Population Genetic Studies In Razor Clam (Sinonovacula Constricta)

To better protect and 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 two sections.1. High variation and low differentiation in wide ranging Razor clam (Sinonovacula constricta):insights from AFLPThe genetic variation and differentiation of the razor clam S. constricta distributed along the coast of China from north to south was studied through amplified fragment length polymorphism (AFLP). Six primer combinations generated 193 fragments. The He values varied from 0.322 to 0.463 and the percentage of polymorphic loci ranged from 74.1% to 98.4%, which indicates a high level of genetic diversity. Cluster analysis by Nei's pairwise distances grouped all specimens by geographical origins. AMOVA consistently showed that genetic variations among populations were very low (8.71%), and most of the variations came from the genetic variation within populations (91.29%). Genetic differentiation among the six populations is low as indicated by pairwise Fst (0.0282-0.1480), which indicated that S. constricta populations along the coast of China are genetically linked. Among all the six populations, the Beihai one is more differentiated from the others, suggesting that Hainan Island and Leizhou Peninsula may act as barriers of gene flow. All populations abide to isolation by distance model as indicated by Mantel test, except for ZS(Zhoushan) and YQ(Yueqing) populations. Information obtained in this study will provide guidelines for conservation and fishery management of this species in the future.2. Genetic variation of wild population of the Razor clam Sinonovacula constricta Lamarck assessed by microsatellite markersGenetic diversity and differentiation of razor clam S. constricta populations from the coast of China were studied based on ten microsatellite loci. All loci displayed high polymorphism for all six S. constricta populations, with an average number of allele per locus of 4-10 and an average expected heterozygosity of 0.824-0.853. Significant departures from Hardy-Weinberg equilibrium and deficits of heterozygotes were observed over most populations at each locus, which can be explained by null alleles. The pairwise Fst indicate moderated genetic differentiation among all populations except DL, BZ, and LYG, of which genetic differentiation are little. According to the neighbor-joining tree constructed on the basis of the DA distance, the six populations fell into three regional groups (the North,the Middle and the South group), showing that the the Hainan Island-Leizhou peninsula and the inflow of Yangtze river may act as two major gene flow barriers.