On Christmas morning, many families gather around the tree to enjoy gifts brought via reindeer-powered sleigh. However, Santa’s reindeer waited for the end of the last Ice Age to celebrate a family reunion with their caribou cousins. Now, climate change could tear them apart.

A recent DNA analysis of caribou, aka reindeer (Rangifer tarandus), mapped how the mammals survived in North America during the past 21,000 years. During the last Ice Age, caribou herds retreated to pockets of stable habitat further south or between the glaciers.The reduction in the animals’ populations and inability to mate with caribou in other refuges left a genetic signature in the modern animals. Nature Climate Change published the results of the analysis.

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After the ice melted, the isolated populations recovered and interbred with a fresh wave of reindeer that crossed over from Eurasia. The Eurasian newcomers were long-lost relatives of the caribou. Biologists consider Eurasian reindeer and caribou in North America to be the same species. Rangifer tarandus goes by the name reindeer in Europe, where the Sami and other cultures have herded and hitched them to sleds for centuries. In the western hemisphere, the Micmac people called the animals yalipu, which became caribou in Canadian French.

The International Union for the Conservation of Nature lists the reindeer/caribou as a species of least concern, because plentiful numbers of the beasts populate the Arctic from Scandinavia to eastern Canada. However, biologists note that certain groups of reindeer/caribou are genetically and behaviorally different. Some of these subgroups, such as woodland caribou, face threats that could wipe out their distinct populations, even while other groups thrive.

Climate change is one of those threats to particular caribou/reindeer populations. As the Arctic warms, caribou in North America could lose chunks of their home range, warned the authors of the recent genetic analysis. The scientists predicted that by 2080, North American caribou may have to shift their range further north. Southern populations may die out, while those in the northeast may lose up to 89 percent of their current homeland.

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“The woodland caribou is already an endangered species in southern Canada and the United States,” said study co-author Marco Musiani of the University of Calgary. “The warming of the planet means the disappearance of their critical habitat in these regions. Caribou need undisturbed lichen-rich environments and these types of habitats are disappearing.”

Splintering the caribou community could reduce their ability to interbreed, which would reduce their genetic diversity.

“When a population loses genetic diversity, they lose the ability to adapt to change,” said Kris Hundertmark, study co-author and wildlife biologist-geneticist at the Institute of Arctic Biology at the University of Alaska Fairbanks, in a press release. “Those caribou herds that shift their range to remain within their habitat and those herds that are reduced in size and become isolated from neighboring herds are those most threatened with loss of genetic diversity. That is why it is important to know what areas will be have the most habitat stability in the future.”

IMAGE: Caribou Herd and Isanotski Peak. Isanotski Peak is located on Unimak Island, Alaska (John Sarvis, U.S. Fish and Wildlife Service, Wikimedia Commons)