Differential population structuring and demographic history of two closely related fish species, Japanese sea bass (Lateolabrax japonicus) and spotted sea bass (Lateolabrax maculatus) in Northwestern Pacific.

The Quaternary cold periods in the Northwestern Pacific are thought to have heavily influenced the amount and distribution of intraspecific genetic variation in marine fishes. To estimate the demographic history and genetic structure of Lateolabrax maculatus and L. japonicus in the Northwestern Pacific, 256 individuals were sampled from 19 localities throughout the distribution range of the two species. Mitochondrial DNA variation was analyzed using DNA sequence data from the cytochrome b gene and control region. Nucleotide diversity was much higher in L. japonicus (0.030) than in L. maculatus (0.012). The demographic history of the two species was examined using neutrality tests and mismatch distribution analyses and results indicated Pleistocene population expansion in both species. Estimates of population expansion time suggested earlier population expansion in L. japonicus than in L. maculatus. Molecular variance analyses showed differential genetic structuring for these two closely related species. The results indicated that L. japonicus is panmictic throughout its range. In contrast, populations of L. maculatus showed statistically significant levels of genetic structuring. Pattern of isolation by distance was observed in L. maculatus, suggesting that L. maculatus is in genetic equilibrium. In contrast, L. japonicus did not exhibit isolation by distance.