Population structure and historical demography of the spotted mackerel (Scomber australasicus) off Taiwan inferred from mitochondrial control region sequencing

The strong debate as to whether or not the spotted mackerel (Scomber australasicus) off Taiwan is genetically structured continues. Sequence analyses of the complete mitochondrial DNA control region (886 bp in length) were conducted to elucidate the population structure and historical demography of spotted mackerel off Taiwan. In total, 157 individuals were separately collected from the East China Sea (ECS), waters off Ilan (ILAN, northeastern Taiwan), Taitung (TT, southeastern Taiwan), and Linyan (LY, southern Taiwan), and the South China Sea (SCS), and 132 haplotypes were obtained. The haplotype diversity (h) was high for all samples (99.6%), with values from 99.1% (ECS) to 99.8% (SCS). Nucleotide diversity (pi) was low for all samples (0.70%), with values from 0.61% (LY) to 0.75% (ILAN). A median-joining network of 132 haplotypes revealed no significant phylogeographic structure. Analysis of molecular variance (AMOVA) and spatial analysis of molecular variance (SAMOVA) indicated no significant heterogeneity. F-ST values indicated no significant difference in each pairwise combination of these 5 sampled areas except the one between the ECS and SCS samples. These results suggest that spotted mackerel off Taiwan belong to the single gene pool. Both mismatched distribution analysis and neutrality tests suggested that spotted mackerel in these waters have experienced population expansion since the late Pleistocene (approximately between 46,399 and 8,980 yr ago).