High and dry: intermittent watersheds provide a test case for genetic response of desert fishes to climate change

Abstract

In desert streams, fishes and other organisms that depend on surface water are predicted to inhabit smaller and more isolated wetted reaches, while the frequency and severity of disturbance is expected to increase under most climate change models. Together, these factors should reduce population genetic diversity and persistence probabilities. In this study, our goal was to understand genetic responses of stream fish populations to disturbance in an intermittent stream network. This network is occupied by Rio Grande sucker (Pantosteus plebeius) that is native to highland desert streams in North America. Sample localities in upland perennial reaches were connected by moderate to high levels of gene flow even when separated by up to a 30-km intermittent reach. However, drier and lower-elevation reaches were significant barriers to gene flow. Effects of genetic drift (lower allelic diversity and higher levels of inbreeding) were more pronounced in the watershed with fewest wetted reaches. Temporal analysis of genetic diversity indicated that streams with several spatially distinct wetted reaches were more genetically resistant to wildfire-induced demographic bottlenecks than a stream with only one wetted reach. Maintenance of multiple wetted reaches within streams and facilitated gene flow among watersheds could slow losses of genetic diversity in upland desert stream fishes, and will be important strategies for conserving stream biodiversity in the face of habitat fragmentation and disturbance related to climate change.