Population Genetic Studies In Zhikong Scallop (Chlamys Farreri) And Xishishe Clam (Coelomactra Antiquata)

To better protect and effectively utilize bivalve resources in China, molecular genetic analyses in commercially important bivalves are necessary, which are also basic to study on shellfish genetic breeding.This dissertation consists of three sections.1. Isolation and characterization of EST-derived microsatellite markers for Zhikong scallop (Chlamys farreri)169 SSRs (simple sequence repeats) were identified among 3466 ESTs (expressed sequence tags) of zhikong scallop (C. farreri). 15 EST-SSR markers were detected polymorphisms of the thirty SSR primer pairs derived from C. farreri ESTs. The number of alleles per locus ranged from two to 13, with an average of 6.3 alleles per locus. The expected and observed heterozygosities ranged from 0.282 to 0.864 and 0.267 to 0.867, respectively. These loci were further tested for their cross-species transferability to bay scallop (Argopecten irradians irradians) and Japanese scallop (Patinopecten yessoensis). Because of their high level of polymorphism and transferability, those 15 EST-SSR markers will be valuable tools for many genetic approaches not only in C. farreri but also in related species.2. Inheritance of AFLP markers and their use for genetic diversity analysis in wild and farmed Zhikong scallop (C. farreri)Inheritance patterns of amplified fragment length polymorphism (AFLP) phenotypes were tested in three full-sib families of Zhikong scallop Chlamys farreri. Overall, 9.3% of analyses exhibited non-Mendelian segregation ratios before Bonferroni correction, with 0.8% significant after correction, demonstrating that AFLP markers can be considered Mendelian traits. AFLP markers were used to investigate levels of genetic diversity within cultured populations of C. farreri and to compare them with the wild populations. Six pairs of primers generated 293 loci among 139 individuals in four cultured and two wild populations. High polymorphism at the AFLP markers was found within both cultured and wild C. farreri populations. The expected heterozygosity ranged from 0.291 (hatcheries) to 0.295 (wild), while the percentage of polymorphic loci ranged from 92.1% (hatcheries) to 93.9% (wild), respectively. This suggests that more than 30 years of artificial cultivation have not substantially reduced the genetic variability of the cultured populations of C. farreri. Significant genetic differentiation was observed between the cultured populations, and between the cultured and wild populations. The information derived from this study is useful for future genetic improvement by selective breeding, and for designing suitable management guidelines for these genetic materials.3. Microsatellites analysis on genetic variation in wild populations of xishishe clam (Coelomactra antiquata)C. antiquata is a commercially exploited bivalve, and its populations have been severely declining in the coast of China during the last decade. In order to provide guidelines for conservation strategies and management programs, genetic diversity of five wild populations of the clam C. antiquata (Spengler) from coast of China was analyzed using five microsatellite markers, and the degrees of genetic differentiation between them were compared. The allelic diversity in terms of number of alleles per locus and expected heterozygosities in wild populations (N=10-26, He=0.591-0.901) was very high; Allele distributions at all five microsatellites indicated that there are some rare alleles belonging to wild populations. Moreover, significant genetic differentiation between the Changle population and other four wild populations was detected using Fst values. Genetic structuring between the Changle and other populations could be the result of short planktonic phase, limited diffusivity of C. antiquata and the barrier caused by the outflow of freshwater at the delta of Yangtze River.