Molecular Phylogeography Of Three Marine Fishes

In this study, the phylogeography and genetic structures of Pennahia argentata, Nibea albiflora and Ammodytes personatus were studied by mtDNA, AFLP and isozyme markers. We discussed the role of Pleistocene ice ages and present environmental factors in shaping the phylogeographic pattern and genetic structures of marine species.1,One hundred and thirty two individuals of Pennahia argentata were sampled from 12 localities throughout its distribution range, to estimate the demographic history and genetic structure based on mitochondrial DNA cytochrome b gene and control region sequences. Two distinct clades with net genetic divergence of 3% in the control region were detected, one in the Chinese coastal waters and the other in the Japanese coastal waters. These clades may have been isolated and diverged during Pleistocene low sea levels. Nucleotide diversity was much higher in the Chinese clade than that in the Japanese clade. The demographic history of the two clades was examined using neutrality tests and mismatch analyses, and the results indicated Pleistocene population expansion in both clades. Molecular variance analyses and pairwise FST revealed significant differentiation between two Japanese populations and lack of genetic structure in the Chinese populations. The significant geographic structure in white croaker suggests low level of dispersal in this species. The lack of phylogeographical structure in China coastal waters may reflect a recent range expansion after the last glacial maximum and insufficient time to attain migration-drift equilibrium.2,The genetic structures of four populations of P. argentata were analyzed by AFLP technology. A total of 304 putative loci were detected by the five primer combinations, of which 200 were polymorphic. The proportion of polymorphic loci among four populations varied from 47.13% to 57.63%. The population with the highest Nei's genetic diversity and Shannon diversity index was Ariake Sea population, the lowest Nei's genetic diversity and Shannon diversity index was found in Ise Bay population. Two clades were detected, molecular variance analyses and pairwise FST also supported the separation of Chinese and Japanese populations of P. argentata.3,To investigate the genetic structure and differentiation of different wild populations of P. argentata, horizontal starch gel electrophoresis was performed on 133 individuals collected from five different locations in China and Japan. The eleven enzyme systems revealed 15 putative loci, of which eleven were polymorphic. The proportions of polymorphic loci of P. argentata populations varied from 0.0667 to 0.5333; the mean observed and expected heterozygosity varied from 0.0033 to 0.0133 and 0.0032 to 0.0191, respectively. The heterozygosity revealed a low genetic variability for P. argentata in comparison with other marine fishes. The genetic distance among populations varied from 0.00005 to 0.00026. A weak differentiation observed within each clade; and no significant differences in gene frequencies among populations were observed in P. argentata. Among five populations, Chinese populations showed more genetic variability than that in Japanese populations.4,The population genetic structure and level of gene flow of Nibea albiflora from the Yellow and the East China seas were examined with a 479bp segment of mtDNA control region. A total of 65 samples were collected from three locations and 37 haplotypes were obtained. Mean haplotype diversity and nucleotide diversity for the three populations ranged from 0.9130±0.0308 (Zhoushan) to 0.9926±0.0230 (Xiamen), and from 0.0073±0.0043 (Qingdao) to 0.0099±0.0057 (Xiamen), respectively. AMOVA and pairwise FST revealed little genetic structure between the Yellow and the East China seas in N. albiflora. But based on the exact test of differentiation, the null hypothesis that N. albiflora within the Yellow and East China seas constitutes a panmictic mtDNA gene pool was rejected. This might be caused by the broad spawning areas but not by the Yangtze River outflow. Mismatch distribution revealed that N. albiflora has undergone population expansion, possibly before last 85,000–170,000 years. The existence of high gene flow between stocks in the studied area was supported by our results. Annual migrations, larval drift in the ocean currents, and recent range expansion could be the reasons for little genetic structure in the studied area.5,AFLP was used to analyze the genetic diversity of two populations of N. albiflora from Qingdao and Xiamen sea area. A total of 47 individuals were studied using five primer combinations. A total of 461 loci were detected, of which 265 were polymorphic. The results showed that the genetic diversity of these two populations was at the same level. The proportion of polymorphic loci, the Nei's genetic diversity and Shannon diversity index of Qingdao and Xiamen populations were 51.70% and 51.99%, 0.1022 and 0.0996, 0.1643 and 0.1622, respectively. Gst value, Shannon diversity index and AMOVA analysis indicated that the genetic variation mainly came from individuals within populations and there was no significant genetic differentiation between populations. Mismatch distribution analysis and dominant gene frequency revealed that these two populations have the same genetic population structure. The results of AFLP analysis indicated that there is no significant genetic differentiation between two populations due to high gene flow.6,To assess the role of historical process and contemporary factors in shaping population structures in the northwestern Pacific, mitochondrial control region sequences were analyzed to characterize the phylogeography and population structure of the Japanese sand lance Ammodytes personatus. A total of 429 individuals sampled from 17 populations through the species'range were sequenced. Two distinct lineages were detected, which might be divergent in the Sea of Japan and Pacific coastal waters of Japanese Island, during the low sea level. Significant genetic structure was revealed as expected between the Kuroshio and Oyashio Currents. However, significant genetic structure was also detected in the Sea of Japan, contracting expected homogenization hypothesis in Tsushima Current. The haplotype frequency of lineages in both sides of Japanese Island and significant genetic structure between north and south groups revealed that the distribution of lineage B and north group were highly limited by the annual sea temperature. The lack of lineage B in Qingdao populations with low sea temperature reflects the sea temperature barrier. Lack of genetic structure in the north group and south group populations indicate that ocean currents within groups facilitate the dispersal of A. personatus. 7,AFLP markers were also used to analyze the genetic structures of A. personatus and status of north and south groups. Two hundred and eleven individuals of A. personatus and 37 individuals of Ammodytes hexapterus were amplified by four primer combinations. The results showed north group and south group were reciprocally monophyletic. Complete reproductive isolation may exist between the two groups. These results suggest that the two groups have already reached a stage of sufficient genetic differentiation to be considered as two distinct species.