Genetic diversity, population structure and phylogeography among belugas (Delphinapterus leucas) in Canadian waters: broad to fine-scale approaches to inform conservation and management strategies
This thesis examines the genetic diversity, population structure and phylogeography of belugas (Delphinapterus leucas) in Canadian waters that encounter multiple stressors throughout their seasonal distributions. Data were collected from multiple scales, including: samples covering a temporal scale of 25 years; broad geographic comparisons to finer-scale, within-group comparisons; and varying amounts of genetic information from partial mtDNA sequences to whole mitogenome sequences, and multiple nuclear microsatellite loci. At least nine genetically distinct summer aggregations, with an additional distinct winter sample collection of unknown summer distribution, were identified. This information contributed to the identification of Designatable Units (DUs) of belugas for future assessments by the Committee on the Status of Endangered Wildlife in Canada (COSEWIC). Phylogenetic analyses of mtDNA sequences revealed that the most divergent lineages are found at the east, west and southern edges of the Canadian distribution, with the central area characteristic of a contact zone displaying an admixture of lineages marked by incomplete lineage sorting. The geographic distribution of these lineages suggests multiple glacial refugia as sources of ancestral beluga populations that recolonized Canadian Arctic and sub-Arctic waters. Preliminary tests of selection detected the presence of purifying selection on all mtDNA protein-coding genes of belugas. However, no signals of adaptive selection were detected among genetic lineages or geographic groups. Within nearshore summer aggregations of Beaufort Sea belugas, three distinct maternal lineages were identified and patterns of genetic relatedness suggest clusters of related females form in the overall area. However, these clusters of related belugas did not form fine-scale kin structure corresponding to aggregation/harvesting locations. Thus, disturbances and subsistence harvesting in particular areas where belugas are aggregating will not be necessarily putting a discrete genetic unit of the stock at risk. These results provide a better understanding of the diversity and spatial differentiation among and within Canadian beluga stocks, inferences about past responses to climate changes, approaches to investigate fine-scale structure within seasonal aggregations, and new tools to infer adaptive potential of these whales. This information, and studies of beluga fossils plus additional samples across global distributions, will improve conservation and management planning for this culturally important and charismatic species.