Intra- and Interspecific Variation in Sexual Dimorphism Patterns of Mud Crab Genus Scylla Along the Equatorial Region

Khor Waiho,Mhd Ikhwanuddin,Ghazali Azmie,Muyassar H Abualreesh,Mohamad Jalilah,Sairatul Dahlianis Ishak,Alexander Chong Shu-Chien,Hanafiah Fazhan

doi:10.3389/fmars.2021.690836

Abstract

Sexual dimorphism is generally obvious in brachyurans, and sexual dimorphism between species is of a higher degree to allow separation of trophic niches compared to the lower intraspecific variations between sexes. Mud crab genus Scylla are distributed along the Indo-West Pacific region, and species within this genus often exhibit overlapping niches and similar external morphologies. This study compared the intra- and interspecific sexual dimorphism patterns of three sympatric Scylla species from four distinct geographical locations along the equatorial region based on 24 morphometric characters. The consistency of sexual dimorphism patterns between locations was higher than between species. However, reproduction-related characters such as cheliped dimensions and abdomen width (AW) exhibited similar sexual dimorphism patterns across species. Discriminant function analysis based on the 23 morphometric ratios revealed the morphometric intraspecific divergence in all three Scylla species from the Asajaya mangrove forest. The cause for this regional intraspecific differentiation of mud crabs from the Asajaya mangrove forest remains unknown.

Highlights

Sexual dimorphism in terms of morphological characters is of functional significance and an outcome of the interaction between natural and sexual selection (Darwin, 1871; Hamasaki et al, 2020)
Sexual size dimorphism in terms of carapace width (CW) was consistently malebiased across locations only in S. olivacea
Females of S. tranquebarica from Terengganu exhibited larger CW compared to their male counterparts (P = 0.018), whereas CW of S. tranquebarica from Sarawak (P = 0.893) and S. paramamosain from Sabah and Sarawak showed no significant difference between sexes (PSabah = 0.087; PSarawak = 0.793)

Summary

Introduction

Sexual dimorphism in terms of morphological characters is of functional significance and an outcome of the interaction between natural and sexual selection (Darwin, 1871; Hamasaki et al, 2020). Sexual Dimorphism of Mud Crab and require the aid of quantitative analyses to assess the degree of sexual dimorphism (Bertin et al, 2002). Some of these features that are often used in morphometric discrimination of brachyurans include merus and/or propodus length (PL) of periopods (Simpson et al, 2016) and supraorbital dimension (Alencar et al, 2014)

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