Migrating is in the genes of reindeer – but not in all of them | Polarjournal
Caribou and reindeer are indeed the same species. But while the latter are native to Europe and Siberia, caribou are at home in North America and live as different subspecies in different regions with likewise different migratory behavior. Picture: Ben Townsend via Flickr CC BY-SA 3.0

Reindeer are an epitome of Arctic and of migrations. The large caribou herds in Canada and Alaska, in particular, travel long distances each year to migrate from the interior to the coasts and then back again. The reasons given are food availability and protection from the mosquito swarms. But a study by Canadian and American researchers has now shown that it has been in the genes of animals to migrate for thousands of years. But not all of them.

The research team, which included first author Maria Cavedon and study leader Marco Musiani of the University of Calgary, concluded after genetic studies that caribou in Alaska and Canada can be divided into two gene subgroups, a northern and a southern. According to the researchers, this division was formed during the last ice age, when a huge ice sheet divided the reindeer populations. The results of the work further show that the offspring of the northern gene subgroup have mutations in genes associated with pronounced migratory behavior, in contrast to the southern subgroup. “We determine that propensity to migrate depends upon the proportion of ancestry in individual caribou, and thus on the evolutionary history of its migratory and sedentary subspecies,” the research team wrote in its paper, which appeared in the journal PLOS Genetics last week.

Reindeer are found throughout the Arctic and were once found as far as Ireland, Scotland and as far as the Midwest in the United States. While North American caribou are virtually all wild, reindeer in Europe (except on Svalbard) are more often semi- or fully domesticated. Picture: Stefan Leimer

For its study, the research team examined a total of 139 caribou from different herds that occur in different habitats in Alaska and Canada. Indeed, caribou are not only tundra dwellers, but also occupy other niches in North America such as in coniferous forests and even the barren areas of northern Nunavut and the Northwest Territories. Therefore, they are also divided into different subspecies by researchers. Since the 139 animals studied had all also been equipped with GPS transmitters, Cavedon was able to link the animals’ migratory behavior with their genetic information and compare each individual animal. This showed that animals with more pronounced migratory behavior had mutations in genes that could already be linked to migratory behavior in other animal species. These are mainly genes related to brain activity, cognition and fat deposition in the body.

The “barren ground” subspecies of reindeer has adapted over time to the barren conditions of Nunavut, Greenland and the Northwest Territories. It belongs to the reindeer with distinct migratory behavior and thus to the northern gene subgroup. Picture: Michael Wenger

Another, rather surprising result of the study was the fact that even individual animals in the subspecies that normally do not migrate as far showed the dispositions for increased migration and also migrate correspondingly further than their conspecifics. The research team concludes that there may be an intrinsic driver that helps control migration behavior. An additional factor could be the evolutionary history of each animal, that is, how high the genetic proportion of northern and southern populations is within each animal.

Whether reindeer or caribou, animals in many Arctic regions are under pressure not only from climate change, but also from barriers, resource extraction, pathogens and pollution. Genetic control of migration would make it more difficult for animals to adapt to new conditions. Picture: Michael Wenger

One conclusion of the study is that migration, and the genetic information for it, is unequally distributed in different populations. From this, Cavedon and her colleagues conclude that genetically influencing caribou migrations could be a problem for the animals in the future. Because reindeer, which are already negatively affected in some places by various factors, would not be able to look for new areas due to the complete loss of genetic information, could therefore become locally extinct. This, the team said, could “perhaps be averted with the maintenance of critical seasonal habitats for caribou within and between seasonal ranges — a strategy also allowing for long-range movements and migration.”

Dr Michael Wenger, PolarJournal

Link to the study: Cavedon M, vonHoldt B, Hebblewhite M, Hegel T, Heppenheimer E, Hervieux D, et al. (2022) Genomic legacy of migration in endangered caribou. PLoSGenet 18(2): e1009974.

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