Post-glacial expansion into the Paleozoic Plateau: evidence of an Ozarkian refugium for the Ozark minnow Notropis nubilus (Teleostei: Cypriniformes).

Genetic variation was examined within the Ozark minnow Notropis nubilus using complete mtDNA cytochrome b gene sequences from 160 individuals representing 30 localities to test hypotheses on the origin of the distribution. Phylogenetic analyses revealed three strongly supported clades of haplotypes consistent with geographic distributions: a clade from the Western Ozarks, a clade from the Southern Ozarks and a clade from the Northern Ozarks and upper Mississippi River basin. The estimated mean ages of these clades indicated that they diverged during pre-Illinoian glacial cycles extending from the late Pliocene into the early Pleistocene. Results of demographic analyses based on coalescent approaches supported the hypothesis that the Paleozoic Plateau was not a refugium for N. nubilus during periodic glacial advances. There is evidence of a genetic signature of northern expansion into the Paleozoic Plateau from a Southern Ozarkian refugium. Populations expanded out of drainages in the Northern Ozarks into the Paleozoic Plateau during the late Pleistocene. Subsequently, the two regions were isolated due to the recent extirpation of intervening populations caused by the loss of suitable habitat.