Mitochondrial DNA haplotype genealogies and population histories in the late Pleistocene: contrasts of pink salmon broodyears

Abstract

Seven segments of mtDNA, comprising 97% of the mitochondrial genome, were PCR-amplified and examined for restriction site variation using 13 restriction endonucleases in three Oncorhynchus species: pink (O. gorbuscha), chum (O. keta), and sockeye (O. nerka) salmon. Multiple haplotypes, but shallow mtDNA trees were observed for each species. 'Star-like' structures indicating historical population explosions were observed in haplotype genealogies. Given reasonable rates of mtDNA sequence evolution, this may reflect recolonization of vast areas in Alaska after the last (Wisconsinian) or preceding (Illinoian) glacier retreats. The phylogeographic survey of 18 Alaskan and Eastern Asian pink salmon populations revealed a distinct phylogeographic break between Alaska and Asia in even-year, but continuous distributions of the mtDNA lineages throughout the same range in the odd-year broodline. A nested cladistic analysis of geographical distances indicates that spatial distribution of mtDNA lineages in both broodlines resulted from interplay between historical range expansions and isolation by distance.