ALLOZYME PERSPECTIVE ON MITOCHONDRIAL-DNA VARIATION AND EVOLUTION OF THE DEATH-VALLEY PUPFISHES (CYPRINODONTIDAE, CYPRINODON)

We used allozymes encoded by 32 gene loci in 12 species of Cyprinodon (Cyprinodontidae) to examine the evolution of the C. nevadensis complex, a group of four species (seven extant subspp.) in the Death Valley System of California and Nevada. The most parsimonious phylogenetic trees supported monophyly of the C. nevadensis complex (C. diabolis, C. nevadensis, and C. salinus from Ash Meadows-Death Valley, and C. radiosus from Owens Valley). However, a hypothesis involving a diphyletic origin of the complex was nearly as parsimonious. The geographic distribution of alleles, together with results from an earlier study of mtDNA variation, suggest that introgressive hybridization has occurred between two divergent pupfishes that gained access to the Death Valley System. We suggest that secondary contact and introgressive hybridization among western pupfishes may have been more common in wetter times of the past than is generally appreciated. Such an event would explain conflicting phylogenetic statements from allozymes and mtDNA, as well as a variety of additional observations on variation in the western pupfishes.