Molecular Phylogeography Of Six Marine Fishes In The Northwestern Pacific

In this study, the molecular phylogeography of Larimichthys polyactis, Cleisthenes herzensteini, Glyptocephalus stelleri, Tanakius kitaharai, Branchiostoma, Trichiurus japonicus in the Northwestern Pacific were studied by mitochondrial DNA marker. The phylogeographic patterns, genetic diversities and population structures of the six marine fishes were carried out and the population dynamics of historical evolution were also reconstructed in the present studies. We discussed the role of historical and contemporary factors in shaping the phylogeographic pattern and genetic structures of marine species.1,The genetic diversity and population genetic structure of the small yellow croaker (Larimichthys polyactis) were investigated.298 individuals were sampled from 16 localities ranged its distribution. Genetic variation in DNA sequences were examined from the first hypervariable region (HVR-1) of the mitochondrial DNA control region. High levels of haplotype diversity (h=0.992±0.002) in the HVR-1 region were detected, indicating a high level of genetic diversity. Hierarchical molecular variance analysis (AMOVA) and conventional population Fst comparisons revealed significant genetic structure throughout its range, which is inconsistent with previous findings based on the morphological and ecological studies. Two distinct lineages were found, which might be isolated and diverged in different marginal seas of the Northwestern Pacific during Pleitocene low sea level stands. There were strong geographical differences in haplotype frequencies of the 2 lineages. The star burst structure of the minimum spanning tree also suggested a very recent origin for most haplotypes. The demographic history of L. polyactis was examined by using neutrality tests and mismatch distribution analysis, which indicated a Pleistocene population expansion at about 61,000～245,000 years ago. 2,Intraspecific phylogenies can provide useful insights into how populations have been shaped by historical and contemporary processes. To determine the population genetic structure and the demographic and colonization history of Cleisthenes herzensteini in the Northwestern Pacific, one hundred and twenty-one individuals were sampled from six localities along the coastal regions of Japan and the Yellow Sea of China. Mitochondrial DNA variation was analyzed using DNA sequence data from the 5'end of control region. High levels of haplotype diversity (>0.96) were found for all populations, indicating a high level of genetic diversity. No pattern of isolation by distance was detected among the population differentiation throughout the examined range. Analyses of molecular variance (AMOVA) and the conventional population statistic Fst revealed no significant population genetic structure among populations. And according to the exact test of differentiation among populations, the null hypothesis that C. herzensteini within the examined range constituted a panmictic mtDNA gene pool was accepted. The demographic history of C. herzensteini was examined using neutrality test and mismatch distribution analyses and results indicated Pleistocene population expansion (about 94kya～376kya) in the species, which was consistent with the inference result of nested clade phylogeographical analysis (NCPA) showing contiguous range expansion for C. herzensteini. The lack of phylogeographical structure for the species may reflect a recent range expansion after the glacial maximum and insufficient time to attain migration-drift equilibrium.3,The demographic history and population genetic structure of blackfin flounder (Glyptocephalus stelleri) along coastal regions of Japan were investigated. Genetic variation in DNA sequences were examined from the first hypervariable region (HVR-1) of the mitochondrial DNA control region. High level of haplotypic diversity (h=0.99±0.004) was detected, indicating a high level of intrapopulation genetic diversity. The starburst structure of the minimum spanning tree (MST) suggested a very recent origin for most haplotypes. The demographic history of G stelleri was examined by using neutrality tests and mismatch distribution analysis, which also indicated a Pleistocene population expansion at about 124,100-413,400 years ago. Hierarchical molecular variance analysis (AMOVA) and conventional population Fst comparisons revealed no significant genetic differentiation existed throughout the examined range.4,The first hypervariable region (HVR-1) of the mitochondrial DNA control region was utilized for determination of genetic variation and population structure in willowy flounder (Tanakius kitaharai) collected from Aomori, Ibaraki and Niigata. A total of 35 haplotypes were detected among 66 individuals with a total of 30 variable sites out of 387 bp sequenced. Average sequence differences between populations (1.0 1.1%) were comparable to those within populations (0.9-1.2%), suggesting no genetic heterogeneity among samples. The pattern of distribution of genetic variability with high level of haplotype diversity (h=0.94) and moderate nucleotide diversity (n=1.0%) was also detected in the HVR-1 region of the mitochondrial DNA control region. AMOVA tests and the conventional populationΦst comparisons revealed no significant genetic structure among the populations. Partitioning populations into coherent geographic groups divided willowy flounder samples (Φct=-0.007, P>0.05) into two major groups:a Sea of Japan group composed of Aomori and Niigata populations; a Pacific Ocean group composed of Ibaraki populations. The minimum spanning tree constructed with 35 haplotypes showed four low-divergent clades, corresponding to those defined in the NJ tree. However, these clades did not appear to have geographic structure. Altogether, the results indicate that willowy flounder is panmictic throughout the examined range in Aomori, Ibaraki and Niigata.5,It is commonly accepted that the Branchiostoma lancelets in South and North China belong to Branchiostoma belcheri belcheri (Gray,1847) and Branchiostoma belcheri tsingtauense (Tchang and Koo,1934), respectively. Three partial mitochondrial DNA (mtDNA) fragments of cytochrome oxidase c subunit I (COI), cytochrome b (Cytb), and 16S ribosomal RNA (16S rRNA) genes were sequenced to analyze phylogenetic relationships of the Branchiostoma lancelets from South (Xiamen) and North (Qingdao and Rizhao) China, and phylogenetic trees constructed also included the existing data from Japanese waters. The genetic distances of the lancelets between South and North China averaged 0.19,0.21, and 0.17 based on partial sequences analysis of COI, Cytb, and 16S rRNA genes, respectively, which were much higher than those were observed in other intraspecific variations. However, the value between North China and Japanese waters was only 0.01 based on partial sequences analysis of three mtDNA genes, which indicated low intraspecific genetic divergence existed in the two areas. The results also clearly indicated two monophyletic clades (clade A (North China and Japanese waters), clade B (South China)) existed in the specimens, corresponding to the South and North China, respectively. Above all, our results indicate that the Branchiostoma lancelets in South and North China should belong to different species, and the subspecies B. belcheri tsingtauense together with the lancelets in most Japanese waters is an independent species. According to the rule of priority and present studies, the Branchiostoma lancelets in North China and most Japanese waters should be revised to B. tsingtauense. The divergence time between B. belcheri and B. tsingtauense was estimated at about 39.90-43.24 million years ago.6,The genetic diversity and population genetic structure of Trichiurus japonicus were investigated. Fifty-four individuals were sampled from 3 localities of East China Sea and South China Sea. Genetic variation in DNA sequences were examined from the mitochondrial DNA control region. High levels of haplotype diversity (h=0.98±0.01) in the control region were detected, indicating a high level of genetic diverstiy. A total of 42 polymorphic sites were found, and 40 haplotypes were defined. The pairwise nucleotide differences between samples ranged from 4.65±2.38 to 4.87±2.48. The demographic history of T. japonicus was examined by using neutrality tests and mismatch distribution analysis, which indicated a Pleistocene population expansion at about 49,300-197,000 yeas ago. The star burst structure of the minimum spanning tree also suggestted a very recent origin for most haplotypes. Hierarchical molecular variance analysis (AMOVA) and conventional population Fst comparisons revealed no significant genetic structure throughout the examined range. And according to the exact test of differentiation among populations, the null hypothesis that T. japonicus within the examined range constituted a panmictic mtDNA gene pool was accepted. Recent population expansion and larval dispersal likely have contributed to the genetically homogeneous population structure of the species. The knowledge on genetic diversity and genetic structure will be crucial to establish appropriate fishery management stocks for the species.