Influence of Pleistocene Glaciations and Human Intervention upon Mitochondrial DNA Diversity in White Sturgeon (Acipenser transmontanus) Populations

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Abstract
The influence of recent genetic bottlenecks on two Northwest Pacific populations of white sturgeon (Acipenser transmontanus) was studied using restriction enzyme site differences in mitochondrial DNA (mtDNA). A total of 10 mtDNA genotypes were detected in 178 sturgeon from the Columbia and Fraser rivers. Nearly 61% of individuals from both rivers had a common genotype. However, one genotype was found only in the Fraser River. Geographical substructuring was not evident in the phylogenetic analysis. The Columbia River, a Pleistocene refugium, is suggested as the source of founders for the Fraser River following the last glacial recession, about 10 000–12 000 yr ago. MtDNA genotypic frequencies were significantly different between the rivers. Estimates of mtDNA (h) and nucleotide (π) diversity were consistently higher for the recently colonized Fraser River compared with the Columbia River refugium. This condition is the reverse of all known studies of mtDNA diversity between refugium and colonized animal populations. Recent overexploitation and habitat destruction are suggested as a severe genetic bottleneck that has reduced mtDNA diversity in Columbia River sturgeon.