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UBC Theses and Dissertations

Genomics of adaptation in interior spruce to past, present, and future climates of western Canada Degner, Jonathan


The interior spruce of western Canada comprises complex hybrids of white spruce (Picea glauca) and Engelmann spruce (Picea engelmannii). These trees are a keystone of their ecosystems and are economically important to forestry in western Canada. As rapid climate change is a particular threat to long-lived forest trees, understanding climate adaptation in this species complex is critical to anticipate and mitigate impacts to our forests. Using an existing dataset of genotyped seedlings representing 254 provenances throughout British Columbia and Alberta, I assessed the role of hybridization in climate adaptation within this species complex. Using a novel climatic similarity index, I determined that the hybrid zone is a climatic mosaic of its parent species’ ranges, with a precipitation regime more similar to white spruce and a winter temperature regime more similar to Engelmann spruce. I identified SNPs with an excess of alleles from one parent species across a broad range of hybrids. SNPs with a bias towards Engelmann spruce alleles tended to be strongly correlated with temperature variables, while SNPs with higher white spruce allele frequencies were more correlated with precipitation variables, suggesting that favorable parental alleles efficiently introgress into hybrids and allow them to adapt to novel climates. Using the strong relationship between hybrid index and climate, I combined genomic and climate data with existing ecological plot data to model hybrid index throughout western Canada. These models were applied to paleoclimatic simulations which, combined with mitochondrial haplotypes, allowed me to infer the colonization history of spruce in western Canada following deglaciation. I also used these hybrid index models to estimate the impacts of contemporary and future climate change on the hybrid zone, predicting large shifts in species ranges and large genomic shifts in areas where spruce persists. Together, these results demonstrate that hybridization has greatly contributed to local climate adaptation in interior spruce, and that climate change poses an existential threat to forests in the finely tuned adaptive landscape of this hybrid zone. This knowledge of local adaptation can inform our reforestation practices, as human intervention will be necessary to align genotypes to climates over the coming decades.

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