Molecular Phylogeography Of Two Marine Fishes In Northwestern Pacific And Application Of Molecular Marker In Fishery Stock Enhancement Of Paralichthys Olivacens

In the present study, mitochondrial DNA and AFLP were used to estimate the phylogeographic patterns of two marine fishes in Northwestern Pacific, Synechogobius ommaturus and Trachurus japonicus. To assess the genetic divergence between cultured and wild populations, track the released fish and evaluate the effect of stock enhancement, these two molecular markers were also used to study Paralichthys olivacens across China coastal area. The results of the present study were as follow:1. Molecular phylogeography of Synechogobius ommaturus and Trachurus japonicus:(1) The species validation of Synechogobius hasta was studied by comparing the morphological and genetic variability of S. ommaturus and S. hasta. The analysis results of morphological characters showed that the differentiation of meristic counts between two species was not significant, and the significant differentiation mainly existed among the measurable characters. The morphological results revealed that the significant differentiation was mainly the result of variation of measurable characters rather than meristic counts between these two species. The head length of S. hasta was relatively shorter, whereas the tail fin length was relatively longer than S. ommaturus. The genetic distance between two species was only 0.006 based on partial mitochondrial control region sequence, which is similar with distance intraspecies. The topology constructed by NJ and MP method also showed no striking variations between two species. The results indicated that S. hasta should not be regarded as a valid species, which could be the synonym of S. ommaturus.(2) To examine population genetic structure of spottedtail goby Synechogobius ommaturus, a 478-bp fragment of the hypervariable portion of the mtDNA control region was sequenced and used to interpret life history characteristics and larval dispersal strategy. One hundred and eighty six individuals from 10 locations on the coasts of China and Korea were analyzed, and 44 haplotypes were obtained. Higher levels of haplotype and nucleotide diversity were found in East China Sea populations than in other populations. Both the phylogenetic tree and minimum spanning tree showed that no significant genealogical structures corresponding to sampling locations existed. AMOVA and pairwise Fst revealed significant genetic differentiation between populations from Korea and China (φst=0.16; P<0.01). A significant isolation by distance pattern was observed in this species (r=0.53, P<0.001). Both mismatch distribution analysis and neutrality tests showed S. ommaturus to have experienced a recent population expansion.(3) Larval dispersal may have an important impact on genetic structure of benthic fishes. To examine population genetic structure of spottedtail goby S. ommaturus, samples from five different locations of China and Kunsan population in Korea were analyzed by using AFLP technology. The average gene diversity and Shannon's information index were low for S. ommaturus (h=0.067-0.088; I=0.105-0.140). The pairwise Fst values ranged from 0.022 to 0.201. The results of AMOVA analysis indicated that 90.54% of the genetic variation contained within populations and 9.46% occurred among populations. No significant genealogical branches or clusters were recognized on the UPGMA tree. The results support the hypothesis that larval dispersal ability can be responsible for the genetic diversity and population structuring.(4) Trachurus japonicus, widely distributed from China, Korea to Japan, is a pelagic fish. Severe climatic shifts by Pleistocene ice ages can produce great changes in species'geographical distribution and abundance, which can be expected to have genetic consequences. Two populations from the South China Sea and 6 populations from the coastal waters of Japan containing 186 individuals were analyzed in the present study. All the populations of T. japonicus showed high haplotype diversity (h=0.9644-1.000). The results of the NJ tree and minimum spanning tree showed no significant genealogical branches or clusters corresponding to sampling localities. The pairwise Fst values (-0.019-0.052) and the results of AMOVA analysis indicated there was no genetic divergence among different geographic populations. Both mismatch distribution analysis and neutrality tests (Fs=?24.579, P=0.000; D=-1.418, P=0.047) indicated T. japonicus to have experienced a recent population expansion. Pleistocene ice ages had a major impact on the phylogeographic pattern of T. japonicus.(5) AFLP was used to investigate the population genetic structure of T. japonicus. Samples from 2 populations in China and 6 populations in Japan were analyzed. T. japonicus showed high gene diversity and Shannon's information index (h=0.107-0.210; I=0.176-0.325). No significant genealogical branches or clusters corresponding to sampling localities were detected by UPGMA tree. The results of AMOVA analysis and pairwise Fst values (0.016-0.107) showed no genetic divergence among different geographic populations and high gene flow was existed. The results of AFLP were in accordance with the results of mtDNA.2. Application of molecular marker in fishery stock enhancement of Paralichthys olivacens(1) To examine the present population genetic diversity and variability of Paralichthys olivacens, a 394-bp hypervariable fragment of mtDNA control region was sequenced. A total of 215 individuals from 2 wild and 8 cultured populations were analyzed. The genetic diversity of cultured populations (h=0.443-0.844; I=0.010-0.030; k=3.745- 11.838),was obviously lower than that of the wild populations (h=0.987-0.989; I=0.031-0.032; k=12.320-12.718). Pairwise Fst and AMOVA revealed that significant genetic differentiation mainly existed among cultured populations and. It may be due to farm propagation and low number of broodstock.(2) Moreover, mtDNA was successfully used to distinguish the released individuals in the present study. However, there were still some individuals that can not be distinguished from wild ones. More exact background information about broodstock and F1 should be collected to establish the haplotype database for further study.(3) To further study genetic divergence between cultured and wild populations of P. solivacens by nuclear gene, 2 wild and 4 cultured populations were analyzed by AFLP. The gene diversity and Shannon's information index of cultured populations (h=0.130-0.150; I=0.201-0.236) were similar with wild populations (h=0.123-0.136; I=0.199-0.220), which is not in accordance with the results of mtDNA. The UPGMA tree showed some small clusters corresponding to the different hatchery, but haplotypes of cultured populations were mixed with haplotypes of wild populations. Pairwise Fst and AMOVA revealed significant genetic differentiation among them.