MORPHOLOGICAL SIGNATURES OF HYBRIDIZATION BETWEEN THE ENDEMIC ENDANGERED PECOS GAMBUSIA (GAMBUSIA NOBILIS) AND INVASIVE GAMBUSIA SPP. AT BITTER LAKE NATIONAL WILDLIFE REFUGE, NEW MEXICO

Fishes of the southwestern United States are among the most imperiled fishes in the world. Of the risks that these fishes face, extinction through hybridization is potent and is often facilitated by human activities. For example, native fish species may hybridize with closely related, introduced congeners. Moreover, these hybridization events are often difficult to detect and even more so among small, cryptic species. I attempt to identify and quantify the sites and extent of hybridization between the native Gambusia nobilis and introduced Gambusia affinis or Gambusia geiseri at Bitter Lake National Wildlife Refuge in Chaves Co., New Mexico, U.S.A., as well as identifying any possible barriers to fish movement on the property. This was done through studying the range of variability of morphological characteristics within populations and salinity throughout different wetlands at Bitter Lake National Wildlife Refuge. Morphology suggestive of invasive or hybrid Gambusia populations were found at sites in the southern portion of the property. The morphology of fish sampled from bitter creek and sinkholes were more indicative of G. nobilis and showed less variability in morphology relative to southern sampling sites. Bitter Lake, with a salinity 2.3 times that of seawater, may be halting the progress of invasive Gambusia spp. northward through the property.