Genetic Population Structure and Origin of Life History Types in Chinook Salmon in British Columbia, Canada

Abstract

We used protein electrophoresis to examine genetic population structure and origin of life history types of chinook salmon Oncorhynchus tshawytscha in British Columbia, Canada. Among 31 allozyme loci resolved in 91 samples from 63 populations of chinook salmon in rivers and hatcheries throughout British Columbia, population heterozygosities averaged 0.084 (range 0.048–0.108) and were typical of values for populations in other regions. A hierarchical gene diversity analysis indicated that 91.3% of the total allele-frequency diversity was attributable to within-population variability; the remaining 8.7% was attributable to geographic variability among populations, which was partitioned into among-river (3.3%), among-area (3.5%), and among-region (1.9%) components. Two major groups of populations appeared in the principal components analysis and in cluster analysis of genetic distances. A coastal group included populations in four subgroups: Central coast, Georgia Strait, lower Fraser River, and west Vancouver Island. An inland group included six subgroups: Nass River, Skeena River, north Thompson River, upper and mid-Fraser River, south Thompson River, and lower Thompson River. The geographic extents of the inland and coastal groups largely coincided with the geographic distributions of stream- and ocean-type juvenile forms and may reflect postglacial colonization by two ancestral lineages that survived in Pleistocene refugia. The presence of genetically undifferentiated stream-type fish in coastal streams populated by ocean-type fish may reflect either postglacial life history differentiation from ancestral ocean-type fish or life history flexibility of ocean-type fish.