Population Genetics Of The Ark Shell, Scapharca Kagoshimensis

The ark shell Scapharca kagoshimensis, which lives in the muddy sediment of shallow coastal waters of the northwestern Pacific, is a commercially important bivalve species in China, Japan and Korea. However, due to the current huge market demands and over-exploitation of near-shore environment, natural resources of this species have been declining dramatically in recent years. Therefore, the genetic conservation and genetic survey are becoming essential to ensure that genetic diversity of this species is not seriously eroded and evolutionary potential of wild populations is protected.1. Development of microsatellite markers from S. kagoshimensis and their validation in parentage assignmentSince microsatellite markers are useful tools in analysis of genetic diversity and population structure, we present development and multiplex genotyping of 20 microsatellite markers into 7 di-and triplex PCR panels for S. kagoshimensis to help promote the genetic conservation for the species in the future. These loci were screened from an enriched genomic library constructed with 5’-biotinlabeled oligoprob (CA)12 and streptavid coated magnetic beads.The number of alleles per locus ranged from 5 to 26. Observed and expected heterozygosities ranged from 0.563 to 0.886 and from 0.733 to 0.960, respectively. After sequential Bonferroni correction,2 of the 20 loci deviated significantly from HWE probably due to the excess of homozygotes. There was no evidence of linkage disequilibrium between one pair of loci. These markers will be useful for conservation of genetics resources of S. kagoshimensis.2. Genetics of S. kagoshimensis local populations12 local populations of S. kagoshimensis were collected from China offshore. Mitochondrial DNA sequence DNA markers were used to estimate the genetic diversity and population structure of these samples. Based on genetic structure and phylogenetic inferences, we identified 2 evolutionary significant units (ESUs). We concluded that freshwater discharge from the Yangtze River is especially important in determining the separation of S. kagoshimensis.3. The study of genetic diversity in cultured and wild poplations of S. kagoshimensisFive cultured populations and two wild populations of S. kagoshimensis were examined at 10 microsatellite loci. The genetic diversity of each populattion and relationships among populations were assessed. The result indicated that there was no significant reduction in allelic richness and expected heterozygosity between cultured and wild populations. Genetic divergence parameters, such as FST and genetic distance (Dc), showed that the differentiation between cultured and wild populations was significant. These results obtained in this study indicated that a larger brood stock number might be responsible for the high genetic diversity of the culture populations.4. Effective population size estimation in mass spawning ark shell, S. kagoshimensis based on microsatellite analysisEight polymorphic microsatellite loci were used detected to determine pedigrees in a mass spawing of S. kagoshimensis and to estimate the effective breeding population size. A total of 240 offspring were tested successfully,8 candidate fathers and 7 candidate mothers were analysed. The result indicated that real pedigree analysis were consisted with simulation result and more than 95% offspring were successfully assigned to their parents. The parents and offspring had similar allelic diversity and observed heterozygosity levels, but expected heterozygosity were decreased significantly in offspring populations. Because of the different contribution of each parent, the effective breeding population size were declined to 10.69. The inbreeding rate of the mass spawning population was only 1.4%. These result suggested that use enough a large number of parents for reproduction was important since males and females contributed to next generation unequally.