Genetic population structure of mud crab (Scylla olivacea) in the Bay of Bengal inferred from mitochondrial DNA and microsatellite markers

Abstract

The increasing exploitation of Scylla olivacea, one of the most commercially consumed mud crabs inhabiting mangroves and estuaries of the Bay of Bengal has been seriously experiencing a constant decline of its population. Information on its genetic population structure is crucial for the conservation of S. olivacea. Here, partial sequences of the mitochondrial cytochrome c oxidase subunit I (COI) gene and ten microsatellite loci were used to estimate population genetics from four localities in the Bay of Bangladesh. Genotypes of mitochondrial DNA (mtDNA) were identified with an 848 bp fragment sequence of COI gene, defining 32 different haplotypes from H1 to H32. H4 was the most frequently observed haplotype, existing in all four localities, while the majority of haplotypes were rare ones, existing in only one individual. Neutrality tests and mismatch analysis conferred a potential population expansion event for this crab species. Diploid genotypes were determined with microsatellite loci, delineating several alleles at each locus, significant linkage disequilibrium and deviation from Hardy-Weinberg equilibrium. The AMOVA analysis of mtDNA suggested a low level of genetic differentiation among four localities (FST = 0.0172, P > 0.05) while microsatellite markers showed a moderate genetic differentiation (FST = 0.0687, P > 0.05). The lower level of differentiation of mtDNA than microsatellites possibly resulted from female-mediated gene flow between populations, biased sex ratios, natural selection, or mutation.