Genetic population structure and origin of life history types in chinook salmon in British Columbia, Canada

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 fr om 63 populations of chinook salmon in rivers and hatcheries throughout Bri tish Columbia, population heterozygosities averaged 0.084 (range 0.048-0.10 8) and were typical of values for populations in other regions. A hierarchi cal gene diversity analysis indicated that 91.3% of the total allele-freque ncy diversity was attributable to within-population variability; the remain ing 8.7% was attributable to geographic variability among populations, whic h was partitioned into among-river (3.3%), among-area (3.5%), and among-reg ion (1.9%) components. Two major groups of populations appeared in the prin cipal components analysis and in cluster analysis of genetic distances. A c oastal group included populations in four subgroups: Central coast, Georgia Strait, lower Fraser River, and west Vancouver Island. An inland group inc luded six subgroups: Nass River, Skeena River, north Thompson River, upper and mid-Fraser River, south Thompson River, and lower Thompson River. The g eographic extents of the inland and coastal groups largely coincided with t he geographic distributions of stream- and ocean-type juvenile forms and ma y 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 eith er postglacial life history differentiation from ancestral ocean-type fish or life history flexibility of ocean-type fish.