Rare Family of Hybrid ‘Grolar’ Bears Found in Canadian Arctic

Eight grolars—polar-grizzly bear hybrids— live in Canada's Arctic. The family of bears are the only grolars known to exist in the world. GNWT/Jodie Pongracz

Canada is home to the world’s only known group of “grolars,” a family of eight polar and grizzly bear hybrids that live in the Far North, according to a newly published study.

A team of North American researchers studied 819 wild grizzly and polar bears across Canada, Alaska, and Greenland, to determine if the two species of bears were regularly intermingling.

The findings, published last week in the journal Conservation Genetics Resources, have allayed fears by some scientists that climate change could be leading to regular interbreeding between the two species, at least for the present.

“I had anticipated finding more hybrids other than the eight that we already knew about,” study author Ruth Rivkin told The Epoch Times.

“Grizzly bears are coming increasingly into contact with polar bears during their breeding season, which should make the possibility of hybrids more likely. Since we didn’t find any recent hybrids other than those eight, I think that hybridization is quite rare.”

All eight grolars belong to a single family spanning three generations, the study found. The hybridization occurred when a female polar bear born in 1989 mated with two different grizzly bears on separate occasions, producing four hybrid cubs. One of her cubs also mated with the same grizzly males, producing four additional grolars, an occurrence referred to as “backcrossing.”

Habitat Overlap

Canada’s western Arctic is the most likely location for hybridization to occur, says Ms. Rivkin, a postdoctoral research fellow at the University of Manitoba. That’s because it is one of the few regions worldwide where grizzly and polar bear habitats have begun to overlap.

Although hybridization between the species has yet to become a common occurrence, Ms. Rivkin said it is important the populations be monitored.

That is where the genetic sequencing chip known as the Ursus maritimus V2 comes in. The chip, which was used in the previous study to analyze the DNA of 371 polar bears and 440 grizzly bears, could continue to be used to track hybridization, Ms. Rivkin said. The samples were collected between 1975 and 2015.

The chip, which “looks a bit like a microscope slide,”  has four slots where bear DNA samples are placed, Ms. Rivkin said.

“The chip was designed to pick out genetic markers that correspond specifically to grizzly bears and polar bears,” she said. “When a grizzly sample is loaded, the grizzly markers will be sequenced and will show up in the output, whereas when a polar bear sample is loaded, the polar markers will be flagged.”

Hybrid bears will have both sets of markers. For instance, hybrid DNA could show up as 50 percent grizzly and 50 percent polar bear, indicating recent interbreeding while later generations could show up as 75 percent grizzly and 25 percent polar bear.

“We can detect those bears on the chip so we are able to determine how many generations of hybridization have happened to create the bear that we are sampling,” Ms. Rivkin said.

“We’re able to detect up to three generations of backcrossing with very high accuracy. After that point, the hybrids are too genetically similar to the parental species (grizzly bear or polar bear) to be told apart.”

‘Special Concern’

Polar bears are currently labelled as of “special concern” by the World Wildlife Fund Canada, meaning they are currently at risk of becoming threatened or endangered. If interbreeding were to become more common, it would be a major concern, the study found, adding that “unchecked hybridization” would become a conservation threat if the two species were to collapse into a “hybrid swarm.”

If hybridization became rampant, the unique genetic variation polar bears possess could eventually be lost, meaning that the bear population in those colder regions could become exclusively grizzly, Ms. Rivkin said.

A second, less likely scenario would be that hybridization between polar bears and grizzlies would create warm-adapted genetic markers in to the polar bear population, she said.

“Grizzlies live in warmer environments than polar bears, and some likely carry specific genetic adaptations that help them survive warmer summers,” she said. “Low levels of hybridization may allow those genetic adaptations to spread into polar bears.”

For this to occur, however, the hybrid bears would need to mate with polar bears, something that does not typically occur. All hybrid bears studied thus far have “backcrossed” with grizzlies, rather than polar bears, Ms. Rivkin said.

While only eight hybrid bears were identified in the more than 800 samples tested, that doesn’t mean more hybrids don’t exist outside of the sampled population. It is also possible that hybrids were born after 2015, the last year included in the study. Still, testing suggests this occurrence is “very rare,” Ms. Rivkin said.

Despite that rarity, monitoring the northern bear populations “will be important … so that we know as soon as possible if hybridization starts to become more frequent.”