Phylogeography of Rhinichthys cataractae (Teleostei: Cyprinidae): pre-glacial colonization across the Great Continental Divide and Pleistocene diversification within the Rio Grande drainage

The longnose dace, Rhinichthys cataractae, is a primary freshwater fish inhibiting riffle habitats in small headwater rivers and streams across the North American continent, including drainages east and west of the Continental Divide. Phylogenetic analyses of 1140 base pairs (bp) of the mitochondrially encoded cytochrome b gene and 2298-2346 bp of the nuclear-encoded genes S7 and RAG1 were obtained from 87 individuals of R. cataractae (collected throughout its range) and from several close relatives recovered a monophyletic R. cataractae species-group that contained R. evermanni, R. sp ?Millicoma dace? and R. cataractae; a monophyletic R. cataractae was not recovered. Within the R. cataractae species-group, two well-supported clades were identified, including a western clade (containing R. evermanni, R. sp. ?Millicoma dace? and individuals of R. cataractae from Pacific slope drainages) and an eastern clade (containing individuals of R. cataractae from Arctic, Atlantic, and Gulf slope drainages). Within the eastern clade of R. cataractae, two well-supported groups were recovered: a southeastern group, containing individuals from the Atlantic slope, southern tributaries of the Mississippi River drainage, and the Rio Grande drainage; and a northeastern group, containing individuals from the Arctic slope and northern tributaries to the Mississippi River. Estimates of the timing of divergence within the R. cataractae species-group, combined with ancestral area-reconstruction methods, indicate a separation between the eastern and western clades during the Pliocene to early-Pleistocene, with a direction of colonization from the west of the Continental Divide eastward. Within the southern portion of its range, Rhinichthys cataractae likely entered the Rio Grande drainage during the Pleistocene via stream capture events between the Arkansas River (Mississippi River drainage) and headwaters of the Rio Grande. A close relationship between populations of R. cataractae in the Rio Grande drainage and the adjacent Canadian River (Mississippi River drainage) is consistent with hypothesized stream capture events between the Pecos and Canadian rivers during the late-Pleistocene. The population of R. cataractae in the lower Rio Grande appears to have separated from other populations in the Rio Grande drainage (upper Rio Grande and Pecos River) and Canadian River (Mississippi River drainage) during the late-Pleistocene, well before initiation of recent and significant anthropogenic disturbance within the Rio Grande drainage.