Molecular phylogeography and population history of Crassostrea sikamea (Amemiya, 1928) based on mitochondrial DNA

Climatic oscillations between glacial and interglacial periods during the Pleistocene markedly influenced the geographical distribution and genetic structure of marine species. To examine the genetic structure and historical demography of Crassostrea sikamea, fragment of cytochrome C oxidase subunit I (COI) gene was sequenced and analyzed in this study, a total of 366 individuals from 20 locations along coastal regions of the Northwest Pacific were taken into analysis. Significant genetic differentiation was found among Chinese, Korean, and Japanese populations according to the results of pairwise FST and analysis of molecular variance. Furthermore, isolation by distance analysis showed that the genetic differentiation among these three groups was related to the geographic distance. All three groups have experienced population expansion events in their histories, the time of expansion for all the populations was estimated to be approximately 197–236 thousand years ago which corresponds to the late Pleistocene. The genetic structure of C. sikamea could have been affected by not only the population expansion and geographic expansion in the Pleistocene, but also by geographic distances and ocean currents.