| The Chinese surf clam (Mactra chinensis) is a commercially important bivalve in China. For its advantages of fast growth rate, high living density and high nutritional value, the Chinese surf clam is suitable for extensive breeding in Northern China, and has broad development prospects for aquaculture. However, due to over-exploitation and changes in environmental conditions, wild populations of the Chinese surf clam is threatened in recent years. At present, seeds for Mactra chinensis aquaculture mainly depend on collecting wild seeds, so insufficiency of seeds hampered the development of Mactra chinensis aquaculture industry. To protect current wild resources and formulate effective protective measures, it is essential to investigate genetic diversity of the Chinese surf clam with molecular techniques. It will also help promote the process of artificial breeding, and achieve sustainable development in aquaculture of Mactra chinensis. In the present study, polymorphic microsatellite markers were isolated from the Chinese surf clam by magnetic selective hybridization. To provide information for fisheries management and artificial breeding, genetic variation and population structure of Mactra chinensis in Northern China were investigated using these microsatellite loci. Phylogenetic relationships of Mactridae were analyzed based on partial sequences of mitochondrial COI and 16S rRNA genes. The main results are as follows:Nineteen polymorphic microsatellite loci were developed from genomic DNA of Mactra chinensis using magnetic selective hybridization. Polymorphism of the microsatellite loci were estimated with 30 Chinese surf clam individuals. The number of alleles varied from 3 to 24 per locus. The expected and observed heterozygosities ranged from 0.419 to 0.953 and from 0.000 to 1.000, respectively. The polymorphic information content (PIC) per locus ranged from 0.353 to 0.933, with an average of 0.790.Genetic diversity and population structure of nine Mactra chinensis populations in Northern China were investigated with microsatellites. Nine microsatellites revealed high allelic diversity with 14-36 alleles per locus. Observed and expected heterozygosity varied from 0.593 to 0.945 and from 0.638 to 0.958, respectively. Pairwise FST values indicated that all population pairs had small but significant genetic differentiation. Results of AMOVA analysis revealed that most of the variance was distributed within populations (97.50 %). A Mantel test showed statistically significant correlations between genetic distance and geographical distance, indicating that genetic differentiation of the Chinese surf clam conformed to a pattern of isolation-by-distance. Cluster analysis using neighbor-joining separated the eight populations into three groups. The three areas of low gene flow identified by barrier analysis corresponded with local oceanographic features, suggesting that marine currents and peninsulas play an important role in population structuring of this species.The partial sequences of mitochondrial COI and 16S rRNA genes from 36 specimens of 11 species of Mactridae were sequenced to infer the phylogenetic relationships and species-level identifications of the family Mactridae. Sequences of two other species in this family gathered from GenBank were included. In the analysis of COI gene, genetic variation between species exceeds variation within species, demonstrating that DNA barcoding gap existed in Mactridae. The barcoding gap based on 16S rRNA gene was not obvious. Except for X3 individual in Coelomactra antiquata, all species of Mactridae fell into reciprocally monophyletic clades with high bootstrap values in neighbour-joining and BI trees. The results indicate that Mactridae species can be efficiently identified through DNA barcoding. Phylogenetic relationships of Mactridae constructed with COI and 16S rRNA genes are almost consistent with traditional morphological classification. |
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