Claw asymmetry in crabs: approaching an old issue from a new point of view

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.

Does Asymmetrical Gonopodium Morphology Predict Lateralized Behavior in the Fish Xenophallus umbratilis?

“…An important property of bilateral symmetry is that it also allows an individual to express handedness, defined here as the propensity to use one side of the body preferentially over the other (Palmer, 2006;Bryden, 2016); we use the term "handed" in its broad sense as defined in previous work (Hata et al, 2011;Buchanan et al, 2015). Handedness is typically understood in a morphological context (Bock and Marsh, 1991), such as differences in the properties of structures [e.g., claw size in crabs (Spani et al, 2020)], or the orientation of structures [e.g., shell torsion in snails (Kurita and Wada, 2011)]. However, handedness can also be expressed behaviorally (Wiper, 2017).…”

Evolvability in the Cephalothoracic Structural Complexity of Aegla araucaniensis (Crustacea: Decapoda) Determined by a Developmental System with Low Covariational Constraint

“…Sexual dimorphism in bilateral asymmetry is a morpho-adaptive pattern widely recognized in decapod crustaceans, for example, the heterochely in the cutter and crusher claws and its consequences in sexual selection, the asymmetry in the female pleopods as a reproductive character and the pleonal asymmetry of hermit crabs facilitating the habitability of gastropod shells [ 59 , 60 , 61 , 62 ]. We report significant sexual dimorphism in the cephalothoracic asymmetry of A. araucaniensis , which is explained by two factors of origin with antagonistic covariational effects whose interactions have consequences in the capacity for adaptive change of the developmental modularity.…”

Pliocene and late Pleistocene (MIS 5e) decapod crustaceans from Santa Maria Island (Azores Archipelago: Central Atlantic): systematics, palaeoecology and palaeobiogeography

“…Already, Förster (1979: 254), who attempted to evaluate fossil (Miocene) isolated fingers of brachyuran crabs, noted that: ‘description and illustration of chelipeds have been neglected mostly’. Moreover, the morphology of crab chelipeds is influenced by a number of factors (Smith and Palmer, 1994; Lee, 1995), although ecological convergence was recently shown to have been overemphasised (Spani et al ., 2020). Although sexual dimorphism and heterochely have a major impact on the shape and dentition of crab chelae, various crab taxa have distinctly shaped chelipeds (Schäfer, 1954) and some cheliped characteristics can be of taxonomic significance (Spiridonov et al ., 2014; Spani et al ., 2020).…”