Crushing and Cutting: Shape Variation and Morphological Integration Between the Claws of Two Swimming Crab Species (Brachyura: Portunidae)

Abstract

This study investigated shape variations and morphological integration between the components of crusher and cutter claws in two species of swimming crabs, Callinectes danae and Callinectes ornatus. The propodi and dactyli of the claws were analysed in males and females of both species, using geometric morphometric techniques to identify subtle shape differences and analyse the integration between the components. The analysis of morphological integration assesses the coadaptation between two correlated traits, whose modifications may result in improvements in functional performance. The crusher claws, associated with agonistic interactions and breaking prey with hard tissues, showed greater robustness than the cutter claws, which are specialised in cutting tasks and agile capture. Despite these functional differences, a high degree of morphological integration was found between the propodus and dactylus in both types of claws, regardless of sex or species. Statistical analyses confirmed significant differences in the shape of the structures between crusher and cutter claws, highlighting variations in robustness and proportions of the components. These findings indicate that, even though each type of claw is frequently used to acquire different resources, they do not differ in terms of morphological integration, as they are coadapted to perform different functions with high efficiency.