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'Grolar' hybrid bears confirmed in Canadian study

Few hybrid bears suggest Canadian polar bears not yet getting 'genetically swamped' by grizzlies, say researchers
Scientists with the Environment and Climate Change Canada and the Northwest Territory government spot a polar bear-grizzly hybrid in 2012 while surveying the Viscount Melville polar bear subpopulation.

The existence of eight hybrid ‘grolar’ bears — part grizzly, part polar bear — has been confirmed off the north coast of Canada in new research experts say is a good sign the ice-dwelling ursine species won't be bred out of existence anytime soon.

The study, published in the journal Conservation Genetics Resources Thursday, brought together a North American team of researchers to examine old genetic samples spanning 1975 to 2015.

While polar bears evolved from grizzly bears several hundred thousand years ago, the hybrid bears didn’t show up until about 20 years ago, a phenomenon likely brought on by climate change, said corresponding author Ruth Rivkin, a postdoctoral research fellow with Polar Bears International at the University of Manitoba.

A warming Canadian Arctic means the two bear species are likely to come into contact more frequently as male grizzlies are able to move further onto sea ice, encounter reproductively active female polar bears, and mate with them, she said. 

“Previously, with colder temperatures, they wouldn't be able to find enough food sources to be able to survive in these high arctic environments,” said Rivkin of the male grizzlies. “And now we're seeing more often that they are surviving.” 

Genetic tool used to 'fish' bear DNA

The study’s researchers used a new technology, which can quickly and accurately track more than 8,000 polar bear genetic markers using a tissue or blood sample.

Joshua Miller, the study's lead author and an assistant professor of Biological Science at MacEwan University in Edmonton, helped build the technology. He said the chip looks similar to a large glass slide you might see in a high school biology classroom.

Slightly smaller than an smartphone, when researchers introduce a sample to the chip, DNA already embedded on its surface acts like bait that draws out tens of thousands of genetic matches.

“Their job is to kind of fish out the corresponding sequence from the polar bear or the grizzly bear sample,” Miller said. 

The researchers then take a photo through a microscope and compare the 8,000 genetic markers they see to known genetic sequences of the two bear species. A solid match will tell them whether it's a polar bear, grizzly or something in between.

The team analyzed old genetic samples from 371 polar bears and 440 grizzly bears from across Canada, Alaska and Greenland. Of those, only eight were found to be hybridizations, a slim one per cent of all samples.

Rivkin, who also works with the San Diego Zoo Wildlife Alliance, said the hybrids all came from a single female polar bear, whose hybrid offspring have since mated again. That makes all Canada’s known hybrids ‘grolar’ bears, the term given to a hybrid whose father is a grizzly. A ‘pizzly’ bear, by contrast, has a polar bear for a father. 

Rivkin said so far no pizzlies have been genetically identified in Canada, but that doesn’t mean they — or more grolars — don’t exist. Indigenous communities have a long reported the existence of hybrid bears and continue to do so today. What’s challenging, said Rivkin, is confirming that with a genetic analysis. 

“We do have lots of visual reports about hybrids,” she said. “But it can be really hard to tell just by looking at a bear if it is a hybrid or if it's possibly just a dirty polar bear.”  

As ice thins, hunting becomes harder and 'genetic swamping' more likely

Telling the bears apart is important to understand how polar bears are adapting to a warming planet. Climate change is heating up Canada’s north four times faster than the rest of the world, and as sea ice melts, the movement of the bears, including their ability to hunt on the ice and find mates to breed is expected to be challenged.

In another study published Thursday, a second group of researchers from the University of Manitoba found a sub-population of polar bears in Hudson's Bay might only have about a decade left as sea ice they cross to hunt is becoming too thin to support them.

“In the face of global climate change, species have a limited number of possible responses: move to more favourable habitats, adapt to the new conditions, or suffer local extinction,” wrote Miller and his colleagues.

In the past, bear hybridization through “genetic swamping” was more common. The descendants of grizzlies, polar bears have also been completely displaced by their ancestors through inter-breeding. Research on the Alaskan islands of  Admiralty, Baranof and Chichagof, found ABC Island bears are the descendants of a polar bear population that was gradually converted as male brown bears bred with the previous population.

Rivkin says she and her colleagues began their latest study worried that the same thing was increasingly happening across the Arctic. She said the fact they didn’t find any new hybridization across the Arctic is a positive sign grizzly genetics won't drive out polar bears as a unique species any time soon. But it doesn’t mean that climate change isn't already accelerating that possibility. 

Uncertain adaptations

Miller said he hopes to use the new technology to expand genetic studies of polar bears across the Arctic Circle. Researchers also plan to use the chip to analyze genetic diversity within polar bear populations. 

That matters, said Miller, because genetic diversity is the “fuel” for evolution, allowing species to persist and adapt to the future. And while hybridization could allow polar bears to gain some of the adaptations that help grizzlies survive a warmer climate, it can also lead to uncertain outcomes.

Evan Richardson, a research scientist from Environment and Climate Change Canada who co-authored the study, captured a hybrid bear several years ago. When he examined the animal, he found claws longer than a grizzly's but less hooked than those a polar bear uses to gaff seals.

“You get these hybrids who aren’t very good at anything,” said Richardson.

On the other hand, a few years later, Richardson said he came across a second generation of hybrid cubs that looked very similar to a grizzly, at least on the outside. 

“We think they’re trying to live like polar bears. Their mother was a polar bear and so we think she taught them to be polar bears,” he said. 

“It would be great to run into these hybrids again and see if they’re surviving.”

Stefan Labbé

About the Author: Stefan Labbé

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