Migrating caribou have a long way to go — and so do scientists trying to unravel the mysteries of how mammals, fish and birds make those long and arduous journeys season after season.
A recent paper by researchers out of the University of Calgary sheds more light on how caribou migrations across the North and the Rockies might be influenced by DNA passed down from ice age relatives.
“Basically, I wanted to see if there was a genetic component to migratory behaviour in different populations of caribou,” said Maria Cavedon, a postdoctoral fellow from the University of Calgary and the lead author on the study.
“There are many, many theories [about migration]. It could be, for example, that some animals learn from each other. Some animals may follow environmental clues, like the availability of resources and some animals might have a genetic mutation that forces them to migrate, and some animals have a combination of all these aspects or together.
“In my case, I just explored a potential component of genetics. It doesn’t exclude others. But I found that there might be a genetic component,” she said.
The researchers used GPS tracking and DNA sequencing to investigate the genes of 139 female caribou living in tundra or woodland habitats across western North America. Yukon-specific herds included the Kluane, Laberge, Tay River, Coal River and Hart River.
Among herds of Canadian caribou, migration levels vary. The barren ground caribou, a distinctive subspecies found in Alaska and northern Canada, makes the longest land migration in the world between their winter and summer grounds.
Other populations of woodland caribou, like boreal, central mountain and northern mountain inhabitants, make shorter migrations or remain fairly sedentary their whole lives.
The how and why of animal migration is still a mystery to scientists, but theories do exist around genetics, environmental triggers or “cultural” learning passed down to calves from adults. For this study, the researchers focused on genetic factors related to migration.
They identified over 50 genetic mutations associated with migratory behaviour. Twenty-seven of those were located in genes involved in brain activity, fat and energy metabolism, body development or hormone production.
Starting around 100,000 years ago, the last ice age resulted in massive glaciation that separated different caribou populations on either side of the Rockies. While that hard barrier no longer exists, there are still distinctive pools of genes associated with northern and southern ancestors.
“Possibly, this kind of behaviour comes from the past, like during the ice ages, when ice covered all of North America,” said Cavedon.
The researchers found that caribou with a greater proportion of genes from northern ancestors were more likely to migrate longer distances. This adaptation allowed them to survive in the harsher tundra landscape and avoid predators.
Caribou with more southern genes are likely to be more sedentary, adapted for the boreal forest where migration is less useful.
In the hybrid zone, where these populations have mixed in the Rockies, caribou are more likely to be migratory if they carry northern genes. The authors note that while it suggests a genetic link for migration, it does not rule out a “cultural” component, as calves grow up with their mothers.
Migrations are a powerful adaptation that allows animals to follow resources or avoid harsh conditions, but they also make them vulnerable to habitat fragmentation.
If migration is connected to genes – which adapt slowly over an ecological timeline – that could mean conditions are shifting too quickly for the caribou to adapt. And if the descendants of northern lineages go extinct, their ancestral genes for migration could be lost forever.
“Migratory behaviour is important for the ecosystem,” said Cavedon. “So if we lose migration that might have some negative repercussions on the ecosystem. In the case of caribou, there are many populations that are dramatically declining, and some are in very low numbers.
“So there’s a possibility that when the animals die, they might lose the genetic component to make it to migration. And it’s possible genes are declining so fast that they won’t have time to build up the genetic mutation to migrate,” she said.
Cavedon said the findings should support efforts to protect migratory corridors and could also inform larger studies that combine DNA-analysis with environmental factors to further understand how animals maintain their migrations generation after generation.
Contact Haley Ritchie at firstname.lastname@example.org