TY - JOUR
AU - Piras, Paolo
AB - Abstract Crabs are considered exceptional examples of antisymmetry resulting from the phenomenon of heterochely. Here we investigate morphometrically both the size and the shape of heterochely in 28 crab species, distributed unequally along a brachyuran phylogeny. We address the importance of investigating claw size and shape for interspecific comparisons by linking geometric morphometric outputs to phylogenetic data for 134 brachyuran species. New indices introduced as new sexual dimorphic characters of size and shape, namely heterometry (right chela size/left chela size) and heteromorphy (Procrustes distance between right and left chelae shape), revealed sexually dimorphic differences in diverse crab species. We demonstrate that both size and shape heterochely occur amongst the examined species, but there are no ecological correlations. Our study demonstrates that claw similarity between two or more species was due mainly to phylogenetic relatedness rather than ecological convergence, suggesting that claw morphological features could be useful morphological markers in phylogenetic studies. Although further investigation is needed, this study represents one of the first to thoroughly analyse the origin and evolution of heterochely within the Brachyura clade. Brachyura, handedness, heterochely, heterometry, heteromorphy INTRODUCTION Asymmetry in size or shape is a widespread pattern in evolution (Palmer, 1996). This condition may be interpreted as the deviation of an organism, or part of it, from perfect symmetry (Van Valen, 1962). This deviation from bilateral symmetry produces handedness (Graham et al., 2010). According to the distribution of handedness, three main kinds of asymmetries have been recognized (see Klingenberg, 2015): fluctuating asymmetry, where the variance in the right–left (R-L) differences is distributed around a mean of value 0 (Gaussian distribution); directional asymmetry, where R-L differences are distributed around a mean that is significantly different from 0 (Gaussian distribution); and antisymmetry, where the lack of symmetry in normally developing traits is distinguished by a departure from a Gaussian distribution of R-L differences (bimodal distribution). Asymmetries are common among living organisms. Studies have shown that more than 450 species from 67 families in eight phyla of animals and plants exhibit antisymmetry (Palmer, 2005), and current studies are continuing to identify more asymmetries within Animalia (Klingenberg, 2015). Among these animals are some species of crabs (Gecarcinus spp., Cardisoma spp., Uca spp., Acanthocyclus spp., etc.) that have claws of very different sizes and shapes (Rathbun, 1918, 1930; Williams & Heng, 1981; Palmer, 2005; Graham et al., 2010; Klingenberg, 2015). This phenomenon is known as ‘heterochely’: the two chelae are normally referred to as major and minor because of the size difference. Traditionally, major and minor claws were named crusher and cutter, respectively, depending on their functions during alimentary and predator activities. Indeed, a common shape difference is that the occlusal surfaces of the major chela bear rounded ‘molariform’ teeth while those of the minor chela bear numerous conical teeth (Abby-Kalio & Warner, 1989). Usually both sexes of heterochelous species display heterochely, although to different degree, so it is a secondary sexual characteristic in both marine (Castiglioni & Coelho, 2011; Alencar et al., 2014) and freshwater (Trevisan et al., 2012; Spani & Scalici, 2016) crabs. Decapods are considered to represent interesting models for evaluating variations in claw size and shape through geometric morphometrics, due to their rigid exoskeleton with many spines and sutures that allow for accurate biometric measurements (Trevisan et al., 2012; Alencar et al., 2014). The phenomenon of claw asymmetry in the adaptive radiation of brachyurans has been thoroughly studied (see Hartnoll, 1978, 1982; Micheli et al., 1990; Duarte et al., 2008; Juanes et al., 2008; Scalici et al., 2013), but several questions remain (see Scalici & Gherardi, 2008, and references therein). Indeed, some studies have been carried out to better understand chelae use in predation, food manipulation, mate acquisition, defence of resources (such as food and territories), parental care (see Stein, 1976; Raubenheimer, 1986; Gherardi & Micheli, 1989; Liu & Li, 2000; Schenk & Wainwright, 2001) and the generation of different inter-sexual aggressive behaviours during antagonistic fights (see Gabbanini et al., 1995, and references therein). In addition, allometric analyses of the chela have been investigated (e.g. Hartnoll, 1978; Daniels, 2001), but unfortunately most of these studies focused on the major chela (see Spani & Scalici, 2016, and references therein). The well-known phenomenon of heterochely is no longer considered as a difference between claw size solely but rather differences in both size and shape. Here we propose for the first time , to our knowledge, the two new dimensionless indices ‘heterometry’ and ‘heteromorphy’ to quantify differences in chela size and shape of brachyurans by means of geometric morphometrics. Specifically, heterometry is the ratio between the ‘size index’ of the right and left claw, while heteromorphy is the numerical quantification of the shape differences between the right and left claw. By doing so, we overcome the problems of traditional analysis of heterochely, and recognize three different heterochelic patterns in each analysed species (size-heterochely, shape heterochely or both), and whether they could represent new sexually dimorphic characters. In addition, we test for possible links between both heterometry and heteromorphy, and some ecological features (i.e. environment, habitat, feeding types). Finally, we assess possible relationships between claw form (=size + shape sensuCardini & O’Higgins, 2005) and phylogenetic signal among brachyuran species by evaluating geometric morphometric results in a phylogenetic context. MATERIAL AND METHODS Biological model A total of 843 right-handed specimens belonging to 28 brachyuran species were included in the study (Table 1). All studied claws were checked to ensure that they were not in regeneration after autotomy. The specimens came from three sources. First, 198 freshwater and marine specimens (six brachyuran species) were sampled by F.S. from river water and Latium sea coasts: Rio Fiume (Rome, Italy) for freshwater crabs; and Santa Marinella (Rome, Italy) and Passoscuro (Rome, Italy) for several marine individuals captured by snorkelling. Second, the dataset was expanded with 465 specimens (13 brachyuran species) stored in the ‘La Specola’ Zoological Museum (University of Florence, Florence, Italy) and the National Museum of Natural History, Smithsonian Institution (Washington, DC, USA). Selected specimens were photographed by F.S. in loco. Finally, 180 individuals (nine brachyuran species) were recovered, before they had been discarded, from commercial fishermen of Latium (Passoscuro, Santa Marinella and Fiumicino, Rome, Italy) and Veneto (Chioggia, Venice, Italy). Among the 28 species analysed, 21 had five or more male individuals, 18 had five or more female individuals, and 18 had five or more individuals of both male and female individuals. Therefore, the numbers of species and specimens analysed are different amongst our statistical analyses depending on the type of test as well as the individuals involved in the analysis. Specifically, statistical analyses performed on males represented 21 species while analyses performed solely on females represented 18 species. Statistical analyses of sexual dimorphism, which require both males and females, involved those 18 species for which more than five male and female individuals were available. Table 1. List of investigated crab species, number of specimens separated by sex (M = male, F = female), and marks used for each species . Species . M . F . Marks . 1 Atelecyclus rotundatus (Olivi, 1792) 0 1 Ate_rot 2 Acanthocyclus albatrossis Rathbun, 1898 17 22 Aca_alb 3 Ashtoret lunaris (Forskål, 1775) 25 23 Ash_lun 4 Bathynectes maravigna (Prestandrea, 1839) 3 2 Bat_mar 5 Calappa granulata (Linnaeus, 1758) 11 20 Cal_gra 6 Callinectes sapidus (Rathbun, 1896) 11 10 Cln_sap 7 Cancer borealis Stimpson, 1859 25 24 Can_bor 8 Carcinus aestuarii (Nardo, 1847) 26 16 Car_aes 9 Cardisoma guanhumi Latreille, 1828 17 10 Crd_gua 10 Carpilius maculatus (Linnaeus, 1758) 9 14 Crp_mac 11 Daira perlata (Herbst, 1790) 15 25 Dai_per 12 Derilambrus angulifrons (Latreille, 1825) 1 0 Der_ang 13 Ergasticus clouei A. Milne-Edwards, 1882 1 0 Erg_clo 14 Eriphia verrucosa (Forskål, 1775) 0 3 Eri_ver 15 Geryon longipes A. Milne-Edwards, 1882 17 14 Ger_lon 16 Goneplax rhomboides (Linnaeus, 1758) 30 9 Gon_rho 17 Herbstia condyliata (Fabricius, 1787) 1 0 Her_con 18 Liocarcinus depurator (Linnaeus, 1758) 26 29 Lio_dep 19 Macropipus tuberculatus (Roux, 1830) 32 19 Mac_tub 20 Medorippe lanata (Linnaeus, 1767) 19 20 Med_lan 21 Ocypode ryderi Kingsley, 1880 24 4 Ocy_ryd 22 Pachygrapsus marmoratus (Fabricius, 1787) 2 2 Pac_mar 23 Pilumnus townsendi Rathbun, 1923 17 22 Pil_tow 24 Portumnus latipes (Pennant, 1777) 30 30 Por_lat 25 Potamon fluviatile (Herbst, 1785) 30 28 Pot_flu 26 Potamonautes obesus A. Milne-Edwards, 1868 30 37 Ptm_obe 27 Uca vocans (Linnaeus, 1758) 22 0 Uca_voc 28 Xantho pilipes A. Milne-Edwards, 1867 14 4 Xan_pil Total specimens: 843 . Species . M . F . Marks . 1 Atelecyclus rotundatus (Olivi, 1792) 0 1 Ate_rot 2 Acanthocyclus albatrossis Rathbun, 1898 17 22 Aca_alb 3 Ashtoret lunaris (Forskål, 1775) 25 23 Ash_lun 4 Bathynectes maravigna (Prestandrea, 1839) 3 2 Bat_mar 5 Calappa granulata (Linnaeus, 1758) 11 20 Cal_gra 6 Callinectes sapidus (Rathbun, 1896) 11 10 Cln_sap 7 Cancer borealis Stimpson, 1859 25 24 Can_bor 8 Carcinus aestuarii (Nardo, 1847) 26 16 Car_aes 9 Cardisoma guanhumi Latreille, 1828 17 10 Crd_gua 10 Carpilius maculatus (Linnaeus, 1758) 9 14 Crp_mac 11 Daira perlata (Herbst, 1790) 15 25 Dai_per 12 Derilambrus angulifrons (Latreille, 1825) 1 0 Der_ang 13 Ergasticus clouei A. Milne-Edwards, 1882 1 0 Erg_clo 14 Eriphia verrucosa (Forskål, 1775) 0 3 Eri_ver 15 Geryon longipes A. Milne-Edwards, 1882 17 14 Ger_lon 16 Goneplax rhomboides (Linnaeus, 1758) 30 9 Gon_rho 17 Herbstia condyliata (Fabricius, 1787) 1 0 Her_con 18 Liocarcinus depurator (Linnaeus, 1758) 26 29 Lio_dep 19 Macropipus tuberculatus (Roux, 1830) 32 19 Mac_tub 20 Medorippe lanata (Linnaeus, 1767) 19 20 Med_lan 21 Ocypode ryderi Kingsley, 1880 24 4 Ocy_ryd 22 Pachygrapsus marmoratus (Fabricius, 1787) 2 2 Pac_mar 23 Pilumnus townsendi Rathbun, 1923 17 22 Pil_tow 24 Portumnus latipes (Pennant, 1777) 30 30 Por_lat 25 Potamon fluviatile (Herbst, 1785) 30 28 Pot_flu 26 Potamonautes obesus A. Milne-Edwards, 1868 30 37 Ptm_obe 27 Uca vocans (Linnaeus, 1758) 22 0 Uca_voc 28 Xantho pilipes A. Milne-Edwards, 1867 14 4 Xan_pil Total specimens: 843 Open in new tab Table 1. List of investigated crab species, number of specimens separated by sex (M = male, F = female), and marks used for each species . Species . M . F . Marks . 1 Atelecyclus rotundatus (Olivi, 1792) 0 1 Ate_rot 2 Acanthocyclus albatrossis Rathbun, 1898 17 22 Aca_alb 3 Ashtoret lunaris (Forskål, 1775) 25 23 Ash_lun 4 Bathynectes maravigna (Prestandrea, 1839) 3 2 Bat_mar 5 Calappa granulata (Linnaeus, 1758) 11 20 Cal_gra 6 Callinectes sapidus (Rathbun, 1896) 11 10 Cln_sap 7 Cancer borealis Stimpson, 1859 25 24 Can_bor 8 Carcinus aestuarii (Nardo, 1847) 26 16 Car_aes 9 Cardisoma guanhumi Latreille, 1828 17 10 Crd_gua 10 Carpilius maculatus (Linnaeus, 1758) 9 14 Crp_mac 11 Daira perlata (Herbst, 1790) 15 25 Dai_per 12 Derilambrus angulifrons (Latreille, 1825) 1 0 Der_ang 13 Ergasticus clouei A. Milne-Edwards, 1882 1 0 Erg_clo 14 Eriphia verrucosa (Forskål, 1775) 0 3 Eri_ver 15 Geryon longipes A. Milne-Edwards, 1882 17 14 Ger_lon 16 Goneplax rhomboides (Linnaeus, 1758) 30 9 Gon_rho 17 Herbstia condyliata (Fabricius, 1787) 1 0 Her_con 18 Liocarcinus depurator (Linnaeus, 1758) 26 29 Lio_dep 19 Macropipus tuberculatus (Roux, 1830) 32 19 Mac_tub 20 Medorippe lanata (Linnaeus, 1767) 19 20 Med_lan 21 Ocypode ryderi Kingsley, 1880 24 4 Ocy_ryd 22 Pachygrapsus marmoratus (Fabricius, 1787) 2 2 Pac_mar 23 Pilumnus townsendi Rathbun, 1923 17 22 Pil_tow 24 Portumnus latipes (Pennant, 1777) 30 30 Por_lat 25 Potamon fluviatile (Herbst, 1785) 30 28 Pot_flu 26 Potamonautes obesus A. Milne-Edwards, 1868 30 37 Ptm_obe 27 Uca vocans (Linnaeus, 1758) 22 0 Uca_voc 28 Xantho pilipes A. Milne-Edwards, 1867 14 4 Xan_pil Total specimens: 843 . Species . M . F . Marks . 1 Atelecyclus rotundatus (Olivi, 1792) 0 1 Ate_rot 2 Acanthocyclus albatrossis Rathbun, 1898 17 22 Aca_alb 3 Ashtoret lunaris (Forskål, 1775) 25 23 Ash_lun 4 Bathynectes maravigna (Prestandrea, 1839) 3 2 Bat_mar 5 Calappa granulata (Linnaeus, 1758) 11 20 Cal_gra 6 Callinectes sapidus (Rathbun, 1896) 11 10 Cln_sap 7 Cancer borealis Stimpson, 1859 25 24 Can_bor 8 Carcinus aestuarii (Nardo, 1847) 26 16 Car_aes 9 Cardisoma guanhumi Latreille, 1828 17 10 Crd_gua 10 Carpilius maculatus (Linnaeus, 1758) 9 14 Crp_mac 11 Daira perlata (Herbst, 1790) 15 25 Dai_per 12 Derilambrus angulifrons (Latreille, 1825) 1 0 Der_ang 13 Ergasticus clouei A. Milne-Edwards, 1882 1 0 Erg_clo 14 Eriphia verrucosa (Forskål, 1775) 0 3 Eri_ver 15 Geryon longipes A. Milne-Edwards, 1882 17 14 Ger_lon 16 Goneplax rhomboides (Linnaeus, 1758) 30 9 Gon_rho 17 Herbstia condyliata (Fabricius, 1787) 1 0 Her_con 18 Liocarcinus depurator (Linnaeus, 1758) 26 29 Lio_dep 19 Macropipus tuberculatus (Roux, 1830) 32 19 Mac_tub 20 Medorippe lanata (Linnaeus, 1767) 19 20 Med_lan 21 Ocypode ryderi Kingsley, 1880 24 4 Ocy_ryd 22 Pachygrapsus marmoratus (Fabricius, 1787) 2 2 Pac_mar 23 Pilumnus townsendi Rathbun, 1923 17 22 Pil_tow 24 Portumnus latipes (Pennant, 1777) 30 30 Por_lat 25 Potamon fluviatile (Herbst, 1785) 30 28 Pot_flu 26 Potamonautes obesus A. Milne-Edwards, 1868 30 37 Ptm_obe 27 Uca vocans (Linnaeus, 1758) 22 0 Uca_voc 28 Xantho pilipes A. Milne-Edwards, 1867 14 4 Xan_pil Total specimens: 843 Open in new tab Geometric morphometric experimental design Both the right and the left claws of each individual were photographed with a Tamron SP 90-mm F/2.8 Di VC USD 1:1 macro lens mounted on a Canon EOS 700D camera. The camera was set on a stand, and the crabs were positioned in sand to hold the claws parallel to both the camera lens and the stand plane. A total 1686 photographs were taken. To analyse the variation in claw shape, 11 landmarks were selected on homologous structures on the manus and pollex of the propodus (Fig. 1A; Table 2) using tpsDig 2.16 (Rohlf, 2010) according to previous studies (Rosenberg, 2002; Silva & Paula, 2008; Trevisan et al., 2012; Alencar et al., 2014). All landmarks were chosen for (1) their ease of identification and homology in all specimens, and (2) their suitability to capture the general shape of the chela according to Rosenberg (2002). In addition, 23 semi-landmarks were fixed at equal distances along the claw’s external margin by using tpsDig 2.16 to capture shape differences where it was not possible to define homologous landmarks (Silva & Paula, 2008) (Fig. 1B). Semi-landmarks are points with a reduced degree of freedom depending upon landmarks (for details, see Perez et al., 2006). No points were chosen on the dactyl because (1) only a homologous landmark could be identified on the tip, and (2) it represents a supple (hard but not stationary) structure. Table 2. List of landmarks and their definition Landmark list . . 1 Tip of the manus near the dactyl 2 Tip of the manus upper tubercle 3 Base of the manus upper tubercle 4 Upper attachment points of the carpus with the manus, at the edge of the carpal cavity 5 Lower attachment points of the carpus with the manus, at the edge of the carpal cavity 6 Lower tip of the manus 7 Junction between the manus and the pollex on the ventral margin of the claw 8 Tip of the pollex 9 End of the internal margin of the manus 10 Lower point that marks the articulation of the dactyl with the manus 11 Upper point that marks the articulation of the dactyl with the manus Landmark list . . 1 Tip of the manus near the dactyl 2 Tip of the manus upper tubercle 3 Base of the manus upper tubercle 4 Upper attachment points of the carpus with the manus, at the edge of the carpal cavity 5 Lower attachment points of the carpus with the manus, at the edge of the carpal cavity 6 Lower tip of the manus 7 Junction between the manus and the pollex on the ventral margin of the claw 8 Tip of the pollex 9 End of the internal margin of the manus 10 Lower point that marks the articulation of the dactyl with the manus 11 Upper point that marks the articulation of the dactyl with the manus Open in new tab Table 2. List of landmarks and their definition Landmark list . . 1 Tip of the manus near the dactyl 2 Tip of the manus upper tubercle 3 Base of the manus upper tubercle 4 Upper attachment points of the carpus with the manus, at the edge of the carpal cavity 5 Lower attachment points of the carpus with the manus, at the edge of the carpal cavity 6 Lower tip of the manus 7 Junction between the manus and the pollex on the ventral margin of the claw 8 Tip of the pollex 9 End of the internal margin of the manus 10 Lower point that marks the articulation of the dactyl with the manus 11 Upper point that marks the articulation of the dactyl with the manus Landmark list . . 1 Tip of the manus near the dactyl 2 Tip of the manus upper tubercle 3 Base of the manus upper tubercle 4 Upper attachment points of the carpus with the manus, at the edge of the carpal cavity 5 Lower attachment points of the carpus with the manus, at the edge of the carpal cavity 6 Lower tip of the manus 7 Junction between the manus and the pollex on the ventral margin of the claw 8 Tip of the pollex 9 End of the internal margin of the manus 10 Lower point that marks the articulation of the dactyl with the manus 11 Upper point that marks the articulation of the dactyl with the manus Open in new tab Figure 1. Open in new tabDownload slide A, claw regions and landmark + semi-landmark (black and white circles, respectively) configurations. B, claw outline obtained by fixing both landmarks and semi-landmarks. C, example of visual output of the geometric morphometric analyses on deformation grids: red line, medium shape of claw; black line, claw shape at maximum deformation degree; the range of colours shows areas of morphological variation from highest (red) to lowest (blue) deformation degrees. Figure 1. Open in new tabDownload slide A, claw regions and landmark + semi-landmark (black and white circles, respectively) configurations. B, claw outline obtained by fixing both landmarks and semi-landmarks. C, example of visual output of the geometric morphometric analyses on deformation grids: red line, medium shape of claw; black line, claw shape at maximum deformation degree; the range of colours shows areas of morphological variation from highest (red) to lowest (blue) deformation degrees. Statistical analysis of heterochely The size of each configuration was estimated using centroid size (CS), a dimensionless parameter computed as the square root of the sum of the squares of the distances of each landmark from the centroid (Bookstein, 1986). Once CS values for each right (major) and left (minor) chela of males and females of each species had been obtained, the ratio ‘right chela CS/left chela CS’ (heterometry) for each specimen was calculated to give chela size difference in a single parameter. To evaluate possible sexually dimorphic size characteristics within each species, a series of one-way analysis of variance (ANOVA) was then performed on the CS values of both right and left chelae. The effects of variation in position, orientation and scale of the photographed claws may generate a non-shape variation (NSV) after digitization. In this case, NSV must be mathematically removed because the use of raw coordinates as shape variables in the subsequent statistical analyses would be inappropriate (Adams et al., 2004). To do so, for any series of configurations, we used Generalized Procrustes Analysis (GPA; Bookstein, 1991; Goodall, 1991), which align shapes by minimizing the ‘Procrustes distance’. The Procrustes distance is the square root of the sum of squared differences between the positions of the landmarks in optimally (by least-squares) superimposed and scaled configurations. GPA rotates, aligns and scales landmark configurations to unit CS so that shape differences between specimens are not due to rotation, position or size (Rohlf & Slice, 1990). The alignment of landmarks due to GPA generated new coordinates of landmarks and semi-landmarks in each configuration. These new coordinates were used as variables in subsequent multivariate statistical analyses (Rohlf et al., 1996; Rohlf, 1998). A principal component analysis (PCA) was performed on the landmark configurations (see Rohlf & Slice, 1990; Bookstein, 1991; Dryden & Mardia, 1998; Polly, 2003) of both chelae for males and females separately. The principal component scores (PCs) were used in a multivariate analysis of variance (MANOVA) to (1) evaluate the occurrence of statistically significant sexual dimorphism in claw shape and (2) assess interspecific differences for each sex. Finally, Procrustes distances (PDs, vectorial distances) between right and left claws were calculated for each individual to obtain an individual heterochelic shape index (heteromorphy). To calculate heteromorphy, the left chela was reflected along the y-axis. An ANOVA was then performed on PDs to assess both sexually dimorphic and interspecific differences. All procedures described above, and associated statistics, were performed using the R package Morpho (Schlager, 2013). The overlap between form and ecology Information about habitat and feeding types of crabs are very fragmented in the scientific literature and for many species they are not available. In this study, data for environment (i.e. macroscopic conditions where species live: marine, brackish, estuarine and freshwaters), habitat (i.e. benthic conditions where crabs inhabit: rocks, sand and mud) and feeding types of the studied crabs were collected (Supporting Information, Table S1) from several published scientific papers and/or from the World Register of Marine Species (WoRMS; http://www.marinespecies.org). All previous ecological trends were correlated with shape and size variables to understand if heterometry and/or heterochely are associated with these ecological factors. In particular, environment, habitat and feeding types (Table S1) against heterometry and heteromorphy in both sexes were tested by a series of pair-wise ANOVAs to determine if those ecological features could explain heterometry and heteromorphy for interspecific variation and sexual dimorphism. Mapping form on brachyuran phylogeny To compute the phylogenetic signal, several gene regions (12S, 16S, 18S, 28S, Enolase, GADPH, H3, NAK, PEPCK; K.A.C., pers. data) of 134 different crab species (including species from which we collected morphological data) were used to reconstruct a time-calibrated phylogenetic tree aligning all genes using PASTA. PartitionFinder was used to find an optimal data partitioning scheme, Raxml to estimate a phylogeny with the concatenated dataset, and we calibrated tree to time using penalized likelihood in the program ‘treePL’ (the c++ version of the program ‘r8s’). We tested a number of associations of claw morphology with phylogeny: (1) for both the size and the shape of right and left claws in males and females; (2) for sexual dimorphism in right and left claw size and shape; and (3) for heterometry and heteromorphy in males and females. Specifically, branch lengths of each of our taxa were compared with previous morphometric variables (i.e. size, shape, sexual dimorphism in size and shape, heterometry and heteromorphy) by applying a K test (Adams, 2014). This was performed using the R function phylosig from the R package phytools, which computes phylogenetic signals using two different methods (Revell, 2012), namely ‘K’ or ‘lambda’. RESULTS Centroid size and heterometry The CS of both right (R) and left (L) claws, in both sexes of all species, showed significant variation (Figs 2, 3). Statistically significant sexually dimorphic differences in CS were found in ten species in right and/or left claws, while the remaining eight did not show significant sexual dimorphism. Although the number of species was the same for both right and left claws, the taxa were different for each. Among species showing significant sexual dimorphism, nine showed sexually dimorphic differences in CS for both claws. Calappa granulata (Linnaeus, 1758) had significant sexual dimorphism only for the right claw, while Potamon fluviatile (Herbst, 1785) was only sexually dimorphic in the left claw (Table 3). Table 3. Significance (setting α = 0.05) obtained by applying ANOVA for (1) sexual dimorphism (M = male, F = female) in size of both right and left (R = right, L = left) claws, and (2) intra- (for M and F, separately) and intersexual (that is dimorphic) heterometry. Significance of MANOVA for (3) sexual dimorphism in shape of both R and L claws, and (4) intra- and intersexual heteromorphy . Centroid size M vs. F . Heterometry . Shape M vs. F . Heteromorphy . . . . R . L . M . F . M vs. F . R . L . M . F . M vs. F . Aca_alb 0.172 0.704 0.003 0.008 0.001 0.006 0.095 0.001 0.001 0.981 Ash_lun 0.010 0.005 0.9 0.979 0.338 0.001 0.001 0.035 0.137 0.641 Ate_rot NA NA NA NA NA NA NA NA NA NA Bat_mar NA NA NA NA NA NA NA NA NA NA Cal_gra 0.042 0.053 0.748 0.819 0.552 0.002 0.001 0.001 0.001 0.068 Can_bor 0.914 0.986 0.838 0.881 0.889 0.069 0.376 0.001 0.001 0.788 Car_aes 0.001 0.001 0.027 0.028 0.009 0.001 0.004 0.001 0.001 0.003 Cln_sap 0.003 0.003 0.779 0.675 0.248 0.109 0.006 0.002 0.125 0.328 Crd_gua 0.433 0.688 0.024 0.001 0.372 0.017 0.261 0.001 0.001 0.214 Crp_mac 0.137 0.160 0.22 0.012 0.515 0.099 0.042 0.001 0.001 0.337 Dai_per 0.984 0.339 0.077 0.015 0.001 0.004 0.349 0.001 0.001 0.014 Der_ang NA NA NA NA NA NA NA NA NA NA Erg_clo NA NA NA NA NA NA NA NA NA NA Eri_ver NA NA NA NA NA NA NA 0.001 NA NA Ger_lon 0.001 0.001 0.219 0.198 0.014 0.050 0.001 0.001 0.001 0.355 Gon_rho 0.001 0.001 0.376 0.413 0.082 0.001 0.001 0.001 0.002 0.442 Her_con NA NA NA NA NA NA NA NA NA NA Lio_dep 0.012 0.016 0.267 0.1 0.201 0.003 0.038 0.001 0.001 0.453 Mac_tub 0.948 0.418 0.507 0.169 0.004 0.001 0.001 0.001 0.001 0.561 Med_lan 0.001 0.036 0.002 0.921 0.001 0.001 0.001 0.001 0.001 0.001 Ocy_ryd NA NA 0.001 NA NA NA NA 0.001 NA NA Pac_mar NA NA NA NA NA NA NA 0.067 NA NA Pil_tow 0.819 0.855 0.023 0.001 0.528 0.117 0.151 0.001 0.001 0.367 Por_lat 0.001 0.001 0.109 0.134 0.158 0.001 0.003 0.001 0.001 0.004 Pot_flu 0.058 0.036 0.181 0.097 0.251 0.012 0.005 0.001 0.001 0.633 Ptm_obe 0.001 0.004 0.001 0.001 0.002 0.001 0.008 0.001 0.001 0.106 Uca_voc NA NA 0.001 NA NA NA NA 0.001 NA NA Xan_pil NA NA 0.128 NA NA NA NA 0.001 NA NA . Centroid size M vs. F . Heterometry . Shape M vs. F . Heteromorphy . . . . R . L . M . F . M vs. F . R . L . M . F . M vs. F . Aca_alb 0.172 0.704 0.003 0.008 0.001 0.006 0.095 0.001 0.001 0.981 Ash_lun 0.010 0.005 0.9 0.979 0.338 0.001 0.001 0.035 0.137 0.641 Ate_rot NA NA NA NA NA NA NA NA NA NA Bat_mar NA NA NA NA NA NA NA NA NA NA Cal_gra 0.042 0.053 0.748 0.819 0.552 0.002 0.001 0.001 0.001 0.068 Can_bor 0.914 0.986 0.838 0.881 0.889 0.069 0.376 0.001 0.001 0.788 Car_aes 0.001 0.001 0.027 0.028 0.009 0.001 0.004 0.001 0.001 0.003 Cln_sap 0.003 0.003 0.779 0.675 0.248 0.109 0.006 0.002 0.125 0.328 Crd_gua 0.433 0.688 0.024 0.001 0.372 0.017 0.261 0.001 0.001 0.214 Crp_mac 0.137 0.160 0.22 0.012 0.515 0.099 0.042 0.001 0.001 0.337 Dai_per 0.984 0.339 0.077 0.015 0.001 0.004 0.349 0.001 0.001 0.014 Der_ang NA NA NA NA NA NA NA NA NA NA Erg_clo NA NA NA NA NA NA NA NA NA NA Eri_ver NA NA NA NA NA NA NA 0.001 NA NA Ger_lon 0.001 0.001 0.219 0.198 0.014 0.050 0.001 0.001 0.001 0.355 Gon_rho 0.001 0.001 0.376 0.413 0.082 0.001 0.001 0.001 0.002 0.442 Her_con NA NA NA NA NA NA NA NA NA NA Lio_dep 0.012 0.016 0.267 0.1 0.201 0.003 0.038 0.001 0.001 0.453 Mac_tub 0.948 0.418 0.507 0.169 0.004 0.001 0.001 0.001 0.001 0.561 Med_lan 0.001 0.036 0.002 0.921 0.001 0.001 0.001 0.001 0.001 0.001 Ocy_ryd NA NA 0.001 NA NA NA NA 0.001 NA NA Pac_mar NA NA NA NA NA NA NA 0.067 NA NA Pil_tow 0.819 0.855 0.023 0.001 0.528 0.117 0.151 0.001 0.001 0.367 Por_lat 0.001 0.001 0.109 0.134 0.158 0.001 0.003 0.001 0.001 0.004 Pot_flu 0.058 0.036 0.181 0.097 0.251 0.012 0.005 0.001 0.001 0.633 Ptm_obe 0.001 0.004 0.001 0.001 0.002 0.001 0.008 0.001 0.001 0.106 Uca_voc NA NA 0.001 NA NA NA NA 0.001 NA NA Xan_pil NA NA 0.128 NA NA NA NA 0.001 NA NA Statistically significant values are in bold. NA = data not available due to number of specimens being < 5. Open in new tab Table 3. Significance (setting α = 0.05) obtained by applying ANOVA for (1) sexual dimorphism (M = male, F = female) in size of both right and left (R = right, L = left) claws, and (2) intra- (for M and F, separately) and intersexual (that is dimorphic) heterometry. Significance of MANOVA for (3) sexual dimorphism in shape of both R and L claws, and (4) intra- and intersexual heteromorphy . Centroid size M vs. F . Heterometry . Shape M vs. F . Heteromorphy . . . . R . L . M . F . M vs. F . R . L . M . F . M vs. F . Aca_alb 0.172 0.704 0.003 0.008 0.001 0.006 0.095 0.001 0.001 0.981 Ash_lun 0.010 0.005 0.9 0.979 0.338 0.001 0.001 0.035 0.137 0.641 Ate_rot NA NA NA NA NA NA NA NA NA NA Bat_mar NA NA NA NA NA NA NA NA NA NA Cal_gra 0.042 0.053 0.748 0.819 0.552 0.002 0.001 0.001 0.001 0.068 Can_bor 0.914 0.986 0.838 0.881 0.889 0.069 0.376 0.001 0.001 0.788 Car_aes 0.001 0.001 0.027 0.028 0.009 0.001 0.004 0.001 0.001 0.003 Cln_sap 0.003 0.003 0.779 0.675 0.248 0.109 0.006 0.002 0.125 0.328 Crd_gua 0.433 0.688 0.024 0.001 0.372 0.017 0.261 0.001 0.001 0.214 Crp_mac 0.137 0.160 0.22 0.012 0.515 0.099 0.042 0.001 0.001 0.337 Dai_per 0.984 0.339 0.077 0.015 0.001 0.004 0.349 0.001 0.001 0.014 Der_ang NA NA NA NA NA NA NA NA NA NA Erg_clo NA NA NA NA NA NA NA NA NA NA Eri_ver NA NA NA NA NA NA NA 0.001 NA NA Ger_lon 0.001 0.001 0.219 0.198 0.014 0.050 0.001 0.001 0.001 0.355 Gon_rho 0.001 0.001 0.376 0.413 0.082 0.001 0.001 0.001 0.002 0.442 Her_con NA NA NA NA NA NA NA NA NA NA Lio_dep 0.012 0.016 0.267 0.1 0.201 0.003 0.038 0.001 0.001 0.453 Mac_tub 0.948 0.418 0.507 0.169 0.004 0.001 0.001 0.001 0.001 0.561 Med_lan 0.001 0.036 0.002 0.921 0.001 0.001 0.001 0.001 0.001 0.001 Ocy_ryd NA NA 0.001 NA NA NA NA 0.001 NA NA Pac_mar NA NA NA NA NA NA NA 0.067 NA NA Pil_tow 0.819 0.855 0.023 0.001 0.528 0.117 0.151 0.001 0.001 0.367 Por_lat 0.001 0.001 0.109 0.134 0.158 0.001 0.003 0.001 0.001 0.004 Pot_flu 0.058 0.036 0.181 0.097 0.251 0.012 0.005 0.001 0.001 0.633 Ptm_obe 0.001 0.004 0.001 0.001 0.002 0.001 0.008 0.001 0.001 0.106 Uca_voc NA NA 0.001 NA NA NA NA 0.001 NA NA Xan_pil NA NA 0.128 NA NA NA NA 0.001 NA NA . Centroid size M vs. F . Heterometry . Shape M vs. F . Heteromorphy . . . . R . L . M . F . M vs. F . R . L . M . F . M vs. F . Aca_alb 0.172 0.704 0.003 0.008 0.001 0.006 0.095 0.001 0.001 0.981 Ash_lun 0.010 0.005 0.9 0.979 0.338 0.001 0.001 0.035 0.137 0.641 Ate_rot NA NA NA NA NA NA NA NA NA NA Bat_mar NA NA NA NA NA NA NA NA NA NA Cal_gra 0.042 0.053 0.748 0.819 0.552 0.002 0.001 0.001 0.001 0.068 Can_bor 0.914 0.986 0.838 0.881 0.889 0.069 0.376 0.001 0.001 0.788 Car_aes 0.001 0.001 0.027 0.028 0.009 0.001 0.004 0.001 0.001 0.003 Cln_sap 0.003 0.003 0.779 0.675 0.248 0.109 0.006 0.002 0.125 0.328 Crd_gua 0.433 0.688 0.024 0.001 0.372 0.017 0.261 0.001 0.001 0.214 Crp_mac 0.137 0.160 0.22 0.012 0.515 0.099 0.042 0.001 0.001 0.337 Dai_per 0.984 0.339 0.077 0.015 0.001 0.004 0.349 0.001 0.001 0.014 Der_ang NA NA NA NA NA NA NA NA NA NA Erg_clo NA NA NA NA NA NA NA NA NA NA Eri_ver NA NA NA NA NA NA NA 0.001 NA NA Ger_lon 0.001 0.001 0.219 0.198 0.014 0.050 0.001 0.001 0.001 0.355 Gon_rho 0.001 0.001 0.376 0.413 0.082 0.001 0.001 0.001 0.002 0.442 Her_con NA NA NA NA NA NA NA NA NA NA Lio_dep 0.012 0.016 0.267 0.1 0.201 0.003 0.038 0.001 0.001 0.453 Mac_tub 0.948 0.418 0.507 0.169 0.004 0.001 0.001 0.001 0.001 0.561 Med_lan 0.001 0.036 0.002 0.921 0.001 0.001 0.001 0.001 0.001 0.001 Ocy_ryd NA NA 0.001 NA NA NA NA 0.001 NA NA Pac_mar NA NA NA NA NA NA NA 0.067 NA NA Pil_tow 0.819 0.855 0.023 0.001 0.528 0.117 0.151 0.001 0.001 0.367 Por_lat 0.001 0.001 0.109 0.134 0.158 0.001 0.003 0.001 0.001 0.004 Pot_flu 0.058 0.036 0.181 0.097 0.251 0.012 0.005 0.001 0.001 0.633 Ptm_obe 0.001 0.004 0.001 0.001 0.002 0.001 0.008 0.001 0.001 0.106 Uca_voc NA NA 0.001 NA NA NA NA 0.001 NA NA Xan_pil NA NA 0.128 NA NA NA NA 0.001 NA NA Statistically significant values are in bold. NA = data not available due to number of specimens being < 5. Open in new tab Figure 2. Open in new tabDownload slide A, centroidsize values for right claw in female crabs. B, centroid size values for right claw in male crabs. Figure 2. Open in new tabDownload slide A, centroidsize values for right claw in female crabs. B, centroid size values for right claw in male crabs. Figure 3. Open in new tabDownload slide A, centroid size values for left claw in female crabs. B, centroid size values for left claw in male crabs. Figure 3. Open in new tabDownload slide A, centroid size values for left claw in female crabs. B, centroid size values for left claw in male crabs. Interspecific variability was also observed for heterometry in both sexes (Fig. 4). Specifically, significant values of heterometry existed in eight of 21 and seven of 18 species for males and females, respectively (Table 3). Among 18 species with five or more individuals of both sexes, five species showed a significant heterometry while Medorippe lanata (Linnaeus, 1767) showed significant heterometry only in males. Both Carpilius maculatus (Linnaeus, 1758) and Daira perlata (Herbst, 1790) showed significant heterometry only in females. Figure 4. Open in new tabDownload slide Observed values for heterometry in female (A) and male (B) crabs. Figure 4. Open in new tabDownload slide Observed values for heterometry in female (A) and male (B) crabs. Heterometry was a significant sexually dimorphic character for seven of 18 species (Table 3). Males had higher mean values than females in five of these species. Geryon longipes A. Milne-Edwards, 1882 and Macropipus tuberculatus (Roux, 1830) showed the opposite trend with females having higher mean values than males. The sexually dimorphic variation in heterometry is shown in Figure 5A for all studied species using the right claw’s CS as the reference. Figure 5. Open in new tabDownload slide A, variation in heterometry in conspecific (linked) male (triangles) and female (circles) crabs. B, variation in heteromorphy in conspecific (linked) male (triangles) and female (circles) crabs. C, variation in heterometry and heteromorphy in conspecific (linked) male (triangles) and female (circles) crabs. For marks see Table 1. Figure 5. Open in new tabDownload slide A, variation in heterometry in conspecific (linked) male (triangles) and female (circles) crabs. B, variation in heteromorphy in conspecific (linked) male (triangles) and female (circles) crabs. C, variation in heterometry and heteromorphy in conspecific (linked) male (triangles) and female (circles) crabs. For marks see Table 1. Shape analysis and heteromorphy Deformation grids were constructed in association with PCA graphs and consisted of two red and black lines (Fig. 1C): the red line shows medium claw shape (the centroid has coordinates 0,0), while the black line shows the claw shape associated with the two extremes of the axes. Figure 6 shows PCA graphs and relative deformation grids for both claws in males and females. PC1 explained 50.97% of the variation in the right claws of males and 54.65% of the variation in females. Moving from negative to positive PC1 values, shape variation is seen in the stretching of the pollex region and lowering of the manus region (Fig. 6, top and bottom left) in the right claws of both sexes. For the left claws, the same shape variation is observed in both males and females, with PC1 explaining 48.04% and 55.53% of the variation, respectively (Fig. 6, top and bottom right). PC2 explained 27.92% and 13.88% of the variation in the right chela of males and females, respectively, corresponding to stretching of the pollex and heightening of the manus (Fig. 6, top and bottom right). Finally, PC2 explained 30.61% and 13.78% of the variation in the left chela of males and females, respectively, with the variation corresponding to a shortening of the pollex and lowering of the manus (Fig. 6, top and bottom left). Figure 6. Open in new tabDownload slide Graphs of principal component analyses and relative deformation grids for both claws (R = right; L = left) in female (top) and male (bottom) crabs. See text for the percentage variance explained by each principal component. Figure 6. Open in new tabDownload slide Graphs of principal component analyses and relative deformation grids for both claws (R = right; L = left) in female (top) and male (bottom) crabs. See text for the percentage variance explained by each principal component. Statistically significant sexual dimorphism was observed in 13 of 18 species for the right claw. The same number of species (but not the same taxa) had statistically significant sexual dimorphism in the left claw. Ten out of 18 species showed significant dimorphism for both chelae (Table 3). The exceptions included Acanthocyclus albatrossis Rathbun, 1898, Cardisoma guanhumi Latreille, 1828 and Daira perlata, which only showed statistically significant dimorphism in the right claw. Callinectes sapidus (Rathbun, 1896), Carpilius maculatus and Geryon longipes showed statistically significant dimorphism only in the left claw (Table 3). The other species showed no significant sexual dimorphism in either claw. PDs, or heteromorphy, revealed variation in shape among species for males and females (Fig. 7). Significant heteromorphy existed for both sexes. Males showed significant R-L shape differences in all 21 species, while females showed significant differences in 16 of 18 species. Ashtoret lunaris (Forskål, 1775) and Callinectes sapidus showed significant heteromorphy only in males (Table 3). Heteromorphy was found to be a sexually dimorphic characteristic in only four of the 18 species (Table 3), with males having greater values than females in all species. The sexually dimorphic variation in heteromorphy is shown in Figure 5B for all the studied species, using the right claw CS as the reference measurement. Figure 7. Open in new tabDownload slide Values of heteromorphy (i.e. Procrustes distances) for female (A) and male (B) crabs. Figure 7. Open in new tabDownload slide Values of heteromorphy (i.e. Procrustes distances) for female (A) and male (B) crabs. Heterometry vs. heteromorphy Combining information for heterometry and heteromorphy in the same plot (Fig. 5C) allowed us to understand how size and shape varied in males and females, in both intraspecific and interspecific comparisons. The results showed interspecifically large variation in heterometry and small variation in heteromorphy. Despite differences in scale of the x- and y-axes, Figure 5C clearly shows that total variation of heteromorphy occurs within one-tenth of the heteromorphy index (y-axis in Fig. 5C), while total variation of heterometry occurs within two units, excluding Uca vocans (Linnaeus, 1758), which has a total variation of heterometry occurring within four units. Ecological analysis The series of pairwise ANOVAs performed between heterometry and heteromorphy in both sexes, and other ecological features (i.e. environment, habitat, feeding types), revealed no significant differences (all P > 0.05). Phylogenetic signal Statistically significant phylogenetic signal (P < 0.05) was obtained for the right and left claw shape (i.e. PCs) in both males and females (Table 4; Fig. 8). However, other morphological characters previously considered did not show any statistically significant phylogenetic signal (P = n.s.), namely (1) size of right and left claws in males; (2) size of right and left claws in females; (3) sexual dimorphism in right and left claw size; (4) sexual dimorphism in right and left claw shape; (5) heterometry within and between sexes; and (6) heteromorphy within and between sexes. Table 4. Significance (setting α = 0.05) obtained by applying the K test for phylogenetic signals calculated for: (1) right (R) and left (L) claw (ch) size and shape, in males (M) and females (F); (2) sexual dimorphism (Sex. dim.) in right and left claw size and shape; and (3) heterometry within and between males and females, and heteromorphy within and between males and females . M . F . Sex. dim. . R_ch_size 0.483 0.249 0.703 L_ch_size 0.084 0.408 0.695 R_ch_shape 0.003 0.006 0.113 L_ch_shape 0.002 0.001 0.454 Heterometry 0.521 0.13 0.819 Heteromorphy 0.181 0.476 0.143 . M . F . Sex. dim. . R_ch_size 0.483 0.249 0.703 L_ch_size 0.084 0.408 0.695 R_ch_shape 0.003 0.006 0.113 L_ch_shape 0.002 0.001 0.454 Heterometry 0.521 0.13 0.819 Heteromorphy 0.181 0.476 0.143 Open in new tab Table 4. Significance (setting α = 0.05) obtained by applying the K test for phylogenetic signals calculated for: (1) right (R) and left (L) claw (ch) size and shape, in males (M) and females (F); (2) sexual dimorphism (Sex. dim.) in right and left claw size and shape; and (3) heterometry within and between males and females, and heteromorphy within and between males and females . M . F . Sex. dim. . R_ch_size 0.483 0.249 0.703 L_ch_size 0.084 0.408 0.695 R_ch_shape 0.003 0.006 0.113 L_ch_shape 0.002 0.001 0.454 Heterometry 0.521 0.13 0.819 Heteromorphy 0.181 0.476 0.143 . M . F . Sex. dim. . R_ch_size 0.483 0.249 0.703 L_ch_size 0.084 0.408 0.695 R_ch_shape 0.003 0.006 0.113 L_ch_shape 0.002 0.001 0.454 Heterometry 0.521 0.13 0.819 Heteromorphy 0.181 0.476 0.143 Open in new tab Figure 8. Open in new tabDownload slide Significant (setting α = 0.05) phylogenetic signal obtained by applying the K test for both right (R) and left (L) claw shape in female (top) and male (bottom) crabs. V is a vector of phenotypic trait values for each investigated species calculated in R using the shape matrix in phytools. For statistical significance values, see Table 4. Figure 8. Open in new tabDownload slide Significant (setting α = 0.05) phylogenetic signal obtained by applying the K test for both right (R) and left (L) claw shape in female (top) and male (bottom) crabs. V is a vector of phenotypic trait values for each investigated species calculated in R using the shape matrix in phytools. For statistical significance values, see Table 4. DISCUSSION Heterochely in brachyurans is a well-known but not well-understood phenomenon. Studies published in the last 40 years have generally focused on ontogenetic patterns of claw asymmetry, mainly investigating the functional use of the larger chela through traditional morphometric methods (Hartnoll, 1974; Govind & Blundon, 1985; Abby-Kalio & Warner, 1989; Scalici & Gherardi, 2008; Silva et al., 2014). Many other studies have evaluated the distribution of right and left handedness in one or more crab species (Barnwell, 1982; Ng & Tan, 1985; Ladle & Todd, 2006), and only a few studies have analysed shape variation of claws using landmarks(e.g. Rosenberg, 2002; Silva & Paula, 2008; Alencar et al., 2014). Here, we have thoroughly investigated the heterochely phenomenon (heterometry + heteromorphy) within the brachyuran tree by using the widest sample available of crab species with an adequate number of specimens per species (as compared with similar studies). The description of claw form was well supported by the largest number of landmarks (11) + semi-landmarks (23) used in landmark-based studies of brachyurans. Our study focused on variation in the size and shape of both major and minor chela. Furthermore, statistical analysis of size and shape were carried out through geometric morphometric modelling to determine if: (1) heterometry and heteromorphy represent new sexually dimorphic characteristics for the investigated species; and (2) interspecific variation in claw size and shape has a phylogenetic signal. The main findings of this study might contribute to debates regarding heterochely in crabs by providing innovative tools (heterometry index and heteromorphy index) for considering and describing shape and size variation of claws independently, in and between crab species. By using these two indices we were able to recognize three different kinds of heterochely affecting each analysed species: (1) size-heterochely, when the right and left claws are significantly different only in size and not in shape (not observed in our sample); (2) shape-heterochely, when the right and left claws are significantly different only in shape and not in size; and (3) size- and shape-heterochely, when the right and left claws are significantly different in both size and shape. In fact, heterometry and heteromorphy were widely observed in the examined species. Considering our sample, some taxa showed both size- and shape-heterochely, such as Carcinus aestuarii (Nardo, 1847) and Cardisoma guanhumi. Others, such as Calappa granulata, showed only heterochely in shape but not in size. Just one species, Pachygrapsus marmoratus (Fabricius, 1787), was homochelic as previously described by Silva & Paula (2008). Regarding interspecific comparisons between males and females, we offer a new point of view considering heterochely as a sexually dimorphic parameter. In fact, some of our species showed heterometry and/or heteromorphy only for one sex while others showed them for both, thus resulting in the large amount of interspecific variation attributed to sexual dimorphism. We also tested for ecological associations of the claw variation in size and shape by overlapping them with ecological descriptors for each species found in the literature (i.e. environment, habitat, feeding types). We did not find any pattern of association between heterochely and ecological descriptors due to a lack of detail in the published data. In fact, the scattered literature available regarding the ecology and feeding habit of crab species considered in the present work forced us to recognize macro-categories of environment, habitat and feeding types, which may have flattened all interspecific ecological differences. This was probably the main reason we found no significant ecological associations with size/shape. Claw shape in both sexes showed significant phylogenetic signal, meaning that closely related species have similar claw shape and that in each species displaying heterochely it evolved independently for different uses (feeding, mating, fighting). These functions could be therefore considered morphological attributes with sex-dependent differential expression (Hartnoll, 1974; Rosemberg, 1997; Mariappan et al., 2000; Tsuchida et al., 2000; Barrìa et al., 2014). Thus, the shape of the right and left claws in male and female brachyurans could be interpreted as a fixed genetic character that needs to be decoded throughout targeted molecular studies (Lewis, 1969), as demonstrated for Carcinus maenas (Linnaeus, 1758) by Ladle & Todd (2006). On the other hand, Smith & Palmer (1994) observed that Cancer productus Randall, 1840 may show diverse heterochely depending on the administered food in an indoor experiment. Additionally, they demonstrated that when one claw was immobilized, the chelae became asymmetrical. They advanced the hypothesis that short-term adaptive responses to environmental stress, if heritable, could produce long-term evolutionary changes in claw size and could also promote the evolution of claw dimorphism. Proposing a solution to the origin, evolution and adaptive meaning of heterochely within Brachyura therefore remains a challenge and goes beyond the aims of our work. In conclusion, determining the evolutionary and molecular processes involved in the development of heterochely in crabs is complex given all the functions in which claws are involved (e.g. feeding, burrowing, intraspecific antagonism, courtship). Such a variety of functions are evolutionary forces acting simultaneously on these characters, resulting in current claw size and shape, and their pattern of asymmetry. Many previous studies have focused on heterochely in one or a few crab species, but there are no previous comprehensive analyses of the morphological variability of this trait in crabs. In the above context, this study provides advanced numerical indices of heterochely that capture shape and size variation in greater detail, allowing a comparison of chelae polymorphism among species, possibly identifying relationships among phylogenetic history, ecological traits and patterns of asymmetry. Our results show great potential to generate novel and useful information regarding the evolutionary and molecular processes involved in the development of heterochelyin crabs. However, more interdisciplinary studies are needed, to link claw morphology, specifically heterochely, and molecular biology. In light of our findings, it is clear that future studies need to investigate the widespread phenomenon of heterochely not only in crabs, but also in all animal groups showing asymmetrical claws, possibly by applying quantitative methods, such as the indices of heterometry and heteromorphy presented here. SUPPORTING INFORMATION Additional Supporting Information may be found in the online version of this article at the publisher’s website. Table S1. Data about environment, habitat, feeding types and depth (min = minimum depth; max = maximum depth; mean = mean depth) of the studied crabs (species column), collected either from the World Register of Marine Species (WoRMS, http://www.marinespecies.org, indicated by *), or from different published scientific papers (see references column). ND = no data available. ACKNOWLEDGEMENTS This investigation was supported by funds from the Ministry of Education, University and Research for research activities (FFAIRB fund) and by the grant of Excellence Departments, MIUR-Italy (ARTICOLO 1 COMMI 314-337, LEGGE 232/2016). I am grateful to ‘Roma Tre’ University for funding my journey to George Washington University and the Smithsonian Institution as a Visiting Masters Student. Thanks to Karen Reed, Museum Specialist, to Rafael Lemaitre, Research Zoologist at the Department of Invertebrate Zoology, National Museum of Natural History, Smithsonian Institution and to Gianna Innocenti, Museum Curator of Crustacean and Echinoderm Collection at ‘La Specola’ Natural History Museum, University of Florence (Italy), for their guidance and help with their crab collections. We are indebted to Dr Lu Yao for suggested improvements to the text. We thank two anonymous reviewers for their helpful comments. REFERENCES Abby-Kalio NJ , Warner GF. 1989 . Heterochely and handedness in the shore crab Carcinus maenas (L.) (Crustacea: Brachyura) . Zoological Journal of the Linnean Society 96 : 19 – 26 . Google Scholar Crossref Search ADS WorldCat Adams DC . 2014 . A generalized K statistic for estimating phylogenetic signal from shape and other high-dimensional multivariate data . Systematic Biology 63 : 685 – 697 . Google Scholar Crossref Search ADS PubMed WorldCat Adams DC , Rohlf FJ, Slice DE. 2004 . Geometric morphometrics: ten years of progress following the ‘revolution’ . Italian Journal of Zoology 71 : 5 – 16 . Google Scholar Crossref Search ADS WorldCat Alencar CERD , Lima-Filho PA, Molina WF, Freire FAM. 2014 . Sexual shape dimorphism of the mangrove crab Ucides cordatus (Linnaeus, 1763) (Decapoda, Ucididae) accessed through geometric morphometric . The Scientific World Journal 2014 : 206168 . Google Scholar Crossref Search ADS PubMed WorldCat Barnwell FH . 1982 . The prevalence of male right-handedness in the Indo-West Pacific fiddler crabs Uca vocans (Linnaeus) and U. tetragonon (Herbst) (Decapoda: Ocypodidae) . Journal of Crustacean Biology 2 : 70 – 83 . Google Scholar Crossref Search ADS WorldCat Barrìa EM , Santos S, Jara CG, Butler CJ. 2014 . Sexual dimorphism in the cephalothorax of freshwater crabs of genus Aegla Leach from Chile (Decapoda, Anomura, Aeglidae): an interspecific approach based on distance variables . Zoomorphology 133 : 379 – 389 . Google Scholar Crossref Search ADS WorldCat Bookstein FL . 1986 . Size and shape spaces for landmark data in two dimensions . Statistical Science 1 : 181 – 242 . Google Scholar Crossref Search ADS WorldCat Bookstein FL . 1991 . Morphometric tools for landmark data: geometry and biology. Cambridge : Cambridge University Press . Google Scholar Google Preview OpenURL Placeholder Text WorldCat COPAC Cardini A , O’Higgins P. 2005 . Post-natal ontogeny of the mandible and ventral cranium in Marmota species (Rodentia, Sciuridae): allometry and phylogeny . Zoomorphology 124 : 189 – 203 . Google Scholar Crossref Search ADS WorldCat Castiglioni DS , Coelho PA. 2011 . Determinação da maturidade sexual de Ucides cordatus (Crustacea, Brachyura, Ucididae) em duas áreas de manguezal do litoral sul de Pernambuco, Brasil . Iheringia , Série Zoologia 101 : 138 – 144 . Google Scholar Crossref Search ADS WorldCat Daniels SR . 2001 . Allometric growth, handedness, and morphological variation in Potamonautes warreni (Calman, 1918) (Decapoda, Brachyura, Potamonautidae) with a redescription of the species . Crustaceana 74 : 237 – 253 . Google Scholar Crossref Search ADS WorldCat Dryden IL , Mardia KV. 1998 . Statistical shape analysis. Chichester : Wiley and Sons, Ltd . Google Scholar Google Preview OpenURL Placeholder Text WorldCat COPAC Duarte MS , Maia-Lima FA, Molina WF. 2008 . Interpopulational morphological analyses and fluctuating asymmetry in the brackish crab Cardisoma guanhumi Latreille (Decapoda, Gecarcinidae), on the Brazilian Northeast coastline . Pan-American Journal of Aquatic Science 3 : 294 – 303 . Google Scholar OpenURL Placeholder Text WorldCat Gabbanini F , Gherardi F, Vannini M. 1995 . Force and dominance in the agonistic behavior of the freshwater crab Potamon fluviatile . Aggressive Behavior 21 : 451 – 462 . Google Scholar Crossref Search ADS WorldCat Gherardi F , Micheli F. 1989 . Relative growth and population structure of the freshwater crab, Potamon potamios palestinensis, in the Dead Sea area (Israel) . Israel Journal of Zoology 36 : 133 – 145 . Google Scholar OpenURL Placeholder Text WorldCat Goodall C . 1991 . Procrustes methods in the statistical analysis of shape . Journal of the Royal Statistical Society, Series B 53 : 285 – 339 . Google Scholar OpenURL Placeholder Text WorldCat Govind CK , Blundon JA. 1985 . Form and function of the asymmetric chelae in blue crabs with normal and reversed handedness . Biological Bulletin 168 : 321 – 331 . Google Scholar Crossref Search ADS WorldCat Graham JH , Shmuel R, Hagit H, Eviatar N. 2010 . Fluctuating asymmetry: methods, theory, and applications . Symmetry 2 : 466 – 540 . Google Scholar Crossref Search ADS WorldCat Hartnoll RG . 1974 . Variation in growth patterns between some secondary sexual characters in crabs (Decapoda Brachyura) . Crustaceana 27 : 131 – 136 . Google Scholar Crossref Search ADS WorldCat Hartnoll RG . 1978 . The determination of relative growth in Crustacea . Crustaceana 34 : 281 – 293 . Google Scholar Crossref Search ADS WorldCat Hartnoll RG . 1982 . Growth. In: Abele LG, Bliss D, eds. The biology of Crustacea . London : Academic Press , 111 – 196 . Google Scholar Google Preview OpenURL Placeholder Text WorldCat COPAC Juanes F , Lee KT, McKnight A, Kellogg K. 2008 . Claw allometry in green crabs, Carcinus maenas: heterochely, handedness, and sex . Marine Biology 153 : 523 – 528 . Google Scholar Crossref Search ADS WorldCat Klingenberg CP . 2015 . Analyzing fluctuating asymmetry with geometric morphometrics: concepts, methods, and applications . Symmetry 7 : 843 – 934 . Google Scholar Crossref Search ADS WorldCat Ladle RJ , Todd PA. 2006 . A developmental model for predicting handedness frequencies in crabs . Acta Ecologica 30 : 283 – 287 . Google Scholar Crossref Search ADS WorldCat Lewis JE . 1969 . Reversal of asymmetry of chelae in Calappa Weber, 1795 (Decapoda: Oxystomata) . Proceedings of the Biological Society of Washington 82 : 63 – 80 . Google Scholar OpenURL Placeholder Text WorldCat Liu H , Li C. 2000 . Reproduction in the freshwater crab Candidiopotamon rathbunae (Brachyura: Potamidae) in Taiwan . Journal of Crustacean Biology 20 : 88 – 99 . Google Scholar Crossref Search ADS WorldCat Mariappan P , Balasundaram C, Schmitz B. 2000 . Decapod crustacean chelipeds: an overview . Journal of Biosciences 25 : 301 – 313 . Google Scholar Crossref Search ADS PubMed WorldCat Micheli F , Gherardi F, Vannini M. 1990 . Growth and reproduction in the freshwater crab, Potamon fluviatile (Decapoda, Brachyura) . Freshwater Biology 23 : 491 – 503 . Google Scholar Crossref Search ADS WorldCat Ng PKL , Tan LWH. 1985 . Right handedness in the heterochelous calappoid and xanthid crabs, suggestion for functional advantages . Crustaceana 49 : 98 – 100 . Google Scholar Crossref Search ADS WorldCat Palmer AR . 1996 . From symmetry to asymmetry: phylogenetic patterns of asymmetry variation in animals and their evolutionary significance . Proceedings of the National Academy of Sciences USA 93 : 14279 – 14286 . Google Scholar Crossref Search ADS WorldCat Palmer AR . 2005 . Antisymmetry . In: Hallgrímsson B, Hall BK, eds. Variation, a central concept in biology. New York : Elsevier Academic Press , 359 – 398 . Google Scholar Crossref Search ADS Google Preview WorldCat COPAC Perez SI , Bernal V, Gonzalez PN. 2006 . Differences between sliding semi-landmark methods in geometric morphometrics, with an application to human craniofacial and dental variation . Journal of Anatomy 208 : 769 – 784 . Google Scholar Crossref Search ADS PubMed WorldCat Polly PD . 2003 . Paleophylogeography: the tempo of geographic differentiation in marmots (Marmota) . Journal of Mammalogy 84 : 369 – 384 . Google Scholar Crossref Search ADS WorldCat Rathbun MJ . 1918 . The grapsoid crabs of America, Vol. 97 . Washington : US Government Printing Office . Google Scholar Crossref Search ADS Google Preview WorldCat COPAC Rathbun MJ . 1930 . Cancroid crabs of America of the families Euryalidae, Portunidae, Atelecyclidae, Cancridae and Xanthidae . United States National Bulletin 152 : 1 – 609 . Google Scholar OpenURL Placeholder Text WorldCat Raubenheimer CD . 1986 . Aspects of the biology of the freshwater crab, Potamonautes sidneyi, with particular reference to general seasonality and female aggression. MSc. Thesis, University of Natal . Google Scholar Google Preview OpenURL Placeholder Text WorldCat COPAC Revell LJ . 2012 . phytools: An R package for phylogenetic comparative biology (and other things) . Methods in Ecology and Evolution 3 : 217 – 223 . Google Scholar Crossref Search ADS WorldCat Rohlf FJ . 1996 . Morphometric spaces, shape components and the effects of linear transformations . In: Marcus LF, Corti M, Loy A, Naylor GJP, Slice DE, eds. Advances in morphometrics . New York : Springer, 117 – 129 . Google Scholar Crossref Search ADS Google Preview WorldCat COPAC Rohlf FJ . 1998 . On applications of geometric morphometrics to studies of ontogeny and phylogeny . Systematic Biology 47 : 147 – 158 . Google Scholar Crossref Search ADS PubMed WorldCat Rohlf FJ . 2010 . tpsDig, digitize landmarks and outlines.Version 2.16 . New York : Department of Ecology and Evolution, State University of NewYork at Stony Brook . Google Scholar Google Preview OpenURL Placeholder Text WorldCat COPAC Rohlf FJ , Slice DE. 1990 . Extensions of the procrustes method for the optimal superimposition of landmarks . Systematic Biology 39 : 40 – 59 . Google Scholar OpenURL Placeholder Text WorldCat Rosemberg MS . 1997 . Evolution of shape differences between the major and minor chelipeds of Uca pugnax (Decapoda: Ocypodidae) . Journal of Crustacean Biology 17 : 52 – 59 . Google Scholar Crossref Search ADS WorldCat Rosenberg MS . 2002 . Fiddler crab claw shape variation: a geometric morphometric analysis across the genus Uca (Crustacea: Brachyura: Ocypodidae) . Biological Journal of the Linnean Society 75 : 147 – 162 . Google Scholar OpenURL Placeholder Text WorldCat Scalici M , Gherardi F. 2008 . Heterochely and handedness reversal in the freshwater crab Potamon potamios . Crustaceana 81 : 507 – 511 . Google Scholar Crossref Search ADS WorldCat Scalici M , Goretti E, Dörr AJM, D’Allestro V. 2013 . Morphometric homogeneity and allometric growth of Potamon fluviatile in Italy . Crustaceana 86 : 1291 – 1296 . Google Scholar Crossref Search ADS WorldCat Schenk SC , Wainwright PC. 2001 . Dimorphism and the functional basis of claw strength in six brachyuran crabs . Journal of Zoology 255 : 105 – 119 . Google Scholar Crossref Search ADS WorldCat Schlager S . 2013 . Morpho: Calculations and visualisations related to Geometric Morphometrics. R package version 0.23 3. OpenURL Placeholder Text WorldCat Silva IC , Paula J. 2008 . Is there a better chela to use for geometric morphometric differentiation in brachyuran crabs? A case study using Pachygrapsus marmoratus and Carcinus maenas . Journal of the Marine Biological Association of the United Kingdom 88 : 941 – 953 . Google Scholar Crossref Search ADS WorldCat Silva TE , Fumis PB, Almeida AC, Bertini G, Fransozo V. 2014 . Morphometric analysis of the mud crab Hexapanopeus paulensis Rathbun, 1930 (Decapoda, Xanthoidea) from the southeastern coast of Brazil . Latino-American Journal of Aquatic Resources 42 : 588 – 597 . Google Scholar Crossref Search ADS WorldCat Smith D , Palmer AR. 1994 . Effects of manipulated diet on size and performance of Brachyuran crab claws . Science 264 : 710 – 712 . Google Scholar Crossref Search ADS PubMed WorldCat Spani F , Scalici M. 2016 . Allometric sexual dimorphism in the river crab Potamon fluviatile (Herbst, 1785) (Brachyura: Potamidae) . Journal of Crustacean Biology 36 : 274 – 278 . Google Scholar Crossref Search ADS WorldCat Stein RA . 1976 . Sexual dimorphism in crayfish chelae: functional significance linked to reproductive activities . Canadian Journal of Zoology 54 : 220 – 227 . Google Scholar Crossref Search ADS WorldCat Trevisan A , Marochi MZ, Costa M, Santos S, Masunari S. 2012 . Sexual dimorphism in Aegla marginata (Decapoda: Anomura) . Nauplius 20 : 75 – 86 . Google Scholar Crossref Search ADS WorldCat Tsuchida S , Fujikura K. 2000 . Heterochely, relative growth, and gonopod morphology in the bythograeid crab, Austinograea williamsi (Decapoda, Brachyura) . Journal of Crustacean Biology 20 : 407 – 414 . Google Scholar Crossref Search ADS WorldCat Van Valen L . 1962 . A study of fluctuating asymmetry . Evolution 16 : 125 – 142 . Google Scholar Crossref Search ADS WorldCat Williams MJ. Heng PK. 1981 . Handedness in males of Uca vocans (Linnaeus, 1758) (Decapoda, Ocypodidae) . Crustaceana 40 : 215 – 216 . Google Scholar Crossref Search ADS WorldCat Published by Oxford University Press on behalf of The Biological Journal of the Linnean Society 2019. This work is written by (a) US Government employee(s) and is in the public domain in the US. Published by Oxford University Press on behalf of The Biological Journal of the Linnean Society 2019.
TI - Claw asymmetry in crabs: approaching an old issue from a new point of view
JO - Biological Journal of the Linnean Society
DO - 10.1093/biolinnean/blz159
DA - 2020-01-01
UR - https://www.deepdyve.com/lp/oxford-university-press/claw-asymmetry-in-crabs-approaching-an-old-issue-from-a-new-point-of-1xRrUjIdpx
SP - 162
EP - 176
VL - 129
IS - 1
DP - DeepDyve
ER -