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Scientific Report

Genetic Variation and Structure of Chinook Salmon Life History Types in the Snake River

Abstract

We evaluated 25 inland populations of Chinook salmon (Oncorhynchus tshawytscha) in the Snake River with 13 microsatellite loci to test for contemporary genetic differentiation at three scales: between life history types, among regions within life history types, and among populations within regions. The genetic distance and diversity of natural Chinook salmon populations were also contrasted with those of Chinook salmon from several hatcheries. The results provide strong evidence for reproductive isolation among ocean- and stream-type life histories (FST  range, 0.080–0.120). Regional structuring of stream-type Chinook salmon within subbasins was also significant, as all populations were differentiated (FST range, 0.017–0.045), but populations generally clustered together by region in a neighbor-joining dendrogram. This evidence suggests high levels of philopatry to natal areas in stream-type Chinook salmon, but ocean-type collections were not significantly different from one another (FST range, 0.001–0.002). Higher levels of genetic diversity in ocean-type (306 total alleles; allelic richness, 16.5) than in stream-type collections (206 total alleles; allelic richness, 12.2) may also reflect variable levels of gene flow within each life history type and colonization history. The genetic similarity of populations within regions suggests gene flow not only from transplanted stocks but also from natural dispersal that provides metapopulation structure. None of the 25 populations in this study offered significant evidence for a genetic bottleneck (M ratio , 0.68) despite apparent demographic bottlenecks in several populations throughout the Snake River drainage in the last century. The combination of dispersal through metapopulation dynamics and transfers of hatchery stocks may be responsible for reducing the genetic bottleneck signal.

Authors

Shawn R. Narum, Jeff Stephenson, and Matthew R. Campbell

Citation

Narum, S.R., J.J. Stephenson, and M.R. Campbell. 2007. Genetic Variation and Structure of Chinook Salmon Life History Types in the Snake River Life History Types in the Snake River. Transactions of the American Fisheries Society 136:1252-1262.

Date

Jan 1st, 2007

Report No.

TAFS_narum_2007

Media Type

Journal Article

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