Biochemical Genetic Differentiation of Lake Trout (Salvelinus namaycush) Stocks of the Great Lakes Region

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Allelic frequencies for lake trout (Salvelinus namaycush) samples collected from 27 small lakes or spawning shoals on larger lakes did not show significant annual changes. Levels of genetic variability were in the high range for Salmonidae, with 57% of the loci examined polymorphic (1% criterion) and 4.7% average heterozygosity per locus. Twenty-one percent of the total genetic variability was due to differences between stocks. Highly significant allelic frequency differences were found among allopatric as well as sympatric stocks. Genetic differences among sympatric stocks of Lake Superior indicated a significant degree of genetic isolation among these stocks. Genetic diversity within stocks, as measured by the proportion of polymorphic loci, was larger in stocks from large lakes than small lakes or transplanted stocks from large lakes into small lakes. Geographic patterns in allelic frequencies were observed. Samples from the northwestern range of our study area (upper Great Lakes, northwestern Ontario, and Manitoba) could be distinguished from those of the southeastern range by both allelic frequency differences and the presence or absence of alleles. We suggest that these two geographic ranges were colonized by lake trout that survived in different refugia during the Wisconsin glaciation. Unusual stocks of lake trout were found in three small lakes in the Haliburton Highlands of southern Ontario, with alleles at high frequencies that are rare or absent in most other stocks. We propose that the Haliburton Highlands lake trout originated from a glacial relict stock and survived during the last glaciation isolated from refugia used by other lake trout.