The Hybridization between the Endangered Gambusia nobilis and Introduced Gambusia geiseri in Texas

Introduced species are a major cause of biodiversity loss because of predation, competition for limited resources and space, and hybridization with native taxa. Hybridization poses the greatest risk for native taxa when the non-native and native taxa are closely related. This can compromise the genetic structure of native populations and drive those taxa to extinction. Moreover, the extinction risk to native taxa by hybridization with non-native is greatest when native taxa are rare (e.g., endangered or threatened) because rare taxa often lack the genetic variation necessary mitigate ongoing hybridization events. Herein, we provide morphological and genetic evidence to suggest that the introduced Largespring Gambusia (Gambusia geiseri) and endangered Pecos Gambusia (Gambusia nobilis) are hybridizing within the San Solomon Spring complex, Reeves, Co. Texas. We inferred hybridization and gene flow from data collected on seven morphometric characters, nine meristic measurements, and five molecular markers (the mitochondrial gene Cytb; nuclear genes Rag 1, Rag 2, and RPS7; and one microsatellite) from the two species and the putative hybrid. The results support morphological intermediacy and mixed genetic heritage of Gambusia nobilis and Gambusia geiseri in some individuals. In addition, we were able to infer extensive hybridization and introgression over several generations. Thus, alternate conservation efforts may be needed to counteract the effects hybridization on the endangered Pecos Gambusia.