Fall 2019 Tanner Lecture with Dennis Shiozawa

Cutthroat Trout: The History of a Western North American Native
Two native trout of Western North America, the cutthroat trout (Oncorhynchus clarkii) and the rainbow trout (Oncorhynchus mykiss), were thought to have diverged approximately 2 million years ago. About 1 million years later, ancestral cutthroat trout dispersed from the Pacific Coast, via the Columbia River, into the interior of Western North America, generating at least 14 subspecies. However, fossil and molecular data conflict with this, suggesting the cutthroat trout lineage is closer to 10 million years old. Coupled with the geological evolution of Western North America, we suggest that the interior cutthroat trout originated in streams draining to the Pacific from a large, uplifted highland, the Great Basin Altiplano. As this highland collapsed, streams in the central region of the Altiplano began to flow into a developing Great Basin. I hypothesize that this event captured coastal cutthroat trout populations into the western Lahontan Basin and from there the ancestral interior cutthroat trout arose.