Genetic variation and population structure of the Pacific oyster Crassostrea gigas in the northwestern Pacific inferred from mitochondrial COI sequences

The Pacific oyster Crassostrea gigas as one of the important commercial bivalves in the world, is native to the coast of East Asia. The wild populations of this species have declined due to natural or anthropogenic factors in recent years. To provide valuable insights into management and conservation of C. gigas we investigated the genetic variation and population structure of C. gigas in the northwestern Pacific by analyzing partial mitochondrial cytochrome oxidase I gene (COI) with samples from 12 populations. Moderate levels of genetic diversity and low nucleotide diversity were found within the populations. No significant population structure existed in such a big spatial scale; only low but significant genetic differentiation between some of the Chinese and Japanese populations was observed, which highlighted the important roles of current gene flow and historical re-colonization in deceasing genetic differentiation for marine invertebrates with sedentary adults. The results obtained in this study provide useful information on the genetic diversity and phylogeographic pattern of C. gigas and reveal the complex interactions of multiple factors (strong genetic connectivity by dispersal of larvae and ocean currents in this region) in the northwestern Pacific.