Aim To investigate the degree of phylogeographical divergence within pygmy whitefish (Prosopium coulterii) and to test hypotheses concerning the origin of disjunct populations within North America.
Location North America from western Alaska to Lake Superior.
Methods Mitochondrial (ATPase subunit VI) and nuclear (ITS-1, ITS-2) DNA sequence variation was assessed across the species’ North American range to test for the existence of distinct phylogeographical groupings of pygmy whitefish associated with known glacial refugia. Coalescent simulations of the mitochondrial DNA (mtDNA) data were used to test hypotheses of population structure.
Results This species is composed of two monophyletic mitochondrial clades across its North American range. The two mtDNA clades differed by an average 3.3% nucleotide sequence divergence. These clades were also distinguished by ITS-2, but the relationships among lineages were not resolved by the ITS-1 analysis. Coalescent analyses rejected the null hypothesis of the current disjunct distributions being a result of fragmentation of a single widespread ancestral lineage across a variety of effective population sizes and divergence times.
Main conclusions The current range disjunctions of pygmy whitefish in North America probably resulted from isolation, genetic divergence, and selective dispersal from at least two major Pleistocene glacial refugia: Beringia and Cascadia. More recent isolation and dispersal from an upper Mississippi refugium is suggested by relationships within one of the clades and by distributional evidence from co-distributed species. The Beringian and Cascadian refugia have played major roles in the zoogeography of Nearctic temperate aquatics, but the roles of smaller refugia appear more variable among other species.