Climate change may have shaped polar bear origins

ALLISON CROSS
Canwest News Service

DNA extracted from a polar bear fossil found in Norway is giving scientists rare insight into the origin of the species, suggesting that polar bears may have evolved from brown bears in response to climate change in the past.

“Our results confirm that the polar bear is an evolutionary young species that split off from brown bears some 150,000 years ago and evolved extremely rapidly,” said researcher Charlotte Lindqvist, from State University of New York at Buffalo.

“Perhaps adapting to the opening of new habits and food sources in response to climate changes,” Lindqvist said.

But the polar bears’ success in weathering temperature fluctuations over the past 150,000 years doesn’t necessarily mean the bears, like those living in Canada’s North, can make it through global warming today, the researchers said.

Lindqvist explores the evolutionary origins of polar bears in a paper she co-authored with researchers from Penn State University and the University of Oslo, and published recently in the journal Proceedings of the National Academy of Sciences.

Polar bear fossils are rare, but in 2004, a geologist from Iceland found a fossil jawbone and canine tooth in the Svalbard archipelago of Norway, north of the mainland.

After the find, Lindqvist drilled into the bone and tooth to extract powder that could be analyzed. Scientists then sequenced the mitochondrial DNA, which tends to reveal the most useful characteristics when examining the evolution of a species.

Knowing the age of polar bears actually helps scientists better determine which major climate events they lived through, Schuster said.

But it would be wrong to assume that because polar bears were resilient in the past, they are just as resilient now, Schuster said.

“You have to be… careful because a polar bear from 50,000 years ago or 100,000 years ago might have been a different animal,” he said. “There is always a constant change.”

Polar bears live their lives on the ice, so when they die, their remains often sink to the bottom of the ocean or are picked apart by scavengers.

There are only two known polar bear fossils in the world, said Stephan Schuster, from Penn State’s Centre for Comparative Genomics and Bioinformatics, and only one contains any DNA.

Many scientists believe that polar bears in Canada, and elsewhere in the world, are threatened by a loss of their sea ice habitat as a result of warming temperatures.

“The polar bear may be more evolutionarily constrained because it is today very specialized,” Lindqvist said. “[It is] physically and behaviourally well-adapted to living on the edge of Arctic ice, subsisting on a few species of seals.”

There is significant concern that polar bears across the world will become “extirpated,” which means to disappear or retreat from a region, although continue to live in other areas.

Andrew Derocher, a polar bear biologist at the University of Alberta in Edmonton, said some estimates peg the polar bear as being much older than 150,000 years.

Some research indicates they have been around 700,000 years, or for even as long as one million years, he said.

“I don’t think the research tells us very much [about the future] of polar bears,” he said. “But it helps to fill in some of the gaps about the past. That’s really where our understanding of the evolution of polar bears is really challenging us.”