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Population Genetics of the Violet Vinegar Crab (Episesarma versicolor) Along the Andaman Sea Coast of Thailand

Episesarma versicolor is an important commercial fishery product in Southeast Asia. In Thailand, this species is currently being overexploited. In order to provide necessary information for constructing a species management plan, we performed a population genetic analysis of this species living on the Andaman Sea coast of Thailand. Intraspecific variation was determined from complete sequences of the mitochondrial (mt) DNA control region (CR) with a size of 790-798 bp. MtDNA CR sequences of 72 individuals from 5 west coastal areas of southern Thailand, including Satun, Trang, Krabi, Phang Nga, and Ranong, were analyzed. In total, 62 haplotypes with 58 rare haplotypes were identified. Estimated values of haplotype and nucleotide diversities were 0.978 and 0.007, respectively. Neutrality tests (Tajima's D and Fu's FS statistics) showed that Andaman populations of E. versicolor had experienced expansion. However, the analysis of mismatch distribution rejected the sudden expansion model, corresponding to the results of the raggedness indices test and the complex network topology of a minimum spanning network (MSN). The MSN showed 2 major lineages including clade I, a common lineage of E. versicolor living on the Andaman coast, and clade II, a Krabi-specific lineage. Estimated values of τ, q 0, and q 1, and the MSN topology revealed the direction of expansion as northward along the Andaman coast. The approximate time of the expansion was 10,000 yr ago which was during the post late-glacial period of the Holocene Epoch. An AMOVA analysis showed that most of the genetic variation was due to variations within populations. It also showed a lack of variation among populations. The analysis of pairwise differences (FST) also showed no statistically significant difference between all possible regional combinations. Based on these results, an absence of a population structure of E. versicolor on the Andaman Sea coast was possibly caused either by a high level of gene flow due to the high dispersal ability of this species or expansion experienced throughout its demographic history. Both the historical demography and genetic features of E. versicolor on the Andaman Sea coast revealed by this study are necessary information contributing to efficient strategies to conserve this species in Thailand.