As the Arctic continues to warm, it comes as no surprise that cold-adapted species, such as polar bears, are moving north in an effort to survive, while those that favor more moderate temperatures are expanding into regions that have now become hospitable habitats for them. One of these species is the grizzly bear, which seems to be exploring territories that were formerly the domain of bears of the “polar” variety. In fact, between 1996 and 2009, nine grizzlies were spotted in Wapusk National Park, just south of Churchill, Manitoba, Canada.
It may just be the tip of the iceberg, so to speak. According to Dr. Andrew Derocher, a polar bear biologist at the University of Alberta in Edmonton, Canada, who has studied the recent patterns of sea-ice loss in Hudson Bay, it’s unlikely that there will even be polar bears in the park by the end of the century. Soon, Churchill may have to change its nickname from “Polar Bear Capital of the World” to “Grizzly Grain Port of the Great North.”
The “pizzly” (or “grolar”) bear
When grizzlies and polar bears meet, of course, an opportunity for mating occurs. To date, scientists know of one hybridization event in the wild between the two bear species. In 2006, a hunter who thought he was aiming at a polar bear shot a grizzly-polar bear hybrid in the Northwest Territories. After noticing that the bear had brown patches interspersed within its white fur, wildlife officials seized the animal. The bear also had a humped back, long claws and a facial profile that was concave—all traits characteristic of a grizzly bear. Genetic tests confirmed that the hybrid’s father was a grizzly, and its mother was a polar bear.
Then, on April 8, 2010, an Inuvialuit hunter, David Kuptana, from Victoria Island in the Canadian Arctic Archipelago, shot what he thought was a polar bear. But after inspecting the bear, he found that the animal had brown fur on its paws, long claws and a grizzly-shaped head. DNA testing indicated that the bear’s mother was a grizzly-polar hybrid and the father was a grizzly bear. This animal could well be the first recorded second-generation polar-grizzly bear hybrid found in the wild. While some have taken to calling the hybrids “pizzlies,” others prefer “grolar bear.” Canadian authorities suggest “nanulak,” taken from the Inuit words for polar bear (nanuk) and grizzly (aklak).
Evolution on the fast track
While hybrids in nature aren’t all that unusual, the polar-grizzly bear mix may be a different “animal,” so to speak. We may be speeding up evolution, in a way that nature didn’t intend. For at least 10,000 years, the Arctic ice cap has been a continent-sized, physical barrier that kept many species isolated from each other. Animals adapted to their specific environments—over centuries and many generations—by developing DNA changes that suited their climates better than their old genes did. Individuals don’t adapt genetically; it’s populations that do.
Currently, however, we’re losing Arctic sea ice in a matter of decades. Enough time for an adaptive response may just not be there. In theory, hybridization leads to fitter, more well-adapted animals. First-generation hybrids often exhibit excellent survival characteristics, known as “hybrid vigor.” But successive generations typically fall victim to “outbreeding depression,” a rapid falling off in fitness. It could be that pizzlies might not be able to reproduce enough to sustain themselves. Or, they might carry mutations that will kill them. And the fact that the polar bear is an endangered species makes the matter worse. When a species hybridizes, its gene pool can be taken over and “lost.” The polar bear that we know today simply won’t exist anymore. Polar bears appear to be taking a one-two punch: not only are they being lost due to climate change and the resultant melting sea ice, they are suffering from hybridization.
More Arctic hybrids in the future
Last year, whale experts confirmed the existence of a bowhead-right whale hybrid in the Bering Sea. And a narwhal-beluga whale mix was found in Greenland. Unfortunately, the narwhal-beluga (“narluga” or “belwhal”?) lacked the narwhal’s tusk—an important element in narwhal breeding success. Narwhals are rare, and if they waste their reproductive efforts breeding with belugas, soon there will be very few pure narwhals left.
Hybridization is just one more factor in an endangered species’ decline and loss of biodiversity in the world. Unfortunately, the Endangered Species Act has no official policy for dealing with hybrids. In some cases, wildlife managers propose culling hybrid offspring in order to keep genetic lines of endangered species pure.
Do you think that such measures should be taken to ensure the continued existence of pure polar bears? It’s a question we may have to answer—and soon.
Here’s to finding your true places and natural habitats,