Caribou is a species of ecological and cultural significance in Canada and live across North America in various habitats ranging from the vast boreal forests, tundra and mountains to the high Arctic. Unfortunately, some populations are undergoing significant declines resulting in their at-risk status in Canada.

Trent University and Environmental and Climate Change Canada (ECCC), as part of a long-standing national scale project in collaboration with provincial and territorial biologists across Canada, have applied state-of-the art analyses on the complete genomes of caribou representing these populations to assess their ancestral origin and associated genetic diversity.

These results have been published in the prestigious journal Current Biology, entitled, “High genetic load without purging in caribou, a diverse species-at-risk.”

Genetic diversity is a key component of overall biodiversity in promoting adaptability and resilience to changing environmental conditions.

Nine major genetic lineages were identified across the Canadian caribou; a pattern that coincided with a major population expansion starting around 110,000 years ago or at the start of the last glacial period. These results shed new light on the species’ ancestral pattern of diversification that is critical for the delineation of conservation units, or Designatable Units, under the Committee on the Status of Endangered Wildlife in Canada and the Species-at-Risk Act; and the assessment of their at-risk status and their recovery strategies.

There was also evidence of genetic exchange, or gene flow, that supports the finding that caribou maintain a high level of genetic diversity. The high levels of genetic diversity observed in caribou are on par with the most variable terrestrial mammals which is counterintuitive to its current species-atrisk classification.

While genetic diversity in caribou is evident, a more in-depth analyses into caribou gene diversity revealed a “double edged sword” to such high levels of genetic variability in the maintenance of potentially detrimental gene variants.

Many threatened species with small populations have purged these harmful variants, but for caribou as a species-at-risk with high levels of both adaptive and deleterious gene diversity, this poses increased future risk in an already challenged species. For caribou populations presenting larger population sizes such as barren-ground caribou, the harmful variants have less chance of expressing themselves, however, as populations become fragmented and decline, the probability of these variants being expressed increases resulting in an overall loss of fitness.

Conserving the natural genetic diversity for caribou is important for adaptation to a changing global environment, and to prevent the expression of damaging gene variants to expedite the decline of populations.

These findings are part of a 20-year collaborative initiative between ECCC and Trent University through Dr. Micheline Manseau (ECCC) and Dr. Paul Wilson (Trent) as Principal Investigators of the Ecogenomics program, with Dr. Rebecca Taylor having been part of the program through both Trent and ECCC.

“The importance of the long-standing national caribou network established by me and Micheline that includes federal, provincial, territorial, Indigenous and private partners cannot be understated and has seen the transition from genetics into genomics in the research and monitoring of caribou at unprecedented spatial and temporal scales,” says Dr. Wilson, a professor in Trent’s Biology Department.

Dr. Rebecca Taylor, the lead author of the study says, “Caribou are highly genetically diverse, which is good news for their resilience in the face of environmental changes. However, they may be particularly at risk of loss of fitness, or inbreeding depression, especially following rapid population declines when compared to other species.”