Analysis On Genetic Diversity In The Wild Population Of Sea Cucumber (Apostichopus Japonicus) In Weihai

There are 40 kinds of edible holothurians throughout the world, about 20 of which documented in China seas. Sea cucumber Apostichopus japonicus, known as "the king of the holothurians", is one of the most high quality and nutritious holothurians. It is an important marine economic species as well as an endangered one. It is mostly found in shallow waters around North Pacific Ocean, with its north geological boundaries at Sakhalin Russia and coastal areas at Alaska USA, and Kagoshima Japan, Korean peninsular to the south. In China, it distributes in the coastal areas in Shandong, Liaoning and Hebei provinces, mostly in Weihai, Yantai, Dalian and Changshan island. Due to the high quality of the sea cucumber A. japonicus in these natural coastal areas, they are publicly renowned for their tonic effects.With the prosperity of holothurian culture industry, problems in the research, protection and management of its germplasm have emerged in recent years. To prevent the degradation of the germplasm of holothurian in the process of marine culture, and to sustain higher population genetic diversity, finally to effectively protect and utilize the quality germlasm sustainably, it is necessary and urgent to carry out genetic diversity research on holothurian in these areas.Concerning the advantages of mtDNA in the conservation genetics, CO I was amplified via the polymerase chain reaction and 16S rDNA was cloned, respectively. In contrast with other sequences, the genetic diversity in the wild population of the sea cucumber A. japonicus in Weihai was analysed.Fragments from two mitochondrial genes of 35 sea cucumber samples were sequenced. Analysis of gene fragments indicated that 28 and 22 variable sites were determined, 17 and 6 haplotypes were identified respectively in CO I and 16S rDNA. The mean A+T content of CO I and 16S rDNA was 58.9% and 56.2%, which exceeded the content of G+C.Haplotype diversity was 0.902+/-0.030 and 0.334+/-0.097, nucleotide diversity was 0.00699+/-0.00107 and 0.00148+/-0.00065, respectively, showing a high level of genetic diversity and germplasm in this species. This also indicated that 16S rDNA was more conservative than CO I in the evolution of mtDNA.High rate of synonymous vs non-synonymous substitution (d_S / d_N) suggested negative selection, which was also proved in neutrality test in the two fragments from two mitochondrial genes.The phylogenetic tree was constructed with sea urch Stronglocentrotus nudus as outgroup. Sequences of Rongcheng, Laizhou, Yantai, Qingdao, Dalian, Japan and Russia were used to root the tree. The results showed that the sea cucumber A. japonicus in Weihai may have genetic flow with other populations, which was also proved in MJN and TCS network.Through the analysis of two fragments of mitochondrial DNA sequences from the wild population of sea cucumber A. japonicus in Weihai area, this research had laid down a fundamental basis for the assessment of genetic diversity and germplasm resources of the local sea cucumber at the population level, and several valuable suggestions for the efficient management of the sea cucumber population in Weihai area were put forward.