Evolutionary History, Population Genetics and Quantitative Genetics of Thinhorn Sheep

• Author / Creator

  Sim, Zijian

• The field of evolutionary biology is centered on the study of processes that shape the diversity of life on Earth. Processes that shape genetic variation can act on a wide-range of spatial and temporal scales. Large-scale events such as glaciations and mountain uplift have wide-ranging effects across a species range, while diversity may be modified at finer scales by phenomena such as dispersal between populations or by sexual selection in mating groups. Recent advances in genomic technologies offer researchers powerful new tools to interrogate wildlife genomes. While the shift to genomic techniques is occurring throughout the field, organisms that are closely related to well-studied domestic species are considered “genome-enabled” and uniquely able to take advantage of genomic tools developed for domestics. One such species is the charismatic thinhorn sheep of North America. Ovis dalli is an alpine and subalpine ungulate endemic to the mountains of northwestern North America. The thinhorn sheep range stretches from Alaska to the west, east to the Mackenzie Mountains of the Northwest Territories and south through Yukon to northern British Columbia. There are two recognized subspecies of thinhorn sheep, 1) the white coated Dall’s sheep (O. d. dalli), thought to occupy Alaska, Northwest Territories, and western Yukon, and 2) the dark coloured Stone’s sheep (O. d. stonei), which inhabits BC and southeast Yukon. In this thesis, I developed and applied genomic resources to study the processes that shape genetic variation in thinhorn sheep. First, I applied two single nucleotide polymorphism (SNP) arrays, the OvineHD and OvineSNP50 BeadChips, which were originally designed for the domestic sheep, to thinhorn sheep and showed the utility of these cross-species SNPs for phylogenetic and species discrimination analysis. Second, I used genome-wide SNP data gathered using the OvineHD BeadChip to study the phylogeographic history of thinhorn sheep. I found evidence that the evolution of Dall’s and Stone’s sheep was mediated by isolation in separate refugia during the late Pleistocene. Bayesian analysis of admixture also indicates a potential zone of hybridization in southern Yukon where sheep from the two glacial refugia met as they recolonized North America following the recession of the glaciers. Third, I investigated the fine-scale population genetic structure of thinhorn sheep by applying markers developed from the data acquired in earlier chapters to genotype over 2800 rams. I describe the global population genetic structure of thinhorn sheep and revealed three previously unreported Stone’s sheep genetic clusters in the Stikine/Skeena, Cassiar and Rocky Mountains of British Columbia. I also redefined the range for Stone’s sheep and showed that is much more restricted than currently accepted subspecies maps indicate, and almost exclusively confined within BC. Finally, I used genome-wide SNP data and an “animal model” to perform the first estimates for heritability in three fitness-related traits (horn length, horn base circumference and horn volume) in thinhorn sheep without a pedigree. I also performed a genome-wide association analysis for associations between SNP effects and each of the three traits. I found horn length, horn base circumference and horn volume to be moderately heritable and identified two SNP loci with suggestive associations to horn length. Taken together, this thesis provided insights into the evolution of thinhorn sheep and developed genomic tools for other wildlife researchers. Results from this thesis can also be used to inform the conservation management of thinhorn sheep.

• Subjects / Keywords

  • Thinhorn sheep
  • Quantitative genetics
  • Population genetics
  • Phylogeography

• Graduation date

  Spring 2019

• Type of Item

  Thesis

• Degree

  Doctor of Philosophy

• DOI

  https://doi.org/10.7939/r3-f5m5-cr17

• License

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