Population Genetics Of Pacific Herring And Pacific Cod In North Pacific

Marine fish usually exhibited three genetic structuring patterns (i. little genetic differentiations, ii. small but significant genetic differentiations, iii. large genetic divergence with phylogenetic lineages) and three phylogeographic patterns (i. deep phylogenetic break with lineages allopatric, ii. deep phylogenetic break with lineages sympatric, iii. shallow phylogenetic relationship or no genealogy structure). All these patterns of genetic variations involved historical climatical fluctuations, contemporary marine environment factors and life-history traits of marine fish. Pacific herring and Pacific cod are two commercially important fish species in North Pacific. They were considered derived from an Atlantic invader by trans-Arctic dispersal. Large glacial-interglacial circles in Pleistocene and unique oceanographic characters of North Pacific may have influenced heavily the population structuring and phylogeographic patterns in the two species.Morphological, mitochondrial DNA sequence and microsatellite DNA markers were used to estimate the population structure and phylogeographic pattern of Pacific herring in North Pacific, the divergence between Pacific herring and Atlantic herring was also discussed.(1) Meristic and morphometric characters were compared by multivariate analysis for eight populations of total 424 individuals, significant differences were found in means of all these characters among eight populations, and a latitudinal cline was observed in several morphological characters.(2) Three high distinct lineages were detected in 318 individuals from nine populations across the range of the species based on sequence variations of mtDNA control region, which might be isolated and diverged during glacial periods of Pleistocene. One lineage dominated the Northwestern Pacific, while the other two lineages occurred secondary contact in Eastern Pacific. The frequency difference of the three lineages in 9 populations defined two geographic groups, a Northwestern Pacific group and an Eastern Pacific Group.(3) High significant genetic differentiations were found among 9 populations by scanning 9 microsatellite loci variations, which subdivided populations into three groups. This grouping picked up the Yellow Sea population as an independent group. Sea water temperature barriers from Kuroshio Current and Tsushima Current might restrict the gene flows between populations in Yellow Sea and other locations.(4) MtDNA control region sequences were used to investigate temporal population structure of Pacific herring which were collected from three different periods in Yellow Sea. No significant genetic differentiations were detected among the three populations and the result suggested populations in Yellow Sea belong to a single panmictic stock.(5) An Atlantic herring population was also analyzed as an outgroup to discuss the origin and evolution of Pacific herring. Meristic and morphometric characters were compared between the Atlantic herring population and a Pacific herring population from Yellow Sea. A discriminant formula was created with 11 character parameters, and the accuracy was 98.8%. MtDNA variations were analyzed using sequence data from cytochrome b and control region. Based on 8.1% net genetic distance in control region, we postulated the divergence in mtDNA between the two species occurred at about 1.25 million years ago. Three lineages of Pacific herring were considered to diverge during late Pleistocene. Mismatch distribution analyses indicated population expansion in both species. MtDNA sequence and microsatellite DNA markers were used to estimate the population structure and demographic history of Pacific cod in North Pacific.(1) MtDNA control region were analyzed for 259 individuals from nine localities over the species'range. The result showed lack of genealogical structure and remarkably low control region diversity. Small but significant genetic differentiations were detected among Northwestern Pacific populations. Four populations from coastal North America exhibited a trend of isolation by distance. (2) Small but significant genetic structure was also found in four populations of Northwestern Pacific based on microsatellite analyses. Like Pacific herring, large genetic differentiations between the Yellow Sea population and other populations might be also attributed to sea water temperature barriers. Contrary to mtDNA result, microsatellite analyses revealed relative high genetic diversity for Pacific cod.We interpreted such discordance between mitochondrial and microsatellites might be caused by the four-fold higher rate of drift for mtDNA than nuclear genes and fairly high mutation rate for microsatellite DNA. Both mtDNA and microsatellite results suggested a recent bottleneck in Pacific cod.