Could climate change cost polar bears their white fur?

In this circa 2006 photo provided by the Canadian Wildlife Service, hunter Jim Martell, left, is seen with a hybrid bear he shot while on a hunting expedition on Banks Island, Northwest Territories, Canada. According to Dr. Ian Stirling, researcher for the CWS, genetic tests showed the bear had a polar bear for a mother and a grizzly bear for a father.

It's long been known that the brown bears found on islands in Southeast Alaska are more closely related to polar bears than other brown bears. Now scientists wonder if they're a harbinger of what's to come for polar bears in the warming high Arctic. Researcher Beth Shapiro of the University of California in Santa Cruz told the Canadian Press the bears on Admiralty, Baranof and Chichagof islands (known as the ABC bears) appear to be descended from a polar bear population that got cut off from other polar bears when ice retreated after the last ice age.

Shapiro and her team decided to look more closely at the ABC bruins. They employed sophisticated DNA analysis to look deeply into their past. What they found is that ABC bears are genetically close to polar bears because that's what they used to be.

Shapiro's paper suggests that the ABC bears are a remnant of an ancient population of polar bears that lived in the area during the last Ice Age. As that period ended and the ice slowly retreated, the ABC population got cut off from other polar bears.

"They couldn't mate with any more polar bears," Shapiro said.

"As the weather started to get warmer and warmer, brown bears — males, as it turns out — could swim across the channel that separated the ABC islands from the Alaskan mainland and colonize these islands. There they ran into this isolated, trapped population of polar bears and they started hybridizing with them."

Shapiro says recent discoveries of polar bear / brown bear hybrids in the Arctic could be the first step in a similar process of habitat change that over thousands of years could wipe out pure-white bears.

Read more at Climate change could turn polar bears brown, study says