Date of Award


Publication Type

Doctoral Thesis

Degree Name



Great Lakes Institute for Environmental Research


gene expression, genetic architecture, gut microbiota, interspecific competition, non-native species, reintroduction


Heath, Daniel




Reintroduction is the release of a species collected from captive or wild sources into its historical habitat where it has been locally extirpated with the aim to re-establish a self-sustaining population. Increasing pressures on global biodiversity caused by human activities has led to an upsurge in reintroductions in the last decades, but the reintroduction success rate is generally low. Populations can differ in reintroduction performance because of their genetic background which may limit their scope for adapting to novel environments as well as narrow their tolerance ranges for environmental stressors likely to be encountered in the initial acclimation phase of reintroduction. Thus, selecting an appropriate population is very important for conservation related applications including reintroduction. Atlantic salmon (Salmo salar) was extirpated in Lake Ontario by 1900s, and decades of reintroduction attempts have been largely unsuccessful. This dissertation focuses on two important reasons for the unsuccessful reintroduction of Atlantic salmon in Lake Ontario: inappropriate source population selection and stress caused by established non-native salmonids. I explored population differences between two Atlantic salmon populations (LaHave and Sebago) and their responses to interspecific competition by characterization of gene expression and gut microbiota. The regulation of gene expression plays an important role in acclimation and adaptation. The gut microbial community mediates a variety of biological processes and can directly impact host fitness. In this dissertation, I addressed basic genetic (genetic components of gene expression variance), evolutionary (selection versus genetic drift on gene expression variance), and ecological (in response to interspecific competition) theories of gene expression. I also addressed population differences in competitive ability and possible molecular mechanisms that mediated negative effects on Atlantic salmon caused by non-native competitors. I found that populations showed substantial differences in gene expression and genetic components of gene expression variance at rest state, and populations showed different response patterns to interspecific competition in gene expression and gut microbiota. The Sebago population is more suitable for reintroduction in Lake Ontario than the LaHave population. The results highlighted the fact that populations can possess different responses to biotic stressors despite not encountering the stressor during their past evolutionary history.