Forest trees are an important pool of biodiversity at the gene, individual and an ecosystem level. This variation is a result of complex environmental interactions, as well as neutral and selective forces acting on populations. Patterns of standing genetic variation are the result of adaption to past and contemporary climate change, but also historical demographic events, and disentangling the role of these forces is a central problem in population genomics. The overall goal of this study is to characterize the relative effects of demography and selection in the genome of Populus trichocarpa, a riparian deciduous tree species of North America. Specifically, I used a variety of methods to summarize patterns of genetic diversity and population structure in P. trichocarpa, and to reconstruct its demographic history. I subsequently incorporated these demographic insights to guide the application of several methods to identify genome-wide targets of natural selection within and among rangewide populations adapted to heterogeneous selection regimes. Results of this study provide insights into the history of divergence and differentiation in P. trichocarpa populations and help us identify the functional genetic variants contributing to phenotypic divergence and fitness of the individuals in it. / Ph. D. / The extant genetic variation in the forest tree populations is a product of evolutionary history and complex environmental interactions. This genetic variation can therefore be leveraged to identify both the adaptive genetic variation and understand the demographic events that might have caused these patterns. We, in this study, present and analyze the range-wide population genomic dataset of western poplar (Populus trichocarpa) and show that the current distribution of western poplar originated from the southern western poplar populations around hundred thousand years ago. Our study also identified large number of loci associated with environmental local adaptation. We identified number of genes involved in temperature sensing, light signaling pathways, and plant immunity, suggesting role of biotic and abiotic factors as major drivers of adaptation. We also detected significant overlap between highly divergent loci and adaptive genetic variation, indication the role of adaptation in species diversification. Overall, the results of this study advance our understanding of the demographic history and the major drivers of local adaptation in western poplar populations. It also gives us an observational and experimental evidence of role of environment and demographic history in shaping the genetic make-up of organism.
| Identifer | oai:union.ndltd.org:VTETD/oai:vtechworks.lib.vt.edu:10919/87515 |
| Date | 15 August 2017 |
| Creators | Bawa, Rajesh Kumar |
| Contributors | Forest Resources and Environmental Conservation, Holliday, Jason A., Wu, Xiaowei, Zhang, Liqing, McGlothlin, Joel W. |
| Publisher | Virginia Tech |
| Source Sets | Virginia Tech Theses and Dissertation |
| Detected Language | English |
| Type | Dissertation |
| Format | ETD, application/pdf |
| Rights | In Copyright, http://rightsstatements.org/vocab/InC/1.0/ |
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