Intraspecific differences in thermal biology among inland lake trout populations

Abstract

The ability of coldwater species and populations to respond to the predicted temperature increases associated with climate change will largely depend on existing adaptive potential within and among populations. Southern inland populations of Lake Trout Salvelinus namaycush are broadly characterized by two ecotypes (small and large bodied) which differ in their trophic ecology, life history traits, and body size. Using common-garden experiments, we investigated population-specific differences in thermal performance (growth, temperature tolerance, and temperature preference) and whether the differences were consistent between ecotypes. We further explored the role of acclimation temperature on growth and thermal performance in two representative ecotypic populations. The evidence from this study indicated that the differences were population specific rather than ecotype specific. A strong inverse relationship between early growth rate and temperature preference suggests that the differences in early growth among Lake Trout populations are driven by adaptive variation in temperature preference. Acclimation temperature had a greater effect than source population on growth and temperature tolerance, although both significantly influenced temperature preferences. Small-bodied ecotypes were less tolerant of elevated temperatures and exhibited less within-population variation, potentially indicating their greater vulnerability to changing ecological conditions under climate change scenarios. © American Fisheries Society 2013.