Genetic variation of mtDNA COI sequence of Scomberomorus commerson populations in the South China Sea

We analyzed 711 bp segment of the mtDNA cytochrome oxidase subunit Ⅰ of 62 individuals of Scomberomorus commerson collected from Raoping, Yangjiang in Guangdong Province and Dongxing in Guangxi Province, among which 26 mutations and 18 haplotypes were detected. Generally, the haplotype diversity (H_d=0.808±0.040) level was relatively high, while the nucleotide diversity was much poorer (π=0.004 0±0.000 6). Three shallow clades appeared in the Kimura 2-parameter based on neighbor-joining tree and parsimony network; pairwise fixation index F_st value ranged from 0.811 to 0.833 (P<0.001); gene flow ranged from 0.1 to 0.117. Analysis of molecular variance shows that the genetic variation among three clades was 82.61%, suggesting significantly high genetic differentiation. The deduced divergence time was about 890~226.7 ka BP (i.e., during the middle Pleistocene period), and the Glacial interglacial cycles in Pleistocene might be the reason of genetic differentiation. However, individuals from various locations were intertwined together in all clades; pairwise F_st (-0.027~0.066) and gene flow among sampling sites revealed no significant differentiation. AMOVA analysis shows that the percentage of population variation was 96.34%, suggesting a relatively high level of gene flow among sampling sites in the South China Sea. In Clade A, the significant negative values of neutral test and the unimodal mismatch distribution suggest a recent population expansion occurred in this clade about 890 000~226 700 years ago, due to the effects of changed living space and marine currents during Pleistocene glaciations.