Shallow Genetic Structure of Pholis fangi in Bohai Sea and Yellow Sea Inferred from mtDNA Control Region

Pholis fangi is an ecologically important fish species inhabiting Chinese coastal waters of Yellow Sea and Bohai Sea. To investigate the genetic diversity and population genetic structure of P. fangi, a fragment of 487 bp in the first hypervariable region (HVR-1) of the mitochondrial DNA (mtDNA) control region was sequenced for 181 individuals collected from Bohai Sea and Yellow Sea. A total of 18 polymorphic sites were detected, which defined 25 haplotypes. A moderate level of haplotype diversity (h = 0.7052) and a low level of nucleotide diversity (pi = 0.0028) were detected. Both the phylogenetic tree and the haplotype network showed no significant genealogical structure difference among sampling locations. Pairwise F-ST comparison and hierarchical molecular variance analysis (AMOVA) revealed that no significant genetic structure difference existed throughout the investigated regions, suggesting a high gene exchange among different populations. The results of neutrality test and mismatch distribution analysis indicated that a late Pleistocene population expansion (38000-127000 years ago) happened. Seasonal schooling migration may contribute to the genetically homogeneous population structure of the species.