A Simulated Reciprocal Transplant Experiment: Local Adaptation In Reintroduced Populations of a Native North American Fish

An understanding of population-level adaptations to local conditions may be critical for the effective conservation and management of struggling species. However, local adaptations may be difficult to detect without conducting experiments because there are few predictable patterns in their occurrence and because phenotypic plasticity may confound determination of a genetic basis for a trait. Mixed-source reintroductions provide an opportunity to study local adaptations because potentially divergent strains are grown under identical conditions. We identified local adaptations in two strains of reintroduced fish by simulating a reciprocal transplant experiment. We developed strain-specific regression models from multiple common-garden configurations that were represented by the reintroductions sites. Fitness response predictions from these regressions, based on source habitats, indicated divergent local adaptations in each strain through differential responses to habitat features among the reintroduced fish. We described local adaptations by characterizing the relationship of fitness proxies, such as body condition, to habitats at the source and reintroduction sites using multivariate analysis. Thermal regime differences between the source habitats provided potential mechanisms for local adaptation development. Dissimilar optimal growth temperature ranges or maximum growth rate differences may have arisen between source populations as a compensatory response to different temperatures and growing season lengths. A lack of means to predict when there is a great risk of outbreeding depression in crosses between evolutionarily diverged populations may hinder sound management of fragmented species. Population-specific adaptations may also provide opportunities to better maintain a species geographic range despite anthropogenic influences on habitat.