UBC Theses and Dissertations
Genomic differentiation of Northern Goshawks in coastal British Columbia Askelson, Kenneth K.
Understanding the process by which populations become genetically differentiated from one another has been a central goal of population genetics since its inception. With the loss of biodiversity across the globe, we lose information regarding how populations of organisms separate and become genetically distinct. An organism that exemplifies this issue is a subspecies of the Northern Goshawk (Accipiter gentilis laingi; hereafter simple “laingi”) which is classified as Threatened in coastal British Columbia under the Species at Risk Act (Canada) and the Endangered Species Act (USA). Using genotyping-by-sequencing (GBS) data across thousands of SNPs (single nucleotide polymorphisms), we investigate the genetic differentiation of this subspecies and infer the processes governing its distinctiveness. We find that Northern Goshawks on the archipelago of Haida Gwaii are distinct from other populations, clearly separating in principal component analyses, and have a wider distribution of FST and DXY when compared to other populations. In other populations, we recovered weak differentiation ranging from coastal BC to Maine; these populations likely represent the other North American subspecies Accipiter gentilis atricapillus (hereafter, simply “atricapillus”). The second phase of our research was to clarify the range of the laingi subspecies, which previously had been under debate. By selecting laingi-informative single nucleotide polymorphisms (SNPs) from our sequencing data we were able to develop SNP genotyping assays that allowed for the inclusion of hundreds of additional low-quality samples. Using these assays, we find that laingi goshawks are largely restricted to Haida Gwaii. Additionally, we wanted to understand the processes driving differentiation in Haida Gwaii and gene flow between other populations and Haida Gwaii. We found that even though Haida Gwaii is a small population, strong selection is likely shaping the genome. By jointly analyzing our GBS and genotyping data we find that gene flow between Haida Gwaii and other populations is likely low. This thesis contributes to knowledge of a Threatened bird of prey and more generally to how evolutionary distinctness evolves in geographically separated populations of organisms.
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