Molecular Analysis Of Population Of Nemipterus Virgatus In The Northern Continental Shelf Of South China Sea

Population is the basic units for species to live, to reproduce and to evolute, as well, it's also the basic units of community and researches , development and management . The continental shelf of northern South China Sea is the most important districts of fishery . Nemipterus virgatus is one of the most important commercial fishes in the continental shelf of northern South China Sea, which belongs to Nemipterus in Nemipteridae of Perciformes.This research is study the population of N.virgatus in the continental shelf of northern South China Sea by molecular methode, which is based on the morphological characteristic. The population analysis research are focused on the difference of the mitochondrial DNA control region and Cytochrome oxidase subunitⅠ.And the sequence analysis of some other Nemipterus are also studied by comparing the Mitochondrial COⅠGene and Cyt b Gene. Both the population analysis and the sequence are in order to provide theoretical guidance to the exploitation and utilization of fishery resources, as well, to provide information of fishery resources in the rights of China's maritime rights and interests . The main contents are organized as the following : 1. In order to estimate the population of Nemipterus virgatus which are distributed in the northern continental shelf of South China Sea, we amplified 99 mitochondrial control region (D-loop) gene fragments of 5 different geographic populations (B,ZJ,M,DG and SW) by PCR, and examined 472 base-pair nucleotide sequences of D-loop. The results show that all 99 sequences group into 36 haplotypes, and there is one haplotype is shared among 5 different geographic populations. The average contents of the basic group A,T,G,C are 34.1%, 30.4%, 15.6%, 20.0%. After calculating the genetic distance with Kimura-2-parameter model and the fixation index (FST) between species, the results show that the genetic distance between species are only between 0.002-0.003 and the FST are between 0.00201-0.02034. Analysis of molecular variance (AMOVA) indicates that the genetic variability within groups is 98.30% and that among groups is only 1.70%. The genetic structure difference mainly different within populations. Nm also show that the exchange in gene in the 5 geographic populations is frequently. And molecular phylogenetic trees constructed with Collichthys lucidus and Euthynnus pelamis as outgroups using maximum-parsimony (MP) and neighbor-joining (NJ), which suggests that the 5 different geographic populations are all intermix together and those are one population. The higher haplotypes proportion, lower nucleotide diversity and the results of Neutrality Tests by Tajima's D all show that there were an expansion in the history, and maybe the ZJ population was the original population.2. The mitochondrial cytochrome COⅠgene fragment (644bp) of N.virgatus,which are distribute in 4 different geographic populations (B, M,DG and SW) were analysised by PCR. The results show that all 79 sequences group into 11 haplotypes, and there is one haplotype is shared among 4 different geographic populations. The average contents of the basic group A,T,G,C are 30.8%,26.7 %,23.8%,18.8 %. And the Dxy of mtDNA COⅠsequences between the 4 N. virgatus populations are 0.00040-0.00068 After calculating the genetic distance with Kimura-2-parameter model and the fixation index (FST) between species, the results show that the genetic distance between species are only between 0.000-0.001 and the FST are between 0.00032-0.74074. Analysis of molecular variance (AMOVA) indicates that the genetic variability within groups is 41.40% and that among groups is only 58.60%. That maybe because of the conservative characteristics of COⅠsequences.Molecular phylogenetic trees constructed with Scolopsis taenioptera and Eucinostomus currani as outgroups using maximum-parsimony (MP) and neighbor-joining (NJ), which suggests that the 5 different geographic populations are all intermix together.All the COⅠsequences datas show that there were an expansion in the N.virgatus history,and the 4 different geographic populations are belongs to one population.3. This research also studied the relationship between N. virgatus, N. japonicus, N. bathybius, N. nemurus and N. mesoprion by compared with the COⅠ(659bp) and Cyt b (425bp). The average contents of the basic group A,T,G,C are 23.2%, 31.8%, 26.3%, 18.7% in the COⅠgene fragment, and 25.1%, 30.5%, 28.2%,16.2% in Cyt b gene fragment. The G basic group is the least one basic group in both two gene fragments.The datas of the two gene fragments are all showing that N. japonicus and N. nemurus have a very closed relationship and even maybe should be dividied into one species. N. japonicus and N. nemurus are equality in the evolution, and they are the top in the phylogenetic trees which means they maybe the latest species of the 5 in Nemipterus.The 5 species still belong to the same genera ,because of the difference between the 5 are not reach the standard of different genera and N. japonicus and N. mesoprion are not in the same phylogenetic branch. Molecular evolution rate(2% every million year in Cyt b ) showed the divergence of 5 Nemipterus species occurred during the middle pleistocene epoch.