Molecular Phylogeography Of Gadus Macrocephalus Tilesius

Gadus macrocephalus (pacific cod) belongs to the family Gadidae, the genus Gadus. The species is widely distributed in the north coast of Pacific Ocean. It is a commonly occurring fish found from the north coast of California to Japan and from Russia to the north coast of the United States. In china, it is mainly distributed in Shi Dao fishery ground, on the coast of Shandong Province, and Haiyang Dao fishery ground, on the coast of Liaoning Province. It is an important commercial fish in the world.As one of the most important economic fishes in China country, even common to the world, the resources of the pacific cod have declined significantly in the recent years. Though it is an important economic fish in the world, there are few reports on the research of the pacific cod both at home and abroad, and there is even no research on the molecular phylogeography at the present time.Making use of the mitochondrial DNA sequences analysis together with RAPD analysis, this research studies the molecular phylogeography of the pacific cod at different levels. This paper not only showed the genetic structure and genetic diversity of the pacific cod populations, but also discussed the spatial distribution pattern of the population genetic variability, evolutionary history of the population and impact of quaternary palaeoclimate changes on the pacific cod.To estimate the demographic history and genetic structure of pacific cod in the Northern Pacific, 252 individuals were sampled from 10 localities throughout the distribution range of the species. A fragment of 456bp of the 5` end of mtDNA control region was analyzed. Total number of polymorphic sites was 68 polymorphic sites, defined by 75 haplotypes. Moderate haplotype diversity (h) and low nucleotide diversity (л) were found among the populations. No significant genetic structure was found according to the AMOVA analysis among the stocks. Both neutrality test and mismatch distribution analysis indicated population expansion in the species.Forty oligonucleotide primers (S81-S100, S361-S380) were screened and 13 were selected to amplify genomic DNA from 124 samples representing 4 populations. A total of 122 DNA bands were scored among the 4 populations, and 89 polymorphic bands were found. Shannon's information index (H0) of the 4 populations were 0.3201~0.3651, which shows low genetic variation. The result showed that 4.95 percent of genetic variation was distributed among populations and 95.05 percent within populations. Genetic diversity index (Gst) indicated there was no significant genetic differentiation among different pacific cod populations.