Evaluating genetic structure among resident and migratory forms of bull trout (<i>Salvelinus confluentus</i>) in Northeast Oregon

Abstract

Abstract – Many salmonids express multiple behavioural forms within the same population, representing an evolutionary adaptation to a heterogeneous environment. For bull trout, resident and migratory forms co‐occur in streams, but it is unknown whether the two forms assortatively mate. We assessed genetic differentiation between resident and migratory bull trout (using eight microsatellite loci) in the South Fork Walla Walla River. We PIT‐tagged and fin‐clipped bull trout and assigned individuals to behavioural subpopulations based on movement patterns. The pair‐wise F ST value between resident and migratory subpopulations (0.0037) was statistically insignificant, and individual‐based analyses of structure using both multivariate and Bayesian approaches showed a lack of genetic structure within the population. These results have important implications for assessing population status and management; while the population may be managed as a single reproductive unit, the phenotypic variation within this population may have fitness consequences and thus merits conservation.