An Inuit hunter may have shot a polar-bear grizzly hybrid last week -- and while that's an unusual thing right now, scientists believe that such genetic mixtures of the two closely related species will become more common as retreating sea ice forces more polar bears ashore and into brown bear territory.
The hunter, Didji Ishalook, shot the bear in the Canadian province of Nunavut, near Hudson Bay, in accordance with laws that allow Inuit to practice subsistence hunting. He at first thought he had taken a small polar bear; but although its fur was mostly white, its paws were brown and the head was unmistakably shaped like that of a grizzly. (You can check out a picture of the kill here.)
DNA testing has yet to be completed, but polar bear expert Ian Stirling, an emeritus research scientist with Environment Canada and adjunct professor at the University of Alberta, was quoted in the Toronto Star as saying that, "I think it's 99 percent sure that it's going to turn out to be a hybrid."
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That the two species are capable of intermixing is, on a genetic level, not terribly surprising: They evolved from a common ancestor and, even after officially going their separate ways, crossed paths at various stages, primarily as changes in ice cover have brought them into each other's environments. Indeed, the brown bears on one southeast Alaska archipelago are particularly closely related to their Arctic cousins, and may in fact be descendants from an ancient polar bear population.
The greater issue is what provides the environmental and behavioral opportunity and incentive to interbreed?
"The unusual thing here is how did a male grizzly bear bump into a female polar bear," Andrew Derocher of the University of Alberta told the Toronto Star. "Most of the mating activity of polar bears is occurring out on the sea ice, so there's a spacial discontinuity between where a grizzly bear would be in the spring and where a polar bear would be in the spring."
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But as sea ice forms later in fall and melts earlier in spring, and as the tundra on which Arctic grizzlies live expands in extent, interactions between the two are likely increasing. Sometimes those encounters can be hostile, but at other times they are clearly of a different nature. According to CBC News, hunters have reported at least three of the hybrids -- known as grolars if the sire is a grizzly, and pizzlies if it is a polar bear -- since 2006. Furthermore, Derocher told the Washington Post, "What we're starting to see in the Canadian Arctic is three-fourth grizzlies," meaning the offspring of 50-50 hybrids that then mated with grizzlies.
Particularly given the relative expansion and contraction of their respective environments, Derocher feels that, in the long-term, the polar bears are the ones getting the genetic short shrift of this development.
"I hate to say it," he told the Post, "but from a genetic perspective, it's quite likely grizzly bears will eat polar bears up, genetically."
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