DNA Pulled From Paw Prints May Help Researchers Study Elusive Polar Bears

As rising temperatures threaten the Arctic mammals, scientists are turning to new, non-invasive methods to study them

Polar bear walking across a beach with water behind
Polar bears live in rugged, hard-to-reach places in the Arctic. U.S. Fish and Wildlife Service

Polar bears are mostly solitary creatures that can cover huge swaths of rugged, remote terrain in Canada, Norway, Russia, Greenland and Alaska. This makes them difficult to find and study—even as scientists have lots of questions about how they’re faring amid rising global temperatures.

Now, an emerging research method may be able to help. Scientists can identify individual bears by analyzing tiny amounts of DNA they leave behind in footprints as they traipse through the snow, according to two papers published recently in the journal Frontiers in Conservation Science.

This technique could make it cheaper, easier and safer to study polar bears and other similarly elusive creatures, which may ultimately bolster conservation efforts. Polar bears face numerous threats related to human activities, including declining sea ice from human-caused climate change, toxic pollution and habitat loss.

Historically, when scientists have wanted to collect genetic material from polar bears, they’ve had to locate, tranquilize and capture the gigantic mammals, which can weigh up to 1,700 pounds. This invasive method can be dangerous for both the bears and the researchers; in addition, some Indigenous communities oppose the practice over animal welfare concerns or fears of eating meat that’s possibly tainted by sedatives.

So, rather than relying on DNA obtained from the creatures directly, scientists wondered if they could utilize other means of collecting genetic material. They turned their attention toward environmental DNA, also known as eDNA, which animals leave behind as they wander through landscapes. They do so by dropping dead skin cells, shedding bits of fur and depositing feces, for example.

Past studies have successfully used eDNA to study other types of animals, including birds and fish. But this is the first time anyone has been able to link eDNA with an individual animal, reports Science’s Susan Cosier.

In a study published in Frontiers in Conservation Science this summer, researchers described how they identified six individual polar bears and determined the sex of each—based only on snow gathered from the surface of their tracks. The team investigated a total of 130 polar bear paw prints and was able to successfully isolate DNA from 46 percent of them.

In a second paper, published in the same journal this week, a different group of researchers demonstrated similar capabilities with both wild and captive Alaskan polar bears and Swedish Eurasian lynx, as well as a captive snow leopard. From snow gathered from the animals’ footprints, the team isolated DNA in all the captive samples, 59 percent of the wild lynx samples and 88 percent of the wild polar bear samples. They also linked DNA from the wild paw prints with 12 individual bears.

Researchers decided to home in on eDNA from paw prints, rather than from feces, because DNA degrades as it passes through the animal’s digestive system. Tracks, meanwhile, “usually contain fresh cells, and the DNA is intact because of the cold ‘storage’ temperature,” says ecologist Micaela Hellström, lead author of the study published this week and co-founder of the eDNA research company MIX Research Sweden AB, in a statement.

Moving forward, eDNA likely won’t replace all other polar bear research methods entirely. But scientists may be able to use it in concert with other techniques and technologies, such as tracking collars and other wearable devices, aerial studies using synthetic aperture radar and artificial intelligence models, and “bear-dar” detection systems.

“It’s like putting together a puzzle: You get small pieces of information from different sources,” says Jon Aars, a biologist at the Norwegian Polar Institute who was not involved in the new studies, to Science.

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