Heterochely and handedness in the orange mud crab Scylla olivacea: implication for future culture practice optimisation

Abstract

Asymmetric body traits in bilateral organisms are common and serve a range of different functions. In crustaceans, specifically among brachyuran crabs, heterochely and handedness in some species are known to aid in behavioural responses such as food acquisition, and sexual and territorial displays. However, the heterochely of the intertidal mud crab genus Scylla is still poorly understood. This study investigated the cheliped morphometric characteristics of orange mud crab Scylla olivacea and the relation of heterochely and handedness to sex. Scylla olivacea is heterochelous, with predominant right-handed (70.2%). Three morphometric variables, i.e., propodus length (PL), propodus depth (PD), and propodus width (PW) were significantly larger in the right cheliped and the estimated handedness based on these three variables were consistent with the presence of molariform teeth. The effect of sex had no influence on the occurrence of heterochely or handedness. The frequency of left-handedness increased with size, especially in males. We postulate that handedness reversal, a phenomenon seen in other crab species when the dominant hand is lost, also occurs in S. olivacea, thereby resulting in a change in left-handedness frequency. The use of chelipeds by males in mate and territorial defenses might provide an explanation for the higher risk of losing a dominant cheliped and thus, higher left-handedness frequency compared to females. Future behavioural research could shed light on the selective forces that affect the handedness distribution in mud crabs. Knowledge on heterochely and handedness of mud crabs could be useful for future development of less aggressive crab populations by claw reversal and the optimisation of limb autotomy techniques.

A comparative study on the antennae morphology and ultrastructure of three mud crab species of the genus Scylla from Setiu Wetlands, Terengganu, Malaysia

“…The antennae length of mud crabs in the genus Scylla is short, thus their chelipeds would be the first body parts that will be in contact with other conspecifics. Mud crabs are aggressive, and they use their chelipeds for various purposes, including feeding and communication-mate guarding, and play important role in exhibiting signals to attract females (Fazhan et al, 2022;Rozaimi et al, 2023;Waiho et al, 2015). In contrast, antenna-to-antenna contact is commonly exhibited by lobsters and crayfish that possess long antennae (Vickery et al, 2012).…”