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UBC Theses and Dissertations

Physiological, transcriptomic and genomic mechanisms of thermal adaptation in Oncorhynchus mykiss Chen, Zhongqi


Given the rate and magnitude of the ongoing global warming, there is some urgency to understand the underlying mechanism of thermal adaptation to evaluate and predict the ecological consequences. This thesis used Oncorhynchus mykiss from different thermal regimes to examine thermal adaptation at physiological, transcriptomic and genomic levels. Thermal tolerance was examined in three redband trout (O. mykiss gairdneri) populations from warm desert and cool montane climates (Idaho, USA), as well as in a domesticated rainbow trout (O. mykiss) strain raised in a thermally challenging environment for over 19 generations (Western Australia, Australia). Acclimated to 15°C, the desert redband trout had the highest critical thermal maximum (CTMAX; 29.7°C) and maintained an almost constant absolute aerobic scope (AAS) across a broader range of test temperatures (12-24°C) than seen in other strains, but had the lowest peak AAS, suggesting a tradeoff between thermal performance and tolerance. Western Australian rainbow trout had the highest AAS, even when tested at 21°C, which may be a result of hatchery selection for thermal performance. Although the rate transition temperatures for maximum heart rate (Arrhenius breakpoint and arrhythmia temperature for fH,max) were similar among all populations, fH,max was the highest in the desert redband trout population at all temperatures. Cardiac RNA sequencing revealed different patterns of gene regulation among redband trout populations during acute warming. Many genes had different mRNA abundances between populations due to constitutive and induced expression, and the number of differentially expressed genes among populations was positively correlated to the genetic distance, suggesting intraspecific cellular regulatory strategies in response to acute warming. Population and quantitative genetic studies identified potential genomic markers for thermal adaptation. A total of twenty-one loci were putatively under positive thermal selection (“outliers”). In addition, genotypes of some outlier loci had significantly different CTMAX. Genome-wide association study identified twelve loci that were significantly associated with individual CTMAX. Altogether, results in my dissertation demonstrated the capacity of thermal adaptation in O. mykiss populations at multiple organismal levels. This data lays a foundation to improve our understanding on the potential impact of global warming on wild aquatic populations.

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