Conservation Genetics of a Spring‐dwelling Desert Fish, the Pecos Gambusia (Gambusia nobilis, Poeciliidae)

The genetic population structure of the Pecos gambusia was assessed with protein lectrophoresis to determine the best way to preserve the genetic diversity of the species. This small, federally protected live‐bearing fish is endemic to the Chihuahuan Desert region of New Mexico and Texas, where it occupies four isolated spring systems in the Pecos River drainage. Drying of springs due to lowering water tables is the most pervasive threat to the species. Fifty‐two percent of the total gene diversity detected in the species was due to differences between samples at different localities, while 48 percent was due to variability within samples. Most (67%) of the between‐sample diversity was due to differences among populations in the four major areas of occurrence. Populations in the Toyah Creek area of Texas exhibited striking spatial heterogeneity in allele frequencies and, compared with populations in the other three areas, unusually high levels of within‐sample genetic variability. The spatial pattern of genetic variation in the Pecos gambusia closely parallels that of a locally endemic, federally protected pupfish species in each of tux different areas. Also, one or more endemic species of invertebrate occurs in each area occupied by Pecos gambusia Protection of the natural pattern of genetic variability in Pecos gambusia would thus contribute significantly toward conservation of the genetic resources in a diverse assemblage of spring‐adapted species.