Locomotor performance in a running toad: roles of morphology, sex and agrosystem versus natural habitat

Locomotor performance in a running toad: roles of morphology, sex and agrosystem versus natural... Abstract Locomotor performance is often key in animal fitness, and may be affected by habitat anthropization. This study compares locomotor performance of natterjack toads (Epidalea calamita), which move by intermittent runs, from a natural pine grove and surrounding agrosystems. The effects of sex, morphology and habitat on sprint speed and run rate (number of runs per metre) were assessed. Males were faster than females, and had longer limbs, but the latter trait only partially explained sex differences in sprint speed. Sprint speed was directly related to hindlimb length, but not to any of the other morphological traits measured. Thus, other factors, such as amplexus ability, seemingly shape longer forelimbs in males. Habitat did not affect sprint speed, but toads from the agrosystem habitat had a higher run rate, which could help increase vigilance or confound predators, probably related to habitat openness and/or human presence. For a given speed, males used greater run rates than females, probably because males encounter predators more often and face higher predator pressure. Finally, a negative relationship between sprint speed and run rate suggests that slower toads tend to use short runs, which may improve vigilance or help to confuse predators, while faster toads tend to use long runs, probably for fast escape from predators. INTRODUCTION Locomotor performance is often a key trait shaping animal fitness (Huey, Dunham & Overall, 1991; O’Steen, Cullum & Bennett, 2002; Miles 2004). An efficient locomotor performance optimizes refuge use (Martín & López, 2000), enhances prey acquisition (Budick & O’Malley, 2000; Higham, 2007)and aids escape from predators (Watkins, 1996; McGee et al., 2009). In fact, predator pressure shapes locomotor performance (Ingley et al., 2016). Locomotor performance is increased in open areas, where vulnerability to predators is higher (Vanhooydonck & Van Damme, 2003), and can directly increase survival (Jayne & Bennett, 1990; Husak, 2006a, b). Moreover, locomotor performance is positively related to social dominance (Garland, Hankins & Huey, 1990; Perry et al., 2004), as faster individuals can control larger territories (Peterson & Husak, 2006). It can also be favoured by sexual selection (Husak & Fox, 2008). Indeed, faster males are more able to defend females from other males (Husak, Fox & Van Den Bussche, 2008), and therefore have increased reproductive success (Husak et al., 2006). Locomotor performance is closely related to morphology in vertebrates: larger fins in fish (Li et al., 2016), longer limbs in amphibians (Hudson, Brown & Shine, 2016), reptiles (Garland & Losos, 1994) and mammals (Day & Jayne, 2007), and longer wings in birds (Moreno-Rueda, 2003) all enhance locomotion. Even traits not primarily involved in locomotion, such as head shape, may affect performance (Edwards et al., 2016). Morphology is often shaped by locomotion (Botton-Divet et al., 2017; Higham, Gamble & Russell, 2017), and is thus under strong selection (Calsbeek, 2008). Moreover, for identical biometrics, a heavier body mass often impairs locomotion (Witter & Cuthill, 1993; Iriarte-Díaz, 2002). Consequently, animals often lose weight in the presence of predators, which could improve escape ability by means of increased locomotion performance (Pérez-Tris, Díaz & Tellería, 2004). For the same reason, an increase in female body weight caused by reproduction may impair locomotion performance (Magnhagen, 1991; Shaffer & Formanowicz, 1996; but see Zamora-Camacho et al., 2014 for an exception). Hence, due to differential selection on sexes, females and males may differ in locomotor performance, with concomitant sexual dimorphism in morphological traits related to locomotion (Conradsen & McGuigan, 2015; Brandt et al., 2016). When one sex (typically males) is more conspicuous to predators (Promislow, Montgomerie & Martin, 1992), or displays a reproductive strategy that is more dependent on locomotor performance (Magnhagen, 1991), it is expected to show proportionally higher locomotor performance (Kaliontzopoulou, Bandeira & Carretero, 2013). Indeed, males often show better locomotor performance than females (Lailvaux, 2007; Herrel, Vasilopoulou-Kampitsi & Bonneaud, 2014). Locomotor performance demands physiological adjustments (Brijs et al., 2017), is energetically costly (reviewed by Halsey, 2016) and is thus involved in energy trade-offs (Zamora-Camacho et al., 2015). Consistent with evidence that sexual traits are costly (reviewed by Kotiaho, 2001), locomotor performance is often under sexual selection (Peterson & Husak, 2006; Husak & Fox, 2008). Locomotor performance and morphology of locomotor traits can also vary geographically (Huey et al., 1990; Irschick et al., 2005), or even at microhabitat level within habitats, as locomotor performance (Calsbeek & Irschick, 2007) and related morphological traits (Colombo et al., 2016) can be adjusted to habitat use. In fact, the morphology of locomotor traits may determine habitat use (Tulli et al., 2016), and may differ between natural and human-altered habitats (Donihue, 2016). Moreover, predation risk may shape habitat differences in locomotor performance (Melville & Swain, 2000; Goodman, 2009), and animals can interpret human presence, a constant in some anthropized habitats, as predation risk (Frid & Dill, 2002). Human-altered habitats may deteriorate health (reviewed by Acevedo-Whitehouse & Duffus, 2009), alter behaviour (reviewed by Tuomainen & Candolin, 2011), reduce body condition (Martín et al., 2015; Gallego-Carmona, Castro-Arango & Bernal-Bautista, 2016) and even induce evolution (Smith & Bernatchez, 2007). Therefore, human-altered habitats may exert a negative impact on locomotion performance (Fahrig, 2007). In the present study, I investigated locomotor performance of natterjack toads (Epidalea calamita), by comparing females and males from a natural pine grove and from human-altered agrosystem habitats. These toads move exclusively by means of intermittent runs, instead of leaping as in most anurans (Gómez-Mestre, 2014). Whilst locomotion in jumping anurans has long been studied (Reilly et al., 2016), running locomotion patterns in anurans (see Ahn, Furrow & Biewener, 2004 for an exception), and particularly morphological correlates, have received much less attention. Therefore, running locomotion in anurans remains an important gap in locomotor performance studies. In this context, I assessed the effects of morphology, sex and habitat on two parameters of toad locomotor performance, as well as the relationship between both: sprint speed and run rate (number of runs per metre; see below). Based on the aforementioned arguments, I expected locomotor performance to be related to morphology; in particular, I expected a positive relationship with limb length, and a negative relationship with body mass. Also, I predicted greater locomotor performance in males than in females, as males are more conspicuous to predators, and face higher predator pressure, mainly while searching for and defending their territories, and calling to attract females (Gómez-Mestre, 2014). Moreover, a different strategy is expected according to perceived predation risk in toads from the agrosystem habitat owing to stressful conditions in this human-altered habitat. Agrosystem E. calamita toads are indeed shorter-lived (but larger-bodied) than pine grove conspecifics (Zamora-Camacho & Comas, 2017). MATERIAL AND METHODS Epidalea calamita is a medium-sized [49–86 mm snout–vent length (SVL) in this system] bufonid toad that occurs in a fairly continuous wide area in central and south-west Europe (Gómez-Mestre, 2014). Within its distribution range, it is generally an abundant species, and, due to its ecological versatility, it occupies diverse habitats, from pristine environments to human-altered locations (Gómez-Mestre, 2014). Toads are terrestrial except briefly during amplexus, and are active mainly on wet, warm nights; while inactive they remain sheltered under logs, rocks or in holes they burrow in the ground (Gómez-Mestre, 2014). The period of toad activity varies geographically: they hibernate in winter and reproduce in late spring or early summer in northern cold habitats, but instead aestivate and mate in late winter or early spring in southern hot, dry climates (Gómez-Mestre, 2014). During the breeding season, males can be distinguished because they show blackish nuptial pads in their forelimbs, and their vocal sacs appear pinkish or purple (Gómez-Mestre, 2014). The larval stage is brief (often less than 2 months), and eggs are frequently laid in shallow, small, sunny, ephemeral ponds (Gómez-Mestre, 2014). Toads prey on diverse invertebrates, showing no clear selectivity (Boomsma & Arntzen, 1985). Fieldwork was conducted between January and April 2015, in the natural pine grove Pinares de Cartaya (south-west Spain: 37°20′N, 7°09′W) and surrounding agrosystems, within the natural distribution range of toads. Winters in this area are moderately rainy and warm, usually with no frosts, and summers are dry and hot. Therefore, toads do not hibernate in this region, but skip summer aridity by aestivating. The pine grove used for this study was a stone pine (Pinus pinea) forest, with an undergrowth dominated by Cistus ladanifer, Rosmarinus officinalis and Pistacea lentiscus bushes. Although the autochthonous or anthropogenic origin of the vegetation in this habitat is unclear, it has been the dominant landscape at least over the last 4000 years (Martínez & Montero, 2004). Therefore, I considered this pine grove as a natural habitat for toads. In turn, agrosystems were located 5 km from the pine grove. They consisted of traditional extensive vegetable crops, which have been changed in recent decades to intensive strawberry, raspberry and orange plantations, among others. Crops are artificially irrigated during the summer, and manure, fertilizers, herbicides, pesticides and fungicides are added in different amounts according to landowners’ discretion. During the toad mating season, small temporary ponds where toads reproduce are abundant in both habitats. I captured toads (37 females and 25 males in agrosystems; 30 females and 31 males in pine grove) while they were active on rainy nights, or actively searched for them while they were resting in their shelters, randomly in both habitats. However, as crops are private properties, in agrosystem habitats only public areas, such as meadows, areas of empty ground, tracks, ditches, etc., could be accessed. All toads captured were in their reproductive period: vocal sacs and nuptial pads were clearly visible in males, and eggs could be felt by gently pressing the lower abdomen of females. Since these toads drastically reduce activity after they reproduce (Gómez-Mestre, 2014), the ecological relevance of locomotion is maximal during that period. I took toads to a laboratory facility, where room temperature was controlled (19 °C). I measured SVL (from the tip of the snout to the urostyle), and forelimb and hindlimb length (from the insertion point of the limb to the tip of the longest toe) with a ruler to the nearest millimetre. I calculated limb ratio as forelimb length divided by hindlimb length. During captivity (and 24 h before the trials), I kept toads individually enclosed in plastic terraria (20 × 13 × 9 cm) with soaked peat as a substrate and a piece of opaque plastic as a shelter. In this way, all individuals were fully hydrated, controlling for the potential effects of different hydration states on toad locomotion (Preest & Pough, 1989). On the day after capture, I emptied each toad’s bladder by gently but firmly pressing on its lower abdomen (Walvoord, 2003; Prates et al., 2013). This technique standardizes bladder water burden, which could affect locomotor performance, by reducing it to zero (Preest & Pough, 1989; Walvoord, 2003; Prates et al., 2013). I then immediately measured toad body mass (standard mass sensuRuibal, 1962: body mass of a fully hydrated amphibian with an empty bladder) with a balance (model CDS-100, precision 0.01 g). Toads were then returned to their terraria. One hour later, toads were individually recorded (with a Canon EOS 550D video camera, at 25 frames/s) while they were running on a brown cardboard linear runway (200 × 15 × 15 cm) divided into 10-cm stretches with white stripes stuck perpendicularly along the bottom of the runway. White stripes contrasted with brown cardboard, so each stretch could be perfectly distinguished in the video. Cardboard provided a surface rough enough for appropriate traction, as substrate may affect locomotor performance (Vanhooydonck et al., 2015). I placed a black background at the end of the runway, so that toads would mistake it for a shelter and were encouraged to move. Toads were released at the other end of the runway. Trials were always performed during the night, within the daily activity period of toads. A 60-W bulb 2.5 m above the centre of the runway provided the same illumination in all trials. Toads were chased constantly during the trials to stimulate their moving forward, until they reached the end of the runway. Since body temperature may affect amphibian motility (Preest & Pough, 2003), I verified that all toads performed the trials at the same body temperature (room temperature: 19 °C) by inserting a 1-mm-diameter thermocouple, connected to a Hibok 18 thermometer (precision: 0.1 °C) 8 mm inside their cloacae. As soon as possible after the trials, I released toads at the same spots where I had collected them. No toad suffered any visible damage or died as a consequence of this study. Speed was calculated from videos with the software Tracker v.4.92, which allows a frame-by-frame video analysis. I calculated the time (precision: 0.01 s) that toads needed to cover each stretch, starting and finishing when the snout of the toad reached the perpendicular strips delimiting either end of each stretch (Martín & López, 2001; Zamora-Camacho et al., 2014). I thus calculated toad sprint speed (cm/s) in each stretch by dividing 10 cm (the length of every stretch) by the time (s) needed to cover it. I conducted analyses based on the = fastest stretch speed by each toad, because the objectives of this related to maximum speed (hereafter sprint speed). I also calculated average speed. However, because toads frequently stopped during the trials, and sprint speed is the most informative measure, results involving average speed are presented in the Supporting Information. I also counted the number of runs-and-stops (how many times toads stopped running in each trial) that each toad used to cover the whole runway, and divided it by the length of the runway in metres, to obtain run rate as the number of runs per metre for each individual. As the data met the criteria of residual normality and homoscedasticity, parametric statistics were performed (Quinn & Keough, 2002). I did not include body mass and SVL at the same time in any model due to their high collinearity (r = 0.925; P < 0.001). Firstly, I conducted fully saturated ANOVAs to test the effects of sex, habitat and their interaction on morphometric variables (body mass, SVL, fore- and hindlimb length, and limb ratio; shown in the Supporting Information) as well as average speed (also shown in the Supporting Information), sprint speed and run rate. I then conducted a set of individual ANCOVAs to assess the relationships between each morphometric variable (body mass, SVL, forelimb length, hindlimb length and limb ratio, each included as a covariate in an individual ANCOVA) plus run rate (included as a covariate in an individual ANCOVA) on sprint speed (dependent variable), controlling for sex, habitat (categorical variables) and their interaction. In each of these ANCOVAs, only one covariate was included at a time. A similar set of ANCOVAs was used to test the relationships of morphometric variables plus run rate (included as covariates in individual ANCOVAs) on average speed (dependent variable), controlling for sex, habitat (categorical variables) and their interaction (Supporting Information). Finally, I performed a similar set of ANCOVAs to test the effects of morphometric variables plus sprint speed (included as covariates in individual ANCOVAs) on run rate (dependent variable), in which sex, habitat (categorical variables) and their interaction were also controlled for. All analyses involving fore- or hindlimb length were controlled for SVL, introducing it as a covariate. Statistical analyses were conducted in the software Statistica 8.0 (StatSoft Inc., Tulsa, OK, USA). RESULTS Body mass (Supporting Information Table S1, Fig. S1a) and SVL (Table S1, Fig. S1b) were greater in agrosystem toads than in pine grove toads. The interaction was significant for body mass (Table S1, Fig. S1a), which was similar in both sexes in the pine grove, while females were heavier than males in agrosystems. Forelimbs (Table S1, Fig. S1c) and hindlimbs (Table S1, Fig. S1d) were longer in males, although they did not differ between habitats. The interaction was nearly significant for forelimb length (Table S1, Fig. S1c), and significant for hindlimb length (Table S1, Fig. S1d), sex differences being greater in agrosystem toads. Limb ratio was greater in females than in males, with no effect of habitat (Table S1, Fig. S1e), so male forelimbs were relatively shorter than hindlimbs. Sprint speed was higher in males (F1,116 = 50.420, P < 0.001; Fig. 1a), with no effect of habitat (F1,116 = 0.235, P = 0.629; Fig. 1a) or sex × habitat interaction (F1,116 = 0.348, P = 0.557; Fig. 1a). Results were qualitatively similar for average speed (Table S1, Fig. S1f). Meanwhile, run rate was higher in agrosystems (F1,116 = 7.042, P = 0.009; Fig. 1b), but did not differ between sexes (F1,116 = 0.131, P = 0.0.718; Fig. 1b), and the sex × habitat interaction was non-significant (F1,116 = 0.480, P = 0.490; Fig. 1b). Figure 1. View largeDownload slide Sex and habitat differences in sprint speed (a) and run rate (b). Sample sizes are indicated in (a). Vertical bars represent standard errors. Figure 1. View largeDownload slide Sex and habitat differences in sprint speed (a) and run rate (b). Sample sizes are indicated in (a). Vertical bars represent standard errors. Among all morphometric variables, only hindlimb length showed a significant, positive relationship with sprint speed (Table 1). Sex differences remained significant in this model (Table 1). In all cases, introducing morphometric variables and run rate as covariates resulted in higher sprint speeds in males with no effect of habitat (Table 1). Sprint speed was negatively related to run rate (Tables 1 and 2). Results were qualitatively similar for average speed, although the effect of hindlimb length was not significant in this case (Supporting Information, Table S2). Table 1. Individual models testing the effects of body mass, snout–vent length, fore- and hindlimb length, limb ratio, and run rate on sprint speed Co-variables  Co-variable F1,115  Co-variable β-value  Sex F1,115  Habitat F1,115  Sex × Habitat F1,115  Body mass  0.338NS  0.050  50.380***  0.435NS  0.222NS  Snout–vent length  1.747NS  0.106  51.436***  0.616NS  0.434NS  Forelimb length  0.770NS  0.091  46.338***  0.661NS  0.305NS  Hindlimb length  5.617*  0.346  10.817**  0.859NS  0.356NS  Limb ratio  1.528NS  −0.113  28.394***  0.334NS  0.277NS  Run rate  53.543***  −0.483  69.037***  1.401NS  0.057NS  Co-variables  Co-variable F1,115  Co-variable β-value  Sex F1,115  Habitat F1,115  Sex × Habitat F1,115  Body mass  0.338NS  0.050  50.380***  0.435NS  0.222NS  Snout–vent length  1.747NS  0.106  51.436***  0.616NS  0.434NS  Forelimb length  0.770NS  0.091  46.338***  0.661NS  0.305NS  Hindlimb length  5.617*  0.346  10.817**  0.859NS  0.356NS  Limb ratio  1.528NS  −0.113  28.394***  0.334NS  0.277NS  Run rate  53.543***  −0.483  69.037***  1.401NS  0.057NS  Sex, habitat and their interaction were controlled for in all models. F- and β-values are indicated. Note that the effects of limb length were controlled for snout–vent length, so degrees of freedom were 1 and 114. NSNon-significant * P < 0.05 ** P < 0.01 *** P < 0.001. Significant results are in bold type. View Large Run rate was not affected by any morphometric variable (Table 2), but showed a significant, negative relationship with sprint speed (Tables 1 and 2). In all cases, introducing morphometric variables as covariates resulted in a higher run rate in agrosystem toads, with no effect of sex (Table 2). Remarkably, when sprint speed was introduced as a covariate, habitat differences in run rate persisted, and sex differences arose, run rate being higher in males (Table 2, Fig. 2). Table 2. Individual models testing the effects of body mass, snout–vent length, fore- and hindlimb length, limb ratio, and sprint speed on run rate Co-variables  Co-variable F1,115  Co-variable β-value  Sex F1,115  Habitat F1,115  Sex × Habitat F1,115  Body mass  0.713NS  −0.084  0.214NS  7.710**  0.276NS  Snout–vent length  1.799NS  −0.125  0.174NS  8.435**  0.268NS  Forelimb length  0.008NS  0.011  0.180NS  8.335**  0.245NS  Hindlimb length  0.113NS  −0.059  0.002NS  8.450**  0.325NS  Limb ratio  0.161NS  0.043  0.008NS  7.112**  0.447NS  Sprint speed  53.542***  −0.658  13.424***  8.218**  0.188NS  Co-variables  Co-variable F1,115  Co-variable β-value  Sex F1,115  Habitat F1,115  Sex × Habitat F1,115  Body mass  0.713NS  −0.084  0.214NS  7.710**  0.276NS  Snout–vent length  1.799NS  −0.125  0.174NS  8.435**  0.268NS  Forelimb length  0.008NS  0.011  0.180NS  8.335**  0.245NS  Hindlimb length  0.113NS  −0.059  0.002NS  8.450**  0.325NS  Limb ratio  0.161NS  0.043  0.008NS  7.112**  0.447NS  Sprint speed  53.542***  −0.658  13.424***  8.218**  0.188NS  Sex, habitat and their interaction were controlled for in all models. F- and β-values are indicated. Note that the effects of limb length were controlled for snout–vent length, so degrees of freedom were 1 and 114. NSNon-significant; §marginally non-significant * P < 0.05 ** P < 0.01 *** P < 0.001. Significant results are in bold type. View Large Figure 2. View largeDownload slide Sex and habitat differences in run rate when sprint speed was controlled for. Sample sizes are indicated in Figure 1(a). Vertical bars represent standard errors. Figure 2. View largeDownload slide Sex and habitat differences in run rate when sprint speed was controlled for. Sample sizes are indicated in Figure 1(a). Vertical bars represent standard errors. DISCUSSION Clarifying the relationships between morphology and locomotion provides a fundamental framework for advancing evolutionary ecology. The results herein demonstrate a positive relationship between sprint speed and hindlimb length. This was an expected result, as several jumping anurans show a positive effect of hindlimb length on locomotor performance (Tejedo, Semlitsch & Hotz, 2000; Choi, Han Shim & Ricklefs, 2003; Johansson, Lederer & Lind, 2010), probably related to more massive muscles (James et al., 2005). Therefore, hindlimbs are also suggested to be the main factor responsible for toad propulsion in this running species. No other morphological variable proved to affect toad sprint speed. Neither forelimb length nor limb ratio showed a relationship with sprint speed, which reinforces the idea that toad sprint speed relies mainly on hindlimbs. The finding that SVL had no effect on sprint speed contrasts with that of Llewelyn et al. (2010), who detected a positive relationship between body length and sprint speed in terrestrial Rhinella marina toads. Moreover, contrary to expectation, body mass did not have a negative effect on sprint speed. Other studies on anuran locomotor performance also found no relationship with body mass, or even a positive relationship, during terrestrial locomotion (Wilson, Franklin & James, 2000; Álvarez & Nicieza, 2002). Males were faster than females. Accordingly, male hindlimbs were longer, and a lower male limb ratio indicates that hindlimbs in males are proportionally longer than forelimbs. Similarly, other anurans, such as Xenopus tropicalis frogs, show sexual dimorphism in morphology and locomotor performance, males having longer limbs and proportionally higher burst speeds (Herrel et al., 2012). However, males were still faster when hindlimb length was controlled for, which suggests that other factors, such as greater muscle mass in male toads (Lee & Corrales, 2002; Zhiping, 2013), may drive sex differences in sprint speed. The finding that the longer forelimbs of males were not related to higher sprint speed suggests a different function of forelimbs in both sexes besides locomotion. Sex differences in forelimb length may be caused by their role during amplexus in males (Clark & Peters, 2006; Navas & James, 2007). Interestingly, males and females did not differ in SVL or body mass, which showed no effect on sprint speed. Sprint speed was similar in agrosystem and natural pine grove toads. Accordingly, neither forelimb nor hindlimb length differed between habitats, despite a greater body size in agrosystem toads, which was controlled for (by including SVL as a covariate) in all models testing the effects of limb length. Remarkably, significant or nearly significant sex × habitat interactions for body mass as well as forelimb and hindlimb length resulted in higher sex differences in agrosystem toads. In this system, agrosystem toad lifespans are shorter (probably as a consequence of high mortality in stressful environmental conditions), while indicators of reproductive investment are higher (Zamora-Camacho & Comas, 2017). The result that sexual dimorphism is more accentuated in agrosystem toads could suggest greater sexual selection in agrosystem toads (Zamora-Camacho & Comas, 2017), a probable consequence of reduced lifespan according to life-history theory (Stearns, 2000): reproduction is evolutionarily prioritized under circumstances that shorten lifespan. Run rate was significantly higher in agrosystem toads, so they use more runs than pine grove conspecifics to cover a given distance. Toads could save energy (Edwards & Gleeson, 2001) and enhance endurance (Weinstein & Full, 1999) by increasing locomotion intermittence. In fact, locomotion is an energetically costly trait for anurans (Walton & Anderson, 1988). However, the energetic cost of walking for anurans proved to be relatively low (Walton, Peterson & Bennett, 1994). Moreover, toads from both habitats have similar prey resources in this system (Zamora-Camacho & Comas, 2017), which does not support an energy limitation triggering higher run rate in agrosystem toads. McLaughlin & Grant (2001) detected no effect of intermittent locomotion on energy expenditure or endurance in brook charr (Salvelinus fontinalis). Contrastingly, intermittent locomotion in desert iguanas (Dipsosaurus dorsalis) increases metabolic costs (Hancock & Gleeson, 2005). Therefore, the energy basis of intermittent locomotion remains unclear in this case. An alternative and not mutually exclusive explanation is that intermittent locomotion may increase chances for vigilance against predators (McAdam & Kramer, 1998). Indeed, Octodon degus degus (Vásquez, Ebensperger & Bozinovic, 2002) and Psammodromus algirus lizards (López & Martín, 2013) increase vigilance by interrupting locomotion in open habitats, where exposure to predators is greater. Therefore, agrosystem toads could have enhanced vigilance behaviour due to openness in such habitat. Also, frequent stops in agrosystem toads could allow them to remain unseen or to confound predators via intermittent movement patterns (Martell & Dill, 1995). Accordingly, animals can perceive human presence, a constant in agrosystems, as a form of predator pressure (Beale & Monaghan, 2004). Run rate was similar in both sexes. However, when sprint speed was controlled for, males showed a higher run rate than females, which indicates that, for a given speed, males used more runs than females. Assuming that intermittent locomotion increases opportunities for vigilance against predators in this species (Trouilloud, Delisle & Kramer, 2004), this finding, along with increased male speed, reinforces the idea that males are better suited for predator avoidance, and probably experiencegreater predator pressure. These differences are a probable consequence of E. calamita males performing more conspicuous activities in territory defence (Miaud, Sanuy & Avrillier, 2000) or mating (Sinsch, 1988). I also detected an interesting negative relationship between sprint speed and run rate. An individual’s escape strategy seems to consist of a continuum from slow, multiple short movements to a few fast, long runs. Slower toads may remain unnoticed by reducing movements, to confound predators by increasing the number of short runs (Martell & Dill, 1995), or to increase predator vigilance by frequent stops (McAdam & Kramer, 1998). Conversely, faster toads may rely on their speed and use longer runs to escape predators or find a shelter as soon as possible (Lima & Dill, 1990). Sprint speed proved highly constrained by hindlimb length. On the other hand, the fact that run rate was unaffected by morphology suggests that it could be a behavioural trait rather than a morphology-limited ability, which contrasts with other findings that morphology affects locomotion (Miller, Samuk & Rennison, 2016). This negative relationship between sprint speed and run rate thus suggests that locomotion mode in this running toad is a combination of morphology-limited sprint ability influencing behavioural decisions of locomotion pace. CONCLUSIONS In summary, sprint speed was directly related to hindlimb length, but not to forelimb length, SVL or body mass in natterjack toads. Males were faster than females, and had longer limbs, but sex differences in sprint speed were not explained solely by longer limbs of males. Males’ longer forelimbs were not related to higher speed, so other factors, probably use of forelimbs during amplexus, seem to drive differences in forelimb length. Habitat had no effect on sprint speed, but run rate was higher in agrosystem toads, which suggests increased vigilance against predators, probably related to habitat openness and/or to human presence. For a given speed, males showed higher run rates than females, which, along with higher speed, suggests a greater effect of predator pressure on shaping male locomotion. Finally, a negative relationship between sprint speed and run rate suggests that locomotion pace is affected by sprint speed abilities: slower toads tend to use short runs, which probably helps them to remain unseen or confound predators, while faster toads tend to use long runs, probably to flee from predators or find a shelter as soon as possible. ACKNOWLEDGEMENTS The author was partly supported by a Fundación Ramón Areces postdoctoral fellowship, and by a Juan de la Cierva-Formación postdoctoral fellowship from the Spanish Ministerio de Economía, Industria y Competitividad. Toad capture was conducted according to permits by the Junta de Andalucía issued to the author (Reference AWG/MGD/MGM/CB). Comments by six anonymous reviewers improved the manuscript. This research did not receive any specific grant from funding agencies in the public, commercial or not-for-profit sectors. SUPPORTING INFORMATION Additional Supporting Information may be found in the online version of this article at the publisher’s web-site: Table S1. Individual ANOVAs testing the effect of sex, habitat, and their interaction on body mass, snout–vent length, fore- and hindlimb length, limb ratio, and average speed. Note that fore- and hind limb length were controlled for snout–vent length, so degrees of freedom were 1 and 115. F-values are indicated. NSNon-significant; §marginally non-significant; *P < 0.05; ***P > 0.001. Significant results are in bold type. Table S2. Individual models testing the effects of body mass, snout–vent length, fore- and hind limb length, limb ratio, and run rate on average speed. Sex, habitat and their interaction were controlled for in all models. F- and ß-values are indicated. Note that the effects of limb length were controlled for snout–vent length, so degrees of freedom were 1 and 114. NSNon-significant; §marginally non-significant; *P < 0.05; **P < 0.01; ***P < 0.001. Significant results are in bold type. Figure S1. Sex and habitat differences in body mass (a), SVL (b), forelimb length (c), hindlimb length (d), limbratio (e) and average speed (f). Fore- and hindlimb length were controlled for SVL. Sample sizes are indicated in(a). Vertical bars represent standard errors. References Acevedo-Whitehouse K, Duffus ALJ. 2009. Effects of environmental change on wildlife health. Philosophical Transactions of the Royal Society of London B  364: 3429– 3438. Google Scholar CrossRef Search ADS   Ahn AN, Furrow E, Biewener AA. 2004. Walking and running in the red-legged running frog, Kassina maculata. Journal of Experimental Biology  207: 399– 410. Google Scholar CrossRef Search ADS PubMed  Álvarez D, Nicieza AG. 2002. Effects of induced variation in anuran larval development on postmetamorphic energy reserves and locomotion. Oecologia  131: 186– 195. Google Scholar CrossRef Search ADS PubMed  Beale CM, Monaghan P. 2004. Human disturbance: people as predation-free predators? Journal of Applied Ecology  41: 335– 343. Google Scholar CrossRef Search ADS   Boomsma JJ, Arntzen JW. 1985. Abundance, growth and feeding of natterjack toads (Bufo calamita) in a 4-year-old artificial habitat. Journal of Applied Ecology  22: 395– 405. Google Scholar CrossRef Search ADS   Botton-Divet L, Cornette R, Houssaye A, Fabre AC, Herrel A. 2017. Swimming and running: a study of the convergence in long bone morphology among semi-aquatic mustelids (Carnivora: Mustelidae). Biological Journal of the Linnean Society  121: 38– 49. Google Scholar CrossRef Search ADS   Brandt R, Cury de B arros F, Noronha C, Tulli MJ, Kohlsdorf T. 2016. Sexual differences in locomotor performance in Tropidurus catalanensis lizards (Squamata: Tropiduridae) – body shape, size and limb musculature explain variation between males and females. Biological Journal of the Linnean Society  118: 598– 609. Google Scholar CrossRef Search ADS   Brijs J, Sandblom E, Sundh H, Gräns A, Hinchcliffe J, Ekström A, Sundell K, Olsson C, Axelsson M, Pichaud N. 2017. Increased mitochondrial coupling and anaerobic capacity minimizes aerobic costs of trout in the sea. Scientific Reports  7: 45778. Google Scholar CrossRef Search ADS PubMed  Budick SA, O’Malley DM. 2000. Locomotor repertoire of the larval zebrafish: swimming, turning and prey capture. Journal of Experimental Biology  203: 2565– 2579. Google Scholar PubMed  Calsbeek R. 2008. An ecological twist on the morphology–performance–fitness axis. Evolutionary Ecology Research  10: 197– 212. Calsbeek R, Irschick DJ. 2007. The quick and the dead: correlational selection on morphology, performance, and habitat use in island lizards. Evolution  61: 2493– 2503. Google Scholar CrossRef Search ADS PubMed  Choi I, Han Shim J, Ricklefs RE. 2003. Morphometric relationships of take-off speed in anuran amphibians. Journal of Experimental Zoology  299A: 99– 102. Google Scholar CrossRef Search ADS   Clark DL, Peters SE. 2006. Isometric contractile properties of sexually dimorphic forelimb muscles in the marine toad Bufo marinus Linnaeus 1758: functional analysis and implications for amplexus. Journal of Experimental Biology  209: 3448– 3456. Google Scholar CrossRef Search ADS PubMed  Colombo M, Indermaur A, Meyer BS, Salzburger W. 2016. Habitat use and its implications to functional morphology: niche partitioning and the evolution of locomotory morphology in Lake Tanganyikan cichlids (Perciformes: Cichlidae). Biological Journal of the Linnean Society  118: 536– 550. Google Scholar CrossRef Search ADS   Conradsen C, McGuigan K. 2015. Sexually dimorphic morphology and swimming performance relationships in wild-type zebrafish Danio rerio. Journal of Fish Biology  87: 1219– 1233. Google Scholar CrossRef Search ADS PubMed  Day LM, Jayne BC. 2007. Interspecific scaling of the morphology and posture of the limbs during locomotion in cats (Felidae). Journal of Experimental Biology  210: 642– 654. Google Scholar CrossRef Search ADS PubMed  Donihue C. 2016. Microgeographic variation in locomotor traits among lizards in a human-built environment. PeerJ  4: e1776. Google Scholar CrossRef Search ADS PubMed  Edwards EB, Gleeson TT. 2001. Can energetic expenditure be minimized by performing activity intermittently? Journal of Experimental Biology  204: 599– 605. Google Scholar PubMed  Edwards S, Herrel A, Vanhooydonck B, Measey GJ, Tolley KA. 2016. Diving in head first: trade-offs between phenotypic traits and sand-diving predator escape strategy in Meroles desert lizards. Biological Journal of the Linnean Society  119: 919– 931. Google Scholar CrossRef Search ADS   Fahrig L. 2007. Non-optimal animal movement in human-altered landscapes. Functional Ecology  21: 1003– 1015. Google Scholar CrossRef Search ADS   Frid A, Dill L. 2002. Human-caused disturbance stimuli as a form of predation risk. Conservation Ecology  6: 11– 26. Google Scholar CrossRef Search ADS   Gallego-Carmona CA, Castro-Arango JA, Bernal-Bautista MH. 2016. Effect of habitat disturbance on the body condition index of the Colombian endemic lizard Anolis antonii (Squamata: Dactyloidae). South American Journal of Herpetology  11: 183– 187. Google Scholar CrossRef Search ADS   Garland T, Hankins E, Huey RB. 1990. Locomotor capacity and social dominance in male lizards. Functional Ecology  4: 243– 250. Google Scholar CrossRef Search ADS   Garland T, Losos JB. 1994. Ecological morphology of locomotor performance in squamate reptiles. In: Wainwright PC, Reilly SM, eds. Ecological morphology: integrative organismal biology . Chicago: University of Chicago Press, 240–302. Gómez-Mestre I. 2014. Sapo corredor – Epidalea calamita (Laurenti, 1768). In: Salvador A, Marco A, eds. Enciclopedia Virtual de los Vertebrados Españoles . Museo Nacional de Ciencias Naturales, Madrid. Available at http://www.vertebradosibericos.org Goodman BA. 2009. Nowhere to run: the role of habitat openness and refuge use in defining patterns of morphological and performance evolution in tropical lizards. Journal of Evolutionary Biology  22: 1535– 1544. Google Scholar CrossRef Search ADS PubMed  Halsey LG. 2016. Terrestrial movement energetics: current knowledge and its application to the optimising animal. Journal of Experimental Biology  219: 1424– 1431. Google Scholar CrossRef Search ADS PubMed  Hancock TV, Gleeson TT. 2005. Intermittent locomotor activity that increases endurance also increases metabolic costs in the desert iguana (Dipsosaurus dorsalis). Physiological and Biochemical Zoology  78: 163– 172. Google Scholar CrossRef Search ADS PubMed  Herrel A, Gonwouo LN, Fokam EB, Ngundu WI, Bonneaud C. 2012. Intersexual differences in body shape and locomotor performance in the aquatic frog, Xenopus tropicalis. Journal of Zoology  287: 311– 316. Google Scholar CrossRef Search ADS   Herrel A, Vasilopoulou-Kampitsi M, Bonneaud C. 2014. Jumping performance in the highly aquatic frog Xenopus tropicalis: sex-specific relationships between morphology and performance. PeerJ  2: e661. Google Scholar CrossRef Search ADS PubMed  Higham TE. 2007. The integration of locomotion and prey capture in vertebrates: morphology, behavior and performance. Integrative and Comparative Biology  47: 82– 95. Google Scholar CrossRef Search ADS PubMed  Higham TE, Gamble T, Russell AP. 2017. On the origin of frictional adhesion in geckos: small morphological changes lead to a major biomechanical transition in the genus Gonatodes. Biological Journal of the Linnean Society  120: 503– 517. Hudson CM, Brown GP, Shine R. 2016. Athletic anurans: the impact of morphology, ecology and evolution on climbing ability in invasive cane toads. Biological Journal of the Linnean Society  119: 992– 999. Google Scholar CrossRef Search ADS   Huey RB, Dunham AE, Overall KL. 1991. Variation in locomotor performance in demographically known populations of the lizard Sceloporus merriami. Physiological Zoology  63: 845– 872. Google Scholar CrossRef Search ADS   Huey RB, Dunham AE, Overall KL, Newman RA. 1990. Variation in locomotor performance in demographically known populations of the lizard Sceloporus merriami. Physiological Zoology  63: 845– 872. Google Scholar CrossRef Search ADS   Husak JF. 2006a. Does speed help you survive? A test with collared lizards of different ages. Functional Ecology  20: 174– 179. Google Scholar CrossRef Search ADS   Husak JF. 2006b. Does survival depend on how fast you can run or how fast you do run? Functional Ecology  20: 1080– 1086. Google Scholar CrossRef Search ADS   Husak JF, Fox SF. 2008. Sexual selection on locomotor performance. Evolutionary Ecology Research  10: 213– 228. Husak JF, Fox SF, Van Den Bussche RA. 2008. Faster male lizards are better defenders not sneakers. Animal Behaviour  75: 1725– 1730. Google Scholar CrossRef Search ADS   Husak JF, Fox SF, Lovern MB, Van Den Bussche RA. 2006. Faster lizards sire more offspring: sexual selection on whole-animal performance. Evolution  60: 2122– 2130. Google Scholar CrossRef Search ADS PubMed  Ingley SJ, Camarillo H, Willis H, Johnson JB. 2016. Repeated evolution of local adaptation in swimming performance: population-level trade-offs between burst and endurance swimming in Brachyraphis freshwater fish. Biological Journal of the Linnean Society  119: 1011– 1026. Google Scholar CrossRef Search ADS   Iriarte-Díaz J. 2002. Differential scaling of locomotor performance in small and large terrestrial mammals. Journal of Experimental Biology  205: 2897– 2908. Google Scholar PubMed  Irschick DJ, Carlisle E, Elstrott J, Ramos M, Buckley C, Vanhooydonck B, Meyers J, Herrel A. 2005. A comparison of habitat use, morphology, clinging performance and escape behaviour among two divergent green anole lizard (Anolis carolinensis) populations. Biological Journal of the Linnean Society  85: 223– 234. Google Scholar CrossRef Search ADS   James RS, Wilson RS, de C arvalho JE, Kohlsdorf T, Gomes FR, Navas CA. 2005. Interindividual differences in leg muscle mass and pyruvate kinase activity correlate with interindividual differences in jumping performance of Hyla multilineata. Physiological and Biochemical Zoology  78: 857– 867. Google Scholar CrossRef Search ADS PubMed  Jayne BC, Bennett AF. 1990. Selection on locomotor performance capacity in a natural population of garter snake. Evolution  44: 1204– 1229. Google Scholar CrossRef Search ADS PubMed  Johansson F, Lederer B, Lind MI. 2010. Trait performance correlations across life stages under environmental stress conditions in the common frog, Rana temporaria. PLOS One  5: e11680. Google Scholar CrossRef Search ADS PubMed  Kaliontzopoulou A, Bandeira V, Carretero MÁ. 2013. Sexual dimorphism in locomotor performance and its relation to morphology in wall lizards (Podarcis bocagei). Journal of Zoology  289: 294– 302. Google Scholar CrossRef Search ADS   Kotiaho JS. 2001. Costs of sexual traits: a mismatch between theoretical considerations and empirical evidence. Biological Reviews  76: 365– 376. Google Scholar CrossRef Search ADS PubMed  Lailvaux SP. 2007. Interactive effects of sex and temperature on locomotion in reptiles. Integrative and Comparative Biology  47: 189– 199. Google Scholar CrossRef Search ADS PubMed  Lee JC, Corrales AD. 2002. Sexual dimorphism in hind-limb muscle mass is associated with male reproductive success in Bufo marinus. Journal of Herpetology  36: 502– 505. Google Scholar CrossRef Search ADS   Lima SL, Dill LM. 1990. Behavioral decisions made under the risk of predation: a review and prospectus. Canadian Journal of Zoology  68: 619– 640. Google Scholar CrossRef Search ADS   Llewelyn J, Phillips BL, Alford RA, Schwarzkopf L, Shine R. 2010. Locomotor performance in an invasive species: cane toads from the invasion front have greater endurance, but not speed, compared to conspecifics from a long-colonised area. Oecologia  162: 343– 348. Google Scholar CrossRef Search ADS PubMed  Li J, Lin X, Zhou C, Zeng P, Xu Z, Sun J. 2016. Sexual dimorphism and its relationship with swimming performance in Tanichthys albonubes under laboratory conditions. Chinese Journal of Applied Ecology  27: 1639– 1646. López P, Martín J. 2013. Effects of microhabitat-dependent predation risk on vigilance during intermittent locomotion in Psammodromus algirus lizards. Ethology  119: 316– 324. Google Scholar CrossRef Search ADS   Magnhagen C. 1991. Predation risk as a cost of reproduction. Trends in Ecology and Evolution  6: 183– 186. Google Scholar CrossRef Search ADS PubMed  Martell G, Dill LM. 1995. Influence of movement by coho salmon (Oncorhynchus kisutch) parr on their detection by common mergansers (Mergus merganser). Ethology  99: 139– 149. Google Scholar CrossRef Search ADS   Martín J, López P. 2000. Fleeing to unsafe refuges: effects of conspicuousness and refuge safety on the scape decisions of the lizard Psammodromus algirus. Canadian Journal of Zoology  78: 265– 270. Google Scholar CrossRef Search ADS   Martín J, López P. 2001. Hindlimb asymmetry reduces escape performance in the lizard Psammodromus algirus. Physiological and Biochemical Zoology  74: 619– 624. Google Scholar CrossRef Search ADS PubMed  Martín J, López P, Gutiérrez E, García LV. 2015. Natural and anthropogenic alterations of the soil affect body condition of the fossorial amphisbaenian Trogonophis wiegmanni in North Africa. Journal of Arid Environments  122: 30– 36. Google Scholar CrossRef Search ADS   Martínez F, Montero G. 2004. The Pinus pinea L. woodlands along the coast of South-western Spain: data for a new geobotanical interpretation. Plant Ecology  175: 1– 18. Google Scholar CrossRef Search ADS   McAdam AG, Kramer DL. 1998. Vigilance as a benefit of intermittent locomotion in small mammals. Animal Behaviour  55: 109– 117. Google Scholar CrossRef Search ADS PubMed  McGee MR, Julius ML, Vajda AM, Norris DO, Barber LB, Schoenfuss HL. 2009. Predator avoidance performance of larval fathead minnows (Pimephales promelas) following short-term exposure to estrogen mixtures. Aquatic Toxicology  91: 355– 361. Google Scholar CrossRef Search ADS PubMed  McLaughlin RL, Grant JWA. 2001. Field examination of perceptual and energetic bases for intermittent locomotion by recently-emerged brook charr in still-water pools. Behaviour  138: 559– 574. Google Scholar CrossRef Search ADS   Melville J, Swain ROY. 2000. Evolutionary relationships between morphology, performance and habitat openness in the lizard genus Niveoscincus (Scincidae: Lygosominae). Biological Journal of the Linnean Society  70: 667– 683. Miaud C, Sanuy D, Avrillier JN. 2000. Terrestrial movements of the natterjack toad Bufo calamita (Amphibia, Anura) in a semi-arid, agricultural landscape. Amphibia-Reptilia  21: 357– 369. Google Scholar CrossRef Search ADS   Miles DB. 2004. The race goes to the swift: fitness consequences of variation in sprint performance in juvenile lizards. Evolutionary Ecology Research  6: 63– 75. Miller SE, Samuk KM, Rennison DJ. 2016. An experimental test of the effect of predation upon behaviour and trait correlations in the threespine stickleback. Biological Journal of the Linnean Society  119: 117– 125. Google Scholar CrossRef Search ADS   Moreno-Rueda G. 2003. The capacity to escape from predators in Passer domesticus: an experimental study. Journal of Ornithology  144: 438– 444. Navas CA, James RS. 2007. Sexual dimorphism of extensor carpi radialis muscle size, isometric force, relaxation rate and stamina during the breeding season of the frog Rana temporaria Linnaeus 1758. Journal of Experimental Biology  210: 715– 721. Google Scholar CrossRef Search ADS PubMed  O’Steen S, Cullum AJ, Bennett AF. 2002. Rapid evolution of escape ability in Trinidadian guppies (Poecilia reticulata). Evolution  56: 776– 784. Google Scholar CrossRef Search ADS PubMed  Pérez-Tris J, Díaz JA, Tellería JL. 2004. Loss of body mass under predation risk: cost of antipredatory behaviour or adaptive fit-for-escape? Animal Behaviour  67: 511– 521. Google Scholar CrossRef Search ADS   Perry G, Levering K, Girard I, Garland T. 2004. Locomotor performance and social dominance in male Anolis cristatellus. Animal Behaviour  67: 37– 47. Google Scholar CrossRef Search ADS   Peterson CC, Husak JF. 2006. Locomotor performance and sexual selection: individual variation in sprint speed of collared lizards (Crotaphytus collaris). Copeia  2006: 216– 224. Google Scholar CrossRef Search ADS   Prates I, Angilleta MJ, Wilson RS, Niehaus AC, Navas CA. 2013. Dehydration hardly slows hopping toads (Rhinella granulosa) from xeric and mesic environments. Physiological and Biochemical Zoology  86: 451– 457. Google Scholar CrossRef Search ADS PubMed  Preest MR, Pough FH. 1989. Interaction of temperature and hydration on locomotion of toads. Functional Ecology  3: 693– 699. Google Scholar CrossRef Search ADS   Preest MR, Pough FH. 2003. Effects of body temperature and hydration state on organismal performance of toads, Bufo americanus. Physiological and Biochemical Zoology  76: 229– 239. Google Scholar CrossRef Search ADS PubMed  Promislow DEL, Montgomerie R, Martin TE. 1992. Mortality costs of sexual dimorphism in birds. Proceedings of the Royal Society B  250: 143– 150. Google Scholar CrossRef Search ADS   Quinn GP, Keough MJ. 2002. Experimental design and data analysis for biologists . Cambridge: Cambridge University Press. Google Scholar CrossRef Search ADS   Reilly SM, Montuelle SJ, Schmidt A, Krause C, Naylor E, Essner RL. 2016. Functional evolution of jumping in frogs: interspecific differences in take-off and landing. Journal of Morphology  277: 379– 393. Google Scholar CrossRef Search ADS PubMed  Ruibal R. 1962. The adaptive value of bladder water in the toad, Bufo cognatus. Physiological Zoology  35: 218– 223. Google Scholar CrossRef Search ADS   Shaffer LR, Formanowicz DR. 1996. A cost of viviparity and parental care in scorpions: reduced sprint speed and behavioural compensation. Animal Behaviour  51: 1017– 1024. Google Scholar CrossRef Search ADS   Sinsch U. 1988. Temporal spacing of breeding activity in the natterjack toad, Bufo calamita. Oecologia  76: 399– 407. Google Scholar CrossRef Search ADS PubMed  Smith TB, Bernatchez L. 2007. Evolutionary change in human-altered environments. Molecular Ecology  17: 1– 8. Google Scholar CrossRef Search ADS   Stearns SC. 2000. Life history evolution: successes, limitations, and prospects. Naturwissenchaften  87: 476– 486. Google Scholar CrossRef Search ADS   Tejedo M, Semlitsch RD, Hotz H. 2000. Differential morphology and jumping performance of newly metamorphosed frogs of the hybridogenetic Rana esculenta complex. Journal of Herpetology  34: 201– 210. Google Scholar CrossRef Search ADS   Trouilloud W, Delisle A, Kramer DL. 2004. Head raising during foraging and pausing during locomotion as components of antipredator vigilance in chipmunks. Animal Behaviour  67: 789– 797. Google Scholar CrossRef Search ADS   Tulli MJ, Cruz FB, Kohlsdorf T, Abdala V. 2016. When a general morphology allows many habitat uses. Integrative Zoology  11: 483– 499. Google Scholar CrossRef Search ADS PubMed  Tuomainen U, Candolin U. 2011. Behavioural responses to human-induced environmental change. Biological Reviews  86: 640– 657. Google Scholar CrossRef Search ADS PubMed  Vanhooydonck B, Measey J, Edwards S, Makhubo B, Tolley KA, Herrel A. 2015. The effects of substratum on locomotor performance in lacertid lizards. Biological Journal of the Linnean Society  115: 869– 881. Google Scholar CrossRef Search ADS   Vanhooydonck B, Van Damme R. 2003. Relationships between locomotor performance, microhabitat use and antipredator behaviour in lacertid lizards. Functional Ecology  17: 160– 169. Google Scholar CrossRef Search ADS   Vásquez RA, Ebensperger LA, Bozinovic F. 2002. The influence of habitat on travel speed, intermittent locomotion, and vigilance in a diurnal rodent. Behavioral Ecology  13: 182– 187. Google Scholar CrossRef Search ADS   Walton BM, Anderson BD. 1988. The aerobic cost of saltatory locomotion in the Fowler’s toad (Bufo woodhousei fowleri). Journal of Experimental Biology  136: 273– 288. Google Scholar PubMed  Walton BM, Peterson CC, Bennett AF. 1994. Is walking costly for anurans? The energetic cost of walking in the northern toad Bufo boreas halophilus. Journal of Experimental Biology  197: 165– 178. Google Scholar PubMed  Walvoord ME. 2003. Cricket frogs maintain body hydration and temperature near levels allowing maximum jump performance. Physiological and Biochemical Zoology  76: 825– 835. Google Scholar CrossRef Search ADS PubMed  Watkins TB. 1996. Predator-mediated selection on burst swimming performance in tadpoles of the Pacific tree frog, Pseudacris regilla. Physiological Zoology  69: 154– 167. Google Scholar CrossRef Search ADS   Weinstein RB, Full RJ. 1999. Intermittent locomotion increases endurance in a gecko. Physiological and Biochemical Zoology  72: 732– 739. Google Scholar CrossRef Search ADS PubMed  Wilson RS, Franklin CE, James RS. 2000. Allometric scaling relationships of jumping performance in the striped marsh frog Limnodynastes peronii. Journal of Experimental Biology  203: 1937– 1946. Google Scholar PubMed  Witter MS, Cuthill IC. 1993. The ecological costs of avian fat storage. Philosophical Transactions of the Royal Society of London B  340: 73– 92. Google Scholar CrossRef Search ADS   Zamora-Camacho FJ, Comas M. 2017. Greater reproductive investment, but shorter lifespan, in agrosystem than in natural-habitat toads. PeerJ  5: e3791. Google Scholar CrossRef Search ADS PubMed  Zamora-Camacho FJ, Reguera S, Rubiño-Hispán MV, Moreno-Rueda G. 2014. Effects of limb length, body mass, gender, gravidity, and elevation on escape speed in the lizard Psammodromus algirus. Evolutionary Biology  41: 509– 517. Google Scholar CrossRef Search ADS   Zamora-Camacho FJ, Reguera S, Rubiño-Hispán MV, Moreno-Rueda G. 2015. Eliciting an immune response reduces sprint speed in a lizard. Behavioral Ecology  26: 115– 120. Google Scholar CrossRef Search ADS   Zhiping MI. 2013. Sexual dimorphism in the hindlimb muscles of the Asiatic toad (Bufo gargarizans) in relation to male reproductive success. Asian Herpetological Research  4: 56– 61. Google Scholar CrossRef Search ADS   © 2017 The Linnean Society of London, Biological Journal of the Linnean Society http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png Biological Journal of the Linnean Society Oxford University Press

Locomotor performance in a running toad: roles of morphology, sex and agrosystem versus natural habitat

Loading next page...
 
/lp/ou_press/locomotor-performance-in-a-running-toad-roles-of-morphology-sex-and-k00Q4f5yet
Publisher
The Linnean Society of London
Copyright
© 2017 The Linnean Society of London, Biological Journal of the Linnean Society
ISSN
0024-4066
eISSN
1095-8312
D.O.I.
10.1093/biolinnean/blx147
Publisher site
See Article on Publisher Site

Abstract

Abstract Locomotor performance is often key in animal fitness, and may be affected by habitat anthropization. This study compares locomotor performance of natterjack toads (Epidalea calamita), which move by intermittent runs, from a natural pine grove and surrounding agrosystems. The effects of sex, morphology and habitat on sprint speed and run rate (number of runs per metre) were assessed. Males were faster than females, and had longer limbs, but the latter trait only partially explained sex differences in sprint speed. Sprint speed was directly related to hindlimb length, but not to any of the other morphological traits measured. Thus, other factors, such as amplexus ability, seemingly shape longer forelimbs in males. Habitat did not affect sprint speed, but toads from the agrosystem habitat had a higher run rate, which could help increase vigilance or confound predators, probably related to habitat openness and/or human presence. For a given speed, males used greater run rates than females, probably because males encounter predators more often and face higher predator pressure. Finally, a negative relationship between sprint speed and run rate suggests that slower toads tend to use short runs, which may improve vigilance or help to confuse predators, while faster toads tend to use long runs, probably for fast escape from predators. INTRODUCTION Locomotor performance is often a key trait shaping animal fitness (Huey, Dunham & Overall, 1991; O’Steen, Cullum & Bennett, 2002; Miles 2004). An efficient locomotor performance optimizes refuge use (Martín & López, 2000), enhances prey acquisition (Budick & O’Malley, 2000; Higham, 2007)and aids escape from predators (Watkins, 1996; McGee et al., 2009). In fact, predator pressure shapes locomotor performance (Ingley et al., 2016). Locomotor performance is increased in open areas, where vulnerability to predators is higher (Vanhooydonck & Van Damme, 2003), and can directly increase survival (Jayne & Bennett, 1990; Husak, 2006a, b). Moreover, locomotor performance is positively related to social dominance (Garland, Hankins & Huey, 1990; Perry et al., 2004), as faster individuals can control larger territories (Peterson & Husak, 2006). It can also be favoured by sexual selection (Husak & Fox, 2008). Indeed, faster males are more able to defend females from other males (Husak, Fox & Van Den Bussche, 2008), and therefore have increased reproductive success (Husak et al., 2006). Locomotor performance is closely related to morphology in vertebrates: larger fins in fish (Li et al., 2016), longer limbs in amphibians (Hudson, Brown & Shine, 2016), reptiles (Garland & Losos, 1994) and mammals (Day & Jayne, 2007), and longer wings in birds (Moreno-Rueda, 2003) all enhance locomotion. Even traits not primarily involved in locomotion, such as head shape, may affect performance (Edwards et al., 2016). Morphology is often shaped by locomotion (Botton-Divet et al., 2017; Higham, Gamble & Russell, 2017), and is thus under strong selection (Calsbeek, 2008). Moreover, for identical biometrics, a heavier body mass often impairs locomotion (Witter & Cuthill, 1993; Iriarte-Díaz, 2002). Consequently, animals often lose weight in the presence of predators, which could improve escape ability by means of increased locomotion performance (Pérez-Tris, Díaz & Tellería, 2004). For the same reason, an increase in female body weight caused by reproduction may impair locomotion performance (Magnhagen, 1991; Shaffer & Formanowicz, 1996; but see Zamora-Camacho et al., 2014 for an exception). Hence, due to differential selection on sexes, females and males may differ in locomotor performance, with concomitant sexual dimorphism in morphological traits related to locomotion (Conradsen & McGuigan, 2015; Brandt et al., 2016). When one sex (typically males) is more conspicuous to predators (Promislow, Montgomerie & Martin, 1992), or displays a reproductive strategy that is more dependent on locomotor performance (Magnhagen, 1991), it is expected to show proportionally higher locomotor performance (Kaliontzopoulou, Bandeira & Carretero, 2013). Indeed, males often show better locomotor performance than females (Lailvaux, 2007; Herrel, Vasilopoulou-Kampitsi & Bonneaud, 2014). Locomotor performance demands physiological adjustments (Brijs et al., 2017), is energetically costly (reviewed by Halsey, 2016) and is thus involved in energy trade-offs (Zamora-Camacho et al., 2015). Consistent with evidence that sexual traits are costly (reviewed by Kotiaho, 2001), locomotor performance is often under sexual selection (Peterson & Husak, 2006; Husak & Fox, 2008). Locomotor performance and morphology of locomotor traits can also vary geographically (Huey et al., 1990; Irschick et al., 2005), or even at microhabitat level within habitats, as locomotor performance (Calsbeek & Irschick, 2007) and related morphological traits (Colombo et al., 2016) can be adjusted to habitat use. In fact, the morphology of locomotor traits may determine habitat use (Tulli et al., 2016), and may differ between natural and human-altered habitats (Donihue, 2016). Moreover, predation risk may shape habitat differences in locomotor performance (Melville & Swain, 2000; Goodman, 2009), and animals can interpret human presence, a constant in some anthropized habitats, as predation risk (Frid & Dill, 2002). Human-altered habitats may deteriorate health (reviewed by Acevedo-Whitehouse & Duffus, 2009), alter behaviour (reviewed by Tuomainen & Candolin, 2011), reduce body condition (Martín et al., 2015; Gallego-Carmona, Castro-Arango & Bernal-Bautista, 2016) and even induce evolution (Smith & Bernatchez, 2007). Therefore, human-altered habitats may exert a negative impact on locomotion performance (Fahrig, 2007). In the present study, I investigated locomotor performance of natterjack toads (Epidalea calamita), by comparing females and males from a natural pine grove and from human-altered agrosystem habitats. These toads move exclusively by means of intermittent runs, instead of leaping as in most anurans (Gómez-Mestre, 2014). Whilst locomotion in jumping anurans has long been studied (Reilly et al., 2016), running locomotion patterns in anurans (see Ahn, Furrow & Biewener, 2004 for an exception), and particularly morphological correlates, have received much less attention. Therefore, running locomotion in anurans remains an important gap in locomotor performance studies. In this context, I assessed the effects of morphology, sex and habitat on two parameters of toad locomotor performance, as well as the relationship between both: sprint speed and run rate (number of runs per metre; see below). Based on the aforementioned arguments, I expected locomotor performance to be related to morphology; in particular, I expected a positive relationship with limb length, and a negative relationship with body mass. Also, I predicted greater locomotor performance in males than in females, as males are more conspicuous to predators, and face higher predator pressure, mainly while searching for and defending their territories, and calling to attract females (Gómez-Mestre, 2014). Moreover, a different strategy is expected according to perceived predation risk in toads from the agrosystem habitat owing to stressful conditions in this human-altered habitat. Agrosystem E. calamita toads are indeed shorter-lived (but larger-bodied) than pine grove conspecifics (Zamora-Camacho & Comas, 2017). MATERIAL AND METHODS Epidalea calamita is a medium-sized [49–86 mm snout–vent length (SVL) in this system] bufonid toad that occurs in a fairly continuous wide area in central and south-west Europe (Gómez-Mestre, 2014). Within its distribution range, it is generally an abundant species, and, due to its ecological versatility, it occupies diverse habitats, from pristine environments to human-altered locations (Gómez-Mestre, 2014). Toads are terrestrial except briefly during amplexus, and are active mainly on wet, warm nights; while inactive they remain sheltered under logs, rocks or in holes they burrow in the ground (Gómez-Mestre, 2014). The period of toad activity varies geographically: they hibernate in winter and reproduce in late spring or early summer in northern cold habitats, but instead aestivate and mate in late winter or early spring in southern hot, dry climates (Gómez-Mestre, 2014). During the breeding season, males can be distinguished because they show blackish nuptial pads in their forelimbs, and their vocal sacs appear pinkish or purple (Gómez-Mestre, 2014). The larval stage is brief (often less than 2 months), and eggs are frequently laid in shallow, small, sunny, ephemeral ponds (Gómez-Mestre, 2014). Toads prey on diverse invertebrates, showing no clear selectivity (Boomsma & Arntzen, 1985). Fieldwork was conducted between January and April 2015, in the natural pine grove Pinares de Cartaya (south-west Spain: 37°20′N, 7°09′W) and surrounding agrosystems, within the natural distribution range of toads. Winters in this area are moderately rainy and warm, usually with no frosts, and summers are dry and hot. Therefore, toads do not hibernate in this region, but skip summer aridity by aestivating. The pine grove used for this study was a stone pine (Pinus pinea) forest, with an undergrowth dominated by Cistus ladanifer, Rosmarinus officinalis and Pistacea lentiscus bushes. Although the autochthonous or anthropogenic origin of the vegetation in this habitat is unclear, it has been the dominant landscape at least over the last 4000 years (Martínez & Montero, 2004). Therefore, I considered this pine grove as a natural habitat for toads. In turn, agrosystems were located 5 km from the pine grove. They consisted of traditional extensive vegetable crops, which have been changed in recent decades to intensive strawberry, raspberry and orange plantations, among others. Crops are artificially irrigated during the summer, and manure, fertilizers, herbicides, pesticides and fungicides are added in different amounts according to landowners’ discretion. During the toad mating season, small temporary ponds where toads reproduce are abundant in both habitats. I captured toads (37 females and 25 males in agrosystems; 30 females and 31 males in pine grove) while they were active on rainy nights, or actively searched for them while they were resting in their shelters, randomly in both habitats. However, as crops are private properties, in agrosystem habitats only public areas, such as meadows, areas of empty ground, tracks, ditches, etc., could be accessed. All toads captured were in their reproductive period: vocal sacs and nuptial pads were clearly visible in males, and eggs could be felt by gently pressing the lower abdomen of females. Since these toads drastically reduce activity after they reproduce (Gómez-Mestre, 2014), the ecological relevance of locomotion is maximal during that period. I took toads to a laboratory facility, where room temperature was controlled (19 °C). I measured SVL (from the tip of the snout to the urostyle), and forelimb and hindlimb length (from the insertion point of the limb to the tip of the longest toe) with a ruler to the nearest millimetre. I calculated limb ratio as forelimb length divided by hindlimb length. During captivity (and 24 h before the trials), I kept toads individually enclosed in plastic terraria (20 × 13 × 9 cm) with soaked peat as a substrate and a piece of opaque plastic as a shelter. In this way, all individuals were fully hydrated, controlling for the potential effects of different hydration states on toad locomotion (Preest & Pough, 1989). On the day after capture, I emptied each toad’s bladder by gently but firmly pressing on its lower abdomen (Walvoord, 2003; Prates et al., 2013). This technique standardizes bladder water burden, which could affect locomotor performance, by reducing it to zero (Preest & Pough, 1989; Walvoord, 2003; Prates et al., 2013). I then immediately measured toad body mass (standard mass sensuRuibal, 1962: body mass of a fully hydrated amphibian with an empty bladder) with a balance (model CDS-100, precision 0.01 g). Toads were then returned to their terraria. One hour later, toads were individually recorded (with a Canon EOS 550D video camera, at 25 frames/s) while they were running on a brown cardboard linear runway (200 × 15 × 15 cm) divided into 10-cm stretches with white stripes stuck perpendicularly along the bottom of the runway. White stripes contrasted with brown cardboard, so each stretch could be perfectly distinguished in the video. Cardboard provided a surface rough enough for appropriate traction, as substrate may affect locomotor performance (Vanhooydonck et al., 2015). I placed a black background at the end of the runway, so that toads would mistake it for a shelter and were encouraged to move. Toads were released at the other end of the runway. Trials were always performed during the night, within the daily activity period of toads. A 60-W bulb 2.5 m above the centre of the runway provided the same illumination in all trials. Toads were chased constantly during the trials to stimulate their moving forward, until they reached the end of the runway. Since body temperature may affect amphibian motility (Preest & Pough, 2003), I verified that all toads performed the trials at the same body temperature (room temperature: 19 °C) by inserting a 1-mm-diameter thermocouple, connected to a Hibok 18 thermometer (precision: 0.1 °C) 8 mm inside their cloacae. As soon as possible after the trials, I released toads at the same spots where I had collected them. No toad suffered any visible damage or died as a consequence of this study. Speed was calculated from videos with the software Tracker v.4.92, which allows a frame-by-frame video analysis. I calculated the time (precision: 0.01 s) that toads needed to cover each stretch, starting and finishing when the snout of the toad reached the perpendicular strips delimiting either end of each stretch (Martín & López, 2001; Zamora-Camacho et al., 2014). I thus calculated toad sprint speed (cm/s) in each stretch by dividing 10 cm (the length of every stretch) by the time (s) needed to cover it. I conducted analyses based on the = fastest stretch speed by each toad, because the objectives of this related to maximum speed (hereafter sprint speed). I also calculated average speed. However, because toads frequently stopped during the trials, and sprint speed is the most informative measure, results involving average speed are presented in the Supporting Information. I also counted the number of runs-and-stops (how many times toads stopped running in each trial) that each toad used to cover the whole runway, and divided it by the length of the runway in metres, to obtain run rate as the number of runs per metre for each individual. As the data met the criteria of residual normality and homoscedasticity, parametric statistics were performed (Quinn & Keough, 2002). I did not include body mass and SVL at the same time in any model due to their high collinearity (r = 0.925; P < 0.001). Firstly, I conducted fully saturated ANOVAs to test the effects of sex, habitat and their interaction on morphometric variables (body mass, SVL, fore- and hindlimb length, and limb ratio; shown in the Supporting Information) as well as average speed (also shown in the Supporting Information), sprint speed and run rate. I then conducted a set of individual ANCOVAs to assess the relationships between each morphometric variable (body mass, SVL, forelimb length, hindlimb length and limb ratio, each included as a covariate in an individual ANCOVA) plus run rate (included as a covariate in an individual ANCOVA) on sprint speed (dependent variable), controlling for sex, habitat (categorical variables) and their interaction. In each of these ANCOVAs, only one covariate was included at a time. A similar set of ANCOVAs was used to test the relationships of morphometric variables plus run rate (included as covariates in individual ANCOVAs) on average speed (dependent variable), controlling for sex, habitat (categorical variables) and their interaction (Supporting Information). Finally, I performed a similar set of ANCOVAs to test the effects of morphometric variables plus sprint speed (included as covariates in individual ANCOVAs) on run rate (dependent variable), in which sex, habitat (categorical variables) and their interaction were also controlled for. All analyses involving fore- or hindlimb length were controlled for SVL, introducing it as a covariate. Statistical analyses were conducted in the software Statistica 8.0 (StatSoft Inc., Tulsa, OK, USA). RESULTS Body mass (Supporting Information Table S1, Fig. S1a) and SVL (Table S1, Fig. S1b) were greater in agrosystem toads than in pine grove toads. The interaction was significant for body mass (Table S1, Fig. S1a), which was similar in both sexes in the pine grove, while females were heavier than males in agrosystems. Forelimbs (Table S1, Fig. S1c) and hindlimbs (Table S1, Fig. S1d) were longer in males, although they did not differ between habitats. The interaction was nearly significant for forelimb length (Table S1, Fig. S1c), and significant for hindlimb length (Table S1, Fig. S1d), sex differences being greater in agrosystem toads. Limb ratio was greater in females than in males, with no effect of habitat (Table S1, Fig. S1e), so male forelimbs were relatively shorter than hindlimbs. Sprint speed was higher in males (F1,116 = 50.420, P < 0.001; Fig. 1a), with no effect of habitat (F1,116 = 0.235, P = 0.629; Fig. 1a) or sex × habitat interaction (F1,116 = 0.348, P = 0.557; Fig. 1a). Results were qualitatively similar for average speed (Table S1, Fig. S1f). Meanwhile, run rate was higher in agrosystems (F1,116 = 7.042, P = 0.009; Fig. 1b), but did not differ between sexes (F1,116 = 0.131, P = 0.0.718; Fig. 1b), and the sex × habitat interaction was non-significant (F1,116 = 0.480, P = 0.490; Fig. 1b). Figure 1. View largeDownload slide Sex and habitat differences in sprint speed (a) and run rate (b). Sample sizes are indicated in (a). Vertical bars represent standard errors. Figure 1. View largeDownload slide Sex and habitat differences in sprint speed (a) and run rate (b). Sample sizes are indicated in (a). Vertical bars represent standard errors. Among all morphometric variables, only hindlimb length showed a significant, positive relationship with sprint speed (Table 1). Sex differences remained significant in this model (Table 1). In all cases, introducing morphometric variables and run rate as covariates resulted in higher sprint speeds in males with no effect of habitat (Table 1). Sprint speed was negatively related to run rate (Tables 1 and 2). Results were qualitatively similar for average speed, although the effect of hindlimb length was not significant in this case (Supporting Information, Table S2). Table 1. Individual models testing the effects of body mass, snout–vent length, fore- and hindlimb length, limb ratio, and run rate on sprint speed Co-variables  Co-variable F1,115  Co-variable β-value  Sex F1,115  Habitat F1,115  Sex × Habitat F1,115  Body mass  0.338NS  0.050  50.380***  0.435NS  0.222NS  Snout–vent length  1.747NS  0.106  51.436***  0.616NS  0.434NS  Forelimb length  0.770NS  0.091  46.338***  0.661NS  0.305NS  Hindlimb length  5.617*  0.346  10.817**  0.859NS  0.356NS  Limb ratio  1.528NS  −0.113  28.394***  0.334NS  0.277NS  Run rate  53.543***  −0.483  69.037***  1.401NS  0.057NS  Co-variables  Co-variable F1,115  Co-variable β-value  Sex F1,115  Habitat F1,115  Sex × Habitat F1,115  Body mass  0.338NS  0.050  50.380***  0.435NS  0.222NS  Snout–vent length  1.747NS  0.106  51.436***  0.616NS  0.434NS  Forelimb length  0.770NS  0.091  46.338***  0.661NS  0.305NS  Hindlimb length  5.617*  0.346  10.817**  0.859NS  0.356NS  Limb ratio  1.528NS  −0.113  28.394***  0.334NS  0.277NS  Run rate  53.543***  −0.483  69.037***  1.401NS  0.057NS  Sex, habitat and their interaction were controlled for in all models. F- and β-values are indicated. Note that the effects of limb length were controlled for snout–vent length, so degrees of freedom were 1 and 114. NSNon-significant * P < 0.05 ** P < 0.01 *** P < 0.001. Significant results are in bold type. View Large Run rate was not affected by any morphometric variable (Table 2), but showed a significant, negative relationship with sprint speed (Tables 1 and 2). In all cases, introducing morphometric variables as covariates resulted in a higher run rate in agrosystem toads, with no effect of sex (Table 2). Remarkably, when sprint speed was introduced as a covariate, habitat differences in run rate persisted, and sex differences arose, run rate being higher in males (Table 2, Fig. 2). Table 2. Individual models testing the effects of body mass, snout–vent length, fore- and hindlimb length, limb ratio, and sprint speed on run rate Co-variables  Co-variable F1,115  Co-variable β-value  Sex F1,115  Habitat F1,115  Sex × Habitat F1,115  Body mass  0.713NS  −0.084  0.214NS  7.710**  0.276NS  Snout–vent length  1.799NS  −0.125  0.174NS  8.435**  0.268NS  Forelimb length  0.008NS  0.011  0.180NS  8.335**  0.245NS  Hindlimb length  0.113NS  −0.059  0.002NS  8.450**  0.325NS  Limb ratio  0.161NS  0.043  0.008NS  7.112**  0.447NS  Sprint speed  53.542***  −0.658  13.424***  8.218**  0.188NS  Co-variables  Co-variable F1,115  Co-variable β-value  Sex F1,115  Habitat F1,115  Sex × Habitat F1,115  Body mass  0.713NS  −0.084  0.214NS  7.710**  0.276NS  Snout–vent length  1.799NS  −0.125  0.174NS  8.435**  0.268NS  Forelimb length  0.008NS  0.011  0.180NS  8.335**  0.245NS  Hindlimb length  0.113NS  −0.059  0.002NS  8.450**  0.325NS  Limb ratio  0.161NS  0.043  0.008NS  7.112**  0.447NS  Sprint speed  53.542***  −0.658  13.424***  8.218**  0.188NS  Sex, habitat and their interaction were controlled for in all models. F- and β-values are indicated. Note that the effects of limb length were controlled for snout–vent length, so degrees of freedom were 1 and 114. NSNon-significant; §marginally non-significant * P < 0.05 ** P < 0.01 *** P < 0.001. Significant results are in bold type. View Large Figure 2. View largeDownload slide Sex and habitat differences in run rate when sprint speed was controlled for. Sample sizes are indicated in Figure 1(a). Vertical bars represent standard errors. Figure 2. View largeDownload slide Sex and habitat differences in run rate when sprint speed was controlled for. Sample sizes are indicated in Figure 1(a). Vertical bars represent standard errors. DISCUSSION Clarifying the relationships between morphology and locomotion provides a fundamental framework for advancing evolutionary ecology. The results herein demonstrate a positive relationship between sprint speed and hindlimb length. This was an expected result, as several jumping anurans show a positive effect of hindlimb length on locomotor performance (Tejedo, Semlitsch & Hotz, 2000; Choi, Han Shim & Ricklefs, 2003; Johansson, Lederer & Lind, 2010), probably related to more massive muscles (James et al., 2005). Therefore, hindlimbs are also suggested to be the main factor responsible for toad propulsion in this running species. No other morphological variable proved to affect toad sprint speed. Neither forelimb length nor limb ratio showed a relationship with sprint speed, which reinforces the idea that toad sprint speed relies mainly on hindlimbs. The finding that SVL had no effect on sprint speed contrasts with that of Llewelyn et al. (2010), who detected a positive relationship between body length and sprint speed in terrestrial Rhinella marina toads. Moreover, contrary to expectation, body mass did not have a negative effect on sprint speed. Other studies on anuran locomotor performance also found no relationship with body mass, or even a positive relationship, during terrestrial locomotion (Wilson, Franklin & James, 2000; Álvarez & Nicieza, 2002). Males were faster than females. Accordingly, male hindlimbs were longer, and a lower male limb ratio indicates that hindlimbs in males are proportionally longer than forelimbs. Similarly, other anurans, such as Xenopus tropicalis frogs, show sexual dimorphism in morphology and locomotor performance, males having longer limbs and proportionally higher burst speeds (Herrel et al., 2012). However, males were still faster when hindlimb length was controlled for, which suggests that other factors, such as greater muscle mass in male toads (Lee & Corrales, 2002; Zhiping, 2013), may drive sex differences in sprint speed. The finding that the longer forelimbs of males were not related to higher sprint speed suggests a different function of forelimbs in both sexes besides locomotion. Sex differences in forelimb length may be caused by their role during amplexus in males (Clark & Peters, 2006; Navas & James, 2007). Interestingly, males and females did not differ in SVL or body mass, which showed no effect on sprint speed. Sprint speed was similar in agrosystem and natural pine grove toads. Accordingly, neither forelimb nor hindlimb length differed between habitats, despite a greater body size in agrosystem toads, which was controlled for (by including SVL as a covariate) in all models testing the effects of limb length. Remarkably, significant or nearly significant sex × habitat interactions for body mass as well as forelimb and hindlimb length resulted in higher sex differences in agrosystem toads. In this system, agrosystem toad lifespans are shorter (probably as a consequence of high mortality in stressful environmental conditions), while indicators of reproductive investment are higher (Zamora-Camacho & Comas, 2017). The result that sexual dimorphism is more accentuated in agrosystem toads could suggest greater sexual selection in agrosystem toads (Zamora-Camacho & Comas, 2017), a probable consequence of reduced lifespan according to life-history theory (Stearns, 2000): reproduction is evolutionarily prioritized under circumstances that shorten lifespan. Run rate was significantly higher in agrosystem toads, so they use more runs than pine grove conspecifics to cover a given distance. Toads could save energy (Edwards & Gleeson, 2001) and enhance endurance (Weinstein & Full, 1999) by increasing locomotion intermittence. In fact, locomotion is an energetically costly trait for anurans (Walton & Anderson, 1988). However, the energetic cost of walking for anurans proved to be relatively low (Walton, Peterson & Bennett, 1994). Moreover, toads from both habitats have similar prey resources in this system (Zamora-Camacho & Comas, 2017), which does not support an energy limitation triggering higher run rate in agrosystem toads. McLaughlin & Grant (2001) detected no effect of intermittent locomotion on energy expenditure or endurance in brook charr (Salvelinus fontinalis). Contrastingly, intermittent locomotion in desert iguanas (Dipsosaurus dorsalis) increases metabolic costs (Hancock & Gleeson, 2005). Therefore, the energy basis of intermittent locomotion remains unclear in this case. An alternative and not mutually exclusive explanation is that intermittent locomotion may increase chances for vigilance against predators (McAdam & Kramer, 1998). Indeed, Octodon degus degus (Vásquez, Ebensperger & Bozinovic, 2002) and Psammodromus algirus lizards (López & Martín, 2013) increase vigilance by interrupting locomotion in open habitats, where exposure to predators is greater. Therefore, agrosystem toads could have enhanced vigilance behaviour due to openness in such habitat. Also, frequent stops in agrosystem toads could allow them to remain unseen or to confound predators via intermittent movement patterns (Martell & Dill, 1995). Accordingly, animals can perceive human presence, a constant in agrosystems, as a form of predator pressure (Beale & Monaghan, 2004). Run rate was similar in both sexes. However, when sprint speed was controlled for, males showed a higher run rate than females, which indicates that, for a given speed, males used more runs than females. Assuming that intermittent locomotion increases opportunities for vigilance against predators in this species (Trouilloud, Delisle & Kramer, 2004), this finding, along with increased male speed, reinforces the idea that males are better suited for predator avoidance, and probably experiencegreater predator pressure. These differences are a probable consequence of E. calamita males performing more conspicuous activities in territory defence (Miaud, Sanuy & Avrillier, 2000) or mating (Sinsch, 1988). I also detected an interesting negative relationship between sprint speed and run rate. An individual’s escape strategy seems to consist of a continuum from slow, multiple short movements to a few fast, long runs. Slower toads may remain unnoticed by reducing movements, to confound predators by increasing the number of short runs (Martell & Dill, 1995), or to increase predator vigilance by frequent stops (McAdam & Kramer, 1998). Conversely, faster toads may rely on their speed and use longer runs to escape predators or find a shelter as soon as possible (Lima & Dill, 1990). Sprint speed proved highly constrained by hindlimb length. On the other hand, the fact that run rate was unaffected by morphology suggests that it could be a behavioural trait rather than a morphology-limited ability, which contrasts with other findings that morphology affects locomotion (Miller, Samuk & Rennison, 2016). This negative relationship between sprint speed and run rate thus suggests that locomotion mode in this running toad is a combination of morphology-limited sprint ability influencing behavioural decisions of locomotion pace. CONCLUSIONS In summary, sprint speed was directly related to hindlimb length, but not to forelimb length, SVL or body mass in natterjack toads. Males were faster than females, and had longer limbs, but sex differences in sprint speed were not explained solely by longer limbs of males. Males’ longer forelimbs were not related to higher speed, so other factors, probably use of forelimbs during amplexus, seem to drive differences in forelimb length. Habitat had no effect on sprint speed, but run rate was higher in agrosystem toads, which suggests increased vigilance against predators, probably related to habitat openness and/or to human presence. For a given speed, males showed higher run rates than females, which, along with higher speed, suggests a greater effect of predator pressure on shaping male locomotion. Finally, a negative relationship between sprint speed and run rate suggests that locomotion pace is affected by sprint speed abilities: slower toads tend to use short runs, which probably helps them to remain unseen or confound predators, while faster toads tend to use long runs, probably to flee from predators or find a shelter as soon as possible. ACKNOWLEDGEMENTS The author was partly supported by a Fundación Ramón Areces postdoctoral fellowship, and by a Juan de la Cierva-Formación postdoctoral fellowship from the Spanish Ministerio de Economía, Industria y Competitividad. Toad capture was conducted according to permits by the Junta de Andalucía issued to the author (Reference AWG/MGD/MGM/CB). Comments by six anonymous reviewers improved the manuscript. This research did not receive any specific grant from funding agencies in the public, commercial or not-for-profit sectors. SUPPORTING INFORMATION Additional Supporting Information may be found in the online version of this article at the publisher’s web-site: Table S1. Individual ANOVAs testing the effect of sex, habitat, and their interaction on body mass, snout–vent length, fore- and hindlimb length, limb ratio, and average speed. Note that fore- and hind limb length were controlled for snout–vent length, so degrees of freedom were 1 and 115. F-values are indicated. NSNon-significant; §marginally non-significant; *P < 0.05; ***P > 0.001. Significant results are in bold type. Table S2. Individual models testing the effects of body mass, snout–vent length, fore- and hind limb length, limb ratio, and run rate on average speed. Sex, habitat and their interaction were controlled for in all models. F- and ß-values are indicated. Note that the effects of limb length were controlled for snout–vent length, so degrees of freedom were 1 and 114. NSNon-significant; §marginally non-significant; *P < 0.05; **P < 0.01; ***P < 0.001. Significant results are in bold type. Figure S1. Sex and habitat differences in body mass (a), SVL (b), forelimb length (c), hindlimb length (d), limbratio (e) and average speed (f). Fore- and hindlimb length were controlled for SVL. Sample sizes are indicated in(a). Vertical bars represent standard errors. References Acevedo-Whitehouse K, Duffus ALJ. 2009. Effects of environmental change on wildlife health. Philosophical Transactions of the Royal Society of London B  364: 3429– 3438. Google Scholar CrossRef Search ADS   Ahn AN, Furrow E, Biewener AA. 2004. Walking and running in the red-legged running frog, Kassina maculata. Journal of Experimental Biology  207: 399– 410. Google Scholar CrossRef Search ADS PubMed  Álvarez D, Nicieza AG. 2002. Effects of induced variation in anuran larval development on postmetamorphic energy reserves and locomotion. Oecologia  131: 186– 195. Google Scholar CrossRef Search ADS PubMed  Beale CM, Monaghan P. 2004. Human disturbance: people as predation-free predators? Journal of Applied Ecology  41: 335– 343. Google Scholar CrossRef Search ADS   Boomsma JJ, Arntzen JW. 1985. Abundance, growth and feeding of natterjack toads (Bufo calamita) in a 4-year-old artificial habitat. Journal of Applied Ecology  22: 395– 405. Google Scholar CrossRef Search ADS   Botton-Divet L, Cornette R, Houssaye A, Fabre AC, Herrel A. 2017. Swimming and running: a study of the convergence in long bone morphology among semi-aquatic mustelids (Carnivora: Mustelidae). Biological Journal of the Linnean Society  121: 38– 49. Google Scholar CrossRef Search ADS   Brandt R, Cury de B arros F, Noronha C, Tulli MJ, Kohlsdorf T. 2016. Sexual differences in locomotor performance in Tropidurus catalanensis lizards (Squamata: Tropiduridae) – body shape, size and limb musculature explain variation between males and females. Biological Journal of the Linnean Society  118: 598– 609. Google Scholar CrossRef Search ADS   Brijs J, Sandblom E, Sundh H, Gräns A, Hinchcliffe J, Ekström A, Sundell K, Olsson C, Axelsson M, Pichaud N. 2017. Increased mitochondrial coupling and anaerobic capacity minimizes aerobic costs of trout in the sea. Scientific Reports  7: 45778. Google Scholar CrossRef Search ADS PubMed  Budick SA, O’Malley DM. 2000. Locomotor repertoire of the larval zebrafish: swimming, turning and prey capture. Journal of Experimental Biology  203: 2565– 2579. Google Scholar PubMed  Calsbeek R. 2008. An ecological twist on the morphology–performance–fitness axis. Evolutionary Ecology Research  10: 197– 212. Calsbeek R, Irschick DJ. 2007. The quick and the dead: correlational selection on morphology, performance, and habitat use in island lizards. Evolution  61: 2493– 2503. Google Scholar CrossRef Search ADS PubMed  Choi I, Han Shim J, Ricklefs RE. 2003. Morphometric relationships of take-off speed in anuran amphibians. Journal of Experimental Zoology  299A: 99– 102. Google Scholar CrossRef Search ADS   Clark DL, Peters SE. 2006. Isometric contractile properties of sexually dimorphic forelimb muscles in the marine toad Bufo marinus Linnaeus 1758: functional analysis and implications for amplexus. Journal of Experimental Biology  209: 3448– 3456. Google Scholar CrossRef Search ADS PubMed  Colombo M, Indermaur A, Meyer BS, Salzburger W. 2016. Habitat use and its implications to functional morphology: niche partitioning and the evolution of locomotory morphology in Lake Tanganyikan cichlids (Perciformes: Cichlidae). Biological Journal of the Linnean Society  118: 536– 550. Google Scholar CrossRef Search ADS   Conradsen C, McGuigan K. 2015. Sexually dimorphic morphology and swimming performance relationships in wild-type zebrafish Danio rerio. Journal of Fish Biology  87: 1219– 1233. Google Scholar CrossRef Search ADS PubMed  Day LM, Jayne BC. 2007. Interspecific scaling of the morphology and posture of the limbs during locomotion in cats (Felidae). Journal of Experimental Biology  210: 642– 654. Google Scholar CrossRef Search ADS PubMed  Donihue C. 2016. Microgeographic variation in locomotor traits among lizards in a human-built environment. PeerJ  4: e1776. Google Scholar CrossRef Search ADS PubMed  Edwards EB, Gleeson TT. 2001. Can energetic expenditure be minimized by performing activity intermittently? Journal of Experimental Biology  204: 599– 605. Google Scholar PubMed  Edwards S, Herrel A, Vanhooydonck B, Measey GJ, Tolley KA. 2016. Diving in head first: trade-offs between phenotypic traits and sand-diving predator escape strategy in Meroles desert lizards. Biological Journal of the Linnean Society  119: 919– 931. Google Scholar CrossRef Search ADS   Fahrig L. 2007. Non-optimal animal movement in human-altered landscapes. Functional Ecology  21: 1003– 1015. Google Scholar CrossRef Search ADS   Frid A, Dill L. 2002. Human-caused disturbance stimuli as a form of predation risk. Conservation Ecology  6: 11– 26. Google Scholar CrossRef Search ADS   Gallego-Carmona CA, Castro-Arango JA, Bernal-Bautista MH. 2016. Effect of habitat disturbance on the body condition index of the Colombian endemic lizard Anolis antonii (Squamata: Dactyloidae). South American Journal of Herpetology  11: 183– 187. Google Scholar CrossRef Search ADS   Garland T, Hankins E, Huey RB. 1990. Locomotor capacity and social dominance in male lizards. Functional Ecology  4: 243– 250. Google Scholar CrossRef Search ADS   Garland T, Losos JB. 1994. Ecological morphology of locomotor performance in squamate reptiles. In: Wainwright PC, Reilly SM, eds. Ecological morphology: integrative organismal biology . Chicago: University of Chicago Press, 240–302. Gómez-Mestre I. 2014. Sapo corredor – Epidalea calamita (Laurenti, 1768). In: Salvador A, Marco A, eds. Enciclopedia Virtual de los Vertebrados Españoles . Museo Nacional de Ciencias Naturales, Madrid. Available at http://www.vertebradosibericos.org Goodman BA. 2009. Nowhere to run: the role of habitat openness and refuge use in defining patterns of morphological and performance evolution in tropical lizards. Journal of Evolutionary Biology  22: 1535– 1544. Google Scholar CrossRef Search ADS PubMed  Halsey LG. 2016. Terrestrial movement energetics: current knowledge and its application to the optimising animal. Journal of Experimental Biology  219: 1424– 1431. Google Scholar CrossRef Search ADS PubMed  Hancock TV, Gleeson TT. 2005. Intermittent locomotor activity that increases endurance also increases metabolic costs in the desert iguana (Dipsosaurus dorsalis). Physiological and Biochemical Zoology  78: 163– 172. Google Scholar CrossRef Search ADS PubMed  Herrel A, Gonwouo LN, Fokam EB, Ngundu WI, Bonneaud C. 2012. Intersexual differences in body shape and locomotor performance in the aquatic frog, Xenopus tropicalis. Journal of Zoology  287: 311– 316. Google Scholar CrossRef Search ADS   Herrel A, Vasilopoulou-Kampitsi M, Bonneaud C. 2014. Jumping performance in the highly aquatic frog Xenopus tropicalis: sex-specific relationships between morphology and performance. PeerJ  2: e661. Google Scholar CrossRef Search ADS PubMed  Higham TE. 2007. The integration of locomotion and prey capture in vertebrates: morphology, behavior and performance. Integrative and Comparative Biology  47: 82– 95. Google Scholar CrossRef Search ADS PubMed  Higham TE, Gamble T, Russell AP. 2017. On the origin of frictional adhesion in geckos: small morphological changes lead to a major biomechanical transition in the genus Gonatodes. Biological Journal of the Linnean Society  120: 503– 517. Hudson CM, Brown GP, Shine R. 2016. Athletic anurans: the impact of morphology, ecology and evolution on climbing ability in invasive cane toads. Biological Journal of the Linnean Society  119: 992– 999. Google Scholar CrossRef Search ADS   Huey RB, Dunham AE, Overall KL. 1991. Variation in locomotor performance in demographically known populations of the lizard Sceloporus merriami. Physiological Zoology  63: 845– 872. Google Scholar CrossRef Search ADS   Huey RB, Dunham AE, Overall KL, Newman RA. 1990. Variation in locomotor performance in demographically known populations of the lizard Sceloporus merriami. Physiological Zoology  63: 845– 872. Google Scholar CrossRef Search ADS   Husak JF. 2006a. Does speed help you survive? A test with collared lizards of different ages. Functional Ecology  20: 174– 179. Google Scholar CrossRef Search ADS   Husak JF. 2006b. Does survival depend on how fast you can run or how fast you do run? Functional Ecology  20: 1080– 1086. Google Scholar CrossRef Search ADS   Husak JF, Fox SF. 2008. Sexual selection on locomotor performance. Evolutionary Ecology Research  10: 213– 228. Husak JF, Fox SF, Van Den Bussche RA. 2008. Faster male lizards are better defenders not sneakers. Animal Behaviour  75: 1725– 1730. Google Scholar CrossRef Search ADS   Husak JF, Fox SF, Lovern MB, Van Den Bussche RA. 2006. Faster lizards sire more offspring: sexual selection on whole-animal performance. Evolution  60: 2122– 2130. Google Scholar CrossRef Search ADS PubMed  Ingley SJ, Camarillo H, Willis H, Johnson JB. 2016. Repeated evolution of local adaptation in swimming performance: population-level trade-offs between burst and endurance swimming in Brachyraphis freshwater fish. Biological Journal of the Linnean Society  119: 1011– 1026. Google Scholar CrossRef Search ADS   Iriarte-Díaz J. 2002. Differential scaling of locomotor performance in small and large terrestrial mammals. Journal of Experimental Biology  205: 2897– 2908. Google Scholar PubMed  Irschick DJ, Carlisle E, Elstrott J, Ramos M, Buckley C, Vanhooydonck B, Meyers J, Herrel A. 2005. A comparison of habitat use, morphology, clinging performance and escape behaviour among two divergent green anole lizard (Anolis carolinensis) populations. Biological Journal of the Linnean Society  85: 223– 234. Google Scholar CrossRef Search ADS   James RS, Wilson RS, de C arvalho JE, Kohlsdorf T, Gomes FR, Navas CA. 2005. Interindividual differences in leg muscle mass and pyruvate kinase activity correlate with interindividual differences in jumping performance of Hyla multilineata. Physiological and Biochemical Zoology  78: 857– 867. Google Scholar CrossRef Search ADS PubMed  Jayne BC, Bennett AF. 1990. Selection on locomotor performance capacity in a natural population of garter snake. Evolution  44: 1204– 1229. Google Scholar CrossRef Search ADS PubMed  Johansson F, Lederer B, Lind MI. 2010. Trait performance correlations across life stages under environmental stress conditions in the common frog, Rana temporaria. PLOS One  5: e11680. Google Scholar CrossRef Search ADS PubMed  Kaliontzopoulou A, Bandeira V, Carretero MÁ. 2013. Sexual dimorphism in locomotor performance and its relation to morphology in wall lizards (Podarcis bocagei). Journal of Zoology  289: 294– 302. Google Scholar CrossRef Search ADS   Kotiaho JS. 2001. Costs of sexual traits: a mismatch between theoretical considerations and empirical evidence. Biological Reviews  76: 365– 376. Google Scholar CrossRef Search ADS PubMed  Lailvaux SP. 2007. Interactive effects of sex and temperature on locomotion in reptiles. Integrative and Comparative Biology  47: 189– 199. Google Scholar CrossRef Search ADS PubMed  Lee JC, Corrales AD. 2002. Sexual dimorphism in hind-limb muscle mass is associated with male reproductive success in Bufo marinus. Journal of Herpetology  36: 502– 505. Google Scholar CrossRef Search ADS   Lima SL, Dill LM. 1990. Behavioral decisions made under the risk of predation: a review and prospectus. Canadian Journal of Zoology  68: 619– 640. Google Scholar CrossRef Search ADS   Llewelyn J, Phillips BL, Alford RA, Schwarzkopf L, Shine R. 2010. Locomotor performance in an invasive species: cane toads from the invasion front have greater endurance, but not speed, compared to conspecifics from a long-colonised area. Oecologia  162: 343– 348. Google Scholar CrossRef Search ADS PubMed  Li J, Lin X, Zhou C, Zeng P, Xu Z, Sun J. 2016. Sexual dimorphism and its relationship with swimming performance in Tanichthys albonubes under laboratory conditions. Chinese Journal of Applied Ecology  27: 1639– 1646. López P, Martín J. 2013. Effects of microhabitat-dependent predation risk on vigilance during intermittent locomotion in Psammodromus algirus lizards. Ethology  119: 316– 324. Google Scholar CrossRef Search ADS   Magnhagen C. 1991. Predation risk as a cost of reproduction. Trends in Ecology and Evolution  6: 183– 186. Google Scholar CrossRef Search ADS PubMed  Martell G, Dill LM. 1995. Influence of movement by coho salmon (Oncorhynchus kisutch) parr on their detection by common mergansers (Mergus merganser). Ethology  99: 139– 149. Google Scholar CrossRef Search ADS   Martín J, López P. 2000. Fleeing to unsafe refuges: effects of conspicuousness and refuge safety on the scape decisions of the lizard Psammodromus algirus. Canadian Journal of Zoology  78: 265– 270. Google Scholar CrossRef Search ADS   Martín J, López P. 2001. Hindlimb asymmetry reduces escape performance in the lizard Psammodromus algirus. Physiological and Biochemical Zoology  74: 619– 624. Google Scholar CrossRef Search ADS PubMed  Martín J, López P, Gutiérrez E, García LV. 2015. Natural and anthropogenic alterations of the soil affect body condition of the fossorial amphisbaenian Trogonophis wiegmanni in North Africa. Journal of Arid Environments  122: 30– 36. Google Scholar CrossRef Search ADS   Martínez F, Montero G. 2004. The Pinus pinea L. woodlands along the coast of South-western Spain: data for a new geobotanical interpretation. Plant Ecology  175: 1– 18. Google Scholar CrossRef Search ADS   McAdam AG, Kramer DL. 1998. Vigilance as a benefit of intermittent locomotion in small mammals. Animal Behaviour  55: 109– 117. Google Scholar CrossRef Search ADS PubMed  McGee MR, Julius ML, Vajda AM, Norris DO, Barber LB, Schoenfuss HL. 2009. Predator avoidance performance of larval fathead minnows (Pimephales promelas) following short-term exposure to estrogen mixtures. Aquatic Toxicology  91: 355– 361. Google Scholar CrossRef Search ADS PubMed  McLaughlin RL, Grant JWA. 2001. Field examination of perceptual and energetic bases for intermittent locomotion by recently-emerged brook charr in still-water pools. Behaviour  138: 559– 574. Google Scholar CrossRef Search ADS   Melville J, Swain ROY. 2000. Evolutionary relationships between morphology, performance and habitat openness in the lizard genus Niveoscincus (Scincidae: Lygosominae). Biological Journal of the Linnean Society  70: 667– 683. Miaud C, Sanuy D, Avrillier JN. 2000. Terrestrial movements of the natterjack toad Bufo calamita (Amphibia, Anura) in a semi-arid, agricultural landscape. Amphibia-Reptilia  21: 357– 369. Google Scholar CrossRef Search ADS   Miles DB. 2004. The race goes to the swift: fitness consequences of variation in sprint performance in juvenile lizards. Evolutionary Ecology Research  6: 63– 75. Miller SE, Samuk KM, Rennison DJ. 2016. An experimental test of the effect of predation upon behaviour and trait correlations in the threespine stickleback. Biological Journal of the Linnean Society  119: 117– 125. Google Scholar CrossRef Search ADS   Moreno-Rueda G. 2003. The capacity to escape from predators in Passer domesticus: an experimental study. Journal of Ornithology  144: 438– 444. Navas CA, James RS. 2007. Sexual dimorphism of extensor carpi radialis muscle size, isometric force, relaxation rate and stamina during the breeding season of the frog Rana temporaria Linnaeus 1758. Journal of Experimental Biology  210: 715– 721. Google Scholar CrossRef Search ADS PubMed  O’Steen S, Cullum AJ, Bennett AF. 2002. Rapid evolution of escape ability in Trinidadian guppies (Poecilia reticulata). Evolution  56: 776– 784. Google Scholar CrossRef Search ADS PubMed  Pérez-Tris J, Díaz JA, Tellería JL. 2004. Loss of body mass under predation risk: cost of antipredatory behaviour or adaptive fit-for-escape? Animal Behaviour  67: 511– 521. Google Scholar CrossRef Search ADS   Perry G, Levering K, Girard I, Garland T. 2004. Locomotor performance and social dominance in male Anolis cristatellus. Animal Behaviour  67: 37– 47. Google Scholar CrossRef Search ADS   Peterson CC, Husak JF. 2006. Locomotor performance and sexual selection: individual variation in sprint speed of collared lizards (Crotaphytus collaris). Copeia  2006: 216– 224. Google Scholar CrossRef Search ADS   Prates I, Angilleta MJ, Wilson RS, Niehaus AC, Navas CA. 2013. Dehydration hardly slows hopping toads (Rhinella granulosa) from xeric and mesic environments. Physiological and Biochemical Zoology  86: 451– 457. Google Scholar CrossRef Search ADS PubMed  Preest MR, Pough FH. 1989. Interaction of temperature and hydration on locomotion of toads. Functional Ecology  3: 693– 699. Google Scholar CrossRef Search ADS   Preest MR, Pough FH. 2003. Effects of body temperature and hydration state on organismal performance of toads, Bufo americanus. Physiological and Biochemical Zoology  76: 229– 239. Google Scholar CrossRef Search ADS PubMed  Promislow DEL, Montgomerie R, Martin TE. 1992. Mortality costs of sexual dimorphism in birds. Proceedings of the Royal Society B  250: 143– 150. Google Scholar CrossRef Search ADS   Quinn GP, Keough MJ. 2002. Experimental design and data analysis for biologists . Cambridge: Cambridge University Press. Google Scholar CrossRef Search ADS   Reilly SM, Montuelle SJ, Schmidt A, Krause C, Naylor E, Essner RL. 2016. Functional evolution of jumping in frogs: interspecific differences in take-off and landing. Journal of Morphology  277: 379– 393. Google Scholar CrossRef Search ADS PubMed  Ruibal R. 1962. The adaptive value of bladder water in the toad, Bufo cognatus. Physiological Zoology  35: 218– 223. Google Scholar CrossRef Search ADS   Shaffer LR, Formanowicz DR. 1996. A cost of viviparity and parental care in scorpions: reduced sprint speed and behavioural compensation. Animal Behaviour  51: 1017– 1024. Google Scholar CrossRef Search ADS   Sinsch U. 1988. Temporal spacing of breeding activity in the natterjack toad, Bufo calamita. Oecologia  76: 399– 407. Google Scholar CrossRef Search ADS PubMed  Smith TB, Bernatchez L. 2007. Evolutionary change in human-altered environments. Molecular Ecology  17: 1– 8. Google Scholar CrossRef Search ADS   Stearns SC. 2000. Life history evolution: successes, limitations, and prospects. Naturwissenchaften  87: 476– 486. Google Scholar CrossRef Search ADS   Tejedo M, Semlitsch RD, Hotz H. 2000. Differential morphology and jumping performance of newly metamorphosed frogs of the hybridogenetic Rana esculenta complex. Journal of Herpetology  34: 201– 210. Google Scholar CrossRef Search ADS   Trouilloud W, Delisle A, Kramer DL. 2004. Head raising during foraging and pausing during locomotion as components of antipredator vigilance in chipmunks. Animal Behaviour  67: 789– 797. Google Scholar CrossRef Search ADS   Tulli MJ, Cruz FB, Kohlsdorf T, Abdala V. 2016. When a general morphology allows many habitat uses. Integrative Zoology  11: 483– 499. Google Scholar CrossRef Search ADS PubMed  Tuomainen U, Candolin U. 2011. Behavioural responses to human-induced environmental change. Biological Reviews  86: 640– 657. Google Scholar CrossRef Search ADS PubMed  Vanhooydonck B, Measey J, Edwards S, Makhubo B, Tolley KA, Herrel A. 2015. The effects of substratum on locomotor performance in lacertid lizards. Biological Journal of the Linnean Society  115: 869– 881. Google Scholar CrossRef Search ADS   Vanhooydonck B, Van Damme R. 2003. Relationships between locomotor performance, microhabitat use and antipredator behaviour in lacertid lizards. Functional Ecology  17: 160– 169. Google Scholar CrossRef Search ADS   Vásquez RA, Ebensperger LA, Bozinovic F. 2002. The influence of habitat on travel speed, intermittent locomotion, and vigilance in a diurnal rodent. Behavioral Ecology  13: 182– 187. Google Scholar CrossRef Search ADS   Walton BM, Anderson BD. 1988. The aerobic cost of saltatory locomotion in the Fowler’s toad (Bufo woodhousei fowleri). Journal of Experimental Biology  136: 273– 288. Google Scholar PubMed  Walton BM, Peterson CC, Bennett AF. 1994. Is walking costly for anurans? The energetic cost of walking in the northern toad Bufo boreas halophilus. Journal of Experimental Biology  197: 165– 178. Google Scholar PubMed  Walvoord ME. 2003. Cricket frogs maintain body hydration and temperature near levels allowing maximum jump performance. Physiological and Biochemical Zoology  76: 825– 835. Google Scholar CrossRef Search ADS PubMed  Watkins TB. 1996. Predator-mediated selection on burst swimming performance in tadpoles of the Pacific tree frog, Pseudacris regilla. Physiological Zoology  69: 154– 167. Google Scholar CrossRef Search ADS   Weinstein RB, Full RJ. 1999. Intermittent locomotion increases endurance in a gecko. Physiological and Biochemical Zoology  72: 732– 739. Google Scholar CrossRef Search ADS PubMed  Wilson RS, Franklin CE, James RS. 2000. Allometric scaling relationships of jumping performance in the striped marsh frog Limnodynastes peronii. Journal of Experimental Biology  203: 1937– 1946. Google Scholar PubMed  Witter MS, Cuthill IC. 1993. The ecological costs of avian fat storage. Philosophical Transactions of the Royal Society of London B  340: 73– 92. Google Scholar CrossRef Search ADS   Zamora-Camacho FJ, Comas M. 2017. Greater reproductive investment, but shorter lifespan, in agrosystem than in natural-habitat toads. PeerJ  5: e3791. Google Scholar CrossRef Search ADS PubMed  Zamora-Camacho FJ, Reguera S, Rubiño-Hispán MV, Moreno-Rueda G. 2014. Effects of limb length, body mass, gender, gravidity, and elevation on escape speed in the lizard Psammodromus algirus. Evolutionary Biology  41: 509– 517. Google Scholar CrossRef Search ADS   Zamora-Camacho FJ, Reguera S, Rubiño-Hispán MV, Moreno-Rueda G. 2015. Eliciting an immune response reduces sprint speed in a lizard. Behavioral Ecology  26: 115– 120. Google Scholar CrossRef Search ADS   Zhiping MI. 2013. Sexual dimorphism in the hindlimb muscles of the Asiatic toad (Bufo gargarizans) in relation to male reproductive success. Asian Herpetological Research  4: 56– 61. Google Scholar CrossRef Search ADS   © 2017 The Linnean Society of London, Biological Journal of the Linnean Society

Journal

Biological Journal of the Linnean SocietyOxford University Press

Published: Feb 1, 2018

There are no references for this article.

You’re reading a free preview. Subscribe to read the entire article.


DeepDyve is your
personal research library

It’s your single place to instantly
discover and read the research
that matters to you.

Enjoy affordable access to
over 18 million articles from more than
15,000 peer-reviewed journals.

All for just $49/month

Explore the DeepDyve Library

Search

Query the DeepDyve database, plus search all of PubMed and Google Scholar seamlessly

Organize

Save any article or search result from DeepDyve, PubMed, and Google Scholar... all in one place.

Access

Get unlimited, online access to over 18 million full-text articles from more than 15,000 scientific journals.

Your journals are on DeepDyve

Read from thousands of the leading scholarly journals from SpringerNature, Elsevier, Wiley-Blackwell, Oxford University Press and more.

All the latest content is available, no embargo periods.

See the journals in your area

DeepDyve

Freelancer

DeepDyve

Pro

Price

FREE

$49/month
$360/year

Save searches from
Google Scholar,
PubMed

Create lists to
organize your research

Export lists, citations

Read DeepDyve articles

Abstract access only

Unlimited access to over
18 million full-text articles

Print

20 pages / month

PDF Discount

20% off