Genetic variability assessed by microsatellites in cultured populations of the Pacific oyster (Crassostrea gigas) in China

Five cultured populations of Pacific oyster, Crassostrea gigas, were examined at seven polymorphic microsatellite loci to assess the levels of allelic diversity and heterozygosity within and differentiation among the populations. The genetic variability of the seven loci was high for all the populations. The average numbers of alleles per locus ranged from 19.1 to 26.0, while the average observed and expected heterozygosity ranged from 0.474 to 0.616, and from 0.916 to 0.949, respectively. Fst and Rst values showed significant genetic differentiation among the five cultured populations. Genetic differences between the populations were also detected by pairwise comparison based on allelic distribution. The Neighbor-joining tree topology constructed on the basis of genetic distances between populations showed a clear separation of the northern three populations and southern two populations, suggesting that geographically separated cultured populations of C. gigas could be genetically differentiated unless seeds are transplanted among them. The useful information on the genetic variation and differentiation in cultured populations obtained in this study can be applied for future genetic improvement by selective breeding, and to design suitable management guidelines for the Pacific oyster.