Rare "Blue" Glacier Bears At Risk Of Being Lost To Neighboring Black Bear Populations

A Black bear with two Glacier bear cubs. National Park Service/Wikimedia

Rachael Funnell 28 Jul 2020, 19:32

Earlier this month scientists warned that without effective measures against climate change, warming global temperatures could spell the end of polar bears by 2100, and new research published in the journal Ecology and Evolution predicts this grim fate may be shared by another ice-loving bear with a very different coat.

Glacier bears are genetically black bears, but, as anyone who’s had the rare honor of spotting one in the wild will tell you, their coats are closer to bluish grey and silver than black. They first became distinct from black bears in the middle of the Pleistocene when an enormous ice sheet separated populations in western North America from the rest of the continent.

The separation pushed the populations down a different route of evolution and glacier bears adapted to their new home carved from ice. They now occupy the glacial habitats in Southeast Alaska, and wildlife biologists at the Glacier Bay National Park and Preserve have been studying the populations in the region to find out more about these little-known, little-seen animals.

They identified 10 populations across the National Park that were geographically isolated by fjords, glacier-capped mountains, and ice fields – environments all dependent on a cool temperature. Though not insurmountable, Tania Lewis, one of the world’s experts on glacier bears, told National Geographic that these obstacles have divided the population into functional islands of bears and each group becomes progressively more genetically distinct from their neighbors as time goes by, including black bears.

As well as keeping apart from each other, the bears have failed to spread beyond their local habitats despite there seemingly being nothing to stop them from moving on. “The area where there are not glacier bears has the least amount of barriers to dispersal,” Lewis said. “The mountains aren't that tall; the glaciers aren't that extensive. It's really interesting that there aren't any glacier bears there.”

Glacier bears lighter fur color may be an adaptation to the icy landscapes which they have inhabited since the mid-Pleistocene. National Parks Service/Wikimedia

A possible explanation could be that the ice present in their habitats may be crucial for the bear’s survival, a worrying picture in the face of Alaska’s melting glaciers that are situated in one of the fastest-warming places on Earth. This reliance on ice is also suspected to be the key to understanding their unusual blue coats, which specialists hypothesize may have emerged as a means of camouflage amidst the icy, cool-blue glaciers.

Lewis and colleagues fear that if temperatures continue to climb, the bears could lose more than just their favored habitat. The genes that give glacier bears their characteristic coloration are likely controlled by recessive genes, meaning if the obstacles that have kept these rare animals separate from more common black bears disappear, so too could the glacier bear phenotype as black bear genes become dominant in the population. It’s therefore imperative that steps be taken to control the unprecedented climbs in temperature in this region, lest the glacier bear’s genes become diluted out of existence.

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