Genetic population structure of a reef goby, <Emphasis Type="Italic">Bathygobius cocosensis</Emphasis>, in the northwestern Pacific

To investigate the genetic population structure of a reef goby, Bathygobius cocosensis, in the northwestern Pacific in relation to major oceanic currents (North Equatorial and Kuroshio Currents), the mitochondrial DNA (mtDNA) phylogeny and demography of the species were inferred from partial nucleotide sequences of the mitochondrial NADH dehydrogenase 5 subunit (ND5) gene (945 bp). The resultant mtDNA tree and population genetic analyses showed that the Bonin Islands’ population apparently differed from the other populations in the Japan–Ryukyu–Guam region, which lie along the routes of the North Equatorial and Kuroshio Currents. A test calculation indicated the divergence date to be approximately 1 million years ago. The population expansion parameters indicated that the Bonin Islands’ population had survived during the fluctuations in sea level in the Pleistocene–Holocene age and that the population had expanded thereafter.