Riverscape Genetics of Roundtail Chub in the Upper Colorado Basin

The native big-river fish community in the Upper Colorado River basin is comprised of minnows (Cyprinidae) and suckers (Catostomidae). Both are represented by but a few species, most of which are endemic and either threatened, endangered or considered of conservation concern. Roundtail Chub, Gila robusta is a species of concern and its 91 propagation and/or translocation is a potential tool for adaptive management. A genetic baseline would aid in making appropriate decisions regarding donor and source populations, so as to avoid the potential for outbreeding depression that can result from the intermingling of lineages. In this regard, how genetically distinct are Roundtail Chub populations from the mainstem Colorado River versus those from tributaries? These habitats differ markedly with regard to flow regimes, community composition, and historical selective pressures. Admixing local populations may break apart co-adapted gene complexes and reduce fitness in future generations – complicating recovery efforts. To consider this possibility, we evaluated genetic relationships of 450 Chub collected from mainstem and tributaries in Wyoming, Colorado, and Utah. We analyzed sequence variation across 2 mtDNA genes (842 bp) as a means of identifying genetic relationships reflecting deep history and relating these patterns with geomorphic features. Second, we examined genetic diversity across 16 fast-evolving microsatellite loci to test for contemporary connectivity and demographic independence among local populations. While small sample sizes from some sites limited statistical power, results suggest that management actions should strive to preserve local adaptations among populations and rely upon a drainage-specific focus for adaptive management.