University of Calgary-led study finds natural mechanism that ensures long-term biological diversity in caribou

Like people, caribou are individuals. Each animal has a different colouration pattern, size, metabolism and other characteristics. And each behaves differently, including in specific environments.

But what drives such differences, or diversity, in caribou in the wild? Are such mechanisms similar in other animals, including people? And can understanding what gives rise to such diversity help conserve caribou, a threatened species in Canada, which recently became functionally extinct in the U.S. lower 48?

A five-year international study led by Faculty of Science biologists has identified a natural mechanism in caribou that preserves and ensures long-term genetic and behavioural diversity of the species in various habitats across western North America, from Alaska to the southern Rockies. This mechanism, called “balancing selection,” has resulted in caribou populations having not only distinctly different genetic traits but also diverse and likely adaptive behaviours, including whether individual animals migrate or not.

“This mechanism of balancing selection explains that two or more behaviours or characteristics can be selected at the same time,” says study principal investigator Dr. Marco Musiani, PhD, professor of ecology and evolutionary biology in the Department of Biological Sciences, and Veterinary Medicine (joint appointment). The mechanism balances the benefits of one type of behaviour or appearance (always being on the move or being tall, for example) with the benefits of other types.

Comparison of caribou living in different regions

Researchers compared the complete set of genes, or genomes, of barren-ground caribou that live in northern Canada’s tundra versus woodland caribou in the southern Rockies (an intermediate environment with some alpine tundra and forests) and in the boreal forest.

“We could tell the genomic differences between caribou that seasonally migrated versus caribou that were sedentary, or stay in one area throughout the year,” Musiani notes. These differences emerged even within individual animals in the same population — with some migrating, some not. “The patterns of selection we found in caribou highlight that in the past, we might have underestimated the role of genes in explaining differences of individuals within populations of caribou, as well as in other animals, plants and people.” 

“The most important implication is that, in terms of evolution, one behaviour doesn’t seem to be prevailing over the other,” he notes. “Both are maintained through balancing selection, and together they contribute to the long-term genetic and behavioural diversity of the species.” 

The research sheds light on the selection patterns in evolutionary biology that are common to other animals, including people, and also contributes to conservation biology, Musiani says. “In the future, when we plan conservation of caribou, we have to make sure that in these populations we maintain the diversity of the species, both in terms of genetics and of behaviours, because they are interlinked.” 

The study, “Genomics, Environment and Balancing Selection in Behaviorally Bimodal Populations: the Caribou Case,” is published in the journal Molecular Ecology.    

First-ever genomic study of caribou 

Since the time Darwin postulated the theory of evolution, biologists have struggled to explain a conundrum. If a specific behaviour or appearance is evolutionarily selected over another behaviour in a species, why doesn’t the selected behaviour take over in future generations while the other behaviour disappears altogether? 

The UCalgary-led research is the first genomic study of caribou and the first to confirm the gene-driven balancing selection mechanism in a wild species in nature, Musiani says. 

Researchers extracted DNA from archived samples from 270 caribou and examined 45,000 variable regions within the DNA — including threatened herds in Alberta, British Columbia, Yukon, Northwest Territories. Dr. Maria Cavedon lead author on the study, performed the bulk of this work in Musiani’s laboratory as part of her PhD. 

“Some of these DNA regions could be linked with actual genes that, when expressed, had to do with either morphology (each animal’s appearance) or behavioural characteristics or caribou’s persistence in certain environments,” Cavedon says. 

Researchers also correlated each animal’s genomic profile with a large database on movement and behaviour, gathered by GPS radio collars deployed by government biologists in Alberta, B.C., Yukon and N.W.T. 

The study indicates that whether an individual caribou becomes seasonally migratory or a sedentary resident will be determined by the predisposition of the genes along with the food, shelter (for calving and to avoid predators, for example) and other opportunities offered by the specific environment. 

Findings offer conservation options 

A surprise finding was that the genomic data revealed more similarities than expected between different populations of caribou, such as the Alberta and B.C. herds in the southern Rockies. 

Musiani says these links offer options for conservation managers to collaborate across jurisdictions. Captive breeding and introduction programs, for example, could include genetic screening and selective breeding, to ensure a diversity of genes and behaviour by tapping caribou populations in different locales rather than relying on local populations, some of which have very low numbers. 

“The use of genomic tools for answering questions around caribou conservation holds much promise to inform focused issues of management of small herds and captive breeding programs,” says Dr. Helen Schwantje, wildlife veterinarian in the wildlife and habitat branch of the B.C. Ministry of Forests, Lands and Natural Resource Operations. “We also hope to use this tool to inform the bigger picture of recovery of caribou — to identify interactions among this species, its health, other species and environment in our ever-changing western Canadian landscapes.” 

The international team included wildlife and habitat biologists and veterinarians and other researchers from the Alberta, B.C. and Yukon governments, the University of Princeton, the University of Salford in the U.K., the University of Alberta, the University of Montana, and Panthera, a species conservation organization in the U.S.