Population structure of Fraser River chinook salmon (Oncorhynchus tshawytscha): an analysis using microsatellite DNA markers

Microsatellite DNA analysis was applied in a genetic study of 20 chinook sa lmon populations from four regions within the Fraser River drainage of Brit ish Columbia, Canada. Twelve populations were represented by samples collec ted in different years. A total of 2612 fish were examined at three microsa tellite loci. Each locus was highly polymorphic, with 30 alleles at Ots101, 28 alleles at Ots100, and 35 alleles at Ots102. Average observed heterozyg osities were 86%, 88%, and 71%, respectively. In a dendrogram analysis of p airwise genetic distances, four geographically based groups were observed c onsisting of the lower Fraser River, the middle Fraser River, the upper Era ser River, and the Thompson River. An analysis of molecular variance showed that 97.57% of the genetic variance was within populations and 1.80% of th e genetic variance was partitioned among populations. We detected significa ntly different allele frequencies among populations within regional groupin gs and temporal stability in allele frequencies in populations for which mu ltiple years of samples were analyzed. Regional divergence may reflect colo nization patterns following the last ice age, and divergence among populati ons within regions may reflect local adaptation. The elucidation of populat ion structure of chinook salmon of the Fraser River watershed will be usefu l information for management designed to conserve genetic biodiversity.