Conservation Genomics of Ontario's Southern Boreal Caribou

Background/Question/Methods

Rangifer tarandus is a North American species that has experienced dramatic declines in both range and population size over the past century. In Canada, caribou are divided into 12 evolutionarily significant units; all are currently at risk of extinction. These lineages can broadly be divided by their location during the Pleistocene glaciation: “barren-ground”, north of the Laurentide ice sheet, and “boreal”, south of the ice sheet. Boreal caribou (R. t. caribou) have lost approximately half of their historic range in Canada in the last 150 years, particularly along the southern range edge largely due to habitat loss, although climate change is a growing concern. Despite this overall northward retraction, some populations have managed to persist over 150km south of the continuous caribou range in Ontario, along the coast and near-shore islands of Lake Superior. However, the evolutionary significance of the Lake Superior caribou remains unclear, presenting challenges for management. We are investigating inbreeding and patterns in heterozygosity across the genome by analyzing runs of homozygosity. We are also examining the evolutionary history of boreal caribou using admixture tests, phylogenomic trees, and Principal Component Analysis (PCA) with whole-genome data collected from herds throughout Ontario, Manitoba, and Quebec.

Results/Conclusions

The Lake Superior caribou demonstrate high levels of inbreeding and genetic drift. Despite notable inbreeding, there are several regions across the genome that have consistently maintained high heterozygosity, suggesting strong balancing selection. Investigating potential regions of inbreeding depression as well as genomic regions of adaptation will provide insights into the evolutionary significance of the Lake Superior populations. Furthermore, a recent study indicated that most boreal and eastern migratory caribou in Ontario have undergone historic introgression with the barren-ground subspecies (R. t. groenlandicus). Our preliminary investigations of evolutionary history suggest that due to isolation, the Lake Superior herds may not have introgressed with barren-ground caribou. Due to their southern distribution and potential for local adaptation, these populations may be key to the preservation of caribou in a warming climate. This research will support scientifically informed management of boreal caribou in Ontario, which are currently threatened with extinction.