Preliminary Study On Genetic Diversity Of Copepods In The Yellow Sea And The East China Sea

Copepods, a subclass of the subphylum Crustacea, may be the most numerous multicellular organisms on earth, and they are an important part of marine zooplankton. Currently, there are approximately 11500 known species of copepods divided among about 200 families. Copepods are of particular importance to marine ecosystems because they are a dominant primary consumer and are consumed by everything from invertebrates to fish larvae to whale. Three parts are included in this study. The first part is to discuss the application of mtDNA sequence to the taxonomic identification on the basis of mtDNA gene fragment sequence analysis, and another two parts are using mtDNA gene fragment sequence analysis and Inter-simple sequence repeat (ISSR) respectively to estimate genetic diversity and population structure of copepods in different sea areas.Accurate identification is the precondition and base of life histories, population structure and evolution research. Rapid evolution and unrecombination are characteristic of mtDNA sequence and these make it a strong tool of identification. In this study, we amplify the mtCOI gene fragments of four Calanoid copepods that were collected from the East China Sea. After sequencing, the DNA sequence of a 658bp of mtCOI is determined. When these sequences are compared with those of other copepods, the result shows that there is significant genetic divergence between species, which can be used to reconstruct the phylogenetic relationship among the species. The protocol, based on mtCOI sequence variation, is quite propitious to identify naupliar stages and copepodid stages. Discrimination of all life stages is essential to understanding recruitment and other population dynamic processes of zooplankton assemblage.ISSR is used to estimate genetic diversity and structure of the two populations of Euchaeta plana which belong to the Yellow Sea and the East China Sea. Four primers are selected. The genetic flow Nm is 4.7667 and the gene differentiation coefficient Gst is 0.0949. The result demonstrates that the two populations have high level of similarity but low level of differentiation. These results reveal that the high level of gene flow leads to high genetic identity between the two populations. Euchaeta plana is a warm water species, and appears in the North of Yellow Sea in winter. Some researchers find that the appearance of this species in the Yellow Sea is the consequence of transportation by the Yellow Sea Worm Current (YSWC), which may explain why the two populations have high genetic identity. The distribution pattern of Euchaeta plana shows clearly that the YSWC flows beneath the surface northwards into the Yellow Sea along the Yellow Sea trough, so it can be used as a bio-indicator of YSWC. Further study of Euchaeta plana will make us better understand the relationship between the environments and orgnisms.Currently, DNA sequence analysis is the most accurate protocol to detect the genetic diversity at molecular level. In this study we extract the genome DNA of Calanus sinicus of three populations collected from the Yellow Sea and the East China Sea, and amplify the mtCOI gene fragments for sequencing. Among the 54 individuals, 36 polymorphic sites and 25 haplotypes are detected. The base composition is 23.63%,19.70%,22.72% and 33.95% for the average contents of A, C, G, T. The result indicates that the genetic differentiation of the three populations is at a low level. When we analysis the distributing of the 25 haplotypes, we find that they show regularity among the three populations. However, they do not form evident clades in NJ tree. So, we need more research to determine the genetic differentiation of Calanus sinicus.