Range-wide population structure in a long-lived species and implications for management

Spatial population structure of widespread, long-lived big river fishes in the American West reflects their ecological/ evolutionary success. It also serves as a management tool to gauge severity of anthropogenic impacts at the landscape level. The Bluehead Sucker (Catostomus discobolus; Catostomidae) is one such model organism. It is distributed broadly across the upper Colorado and parts of the Bonneville and Snake river basins, yet is declining range-wide. We evaluated 1,100 Bluehead (39 locations) across two fast evolving mtDNA genes and derived 3 ESUs (Bonneville Basin, Upper Snake River, and Colorado River Basin). We then employed 16 msat loci to further delineate 11 MUs. Three Upper Colorado River mainstem populations were admixed (but 2 tributary populations largely isolated), whereas 3 Lower Basin tributaries and the Grand Canyon were recognized. Genetic diversity in Bluehead is maintained by gene flow and concomitantly eroded within small, isolated populations. A prerequisite for long-term success is retention of distinct gene pools (sources) but with corridors that foster natural gene flow among metapopulations (some of which are sinks). Molecular techniques can gauge these ecological aspects and simultaneously benchmark their diminution as a result of water diversions, dams and impoundments.