ORIGIN OF GILA-SEMINUDA (TELEOSTEI, CYPRINIDAE) THROUGH INTROGRESSIVEHYBRIDIZATION - IMPLICATIONS FOR EVOLUTION AND CONSERVATION

Morphological and genetic characters from cyprinid fishes of the genus Gila were examined to assess a hypothesized hybrid origin of Gila sem inuda from the Virgin River, Arizona-Nevada-Utah. The presumed parents , Gila robusta robusta and Gila elegans, are clearly differentiated fr om one another based on morphology, allozymes, and mtDNA haplotypes. G . seminuda is morphologically intermediate and polymorphic at allozyme loci diagnostic for the parental species. Restriction endonuclease an alysis of mtDNA showed G. seminuda nearly identical to G. elegans. The se results support an origin of the bisexual taxon G. seminuda through introgressive hybridization. The Gila population in the Moapa River, Nevada, also appears to be of hybrid origin and is considered a distin ctive population of G. seminuda. Inter-specific hybridization is poten tially an important mode of evolution among western North American fis hes, and valid species of hybrid origin may exist in other groups as w ell. Consideration of this mode of evolution argues for the need to co nserve entire species complexes.