MITOCHONDRIAL DNA VARIATION AND EVOLUTION OF THE DEATH VALLEY PUPFISHES (CYPRINODON, CYPRINODONTIDAE).

A phylogenetic analysis of mitochondrial DNA (mtDNA) restriction sites was used to examine the geographic history of the Cyprinodon nevadensis complex of pupfishes, a group of four species (seven extant subspp.) in two endorheic (closed) basins of the Death Valley System in California and Nevada (Owens River Valley and Ash Meadows-Death Valley). The mtDNA results suggest that the group contains mtDNAs from two divergent clades. One such clade is represented by the mtDNAs of the Owens Valley pupfish (C. radiosus) and the existing species in the Colorado River (C. macularius), while the other includes the mtDNAs of the Ash Meadows-Death Valley species (C. nevadensis, C. salinus, and C. diabolis) and a species located much farther to the east (C. fontinalis from the Guzman Basin, Chihuahua, Mexico). These results, together with evidence from other studies, suggest two separate invasions of the Death Valley System by pupfishes carrying phylogenetically divergent mtDNAs. The C. nevadensis complex apparently is either an artificial group or else it is monophyletic and its genetic history includes loss of the original mtDNA in either Owens Valley or Ash Meadows-Death Valley following genetic introgression after an invasion by a pupfish carrying a divergent mtDNA.