GENOMIC DATA OFFERS AN INDEPENDENT PERSPECTIVE ON EVOLUTION OF THE LOWER COLORADO RIVER REGION

The Colorado River is not only a major geomorphic and hydrographic feature of the southwestern United States but is also implicated as a major driver of biodiversity across the region. Classically, the 5.3-Myr age for earliest sediment deposition from the river into the northern Gulf of California is also interpreted as the age of divergence for sister species separated by the river today. Isolation due to a physical barrier such as this is important because it contributes to the formation of new species and thus to present-day biodiversity. However, biological data can also be used to understand changes in the physical landscape over time. The emerging use of large-scale whole-genome data provides an independent way to evaluate geological hypotheses because genomes carry the long-term historical signatures of gene flow and isolation. Here, I outline how genomic data can be used to assess the historical connectivity of populations isolated by the Colorado River, with specific focus on the age and existence of paleo-sediment dams (~4.8 Ma) and paleo-lava dams (100–525 ka). As an example from the emergent, widely applicable field of ‘geo-genomics’, this work uses large-scale genomic data of desert tortoises to address longstanding geologic questions on evolution of the lower Colorado River region.