Studies Of Genetic Diversity On Pinctada Martensii And Sinonovacula Constricta

Studies on shellfish resources is getting increasingly urgent in recent years due to overfishing, polution, and loss of natural habitats caused by marine environment deterioration. We studied morphological characteristics, genetic diversity and genetic structure of Pinctada martensii off China coast and Sinonovacula constricta from northern China, utilizing morphological multivariate analysis and several molecular markers. For effective conservation and use of these two shellfishes, it is of great importance to obtain knowledge of their genetic background.To detect population diversity and population genetic structure of P. martensii, we sampled three populations (100individuals) from Guangdong (GD), Hainan (HN) and Guangxi(GX), covering its distribution off China coast. Then we measured and analyzed nine morphological characteristics, two mtDNA sequences (16S rRNA and COI), two ITS sequences and AFLP. Results of morphological analysis indicated that the nine characteristics were competent for distinguishing three populations. Principle component analysis and cluster analysis shown that there were little differentiation between two hatchery populations (GD and HN), while the differentiation between wild population (GX) and two hatchery population (GD and HN) bigger. Difference coefficients shown that these differences are that between geographic populations. Results of mtDNA shown16S rRNA and COI were too conservative for P. martensii population study. However, two haplotypes of COI in HN suggested a higher genetic diversity in this population. Nuclear sequences of ITS showed a high genetic diversity in three populations, with the HN hatchery popultion highest. There were small genetic distance and insignificant genetic differentiation between three populations, exihibiting similar genetic structures. AFLP analysis results also supported the high diversity, but the wild population (GX) showed highest genetic diversity. There were frequent gene flows between three populations. Taking account of the fact that parents of two hatchery population were collected from local wild seas, it’s reasonal to say there were frequent gene flows between wild populations from the three localities, to maitain a high level of genetic diversity. Introduction, exchanges of productive parents and damage of natural genetic structure caused by random expansion of cultured shellfishes in open seas may explain the frequent gene flows. Our results suggested the necessity of using more parents to avoid inbreeding on propagation, and those from natural populations were preferable. To prevent expansion of cultured shellfish in open seas, it’s compelling to strengthen the management of farms.S. constricta is eurythermal and euryhaline, with wide distribution and long history of culturing, there might be some genetic structure in the species. We collected181individuals from three populations in northern China:Dalian (DL), Qingdao (QD) and Dongying (DY), and did research on morphology, mtDNA (16S rRNA and COI) and two ITS sequences. Besides, we compared35haplotypes of COI from our study with125haplotypes from other nine populations, these12populations covered almost the whole distribution of S. constricta in China. Morphological analysis results showed high similarity between DL and QD, while differentiation between DY and the other two populations. Results of mtDNA showed genetic diversity was low in DY, and high in DL and QD; Differentiation between DL and QD was low. Though significant differentiation was detected between DY and the other two populations, they were not as great as that between species. ITS analysis showed high genetic diversity in three populations, DL and QD had a close relationship, while DY showed significant differentiation with the two. On comparison of COI sequences obtained from NCBI and our study, we found that S. constricta off China coast divided into two lineages, they were estimated to split off during late Miocene and middle Pliocene. The two lineages went through population expansion event, respectivly0.195-0.302Myr ago and0.183-0.281Myr ago. Neither lineage was regional, and both had several subdivision. The history of cultivation might be responsible for it. Though genetic differentiation of two lineages was not great as that between species, it is advisable that on account of significant genetic differentiation reginally management on different lineages of S. constricta should be taken to protect rear genes. At the same time, to accelerate the pace of effective breeding is a good solution to sustainable development of S. constricta.