnson MA, Wade J. 2010. Behavioural display systems across nine Anolis lizard species: sexual dimorphisms in structure and function. Proc R Soc B Biol Sci  277: 1711– 9. Johnson MA, Revell LJ, Losos JB. 2009. Behavioral convergence and adaptive radiation: effects of habitat use on territorial behavior in Anolis lizards. Evolution  64: 1151– 9. Johnstone RA. 1996. Multiple displays in animal communication: “backup signals” and “multiple messages”. Philos Trans R Soc B  351: 329– 38. Kamath A, Losos JB. 2017. The erratic and contingent progression of research on territoriality: a case study. Behav Ecol Sociobiol  71: 1– 13. Kamath A, Losos JB. 2018. Estimating encounter rates as the first step of sexual selection in the lizard Anolis sagrei. Proc R Soc B Biol Sci  285: 20172244. Kamilar JM, Cooper N. 2013. Phylogenetic signal in primate behavior, ecology and life history. Philos Trans R Soc B  368: 20120341. Karsten KB, Andriamandimbiarisoa LN, Fox SF, Raxworthy CJ. 2009. Sexual selection on body size and secondary sexual characters in 2 closely related, sympatric chameleons in Madagascar. Behav Ecol  20: 1079– 88. Lailvaux SP, Irschick DJ. 2007. The evolution of performance-based male fighting ability in Caribbean Anolis lizards. Am Nat  170: 573– 86. Lailvaux SP, Herrel A, Vanhooydonck B, Meyers JJ, Irschick DJ. 2004. Performance capacity, fighting tactics and the evolution of life-stage male morphs in the green anole lizard (Anolis carolinensis). Proc R Soc B Biol Sci  271: 2501– 8. Lailvaux SP, Hathway J, Pomfret J, Knell RJ. 2005. Horn size predicts physical performance in the beetle Euoniticellus intermedius (Coleoptera: scarabaeidae). Funct Ecol  19: 632– 9. Lailvaux SP, Gilbert RL, Edwards JR. 2012. A performance-based cost to honest signalling in male green anole lizards (Anolis carolinensis). Proc R Soc B Biol Sci  279: 2841– 8. Lailvaux SP, Leifer J, Kircher BK, Johnson MA. 2015. The incredible shrinking dewlap: signal size, skin elasticity, and mechanical design in the green anole lizard (Anolis carolinensis). Ecol Evol  5: 4400– 9. Lappin AK, Husak JF. 2005. Weapon performance, not size, determines mating success and potential reproductive output in the collared lizard (Crotaphytus collaris). Am Nat  166: 426– 36. Leal M, Rodríguez-Robles JA. 1995. Antipredator responses of Anolis cristatellus (Sauria: polychrotidae). Copeia  1995: 155– 61. Leal M, Rodríguez-Robles JA. 1997. Signaling displays during predator–prey interactions in a Puerto Rican anole, Anolis cristatellus. Anim Behav  54: 1147– 54. Lee JC, Clayton D, Eisenstein S, Perez I. 1989. The reproductive cycle of Anolis sagrei in southern Florida. Copeia  1989: 930– 7. Leimar O, Austad S, Enquist M. 1991. A test of the sequential assessment game: fighting in the bowl and doily spider Frontinella pyramitela. Evolution  45: 862– 74. Lengagne T, Slater PJB. 2002. The effects of rain on acoustic communication: tawny owls have good reason for calling less in wet weather. Proc R Soc Lond B  269: 2121– 5. Leonard ML, Horn AG. 2005. Ambient noise and the design of begging signals. Proc R Soc B Biol Sci  272: 651– 6. Losos JB. 1985. An experimental demonstration of the species-recognition role of Anolis dewlap color. Copeia  4: 905– 10. Losos JB, Butler M, Schoener TW. 2003. Sexual dimorphism in body size and shape in relation to habitat use among species of Caribbean Anolis lizards. In: Fox SF, McCoy JK, Baird TA, editors. Lizard social behaviour . Baltimore: John Hopkins University Press. p. 356– 380. Losos JB. 2009. Lizards in an evolutionary tree: ecology and adaptive radiation of Anoles . Berkeley (CA): University of California Press. p. 528. Maynard-Smith J, Harper D. 2003. Animal signals: Oxford series in ecology and evolution. New York: Oxford University Press. p. 1–166. McMann S. 1998. Display behavior and territoriality in the lizard Anolis sagrei [PhD dissertation]. University of Miami (FL). McMann S. 2000. Effects of residence time on displays during territory establishment in a lizard. Anim Behav  59: 513– 22. Molina-Borja M, Padron-Fumero M, Alfonso-Martin T. 1998. Morphological and behavioral traits affecting the intensity and outcome of male contests in Gallotia galloti galloti (family Lacertidae). Ethology  104: 314– 22. Møller AP, Pomiankowski A. 1993. Why have birds got multiple sexual ornaments. Behav Ecol Sociobiol  32: 167– 76. Muralidhar P, Johnson MA. 2017. Sexual selection and sex ratios in Anolis lizards. J Zool  302: 178– 83. Nicholson KE, Harmon LJ, Losos JB. 2007. Evolution of Anolis lizard dewlap diversity. PLoS One  2: e274. Ord TJ, Blumstein DT, Evans CS. 2001. Intrasexual selection predicts the evolution of signal complexity in lizards. Proc R Soc B Biol Sci  268: 737– 44. Orme D, Freckleton R, Thomas G, Petzoldt T, Fritz S, Isaac N, Pearse W. 2013. Caper: comparative analyses of phylogenetics and evolution in R. R package version 0.5.2 (https://cran.r-project.org/web/packages/caper/; last accessed November 2017). Orrell KS, Jenssen TA. 2003. Heterosexual signaling by the lizard Anolis carolinensis, with intersexual comparisons across contexts. Behaviour  140: 603– 34. Panhuis TM, Wilkinson GS. 1999. Exaggerated eye span influences male contest outcome in stalk-eyed flies. Behav Ecol Sociobiol  46: 221– 7. Pérez I de Lanuza G, Font E, Monterde EL. 2013. Using visual modelling to study the evolution of lizard coloration: sexual selection drives the evolution of sexual dichromatism in lacertids. J Evol Biol  26: 1826– 35. Perry G, Levering K, Girard I, Garland T. 2004. Locomotor performance and dominance in male Anolis cristatellus. Anim Behav  67: 37– 47. Peters RA, Evans CS. 2003. Design of the Jacky dragon visual display: signal and noise characteristics in a complex moving environment. J Comp Physiol A  189: 447– 59. Rand AS. 1967. Ecology and social organization in the iguanid lizard Anolis lineatopus. Proc US Nat Mus  122: 1– 79. Rand AS, Williams EE. 1970. An estimation of redundancy and information content of anole dewlaps. Am Nat  104: 99– 103. Revell LJ. 2010. Phylogenetic signal and linear regression on species data. Methods Ecol Evol  1: 319– 29. Schoener TW, Schoener A. 1980. Densities sex ratios and population structure in four species of Bahamian Anolis lizards. J Anim Ecol  49: 19– 54. Schoener TW, Schoener A. 1982. The ecological correlates of survival in some Bahamanian Anolis lizards. Oikos  392: 1– 26. Scott MP. 1984. Agonistic and courtship displays of male Anolis sagrei. Breviora  479: 1– 22. Setchell JM, Wickings J. 2005. Dominance, status signals, and coloration in mandrills (Mandrillus sphinx). Ethology  111: 25– 30. Simon V. 2011. Communication signal rates predict interaction outcome in the brown anole lizard, Anolis sagrei. Copeia  2011: 38– 45. Sokal RR, Rohlf FJ. 1995. Biometry: the principles and practices of statistics in biological research . New York (NY): Freeman WH. 880 p. Stamps 1983. Sexual selection, sexual dimorphism and territoriality. In. Pianka ER, Schoener TW, editors. Lizard ecology: studies of a model organism . Cambridge (MA): Harvard University Press. p. 169– 204. Stamps JA, Losos JB, Andrews RM. 1997. A comparative study of population density and sexual size dimorphism in lizards. Am Nat  149: 64– 90. Steffen JE, Guyer CC. 2014. Display behaviour and dewlap colour as predictors of contest success in brown anoles. Biol J Linn Soc  111: 646– 55. Tinkle DW, Wilbur HM, Tilley SG. 1970. Evolutionary strategies in lizard reproduction. Evolution 24:55–74. Tokarz RR. 1985. Body size as a factor determining dominance in staged agonistic encounters between male brown anoles (Anolis sagrei). Anim Behav  33: 746– 53. Tokarz RR. 1987. Effects of cortisone treatment on male aggressive behavior in a lizard (Anolis sagrei). Horm Behav 21:358–70. Tokarz RR. 1998. Mating pattern in the lizard, Anolis sagrei: implications for mate choice and sperm competition. Herpetologica  54: 388– 94. Tokarz RR. 2002. An experimental test of the importance of the dewlap in male mating success in the lizard Anolis sagrei. Herpetologica  58: 87– 94. Tokarz RR, Paterson AV, McMann S. 2003. Laboratory and field test of the functional significance of the male’s dewlap in the lizard Anolis sagrei. Copeia  2003: 502– 11. Trivers RL. 1976. Sexual selection and resource-accruing abilities in Anolis garmani. Evolution  30: 253– 69. Vanhooydonck B, Herrel A, Van Damme R, Irschick DJ. 2005a. Does dewlap size predict male bite performance in Jamaican Anolis lizards? Funct Ecol  19: 38– 42. Vanhooydonck B, Herrel A, Van Damme R, Meyers JJ, Irschick DJ. 2005b. The relationship between dewlap size and performance changes with age and sex in a Green Anole (Anolis carolinensis) lizard population. Behav Ecol Sociobiol  59: 157– 65. Vanhooydonck B, Herrel A, Meyers JJ, Irschick DJ. 2009. What determines dewlap diversity in Anolis lizards? An among-island comparison. J Evol Biol  22: 293– 305. Zuk M, Ligon JD, Thornhill R. 1992. Effects of experimental manipulation of male secondary sex characters on female mate preference in red jungle fowl. Anim Behav  44: 999– 1006. © The Author(s) 2018. Published by Oxford University Press on behalf of the Society for Integrative and Comparative Biology. All rights reserved. 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Intraspecific Variation in the Information Content of an Ornament: Why Relative Dewlap Size Signals Bite Force in Some, But Not All Island Populations of Anolis sagrei

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Abstract

Abstract In many animals, male secondary sexual traits advertise reliable information on fighting capacity in a male–male context. The iconic sexual signaling device of anole lizards, the dewlap, has been extensively studied in this respect. For several territorial anole species (experiencing strong intrasexual selection), there is evidence for a positive association between dewlap size and bite capacity, which is an important determinant of combat outcome in lizards. Intriguingly, earlier studies did not find this expected correlation (relative dewlap size–relative bite force) in the highly territorial brown anole lizard, Anolis sagrei. We hypothesize that the dewlap size–bite force relationship can differ among populations of the same species due to interpopulation variation in the degree of male–male competition. In line with this thought, we expect dewlap size to serve as a reliable predictor of bite performance only in those populations where the level of intrasexual selection is high. To tackle this hypothesis, we examined the relationship between male dewlap size and bite force on the intraspecific level in A. sagrei, using an extensive dataset encompassing information from 17 island populations distributed throughout the Caribbean. First, we assessed and compared the relationship between both variables in the 17 populations under study. Second, we linked the relative dewlap size–bite force relationship within each population to variation in the degree of intrasexual selection among populations, using sexual size dimorphism and dewlap display intensity as surrogate measures. Our results showed that absolute dewlap size is an excellent predictor of maximum bite force in nearly all A. sagrei populations. However, relative dewlap size is only an honest signal of bite performance in 4 out of the 17 populations. Surprisingly, the level of signal honesty did not correlate with the strength of intrasexual selection. We offer a number of conceptual and methodological explanations for this unexpected finding. Introduction The evolution of male secondary sexual traits, such as the colossal antlers in deer or the giant horns in rhinoceros beetles, has fascinated biologists ever since Darwin (1871; Andersson 1982; Bradbury and Vehrencamp 1998; Emlen 2008). These elaborate sexual traits can function as real weapons to overpower or even kill male opponents (e.g., mandibles of male fig wasps; Bean and Cook 2001), but also as reliable signals advertising “fighting capacity” without playing a role during actual physical combats (e.g., red coloration in male mandrills; Setchell and Wickings 2005). Traits that honestly signal fighting capacity seem highly beneficial to predict contest outcomes and thereby avoid the costly interactions physical combats may impose (Andersson 1994). This is especially true for species where actual fights between males can result in serious body damage and even in death (e.g., wasps, Bean and Cook 2001; Abe et al. 2003; spiders, Leimar et al. 1991). The idea that male secondary sexual signals communicate reliable information about quality in an intrasexual context has been evidenced by a variety of studies showing a direct link between variation in signal design (especially size and color) and the ability to win male contests (e.g., Jennions and Backwell 1996; Panhuis and Wilkinson 1999; Alonso-Alvarez et al. 2004). In many cases, the size of these sexual traits correlates strongly with overall body size (arguably the most important predictor of contest outcome (e.g., Clutton-Brock et al. 1979; Hughes 1996; Karsten et al. 2009; Hardy and Briffa 2013), and as such acts as a redundant or back-up signal (Zuk et al. 1992; Johnstone 1996; Candolin 2003) when advertising fighting capacity. However, in at least some cases, the size of secondary sexual traits reveals more than just the carrier’s overall body size during agonistic interactions. Here, sexual signal size contains information on fighting capacity independent of overall body size (i.e., relative size), and can therefore be considered as a reliable signal in itself. In dung beetles, for example, relative male horn size accurately predicts pulling force and maximal exertion, two ecologically relevant performance measures associated with fighting success in beetles (Lailvaux et al. 2005). Also in lizards, male signals can act as size-free indices of fighting capacity, quantified by endurance or bite force (e.g., Perry et al. 2004; Lappin and Husak 2005; Vanhooydonck et al. 2005a). Anole lizards in particular have received considerable attention in this respect (e.g., Lailvaux et al. 2004; Vanhooydonck et al. 2005b; Lailvaux and Irschick 2007). They typically have an extendible throat fan, called a dewlap. This sexually selected trait is generally far more elaborated in the male sex and is exceptional for its high degree of interspecific variation in design (Nicholson et al. 2007; Johnson and Wade 2010). Besides, anoles exhibit varying degrees of territoriality and male–male competition (Losos 2009; Johnson et al. 2009; Kamath and Losos 2017), also reflected by their remarkable diversity in sexual size dimorphism (SSD; i.e., predominantly male-biased SSD) (Stamps et al. 1997; Ord et al. 2001; Butler et al. 2007). One obvious question that arises is whether dewlap size indicates fighting capacity in Anolis lizards? The evidence is rather mixed. In highly territorial, sexually dimorphic (high-SSD) species (i.e., A. carolinensis, A. cristatellus, A. evermanni, A. gundlachi, and A. lineatopus), relative dewlap size predicts bite force and thus seems to contain detailed information on fighting capacity (Vanhooydonck et al. 2005a; Lailvaux and Irschick 2007). However, no such relationship was found in less dimorphic (low-SSD) species (i.e., A. angusticeps, A. distichus, and A. valencienni; Vanhooydonck et al. 2005a; Lailvaux and Irschick 2007). The authors explain the lack of this relation in less dimorphic species preliminary by a low degree of territoriality. Bite performance, in particular, might be far less important for males of species that do not actively defend territories or that do not experience a high degree of male–male competition associated with vigorous fights. Lailvaux and Irschick (2007) further corroborated this idea by showing that bite force predicted male combat success only in the high-SSD species and that the incidence of biting increased with SSD. Intriguingly, one species in their dataset defied this putative principle: Anolis sagrei, albeit clearly sexually dimorphic, did not show the expected positive correlation between relative dewlap size and bite performance (although a significant relationship was found between absolute dewlap size and bite force). In accordance, Driessens et al. (2015) also failed to find such a relationship in wild-caught males from Florida, when looking at relative indices. Because of these unexpected results, we aimed to further explore the dewlap size–bite force relationship in this polygynous and highly territorial species (Schoener and Schoener 1980; Tokarz 1998, 2002). Direct physical combats are commonly observed among brown anole males and primarily involve biting, jaw sparring, and interlocking (Scott 1984; Tokarz 1985, 1987; McMann 2000; Steffen and Guyer 2014; Driessens et al. 2014). Anolis sagrei has a yellow-to-reddish dewlap that can show dramatic intraspecific variation in size, color, pattern, and even use (Vanhooydonck et al. 2009; Edwards and Lailvaux 2012; Driessens et al. 2017). Adult males primarily use dewlap displays in combination with push-ups and head-bobs for territorial defense and/or for access to females (e.g., Scott 1984; Simon 2011; Driessens et al. 2014). Recently, display behavior and dewlap color have been reported to predict the outcome of staged contests between size-matched males (Steffen and Guyer 2014), further demonstrating the role of the A. sagrei dewlap in signaling quality to opponents (but see Tokarz et al. 2003). Close-proximity contest experiments additionally revealed that A. sagrei males with enhanced biting capacities are at a competitive advantage for winning fights (Lailvaux and Irschick 2007), highlighting the importance of signaling bite capacity too, during agonistic interactions. The main goal of this study is to look in more detail at the relationship between male dewlap size and bite force, explicitly for A. sagrei. Therefore, we took an intraspecific comparative approach, documenting and comparing this specific relationship in 17 A. sagrei island populations distributed across the Caribbean. We looked at the relationship between dewlap size and bite force, using absolute as well as relative indices. Consistent with previous studies, we expected absolute dewlap size to be a good predictor of absolute bite force for each study population (Lailvaux and Irschick 2007; Cox et al. 2009; Driessens et al. 2015). However, we hypothesize that the relative dewlap size–bite force relationship will differ among populations due to interpopulation variation in the degree of male–male competition. In line with this thought, we expect dewlap size to serve as a reliable predictor of bite performance only in those populations where the level of intrasexual selection is high (following Lailvaux and Irschick 2007). To do so, we linked the dewlap size–bite force relationship within each population to both SSD and display intensity (DI) among populations, taking into account phylogenetic relationships. Materials and methods Animals We sampled a total of 639 adult A. sagrei males from 17 populations distributed across the Caribbean (Fig. 1). Sampling localities included Acklins, Andros, Chub Cay, Crooked Island, Grand Bahama, Pidgeon Cay, Staniel Cay (data collection for these seven populations occurred in April–May 2003), Jamaica (March 2012), Cuba (Santa Clara, Soroa 1, Soroa 2; April–May 2012), San Salvador (January 2013), Cayman Islands (Cayman Brac, Grand Cayman, Little Cayman; March 2013), South Abaco, and South Bimini (March 2015). Since previous studies on A. carolinensis have reported a significant effect of seasonality on dewlap size, bite force, and display behavior (Jenssen et al. 1995, 2001; Irschick et al. 2006; Lailvaux et al. 2015), data were collected during the A. sagrei breeding season (March–September, Lee et al. 1989), apart from one population (i.e., San Salvador) that was sampled in January. We caught 404 A. sagrei males by noose and kept them individually in plastic bags for maximum 48 h, before releasing them back at the location of capture. For these individuals, we measured morphology, quantified dewlap size, and carried out standard bite force measurements. Another 235 male individuals (but only for ten populations) were video-recorded while behaving in their natural habitat. Fig. 1 View largeDownload slide (a) Phylogenetic relationships among the 17 Anolis sagrei study populations presented with corresponding sampling sites (b) distributed across the Caribbean. Circle size represents the mean dewlap size (red) and bite force (blue) of a population. Photograph (c) showing the large dewlap of a male A. sagrei lizard. Fig. 1 View largeDownload slide (a) Phylogenetic relationships among the 17 Anolis sagrei study populations presented with corresponding sampling sites (b) distributed across the Caribbean. Circle size represents the mean dewlap size (red) and bite force (blue) of a population. Photograph (c) showing the large dewlap of a male A. sagrei lizard. Morphology We measured the lizards’ snout–vent length (SVL) and head length (HL; from the tip of the snout to the posterior edge of the parietal scale) using digital calipers (Mitutoyo CD-15DC, accuracy 0.01 mm). For measuring dewlap size, lizards were first positioned on their left side against a 1-cm2 gridded paper. We then gently pulled the base of the ceratobranchial forward with a pair of forceps until the dewlap was fully extended parallel to the grid (Bels 1990). Next, we photographed the dewlap, using a Nikon D70 camera mounted on a tripod. Last, Adobe Photoshop CS3 extended software (AP CS3, version 10.0) was used to trace the outer edge of the dewlap on the digital images and to calculate absolute dewlap area. This standard method for measuring dewlap dimensions has produced highly repeatable results in a previous study (Vanhooydonck et al. 2005a). Bite force Standard methods were used to measure maximum bite force. Briefly, we encouraged lizards to bite on two metal plates connected to an isometric Kistler force transducer (type 9203) and charge amplifier (type 5995); for detailed descriptions of setup and biting procedure, see Herrel et al. (1999a) and Vanhooydonck et al. (2005b). Each individual was subjected to a total of five bite trials with approximately 30 min in between (as in e.g., Herrel et al. 2001; Lailvaux et al. 2004; Irschick et al. 2006; Lailvaux and Irschick 2007). The highest of the five bite force measurements was then used as the maximal bite force capacity in each individual. The applied methodology has been widely used and shown to be effective for obtaining maximal bite forces in lizards (e.g., Herrel et al. 2001; Lailvaux et al. 2004; Vanhooydonck et al. 2005b; Lailvaux and Irschick 2007; Baeckens et al. 2017). Since temperature is known to affect bite performance (Bennett 1985; Herrel et al. 1999b; Anderson et al. 2008), we made sure every lizard had a body temperature between 29°C and 31°C prior to every bite trial (the average field-active body temperature of A. sagrei is 30.6°C; Losos 2009). Body temperature was verified using a cloacal thermometer (APPA51, K-type). Sexual size dimorphism Consistent with Lailvaux and Irschick (2007, and references therein), we calculated SSD as mean SVL in males divided by mean SVL in females. Values of SSD were calculated for each population, and only SVLs of mature males and females were included. Display intensity As in Driessens et al. (2017), we recorded the natural behavior of 20–30 males per population (ten study populations) for a timespan of 10 min, using a high-definition camera (Sony, HDR-CX260VE). First, we located lizards by walking slowly through their natural habitat until an apparently undisturbed individual was spotted. Next, we started filming the lizard’s behavior from approximately 5–15 m using the camera zoom function (30× optical zoom), in order to minimize disturbances caused by our presence. Video recordings were only made during sunny or partly cloudy conditions to avoid possible confounding effects of weather on the lizard’s activity level (Huey 1982; Hertz et al. 1993). All behavioral recordings were scored offline, using JWatcher event-recorder software (Blumstein and Daniel 2007). For each focal individual, we noted the number and duration of three main display types: head-nods (up-and-down movement of the head), push-ups (up-and-down movement of the body and tail caused by flexion of the legs), and dewlap extensions (pulsing of the dewlap). These displays can function in species recognition (e.g., Rand and Williams 1970; Losos 1985), in predator deterrence (e.g., Leal and Rodríguez-Robles 1995, 1997), but most often in social and sexual communication (e.g., Greenberg and Noble 1944; Jenssen 1970; Crews 1975; Carpenter 1978; Driessens et al. 2014; Baeckens et al. 2016). Moreover, DI is typically inter-correlated in the sense that males that frequently perform one display type also exhibit the other types at a high rate (e.g., Scott 1984; McMann 2000; Driessens et al. 2014; Steffen and Guyer 2014). In the remaining, “DI” refers to the proportion of time that individuals spent displaying in their natural setting during the 10 min observation period (averaged per population). Statistical analyses Prior to statistical analyses, data on HL, dewlap size, bite force, and SSD were log10-transformed. Proportion data (i.e., DI) were normalized via arcsin-square root transformation (Sokal and Rohlf 1995). In all cases, assumptions of normality were confirmed using Shapiro–Wilk tests, and probabilities (P) lower than 0.05 were considered significant. All statistical tests involving dewlap size and bite force were done with absolute as well as relative (i.e., size-corrected) data. Consistent with Vanhooydonck et al. (2005a) and Lailvaux and Irschick (2007), we used HL for removing effects of overall size. This metric strongly correlated with dewlap size and bite force, and has previously proven to be most appropriate for calculating relative indices of these two variables (Vanhooydonck et al. 2005a; Herrel and O’Reilly 2006). Relative bite force and dewlap size were calculated by regressing log10 bite force and log10 dewlap size against log10 HL and, subsequently, by extracting the residual values for all individuals. We first ran a univariate general linear model (GLM) to test whether the relationship between dewlap size and bite force (independent and dependent variable, respectively) differed among our study populations. HL was then added to the model as a covariate, to assess the same effects after size correction. Both GLM analyses revealed significant dewlap size * population interaction effects on bite force, which impelled us to subsequently examine this relationship separately within populations. We therefore carried out linear regressions per population with dewlap size as independent and bite force as dependent variable. Following Lailvaux and Irschick (2007), we obtained relative indices by regressing dewlap size and bite force against HL and calculating the residuals for all individuals per population. We then ran a second set of linear regressions, this time with relative bite force against relative dewlap size (i.e., residuals; consistent with Vanhooydonck et al. 2005a; Lailvaux and Irschick 2007). Among-population analyses were performed in an explicit phylogenetic context in order to account for the non-independency of our data points (Felsenstein 1985; Harvey and Pagel 1991). We used the phylogenetic tree proposed by Driessens et al. (2017) in all phylogenetic comparative analyses. Driessens’ tree was created using the exact same populations sampled in this study. To test the idea that reliable information content of the dewlap in itself depends on the local intensity of intrasexual selection, we regressed the slope of the relative “dewlap size–bite force” regression line for each population (i.e., coefficient b) against SSD and DI, respectively. We here employed phylogenetic generalized least squares (pgls) regressions with incorporation of phylogenetic relationships on population level (caper package R, Orme et al. [2013]; for a detailed description of the used phylogenetic tree, see Driessens et al. 2017). This method uses maximum likelihood to simultaneously estimate the regression model and phylogenetic signal (Pagel’s λ) of the residual error (Garland and Ives 2000; Revell 2010), and has shown to do better than a priori tests of phylogenetic signal; especially when sample sizes are smaller than 20 (Blomberg et al. 2003; Revell 2010; Kamilar and Cooper 2013). Because data from one population (i.e., San Salvador) could only be collected outside the breeding season, we ran an additional set of the same pgls regression analyses excluding these particular data. Results Population means and standard deviations for tested variables are provided in Table 1. The relationship between dewlap size and bite force differed significantly among populations (F16,381 = 14.93, P < 0.0001), also after correcting for body size (F16, 380 = 9.36, P < 0.0001). Within-population regression analyses revealed that absolute dewlap size is an excellent predictor of absolute bite force in nearly all study populations (R > 0.65, P < 0.005, Table 2); only for the population of Santa Clara the relationship failed to reach the conventional level of statistical significance (R = 0.38, P = 0.054). However, after correcting for body size, in only 4 out of the 17 tested populations, relative dewlap size still exhibited a significant positive relationship with bite force (Table 2 and Fig. 2). We additionally observed that these results based on relative indices varied widely across populations with estimated slopes ranging from −0.353 in Little Cayman to +0.729 in South Abaco (Table 2). Overall, results of the population sampled outside the breeding season (i.e., San Salvador) did not deviate from the other study populations sampled during the reproductive cycle in A. sagrei (both absolute and relative indices, Tables 1 and 2 and Fig. 1). Table 1 Descriptive statistics of the tested variables Populations  HL (mm)  SVL (mm)  Dewlap size (cm2)  Bite force (N)  SSD  DI  Acklins  15.09 ± 1.06 (10)  56.36 ± 5.24 (10)  2.58 ± 0.68 (10)  5.75 ± 1.45 (10)  1.43 (10, 12)  —  Andros  12.81 ± 0.87 (23)  46.37 ± 3.25 (23)  1.21 ± 0.33 (23)  1.90 ± 0.51 (23)  1.23 (23, 18)  —  Cayman Brac  15.19 ± 1.03 (28)  55.07 ± 4.30 (28)  1.53 ± 0.39 (28)  5.22 ± 1.65 (28)  1.33 (28, 29)  0.01 ± 0.03 (23)  Chub Cay  13.92 ± 0.88 (20)  47.87 ± 3.62 (20)  1.67 ± 0.49 (20)  3.36 ± 0.92 (20)  1.32 (20, 16)  —  Crooked Island  13.68 ± 1.04 (23)  49.86 ± 4.61 (23)  1.81 ± 0.61 (23)  3.66 ± 1.34 (23)  1.25 (23, 20)  —  Grand Bahama  12.82 ± 1.43 (24)  46.78 ± 6.34 (24)  1.59 ± 0.41 (21)  2.26 ± 1.39 (24)  1.33 (24, 11)  —  Grand Cayman  14.47 ± 1.21 (27)  51.74 ± 4.57 (27)  1.64 ± 0.41 (27)  6.11 ± 2.19 (27)  1.28 (27, 29)  0.07 ± 0.11 (24)  Jamaica  13.92 ± 1.00 (32)  48.60 ± 3.98 (32)  1.17 ± 0.27 (32)  6.90 ± 2.17 (32)  1.24 (32, 23)  0.02 ± 0.03 (22)  Little Cayman  15.17 ± 1.06 (28)  53.46 ± 4.35 (28)  2.00 ± 0.56 (28)  5.22 ± 1.57 (27)  1.29 (28, 27)  0.01 ± 0.01 (23)  Pidgeon Cay  14.15 ± 0.80 (16)  48.19 ± 3.28 (16)  1.56 ± 0.39 (16)  2.82 ± 0.79 (16)  1.21 (16, 8)  —  San Salvador  16.27 ± 1.52 (27)  58.13 ± 5.85 (27)  1.96 ± 0.75 (27)  7.99 ± 2.24 (27)  1.35 (27, 14)  0.02 ± 0.02 (24)  Santa Clara  15.80 ± 0.82 (27)  55.21 ± 2.97 (27)  2.06 ± 0.36 (27)  7.68 ± 1.78 (27)  1.33 (27, 24)  0.18 ± 0.13 (24)  Soroa 1  14.84 ± 1.35 (23)  51.10 ± 4.44 (23)  1.91 ± 0.45 (23)  6.63 ± 1.94 (23)  1.24 (23, 21)  0.11 ± 0.11 (24)  Soroa 2  15.50 ± 1.03 (22)  55.45 ± 4.46 (22)  2.27 ± 0.46 (22)  7.53 ± 2.00 (22)  1.32 (22, 24)  0.17 ± 0.14 (30)  South Abaco  13.07 ± 1.16 (26)  46.59 ± 4.15 (26)  1.35 ± 0.48 (26)  2.27 ± 0.96 (25)  1.28 (26, 21)  0.02 ± 0.04 (21)  South Bimini  14.91 ± 1.38 (24)  53.66 ± 4.60 (27)  1.62 ± 0.45 (26)  4.04 ± 1.13 (24)  1.30 (27, 23)  0.02 ± 0.02 (20)  Staniel Cay  13.86 ± 1.16 (26)  51.82 ± 5.41 (26)  1.91 ± 0.69 (26)  3.14 ± 1.05 (26)  1.32 (26, 20)  —  Populations  HL (mm)  SVL (mm)  Dewlap size (cm2)  Bite force (N)  SSD  DI  Acklins  15.09 ± 1.06 (10)  56.36 ± 5.24 (10)  2.58 ± 0.68 (10)  5.75 ± 1.45 (10)  1.43 (10, 12)  —  Andros  12.81 ± 0.87 (23)  46.37 ± 3.25 (23)  1.21 ± 0.33 (23)  1.90 ± 0.51 (23)  1.23 (23, 18)  —  Cayman Brac  15.19 ± 1.03 (28)  55.07 ± 4.30 (28)  1.53 ± 0.39 (28)  5.22 ± 1.65 (28)  1.33 (28, 29)  0.01 ± 0.03 (23)  Chub Cay  13.92 ± 0.88 (20)  47.87 ± 3.62 (20)  1.67 ± 0.49 (20)  3.36 ± 0.92 (20)  1.32 (20, 16)  —  Crooked Island  13.68 ± 1.04 (23)  49.86 ± 4.61 (23)  1.81 ± 0.61 (23)  3.66 ± 1.34 (23)  1.25 (23, 20)  —  Grand Bahama  12.82 ± 1.43 (24)  46.78 ± 6.34 (24)  1.59 ± 0.41 (21)  2.26 ± 1.39 (24)  1.33 (24, 11)  —  Grand Cayman  14.47 ± 1.21 (27)  51.74 ± 4.57 (27)  1.64 ± 0.41 (27)  6.11 ± 2.19 (27)  1.28 (27, 29)  0.07 ± 0.11 (24)  Jamaica  13.92 ± 1.00 (32)  48.60 ± 3.98 (32)  1.17 ± 0.27 (32)  6.90 ± 2.17 (32)  1.24 (32, 23)  0.02 ± 0.03 (22)  Little Cayman  15.17 ± 1.06 (28)  53.46 ± 4.35 (28)  2.00 ± 0.56 (28)  5.22 ± 1.57 (27)  1.29 (28, 27)  0.01 ± 0.01 (23)  Pidgeon Cay  14.15 ± 0.80 (16)  48.19 ± 3.28 (16)  1.56 ± 0.39 (16)  2.82 ± 0.79 (16)  1.21 (16, 8)  —  San Salvador  16.27 ± 1.52 (27)  58.13 ± 5.85 (27)  1.96 ± 0.75 (27)  7.99 ± 2.24 (27)  1.35 (27, 14)  0.02 ± 0.02 (24)  Santa Clara  15.80 ± 0.82 (27)  55.21 ± 2.97 (27)  2.06 ± 0.36 (27)  7.68 ± 1.78 (27)  1.33 (27, 24)  0.18 ± 0.13 (24)  Soroa 1  14.84 ± 1.35 (23)  51.10 ± 4.44 (23)  1.91 ± 0.45 (23)  6.63 ± 1.94 (23)  1.24 (23, 21)  0.11 ± 0.11 (24)  Soroa 2  15.50 ± 1.03 (22)  55.45 ± 4.46 (22)  2.27 ± 0.46 (22)  7.53 ± 2.00 (22)  1.32 (22, 24)  0.17 ± 0.14 (30)  South Abaco  13.07 ± 1.16 (26)  46.59 ± 4.15 (26)  1.35 ± 0.48 (26)  2.27 ± 0.96 (25)  1.28 (26, 21)  0.02 ± 0.04 (21)  South Bimini  14.91 ± 1.38 (24)  53.66 ± 4.60 (27)  1.62 ± 0.45 (26)  4.04 ± 1.13 (24)  1.30 (27, 23)  0.02 ± 0.02 (20)  Staniel Cay  13.86 ± 1.16 (26)  51.82 ± 5.41 (26)  1.91 ± 0.69 (26)  3.14 ± 1.05 (26)  1.32 (26, 20)  —  Notes: Population means ± standard deviations are presented for each population, with the exception of SSD (i.e., mean SVL males divided by mean SVL females). Sample sizes are provided between brackets for each variable separately; for SSD the number of implemented males and females is shown (left and right, respectively). HL, head length; SVL, snout-to-vent length; SSD, sexual size dimorphism; DI, display intensity, as the proportion of time that individuals spent displaying. Table 1 Descriptive statistics of the tested variables Populations  HL (mm)  SVL (mm)  Dewlap size (cm2)  Bite force (N)  SSD  DI  Acklins  15.09 ± 1.06 (10)  56.36 ± 5.24 (10)  2.58 ± 0.68 (10)  5.75 ± 1.45 (10)  1.43 (10, 12)  —  Andros  12.81 ± 0.87 (23)  46.37 ± 3.25 (23)  1.21 ± 0.33 (23)  1.90 ± 0.51 (23)  1.23 (23, 18)  —  Cayman Brac  15.19 ± 1.03 (28)  55.07 ± 4.30 (28)  1.53 ± 0.39 (28)  5.22 ± 1.65 (28)  1.33 (28, 29)  0.01 ± 0.03 (23)  Chub Cay  13.92 ± 0.88 (20)  47.87 ± 3.62 (20)  1.67 ± 0.49 (20)  3.36 ± 0.92 (20)  1.32 (20, 16)  —  Crooked Island  13.68 ± 1.04 (23)  49.86 ± 4.61 (23)  1.81 ± 0.61 (23)  3.66 ± 1.34 (23)  1.25 (23, 20)  —  Grand Bahama  12.82 ± 1.43 (24)  46.78 ± 6.34 (24)  1.59 ± 0.41 (21)  2.26 ± 1.39 (24)  1.33 (24, 11)  —  Grand Cayman  14.47 ± 1.21 (27)  51.74 ± 4.57 (27)  1.64 ± 0.41 (27)  6.11 ± 2.19 (27)  1.28 (27, 29)  0.07 ± 0.11 (24)  Jamaica  13.92 ± 1.00 (32)  48.60 ± 3.98 (32)  1.17 ± 0.27 (32)  6.90 ± 2.17 (32)  1.24 (32, 23)  0.02 ± 0.03 (22)  Little Cayman  15.17 ± 1.06 (28)  53.46 ± 4.35 (28)  2.00 ± 0.56 (28)  5.22 ± 1.57 (27)  1.29 (28, 27)  0.01 ± 0.01 (23)  Pidgeon Cay  14.15 ± 0.80 (16)  48.19 ± 3.28 (16)  1.56 ± 0.39 (16)  2.82 ± 0.79 (16)  1.21 (16, 8)  —  San Salvador  16.27 ± 1.52 (27)  58.13 ± 5.85 (27)  1.96 ± 0.75 (27)  7.99 ± 2.24 (27)  1.35 (27, 14)  0.02 ± 0.02 (24)  Santa Clara  15.80 ± 0.82 (27)  55.21 ± 2.97 (27)  2.06 ± 0.36 (27)  7.68 ± 1.78 (27)  1.33 (27, 24)  0.18 ± 0.13 (24)  Soroa 1  14.84 ± 1.35 (23)  51.10 ± 4.44 (23)  1.91 ± 0.45 (23)  6.63 ± 1.94 (23)  1.24 (23, 21)  0.11 ± 0.11 (24)  Soroa 2  15.50 ± 1.03 (22)  55.45 ± 4.46 (22)  2.27 ± 0.46 (22)  7.53 ± 2.00 (22)  1.32 (22, 24)  0.17 ± 0.14 (30)  South Abaco  13.07 ± 1.16 (26)  46.59 ± 4.15 (26)  1.35 ± 0.48 (26)  2.27 ± 0.96 (25)  1.28 (26, 21)  0.02 ± 0.04 (21)  South Bimini  14.91 ± 1.38 (24)  53.66 ± 4.60 (27)  1.62 ± 0.45 (26)  4.04 ± 1.13 (24)  1.30 (27, 23)  0.02 ± 0.02 (20)  Staniel Cay  13.86 ± 1.16 (26)  51.82 ± 5.41 (26)  1.91 ± 0.69 (26)  3.14 ± 1.05 (26)  1.32 (26, 20)  —  Populations  HL (mm)  SVL (mm)  Dewlap size (cm2)  Bite force (N)  SSD  DI  Acklins  15.09 ± 1.06 (10)  56.36 ± 5.24 (10)  2.58 ± 0.68 (10)  5.75 ± 1.45 (10)  1.43 (10, 12)  —  Andros  12.81 ± 0.87 (23)  46.37 ± 3.25 (23)  1.21 ± 0.33 (23)  1.90 ± 0.51 (23)  1.23 (23, 18)  —  Cayman Brac  15.19 ± 1.03 (28)  55.07 ± 4.30 (28)  1.53 ± 0.39 (28)  5.22 ± 1.65 (28)  1.33 (28, 29)  0.01 ± 0.03 (23)  Chub Cay  13.92 ± 0.88 (20)  47.87 ± 3.62 (20)  1.67 ± 0.49 (20)  3.36 ± 0.92 (20)  1.32 (20, 16)  —  Crooked Island  13.68 ± 1.04 (23)  49.86 ± 4.61 (23)  1.81 ± 0.61 (23)  3.66 ± 1.34 (23)  1.25 (23, 20)  —  Grand Bahama  12.82 ± 1.43 (24)  46.78 ± 6.34 (24)  1.59 ± 0.41 (21)  2.26 ± 1.39 (24)  1.33 (24, 11)  —  Grand Cayman  14.47 ± 1.21 (27)  51.74 ± 4.57 (27)  1.64 ± 0.41 (27)  6.11 ± 2.19 (27)  1.28 (27, 29)  0.07 ± 0.11 (24)  Jamaica  13.92 ± 1.00 (32)  48.60 ± 3.98 (32)  1.17 ± 0.27 (32)  6.90 ± 2.17 (32)  1.24 (32, 23)  0.02 ± 0.03 (22)  Little Cayman  15.17 ± 1.06 (28)  53.46 ± 4.35 (28)  2.00 ± 0.56 (28)  5.22 ± 1.57 (27)  1.29 (28, 27)  0.01 ± 0.01 (23)  Pidgeon Cay  14.15 ± 0.80 (16)  48.19 ± 3.28 (16)  1.56 ± 0.39 (16)  2.82 ± 0.79 (16)  1.21 (16, 8)  —  San Salvador  16.27 ± 1.52 (27)  58.13 ± 5.85 (27)  1.96 ± 0.75 (27)  7.99 ± 2.24 (27)  1.35 (27, 14)  0.02 ± 0.02 (24)  Santa Clara  15.80 ± 0.82 (27)  55.21 ± 2.97 (27)  2.06 ± 0.36 (27)  7.68 ± 1.78 (27)  1.33 (27, 24)  0.18 ± 0.13 (24)  Soroa 1  14.84 ± 1.35 (23)  51.10 ± 4.44 (23)  1.91 ± 0.45 (23)  6.63 ± 1.94 (23)  1.24 (23, 21)  0.11 ± 0.11 (24)  Soroa 2  15.50 ± 1.03 (22)  55.45 ± 4.46 (22)  2.27 ± 0.46 (22)  7.53 ± 2.00 (22)  1.32 (22, 24)  0.17 ± 0.14 (30)  South Abaco  13.07 ± 1.16 (26)  46.59 ± 4.15 (26)  1.35 ± 0.48 (26)  2.27 ± 0.96 (25)  1.28 (26, 21)  0.02 ± 0.04 (21)  South Bimini  14.91 ± 1.38 (24)  53.66 ± 4.60 (27)  1.62 ± 0.45 (26)  4.04 ± 1.13 (24)  1.30 (27, 23)  0.02 ± 0.02 (20)  Staniel Cay  13.86 ± 1.16 (26)  51.82 ± 5.41 (26)  1.91 ± 0.69 (26)  3.14 ± 1.05 (26)  1.32 (26, 20)  —  Notes: Population means ± standard deviations are presented for each population, with the exception of SSD (i.e., mean SVL males divided by mean SVL females). Sample sizes are provided between brackets for each variable separately; for SSD the number of implemented males and females is shown (left and right, respectively). HL, head length; SVL, snout-to-vent length; SSD, sexual size dimorphism; DI, display intensity, as the proportion of time that individuals spent displaying. Table 2 Univariate linear regression analyses of bite force (dependent variable) against dewlap size (independent variable) within population Population  R  F  df  Coefficient b ± SE  P-value  Absolute bite force against dewlap size          Acklins  0.819  16.28  9  0.761 ± 0.189  0.004  Andros  0.806  38.81  22  0.758 ± 0.122  <0.001  Cayman Brac  0.652  19.28  27  0.792 ± 0.180  <0.001  Chub Cay  0.909  85.16  19  0.948 ± 0.102  <0.001  Crooked Island  0.810  40.09  22  0.828 ± 0.131  <0.001  Grand Bahama  0.723  20.82  20  1.503 ± 0.329  <0.001  Grand Cayman  0.784  39.87  26  0.156 ± 0.183  <0.001  Jamaica  0.740  36.31  31  0.933 ± 0.155  <0.001  Little Cayman  0.704  23.55  25  0.682 ± 0.141  <0.001  Pidgeon Cay  0.708  14.03  15  0.622 ± 0.166  0.002  San Salvador  0.904  112.0  26  0.637 ± 0.060  <0.001  Santa Clara  0.375  4.093  26  0.471 ± 0.233  0.054  Soroa 1  0.870  65.69  22  1.078 ± 0.133  <0.001  Soroa 2  0.795  34.45  21  1.254 ± 0.214  <0.001  South Abaco  0.762  31.89  24  0.936 ± 0.166  <0.001  South Bimini  0.729  23.77  22  0.670 ± 0.137  <0.001  Staniel Cay  0.799  42.48  25  0.651 ± 0.100  <0.001  Relative bite force against relative dewlap size        Acklins  0.380  1.352  9  0.214 ± 0.184  0.278  Andros  0.413  4.328  22  0.420 ± 0.202  0.050  Cayman Brac  0.266  1.972  27  −0.303 ± 0.216  0.172  Chub Cay  0.490  5.679  19  0.635 ± 0.267  0.028  Crooked Island  0.108  0.249  22  0.089 ± 0.178  0.623  Grand Bahama  0.305  1.955  20  0.345 ± 0.246  0.178  Grand Cayman  0.153  0.603  26  0.185 ± 0.239  0.445  Jamaica  0.312  3.230  31  0.306 ± 0.170  0.082  Little Cayman  0.273  1.937  25  −0.353 ± 0.254  0.177  Pidgeon Cay  0.221  0.720  15  0.186 ± 0.219  0.411  San Salvador  0.166  0.707  26  0.112 ± 0.134  0.411  Santa Clara  0.212  1.177  26  0.251 ± 0.232  0.288  Soroa 1  0.623  13.36  22  0.639 ± 0.175  0.001  Soroa 2  0.335  2.523  21  0.451 ± 0.284  0.128  South Abaco  0.495  7.460  24  0.729 ± 0.267  0.012  South Bimini  0.243  1.318  22  0.301 ± 0.262  0.264  Staniel Cay  0.271  1.907  25  0.198 ± 0.144  0.180  Population  R  F  df  Coefficient b ± SE  P-value  Absolute bite force against dewlap size          Acklins  0.819  16.28  9  0.761 ± 0.189  0.004  Andros  0.806  38.81  22  0.758 ± 0.122  <0.001  Cayman Brac  0.652  19.28  27  0.792 ± 0.180  <0.001  Chub Cay  0.909  85.16  19  0.948 ± 0.102  <0.001  Crooked Island  0.810  40.09  22  0.828 ± 0.131  <0.001  Grand Bahama  0.723  20.82  20  1.503 ± 0.329  <0.001  Grand Cayman  0.784  39.87  26  0.156 ± 0.183  <0.001  Jamaica  0.740  36.31  31  0.933 ± 0.155  <0.001  Little Cayman  0.704  23.55  25  0.682 ± 0.141  <0.001  Pidgeon Cay  0.708  14.03  15  0.622 ± 0.166  0.002  San Salvador  0.904  112.0  26  0.637 ± 0.060  <0.001  Santa Clara  0.375  4.093  26  0.471 ± 0.233  0.054  Soroa 1  0.870  65.69  22  1.078 ± 0.133  <0.001  Soroa 2  0.795  34.45  21  1.254 ± 0.214  <0.001  South Abaco  0.762  31.89  24  0.936 ± 0.166  <0.001  South Bimini  0.729  23.77  22  0.670 ± 0.137  <0.001  Staniel Cay  0.799  42.48  25  0.651 ± 0.100  <0.001  Relative bite force against relative dewlap size        Acklins  0.380  1.352  9  0.214 ± 0.184  0.278  Andros  0.413  4.328  22  0.420 ± 0.202  0.050  Cayman Brac  0.266  1.972  27  −0.303 ± 0.216  0.172  Chub Cay  0.490  5.679  19  0.635 ± 0.267  0.028  Crooked Island  0.108  0.249  22  0.089 ± 0.178  0.623  Grand Bahama  0.305  1.955  20  0.345 ± 0.246  0.178  Grand Cayman  0.153  0.603  26  0.185 ± 0.239  0.445  Jamaica  0.312  3.230  31  0.306 ± 0.170  0.082  Little Cayman  0.273  1.937  25  −0.353 ± 0.254  0.177  Pidgeon Cay  0.221  0.720  15  0.186 ± 0.219  0.411  San Salvador  0.166  0.707  26  0.112 ± 0.134  0.411  Santa Clara  0.212  1.177  26  0.251 ± 0.232  0.288  Soroa 1  0.623  13.36  22  0.639 ± 0.175  0.001  Soroa 2  0.335  2.523  21  0.451 ± 0.284  0.128  South Abaco  0.495  7.460  24  0.729 ± 0.267  0.012  South Bimini  0.243  1.318  22  0.301 ± 0.262  0.264  Staniel Cay  0.271  1.907  25  0.198 ± 0.144  0.180  Notes: Results are shown for regressions with absolute and relative variables, respectively. Significant results (P < 0.05) are shown in bold font. Table 2 Univariate linear regression analyses of bite force (dependent variable) against dewlap size (independent variable) within population Population  R  F  df  Coefficient b ± SE  P-value  Absolute bite force against dewlap size          Acklins  0.819  16.28  9  0.761 ± 0.189  0.004  Andros  0.806  38.81  22  0.758 ± 0.122  <0.001  Cayman Brac  0.652  19.28  27  0.792 ± 0.180  <0.001  Chub Cay  0.909  85.16  19  0.948 ± 0.102  <0.001  Crooked Island  0.810  40.09  22  0.828 ± 0.131  <0.001  Grand Bahama  0.723  20.82  20  1.503 ± 0.329  <0.001  Grand Cayman  0.784  39.87  26  0.156 ± 0.183  <0.001  Jamaica  0.740  36.31  31  0.933 ± 0.155  <0.001  Little Cayman  0.704  23.55  25  0.682 ± 0.141  <0.001  Pidgeon Cay  0.708  14.03  15  0.622 ± 0.166  0.002  San Salvador  0.904  112.0  26  0.637 ± 0.060  <0.001  Santa Clara  0.375  4.093  26  0.471 ± 0.233  0.054  Soroa 1  0.870  65.69  22  1.078 ± 0.133  <0.001  Soroa 2  0.795  34.45  21  1.254 ± 0.214  <0.001  South Abaco  0.762  31.89  24  0.936 ± 0.166  <0.001  South Bimini  0.729  23.77  22  0.670 ± 0.137  <0.001  Staniel Cay  0.799  42.48  25  0.651 ± 0.100  <0.001  Relative bite force against relative dewlap size        Acklins  0.380  1.352  9  0.214 ± 0.184  0.278  Andros  0.413  4.328  22  0.420 ± 0.202  0.050  Cayman Brac  0.266  1.972  27  −0.303 ± 0.216  0.172  Chub Cay  0.490  5.679  19  0.635 ± 0.267  0.028  Crooked Island  0.108  0.249  22  0.089 ± 0.178  0.623  Grand Bahama  0.305  1.955  20  0.345 ± 0.246  0.178  Grand Cayman  0.153  0.603  26  0.185 ± 0.239  0.445  Jamaica  0.312  3.230  31  0.306 ± 0.170  0.082  Little Cayman  0.273  1.937  25  −0.353 ± 0.254  0.177  Pidgeon Cay  0.221  0.720  15  0.186 ± 0.219  0.411  San Salvador  0.166  0.707  26  0.112 ± 0.134  0.411  Santa Clara  0.212  1.177  26  0.251 ± 0.232  0.288  Soroa 1  0.623  13.36  22  0.639 ± 0.175  0.001  Soroa 2  0.335  2.523  21  0.451 ± 0.284  0.128  South Abaco  0.495  7.460  24  0.729 ± 0.267  0.012  South Bimini  0.243  1.318  22  0.301 ± 0.262  0.264  Staniel Cay  0.271  1.907  25  0.198 ± 0.144  0.180  Population  R  F  df  Coefficient b ± SE  P-value  Absolute bite force against dewlap size          Acklins  0.819  16.28  9  0.761 ± 0.189  0.004  Andros  0.806  38.81  22  0.758 ± 0.122  <0.001  Cayman Brac  0.652  19.28  27  0.792 ± 0.180  <0.001  Chub Cay  0.909  85.16  19  0.948 ± 0.102  <0.001  Crooked Island  0.810  40.09  22  0.828 ± 0.131  <0.001  Grand Bahama  0.723  20.82  20  1.503 ± 0.329  <0.001  Grand Cayman  0.784  39.87  26  0.156 ± 0.183  <0.001  Jamaica  0.740  36.31  31  0.933 ± 0.155  <0.001  Little Cayman  0.704  23.55  25  0.682 ± 0.141  <0.001  Pidgeon Cay  0.708  14.03  15  0.622 ± 0.166  0.002  San Salvador  0.904  112.0  26  0.637 ± 0.060  <0.001  Santa Clara  0.375  4.093  26  0.471 ± 0.233  0.054  Soroa 1  0.870  65.69  22  1.078 ± 0.133  <0.001  Soroa 2  0.795  34.45  21  1.254 ± 0.214  <0.001  South Abaco  0.762  31.89  24  0.936 ± 0.166  <0.001  South Bimini  0.729  23.77  22  0.670 ± 0.137  <0.001  Staniel Cay  0.799  42.48  25  0.651 ± 0.100  <0.001  Relative bite force against relative dewlap size        Acklins  0.380  1.352  9  0.214 ± 0.184  0.278  Andros  0.413  4.328  22  0.420 ± 0.202  0.050  Cayman Brac  0.266  1.972  27  −0.303 ± 0.216  0.172  Chub Cay  0.490  5.679  19  0.635 ± 0.267  0.028  Crooked Island  0.108  0.249  22  0.089 ± 0.178  0.623  Grand Bahama  0.305  1.955  20  0.345 ± 0.246  0.178  Grand Cayman  0.153  0.603  26  0.185 ± 0.239  0.445  Jamaica  0.312  3.230  31  0.306 ± 0.170  0.082  Little Cayman  0.273  1.937  25  −0.353 ± 0.254  0.177  Pidgeon Cay  0.221  0.720  15  0.186 ± 0.219  0.411  San Salvador  0.166  0.707  26  0.112 ± 0.134  0.411  Santa Clara  0.212  1.177  26  0.251 ± 0.232  0.288  Soroa 1  0.623  13.36  22  0.639 ± 0.175  0.001  Soroa 2  0.335  2.523  21  0.451 ± 0.284  0.128  South Abaco  0.495  7.460  24  0.729 ± 0.267  0.012  South Bimini  0.243  1.318  22  0.301 ± 0.262  0.264  Staniel Cay  0.271  1.907  25  0.198 ± 0.144  0.180  Notes: Results are shown for regressions with absolute and relative variables, respectively. Significant results (P < 0.05) are shown in bold font. Fig. 2 View largeDownload slide Relative bite force regressed against relative dewlap size for each A. sagrei population, separately. Straight regression lines represent a significant correlation between both variables, i.e., Andros, Chub Cay, Soroa 1, and South Abaco. Dotted regression lines represent no significant relationship between relative dewlap size and bite force. Detailed statistics are provided in Table 2. The illustration (right, below) visualizes a male brown anole biting on a purpose-built force plate. Fig. 2 View largeDownload slide Relative bite force regressed against relative dewlap size for each A. sagrei population, separately. Straight regression lines represent a significant correlation between both variables, i.e., Andros, Chub Cay, Soroa 1, and South Abaco. Dotted regression lines represent no significant relationship between relative dewlap size and bite force. Detailed statistics are provided in Table 2. The illustration (right, below) visualizes a male brown anole biting on a purpose-built force plate. An among-population regression analysis (pgls) failed to find a significant association between the relative dewlap size–bite force relationship (i.e., slope coefficient b) and SSD (R = 0.11, df = 16, P = 0.662). Thus, in populations characterized by larger SSD, dewlap size in itself was not a more reliable signal of bite force than in populations characterized by lower SSD. The same applies to DI, as no significant correlation was found between the relative dewlap size–bite force relationship and DI (R = 0.23, df = 9, P = 0.532). Excluding the population of San Salvador from the pgls regressions did not alter any of our results (results remained non-significant, SSD: R = 0.12, df = 15, P = 0.657 and DI: R = 0.13, df = 8, P = 0.747). Discussion By studying a series of island populations, we here present our findings on the reliability of dewlap size as a predictor for bite performance in a territorial Caribbean anole, and how this dewlap size–bite force relationship varies so drastically among populations. We used absolute and relative indices to assess the link between dewlap size and bite force, as both indices can differ in the messages they convey (Lailvaux and Irschick 2007). Absolute dewlap size–bite force relationship Our results revealed that dewlap size is an excellent predictor of bite force capacity in nearly all study populations. A strong association between absolute dewlap size and bite force in A. sagrei males has also been reported in all previous studies (Lailvaux and Irschick 2007; Cox et al. 2009; Driessens et al. 2015), emphasizing the generality of this finding. In many animal species, including A. sagrei, body size is the key predictor in determining combat outcome, with larger individuals having a substantial advantage over smaller ones (e.g., Tokarz 1985; Hughes 1996; Hardy and Briffa 2013). Gathering accurate information on the opponent’s body size (assessment game) seems thus crucial to avoid costs associated with escalated fights (Andersson 1994; Emlen 2008). Yet, in reality, the accurate transmission of information is often impeded by ambient noise (e.g., precipitation, low light levels, and windblown vegetation), and particularly when only one signal component is involved (e.g., Fleishman 1992; Lengagne and Slater 2002; Peters and Evans 2003; Leonard and Horn 2005). A commonly adopted signaling strategy to cope with such impeding factors is to repeat the same message in different ways by using redundant signal components (e.g., Zuk et al. 1992; Møller and Pomiankowski 1993; Johnstone 1996). Within all our study populations, absolute dewlap size correlated strongly with overall body size and might as such, serve as a redundant signal for body size to increase signal accuracy during mate assessment. Characterized by a brown to grayish body color, A. sagrei is well camouflaged in the microhabitats it usually occupies (trunk-ground ecomorph; Schoener and Schoener 1982; Losos 2009). In contrast, its bright yellow to reddish dewlap is highly conspicuous, due to high color and pattern contrasts with background vegetation (Endler 1992, 1993, 2012). Thus, by using the combination of a more cryptic body together with a conspicuous dewlap, males can transmit more accurate information on size and consequently, fighting capacity to opponents. The potential role of the A. sagrei dewlap as redundant signal for body size might be most prominent during the early stages of opponent assessment, when signaling still occurs over relatively long distances (more ambient noise), or perhaps during territorial advertisement in order to discourage unseen rival males from intruding (McMann 1998; Orrell and Jenssen 2003). Accordingly, Henningsen and Irschick (2012) showed in their study that surgically reducing the size of the dewlap did not change the outcome of staged close-proximity interactions between size-matched A. carolinensis males; bite force capacity in itself appeared to be more important in determining the outcome of these staged interactions. Based on their results, the authors suggested that dewlap size functions as a signal of bite force primarily during non-directed, long-distance territorial displays, whereas more direct means of assessing one another (e.g., jaw size, head size, body condition, push-ups) may be of higher importance during close-proximity aggressive interaction. In this respect, future behavioral experiments on A. sagrei testing the importance of absolute dewlap size as a redundant signal for size during long-distance versus short-distance male interactions might be a valuable addition. Relative dewlap size–bite force relationship In addition to conveying information on body size, a sexual trait can function as direct, honest signal for advertising fighting capacity (e.g., Panhuis and Wilkinson 1999; Lailvaux et al. 2005). Evidence for a positive link between relative male dewlap size and bite force during the breeding season has been shown for several territorial anole species (Vanhooydonck et al. 2005a; Lailvaux and Irschick 2007). Surprisingly, earlier studies did not observe this correlation in the highly territorial brown anole lizard, A. sagrei (Lailvaux and Irschick 2007; Cox et al. 2009; Driessens et al. 2015). By examining a large set of island populations, we now also found support for a significant relationship between relative dewlap size and bite force within A. sagrei, though, only in 4 out of the 17 tested populations. In contrast to our expectations, the degree of SSD and DI could not explain the observed variation in the relative dewlap size–bite force relationship found among our populations. Thus, populations where relative dewlap size appeared to be an honest signal of bite force were not per se characterized by a higher degree of intrasexual selection, which is inconsistent to earlier findings from Lailvaux and Irschick (2007) (at the species level). Standard errors of the estimated slopes for the relative dewlap size–bite force relationships fell within a relatively narrow range (0.134–0.284, Table 2), and we therefore believe that our failure to find an association between the slopes and SSD or DI is due to the low among-population differences in variance. Another potential reason why we fail to find an association might be due to relative low sample sizes. While the majority of regression analyses showed a high statistical power (power > 0.99), hence, adequate sample sizes, analyses on the populations where relative bite force was not significantly correlated with relative dewlap size were characterized by a relative low statistical power (power < 0.5). Although our sample sizes and statistical power were similar to those of other studies that correlated relative bite force with relative dewlap size (i.e., Vanhooydonck et al. 2005a; Lailvaux and Irschick 2007; Cox et al. 2009), an increase in sample size would have increased the power of our analyses, hence, might have affected our results on an association between the slopes and SSD or DI. Moreover, one can also question the validity of SSD as a measure of the intensity of intrasexual selection. Indeed, it has long been pointed out that SSD may also arise as a consequence of natural selection for reduction of food competition (Darwin 1871) or on clutch size in females (Tinkle et al. 1970). Reassuringly, several studies have found that among-species variation in SSD correlates positively with other aspects of sexual dimorphism (such as dichromatism: Pérez I de Lanuza et al. 2013; Chen et al. 2012; Dale et al. 2015), indicating that SSD is at least to some extent under sexual selection. In a comparative analysis of almost 500 lizard species, Cox et al. (2003) did find significant correlations between SSD and female home range ratio and female home range size, two widely accepted proxies for the strength of intrasexual selection. In Anolis, the use of SSD as an indirect measure of sexual selection intensity has a long tradition (e.g., Trivers 1976; Stamps 1983), although several studies have suggested that variation in SSD may be driven by natural selection as well (e.g., Rand 1967; Losos et al. 2003). In a recent study on our study species A. sagrei, for example, Bonneaud et al. (2016) reported that resource availability can highly influence the degree of SSD among insular populations distributed across the Bahamas. Furthermore, paternity studies on A. sagrei proved that sexual selection is not uniformly directional with respect to male size and, therefore, fails to fully explain the observed male-biased SSD (Calsbeek and Sinervo 2004; Cox et al. 2007). Thus, the use of SSD here as metric for sexual selection is disputable. Besides, DI may be a rather “gross” proxy for the degree of intrasexual selection on each island population, because A. sagrei males may exhibit displays in various contexts (Driessens et al. 2014). Clearly, data on reliable estimates of the intensity of sexual selection are required. Some authors have advocated the use of sex ratios (e.g., Stamps 1983; Muralidhar and Johnson 2017), but others have warned that it is unsure to what extent observed sex ratio reflects operational sex ratio (the ratio of breeding males to breeding females, Cox et al. 2003). Other options include behavioral observations (e.g., number or duration of male–male aggressive interactions) and distributional data (territory size, overlap, number of females per territory, encounter rates; Johnson et al. 2009; Kamath and Losos 2018), but obtaining such data for many populations requires substantial time and effort, which probably explains why, after 50 years of research on anoles, such data remain largely unavailable (Losos et al. 2003). SSD and DI cannot explain differences in the relationship between relative dewlap size and bite force among populations, but what other factors potentially can? One possible explanatory factor may involve intrapopulational variation in body size and the idea that relative indices become particularly important in populations where opponents match more often in body size. Transferring information on body size is likely the first and most crucial step in the assessment game (e.g., Tokarz 1985; Hardy and Briffa 2013), as we already stated in the previous paragraph. However, when males of similar body size encounter each other, dewlap size might become the major signal for advertising fighting capacity. In support of this idea, we would expect relative dewlap size to become a more reliable signal of bite force when variation in body size decreases across populations. We could simply test this prediction with available data by regressing the slope of the relative dewlap size–bite force relationship against variance in body size across populations. Our data did not support the proposed idea (pgls regression: coefficient b variance SVL, R = 0.26, df = 16, P = 0.317), perhaps because encounters between size-matched opponents may not occur that frequently. Moreover, previous studies have shown that when opponents are more similar in size, fights are more likely to escalate (as opposed to merely opponent assessment) and the outcomes harder to predict (Rand 1967; Molina-Borja et al. 1998; Panhuis and Wilkinson 1999). This might challenge the view that honest signals play a major role in the advertisement of fighting capacity during agonistic encounters between size-matched males. Another factor that has recently been reported to affect the relationship between relative dewlap size and bite force is resource availability. Particularly, Lailvaux et al. (2012) showed that under limiting resource conditions, the honest dewlap size–bite force relationship in A. carolinensis gets disrupted. To put this idea to the test, we assessed whether variation in body condition (an estimate for resource availability) could explain the variation in the relative dewlap size–bite force relationship observed within A. sagrei. Indeed, we obtained a significant association with body condition (pgls regression: coefficient b ∼ body mass normalized for SVL, R = 0.62, df = 16, P = 0.009). However, the correlation was negative and, therefore, opposes the findings reported by Lailvaux et al. (2012). We found that for A. sagrei males, dewlap size in itself becomes a more reliable signal of bite force in populations where males are in worse body condition (the relationship with body condition was not significant when using the absolute dewlap size–bite force relationships, P = 0.575). Overall, we suggest that body size remains, independent of resource availability, the key predictor during opponent assessment. Yet, when males of similar body size encounter each other, the use of dewlap size to honestly signal fighting capacity might be particularly important for A. sagrei males in poor body condition. We believe that males in poor body condition will suffer more from the exhaustion and injuries related to physical fights than A. sagrei males in normal or good body condition. Accordingly, in populations where males have a low body condition, the strong need to avoid escalated fights and thus, to precisely assess a size-matched opponent, might be higher (Andersson 1994; Maynard-Smith and Harper 2003). This may explain why dewlap size becomes a more reliable predictor of bite force in such populations. In contrast, males under high resource conditions might directly engage in physical fights when encountering a size-matched opponent (Rand 1967; Molina-Borja et al. 1998). Of course, future experiments are needed to confirm our suggestions and to provide additional evidence that resource availability, indeed, influences the correlation between relative dewlap size and bite force in A. sagrei. Last, several other factors have been found to explain variation only in dewlap size and can as such, also affect the relation between signal size and performance trait. For example, Vanhooydonck et al. (2009) revealed that A. sagrei males had relatively larger dewlaps in populations where curly-tailed lizards (Leiocephalus carinatus), known to predate on anoles, are present. In that same study was also reported that relative dewlap size increased with SSD. Also hormone levels (i.e., testosterone) are proven to change dewlap size in A. sagrei males (Cox et al. 2009) and can, due to fluctuating levels, affect the relationship between dewlap size and bite force throughout seasons. In accordance, a previous study on A. carolinensis has shown that dewlap size is only a reliable signal of bite force during the breeding season, and not during winter (Irschick et al. 2006). Following Lailvaux and Irschick (2007), we sampled our A. sagrei populations during the breeding season, with the exception of one (i.e., population from San Salvador). Results from that latter population did not markedly deviate from the other study populations, indicating that the dewlap–bite force relationship in A. sagrei might not be significantly affected by season. Yet, experiments assessing the link between dewlap size and bite force in the same A. sagrei individuals throughout the year are needed to accurately assess seasonal effects. Conclusion To our knowledge, this is the first study showing evidence for a link between relative dewlap size and bite force within A. sagrei populations, during the breeding season. Based on our results, we suggest that dewlap size in A. sagrei males is in general a redundant signal for body size in the advertisement of fighting capacity (absolute indices), but only in particular cases a direct signal of bite force (relative indices). Our study makes an important contribution by showing that the relationship between signal size and performance trait can differ substantially within one species. We therefore suggest that the use of only one population is not sufficient to draw general conclusions for a whole species, in this respect. Several factors (e.g., degree of territoriality, resource availability, season) are already known to affect the correlation between dewlap size and bite force; however, additional research is needed to shed more light on how these factors exactly affect this relationship. Acknowledgments We acknowledge S. De Decker, J. Harvey, A. Herrel, J. Husak, P. Maillis, J. Mertens, J.J. Meyers, D. Norris, V. Rivalta, L. Schettino, E. Schramme, B. Scott-Edwards, M. Valley, and L. Vandervorst for help during data collection. We further thank G. Reynolds for his useful advice regarding phylogenetic analyses, S. Van Dongen for statistical assistance, and two anonymous reviewers for significantly improving drafts of this manuscript. Funding This work was supported by the Belgian American Education Foundation (BAEF) [to S.B. a postdoctoral fellow]. This study was financed by an FWO-FL research grant [to T.D., an aspirant doctoral fellowship]. K.H. is a postdoctoral fellow of FWO-FL. Additional expenses for field missions were provided by Leopold III fund and the University of Antwerp (DOCOP). All work was carried out in accordance with the local Environmental Agencies and the University of Antwerp animal welfare standard and protocols (ECD 2011-64). References Abe J, Kamimura Y, Kondo N, Shimada M. 2003. Extremely female-biased sex ratio and lethal male–male combat in a parasitoid wasp, Melittobia australica (Eulophidae). Behav Ecol  14: 34– 9. Alonso-Alvarez C, Bertrand S, Devevey G, Gaillard M, Prost J, Faivre B, Sorci G. 2004. An experimental test of the dose-dependent effect of carotenoids and immune activation on sexual signals and antioxidant activity. Am Nat  164: 651– 9. Anderson RA, McBrayer LD, Herrel A. 2008. Bite force in vertebrates: opportunities and caveats for use of a nonpareil whole-animal performance measure. Biol J Linn Soc  93: 709– 20. Andersson M. 1982. Female choice selects for extreme tail length in a widowbird. Nature  299: 529– 34. Andersson M. 1994. Sexual selection . Princeton (NJ): Princeton University Press. 624 p. Baeckens S, Driessens T, Van Damme R. 2016. Intersexual chemo-sensation in a “visually-oriented” lizard, Anolis sagrei. PeerJ  4: e1874. Baeckens S, García-Roa R, Martín J, Ortega J, Huyghe K, Van Damme R. 2017. Fossorial and durophagous: implications of molluscivory for head size and bite capacity in a burrowing worm lizard. J Zool  301: 193– 205. Bean D, Cook JM. 2001. Male mating tactics and lethal combat in the nonpollinating fig wasp Sycoscapter australis. Anim Behav  62: 535– 42. Bels V. 1990. The mechanism of dewlap extension in Anolis carolinensis (Reptilia: iguanidae) with histological analysis of the hyoid apparatus. J Morphol  206: 225– 44. Bennett AF. 1985. Temperature and muscle. J Exp Biol  155: 333– 44. Blomberg SP, Garland T, Ives AR. 2003. Testing for phylogenetic signal in comparative data: behavioral traits are more labile. Evolution  57: 717– 45. Blumstein DT, Daniel JC. 2007. Quantifying behavior the JWatcher way . Sunderland (MA): Sinauer Associates. 211 p. Bonneaud C, Marnocha E, Herrel A, Vanhooydonck B, Irschick DJ, Smith TB. 2016. Developmental plasticity affects sexual size dimorphism in an anole lizard. Funct Ecol  30: 235– 43. Bradbury JW, Vehrencamp SL. 1998. The principles of animal communication . Sunderland (MA): Sinauer Associates. 697 p. Butler MA, Sawyer SA, Losos JB. 2007. Sexual dimorphism and adaptive radiation in Anolis lizards. Nature  447: 202– 5. Calsbeek R, Sinervo B. 2004. Progeny sex is determined by relative male body size within polyandrous females’ clutches: cryptic mate choice in the wild. J Evol Biol  17: 464– 70. Candolin U. 2003. The use of multiple cues in mate choice. Biol Rev  78: 575– 95. Carpenter CC. 1978. Ritualistic social behaviors in lizards. In: Greenberg N, MacLean PD, editors. Behavior and neurology of lizards.  Rockville (MD): NIMH. p. 253– 67. Chen IP, Stuart-Fox D, Hugall AF, Symonds MRE. 2012. Sexual selection and the evolution of complex color patterns in dragon lizards. Evolution  66: 3605– 14. Clutton-Brock TH, Albon SD, Gibson RM, Guinness FE. 1979. The logical stag: adaptive aspects of fighting in red deer (Cervus elaphus L.) Anim Behav  27: 211– 25. Cox RM, Skelly SL, John-Alder HB. 2003. A comparative test of adaptive hypotheses for sexual size dimorphism in lizards. Evolution  57: 1653– 69. Cox RM, Butler MA, John-Alder HB. 2007. The evolution of sexual size dimorphism in reptiles. In: Fairbairn DJ, Blanckenhorn WU, Szekely T, editors. Sex, size & gender roles: evolutionary studies of sexual size dimorphism . Oxford: Oxford University Press. p. 38– 49. Cox RM, Stenquist DS, Henningsen JP, Calsbeek R. 2009. Manipulating testosterone to assess links between behavior, morphology, and performance in the brown anole Anolis sagrei. Physiol Biochem Zool  82: 686– 98. Crews D. 1975. Effects of different components of male courtship behavior on environmentally induced ovarian recrudescence and mating preferences in the lizard Anolis carolinensis. Anim Behav  23: 349– 56. Dale J, Dey CJ, Delhey K, Kempenaers B, Valcu M. 2015. The effects of life history and sexual selection on male and female plumage colouration. Nature  527: 367– 70. Darwin CR. 1871. The descent of man, and selection in relation to sex . London: John Murray. 745 p. Driessens T, Vanhooydonck B, Damme R. 2014. Deterring predators, daunting opponents or drawing partners? Signaling rates across diverse contexts in the lizard Anolis sagrei. Behav Ecol Sociobiol  68: 173– 84. Driessens T, Huyghe K, Vanhooydonck B, Van Damme R. 2015. Messages conveyed by assorted facets of the dewlap, in both sexes of Anolis sagrei. Behav Ecol Sociobiol  69: 1251– 64. Driessens T, Baeckens S, Balzarolo M, Vanhooydonck B, Huyghe K, Van Damme R. 2017. Climate-related environmental variation in a visual signalling device: the male and female dewlap in Anolis sagrei lizards. J Evol Biol  30: 1846– 61. Edwards JR, Lailvaux SP. 2012. Display behavior and habitat use in single and mixed populations of Anolis carolinensis and Anolis sagrei lizards. Ethology  118: 494– 502. Emlen DJ. 2008. The evolution of animal weapons. Annu Rev Ecol Evol  39: 387– 413. Endler JA. 1992. Signals, signal conditions, and the direction of evolution. Am Nat  139: 125– 53. Endler JA. 1993. The color of light in forests and its implications. Ecol Monogr  63: 1– 27. Endler JA. 2012. A framework for analysing colour pattern geometry: adjacent colours. Biol J Linn Soc  107: 233– 53. Felsenstein LJ. 1985. Phylogenies and the comparative method. Am Nat  125: 1– 15. Fleishman LJ. 1992. The influence of the sensory system and the environment on motion patterns in the visual displays of anoline lizards and other vertebrates. Am Nat  139: 36– 61. Garland T, Ives AR. 2000. Using the past to predict the present: confidence intervals for regression equations in phylogenetic comparative methods. Am Nat  155: 346– 64. Greenberg G, Noble GK. 1944. Social behavior of the American chameleon (Anolis carolinensis Voigt). Physiol Zool  17: 392– 439. Hardy ICW, Briffa M. 2013. Animal contests . Cambridge (MA): Cambridge University Press. 379 p. Harvey PH, Pagel MD. 1991. The comparative method in evolutionary biology . Oxford: Oxford University Press. 248 p. Henningsen JP, Irschick DJ. 2012. An experimental test of the effect of signal size and performance capacity on dominance in the green anole lizard. Funct Ecol  26: 3– 10. Herrel A, O’Reilly JC. 2006. Ontogenetic scaling of bite force in lizards and turtles. Physiol Biochem Zool  79: 31– 42. Herrel A, Spithoven L, Van Damme R, De Vree F. 1999. Sexual dimorphism of head size in Gallotia galloti: testing the niche divergence hypothesis by functional analyses. Funct Ecol  13: 289– 97. Herrel A, Aerts P, Fret J, De Vree F. 1999. Morphology of the feeding system in agamid lizards: ecological correlates. Anat Rec  254: 496– 507. Herrel A, Van Damme R, Vanhooydonck B, De Vree F. 2001. The implications of bite performance for diet in two species of lacertid lizards. Can J Zool  79: 662– 70. Hertz PE, Huey RB, Stevenson RD. 1993. Evaluating temperature regulation by field-active ectotherms: the fallacy of the inappropriate question. Am Nat  142: 796– 818. Huey RB. 1982. Temperature, physiology, and the ecology of reptiles. In: Gans C, Pough FH, editors. Biology of the reptilia.  New York (NY): Academic Press. p. 25– 91. Hughes M. 1996. Size assessment via a visual signal in snapping shrimp. Behav Ecol Sociobiol  38: 51– 7. Irschick DJ, Ramos M, Buckley C, Elstrott J, Carlisle E, Lailvaux SP, Bloch N, Herrel A, Vanhooydonck B. 2006. Are morphology–performance relationships invariant across different seasons? A test with the green anole lizard (Anolis carolinensis). Oikos  114: 49– 59. Jennions MD, Backwell PRY. 1996. Residency and size affect fight duration and outcome in the fiddler crab Uca annulipes. Biol J Linn Soc  57: 293– 306. Jenssen TA. 1970. The ethoecology of Anolis nebulosus. J Herpetol  4: 1– 38. Jenssen TA, Greenberg N, Hovde KA. 1995. Behavioral profile of free-ranging male lizards, Anolis carolinensis, across breeding and post-breeding seasons. Herpetol Monogr  9: 41– 62. Jenssen TA, Lovern M, Congdon JD. 2001. Fieldtesting the protandry-based mating system for the lizard Anolis carolinensis: does the model organism have the right model? Behav Ecol Sociobiol  50: 162– 72. Johnson MA, Wade J. 2010. Behavioural display systems across nine Anolis lizard species: sexual dimorphisms in structure and function. Proc R Soc B Biol Sci  277: 1711– 9. Johnson MA, Revell LJ, Losos JB. 2009. Behavioral convergence and adaptive radiation: effects of habitat use on territorial behavior in Anolis lizards. Evolution  64: 1151– 9. Johnstone RA. 1996. Multiple displays in animal communication: “backup signals” and “multiple messages”. Philos Trans R Soc B  351: 329– 38. Kamath A, Losos JB. 2017. The erratic and contingent progression of research on territoriality: a case study. Behav Ecol Sociobiol  71: 1– 13. Kamath A, Losos JB. 2018. Estimating encounter rates as the first step of sexual selection in the lizard Anolis sagrei. Proc R Soc B Biol Sci  285: 20172244. Kamilar JM, Cooper N. 2013. Phylogenetic signal in primate behavior, ecology and life history. Philos Trans R Soc B  368: 20120341. Karsten KB, Andriamandimbiarisoa LN, Fox SF, Raxworthy CJ. 2009. Sexual selection on body size and secondary sexual characters in 2 closely related, sympatric chameleons in Madagascar. Behav Ecol  20: 1079– 88. Lailvaux SP, Irschick DJ. 2007. The evolution of performance-based male fighting ability in Caribbean Anolis lizards. Am Nat  170: 573– 86. Lailvaux SP, Herrel A, Vanhooydonck B, Meyers JJ, Irschick DJ. 2004. Performance capacity, fighting tactics and the evolution of life-stage male morphs in the green anole lizard (Anolis carolinensis). Proc R Soc B Biol Sci  271: 2501– 8. Lailvaux SP, Hathway J, Pomfret J, Knell RJ. 2005. Horn size predicts physical performance in the beetle Euoniticellus intermedius (Coleoptera: scarabaeidae). Funct Ecol  19: 632– 9. Lailvaux SP, Gilbert RL, Edwards JR. 2012. A performance-based cost to honest signalling in male green anole lizards (Anolis carolinensis). Proc R Soc B Biol Sci  279: 2841– 8. Lailvaux SP, Leifer J, Kircher BK, Johnson MA. 2015. The incredible shrinking dewlap: signal size, skin elasticity, and mechanical design in the green anole lizard (Anolis carolinensis). Ecol Evol  5: 4400– 9. Lappin AK, Husak JF. 2005. Weapon performance, not size, determines mating success and potential reproductive output in the collared lizard (Crotaphytus collaris). Am Nat  166: 426– 36. Leal M, Rodríguez-Robles JA. 1995. Antipredator responses of Anolis cristatellus (Sauria: polychrotidae). Copeia  1995: 155– 61. Leal M, Rodríguez-Robles JA. 1997. Signaling displays during predator–prey interactions in a Puerto Rican anole, Anolis cristatellus. Anim Behav  54: 1147– 54. Lee JC, Clayton D, Eisenstein S, Perez I. 1989. The reproductive cycle of Anolis sagrei in southern Florida. Copeia  1989: 930– 7. Leimar O, Austad S, Enquist M. 1991. A test of the sequential assessment game: fighting in the bowl and doily spider Frontinella pyramitela. Evolution  45: 862– 74. Lengagne T, Slater PJB. 2002. The effects of rain on acoustic communication: tawny owls have good reason for calling less in wet weather. Proc R Soc Lond B  269: 2121– 5. Leonard ML, Horn AG. 2005. Ambient noise and the design of begging signals. Proc R Soc B Biol Sci  272: 651– 6. Losos JB. 1985. An experimental demonstration of the species-recognition role of Anolis dewlap color. Copeia  4: 905– 10. Losos JB, Butler M, Schoener TW. 2003. Sexual dimorphism in body size and shape in relation to habitat use among species of Caribbean Anolis lizards. In: Fox SF, McCoy JK, Baird TA, editors. Lizard social behaviour . Baltimore: John Hopkins University Press. p. 356– 380. Losos JB. 2009. Lizards in an evolutionary tree: ecology and adaptive radiation of Anoles . Berkeley (CA): University of California Press. p. 528. Maynard-Smith J, Harper D. 2003. Animal signals: Oxford series in ecology and evolution. New York: Oxford University Press. p. 1–166. McMann S. 1998. Display behavior and territoriality in the lizard Anolis sagrei [PhD dissertation]. University of Miami (FL). McMann S. 2000. Effects of residence time on displays during territory establishment in a lizard. Anim Behav  59: 513– 22. Molina-Borja M, Padron-Fumero M, Alfonso-Martin T. 1998. Morphological and behavioral traits affecting the intensity and outcome of male contests in Gallotia galloti galloti (family Lacertidae). Ethology  104: 314– 22. Møller AP, Pomiankowski A. 1993. Why have birds got multiple sexual ornaments. Behav Ecol Sociobiol  32: 167– 76. Muralidhar P, Johnson MA. 2017. Sexual selection and sex ratios in Anolis lizards. J Zool  302: 178– 83. Nicholson KE, Harmon LJ, Losos JB. 2007. Evolution of Anolis lizard dewlap diversity. PLoS One  2: e274. Ord TJ, Blumstein DT, Evans CS. 2001. Intrasexual selection predicts the evolution of signal complexity in lizards. Proc R Soc B Biol Sci  268: 737– 44. Orme D, Freckleton R, Thomas G, Petzoldt T, Fritz S, Isaac N, Pearse W. 2013. Caper: comparative analyses of phylogenetics and evolution in R. R package version 0.5.2 (https://cran.r-project.org/web/packages/caper/; last accessed November 2017). Orrell KS, Jenssen TA. 2003. Heterosexual signaling by the lizard Anolis carolinensis, with intersexual comparisons across contexts. Behaviour  140: 603– 34. Panhuis TM, Wilkinson GS. 1999. Exaggerated eye span influences male contest outcome in stalk-eyed flies. Behav Ecol Sociobiol  46: 221– 7. Pérez I de Lanuza G, Font E, Monterde EL. 2013. Using visual modelling to study the evolution of lizard coloration: sexual selection drives the evolution of sexual dichromatism in lacertids. J Evol Biol  26: 1826– 35. Perry G, Levering K, Girard I, Garland T. 2004. Locomotor performance and dominance in male Anolis cristatellus. Anim Behav  67: 37– 47. Peters RA, Evans CS. 2003. Design of the Jacky dragon visual display: signal and noise characteristics in a complex moving environment. J Comp Physiol A  189: 447– 59. Rand AS. 1967. Ecology and social organization in the iguanid lizard Anolis lineatopus. Proc US Nat Mus  122: 1– 79. Rand AS, Williams EE. 1970. An estimation of redundancy and information content of anole dewlaps. Am Nat  104: 99– 103. Revell LJ. 2010. Phylogenetic signal and linear regression on species data. Methods Ecol Evol  1: 319– 29. Schoener TW, Schoener A. 1980. Densities sex ratios and population structure in four species of Bahamian Anolis lizards. J Anim Ecol  49: 19– 54. Schoener TW, Schoener A. 1982. The ecological correlates of survival in some Bahamanian Anolis lizards. Oikos  392: 1– 26. Scott MP. 1984. Agonistic and courtship displays of male Anolis sagrei. Breviora  479: 1– 22. Setchell JM, Wickings J. 2005. Dominance, status signals, and coloration in mandrills (Mandrillus sphinx). Ethology  111: 25– 30. Simon V. 2011. Communication signal rates predict interaction outcome in the brown anole lizard, Anolis sagrei. Copeia  2011: 38– 45. Sokal RR, Rohlf FJ. 1995. Biometry: the principles and practices of statistics in biological research . New York (NY): Freeman WH. 880 p. Stamps 1983. Sexual selection, sexual dimorphism and territoriality. In. Pianka ER, Schoener TW, editors. Lizard ecology: studies of a model organism . Cambridge (MA): Harvard University Press. p. 169– 204. Stamps JA, Losos JB, Andrews RM. 1997. A comparative study of population density and sexual size dimorphism in lizards. Am Nat  149: 64– 90. Steffen JE, Guyer CC. 2014. Display behaviour and dewlap colour as predictors of contest success in brown anoles. Biol J Linn Soc  111: 646– 55. Tinkle DW, Wilbur HM, Tilley SG. 1970. Evolutionary strategies in lizard reproduction. Evolution 24:55–74. Tokarz RR. 1985. Body size as a factor determining dominance in staged agonistic encounters between male brown anoles (Anolis sagrei). Anim Behav  33: 746– 53. Tokarz RR. 1987. Effects of cortisone treatment on male aggressive behavior in a lizard (Anolis sagrei). Horm Behav 21:358–70. Tokarz RR. 1998. Mating pattern in the lizard, Anolis sagrei: implications for mate choice and sperm competition. Herpetologica  54: 388– 94. Tokarz RR. 2002. An experimental test of the importance of the dewlap in male mating success in the lizard Anolis sagrei. Herpetologica  58: 87– 94. Tokarz RR, Paterson AV, McMann S. 2003. Laboratory and field test of the functional significance of the male’s dewlap in the lizard Anolis sagrei. Copeia  2003: 502– 11. Trivers RL. 1976. Sexual selection and resource-accruing abilities in Anolis garmani. Evolution  30: 253– 69. Vanhooydonck B, Herrel A, Van Damme R, Irschick DJ. 2005a. Does dewlap size predict male bite performance in Jamaican Anolis lizards? Funct Ecol  19: 38– 42. Vanhooydonck B, Herrel A, Van Damme R, Meyers JJ, Irschick DJ. 2005b. The relationship between dewlap size and performance changes with age and sex in a Green Anole (Anolis carolinensis) lizard population. Behav Ecol Sociobiol  59: 157– 65. Vanhooydonck B, Herrel A, Meyers JJ, Irschick DJ. 2009. What determines dewlap diversity in Anolis lizards? An among-island comparison. J Evol Biol  22: 293– 305. Zuk M, Ligon JD, Thornhill R. 1992. Effects of experimental manipulation of male secondary sex characters on female mate preference in red jungle fowl. Anim Behav  44: 999– 1006. © The Author(s) 2018. Published by Oxford University Press on behalf of the Society for Integrative and Comparative Biology. All rights reserved. For permissions please email: journals.permissions@oup.com This article is published and distributed under the terms of the Oxford University Press, Standard Journals Publication Model (https://academic.oup.com/journals/pages/about_us/legal/notices)

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