Setting Conservation Priorities in a Widespread Species: Phylogeographic and Physiological Variation in the Lake Chub, Couesius plumbeus (Pisces: Cyprinidae)

Abstract

Defining units of conservation below the species level is a widely accepted conservation priority, but is especially challenging for widespread taxa that have experienced diverse geographic histories and exist across heterogenous environments. The lake chub (Pisces: Couesius plumbeus) is a widespread freshwater fish in North America and occurs from the southcentral USA to northwestern Alaska and Canada. We used mtDNA sequence analysis to test for divergent lineages predicted to occur as a result of survival of lake chub in distinct glacial refugia. Lake chub consisted of two major mtDNA lineages separated by 3.8% sequence divergence which are probably late to pre-Pleistocene in origin. We combined these data with those consistent with thermal adaptation in fish living in thermal springs versus those living in a lake with wide seasonal temperature variation, and with data on distribution of lake chub in major watershed units. We assessed these data against objective criteria developed to identify conservation units under Canadian endangered species legislation. Our analysis identified twelve major units of conservation within C. plumbeus that could be assessed under Canada’s Species-at-Risk Act. Our study illustrates how different character traits manifested at very different spatial scales can be used to define conservation units within widely-distributed taxa.

Keywords

• intraspecific variation
• species-at-risk
• phylogeography
• thermal tolerance
• Cyprinidae