UBC Theses and Dissertations
Environmental impacts on hybridization outcomes Kinney, Mackenzie
Hybridization is the process of interbreeding between distinct genomic lineages. Environmental disturbances have been associated with increased hybridization between previously non-interbreeding lineages, suggesting that the production and survival of hybrids is influenced by the ecological conditions in which they occur. However, our understanding of hybridization, hybrid evolution, and the impact of natural selection on hybrid populations is limited compared to that of parent species. To address these gaps, my dissertation focused on investigating the effects of environmental changes on hybrid production and fitness, and the mechanisms driving the evolution of hybrid populations. Threespine stickleback fish served as a model for my thesis as they have diverged at least five times to form limnetic and benthic species capable of producing viable hybrid offspring. These species exhibit strong reproductive isolation and low hybrid fitness under natural conditions, but collapse into a hybrid swarm has been observed once in nature. In Chapter 2, I conducted experiments manipulating pond conditions to examine if eutrophication would disrupt reproductive isolation and influence hybrid survival as a consequence of reduced visibility and an altered ecological fitness landscape. Although our treatment did not appear to affect hybrid production or survival, we nonetheless observed an increase in hybrids independent of the treatment, highlighting the fragility of reproductive isolation in ecologically specialized species. In Chapter 3, inspired by the collapse of stickleback species in Enos Lake, I examined the fitness of F1 hybrids in the presence of crayfish. We observed a slight, but non-significant improvement in relative hybrid fitness as a consequence of changes in parent fitness. Chapter 4 focused on the evolution of three wild stickleback hybrid populations with varying proportions of parental ancestry inhabiting similar environments. We found parallel evolution in both genotypic and phenotypic traits across the hybrid populations, regardless of their ancestry, providing evidence for the significant role of ecological selection in shaping these populations. In summary, my dissertation sheds light on the crucial role of ecological context in mediating the outcomes of hybridization and emphasizes the need to improve our understanding of this process and its implications on the evolution and persistence of hybrid populations.
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