Gene Flow of Common Side-blotched Lizards Across the Colorado River in Arizona and Utah

Corsetti, Tessa

The 1963 completion of the Glen Canyon Dam in Arizona profoundly changed the Colorado River and altered habitat for many species. It created a relatively constant flow rate, much colder temperatures, and eliminated slow moving, warm periods that had historically characterized this system and gave wildlife opportunities to cross the river at certain times of year. The common side-blotched lizard (Uta stansburiana) provides an excellent opportunity to examine the effects of linear water barriers created by impoundments such as Glen Canyon Dam on migration and gene flow in wildlife. To assess the impact of these changes on an ectothermic reptile, we collected tissue samples from 241 common side-blotched lizards at three cross-river study areas in Arizona and Utah and used eight microsatellite loci to estimate gene flow as a function of genetic diversity and structure. One study area (Cataract Canyon) has annual periods of warm temperatures and low flows that most resembled pre-dam conditions, whereas the other two study areas Badger/ Jackass and Tanner/ Basalt) have cold water temperature year-round and no low-flow episodes. We found genetic differentiation between pairs of sampling sites on opposite sides of the river in two out of three study areas. Surprisingly the greatest cross-river gene flow was in one of the two below-dam study areas characterized by cold temperatures and no periods of low flow. We speculate that the lack of a significant rapid in this study area, or the presence of two pedestrian bridges ~27 km away, might facilitate cross-river movement in that study area. These results suggest that this small ectotherm can move across the post-dam Colorado River often enough to facilitate gene flow in under certain conditions, but the river presents a barrier to movement in most cases. Our study provides new genetic data for 241 common side-blotched lizards, a previously understudied species with minimal genetic information. These results provide a foundation for future studies on the effects of dams to animal movement and shed light on the genetic diversity and structure of the common side-blotched lizard in Arizona and Utah.