Development of microsatellite markers for Japanese scallop (Mizuhopecten yessoensis) and their application to a population genetic study.

The Japanese scallop (Mizuhopecten yessoensis) is one of the main fishery products in Japan, but with the expansion of culture operations of the Japanese scallop, various problems have been encountered including high mortality, poor growth, poor seed production, and so on. Moreover, there is concern that many years of cultivation may have affected the genetic structure of the scallop population. To approach these problems and concerns, we developed microsatellite markers as a molecular tool for population genetic studies. By using 4 microsatellite markers as well as a mitochondrial marker, we investigated the genetic structure of samples from the islands of Hokkaido (14 populations) and Honshu (Tohoku, 3 populations) in Japan, and south Primorye (4 populations) in Russia. All the populations sampled had high genetic diversity (average expected heterozygosity, 0.7011 to 0.7622; haplotype diversity, 0.6090 to 0.8848), and almost all showed a tendency of homozygote excess, which was significant in 2 populations. Hierarchical analysis of molecular variance tests based on the microsatellite and mitochondrial markers indicated that the 3 geographic regions were genetically divergent from one another, with little evidence of divergence within regions. Homogeneity in allele frequency distributions between natural and cultured scallops and allele frequency stability over a period of 2 decades indicated that the culturing operations have probably not had a substantial effect on the genetic structure of the populations.

Genetic structure of Japanese scallop population in Hokkaido, analyzed by mitochondrial haplotype distribution.

To examine the genetic structure of Japanese scallop populations (Mizuhopecten yessoensis) in Hokkaido prefecture, Japan, and compare it with those in the Aomori prefecture, we applied a method for lineage analysis based on sequence variation in a mitochondrial DNA segment (NcR2). After showing that there was a low probability of doubly uniparental inheritance of mitochondrial DNA in the scallop, we sequenced the NcR2 regions of 914 individuals from 15 populations (13 in Hokkaido and 2 in Aomori). In total, 103 different haplotypes were detected. Results of homogeneity tests for pairwise populations and the fixation indices indicated that significant heterogeneity (P < 0.0005) and structuring (pairwise fixation index F(ST) = 0.1606-0.4444, P = 0.0000; fixation index among groups F(CT) = 0.1549, P = 0.0078) could be inferred between the Hokkaido and Aomori groups, but not among populations within the groups. Moreover, heterogeneity of the haplotype distribution between populations of the 1980s and 1990s or 2000s at the 4 culturing areas was not observed (P > 0.05), and the haplotype diversity between them was not significant (P = 0.05), suggesting that the culture operations had not imparted a significant effect on the genetic structure during these periods.