Pizzly Bears: Warmer Climate Leads to Hybridization

First Posted: Sep 09, 2015 10:58 AM EDT

For decades, while in captivity, polar bears and grizzly bears have been known to mate and "hybridize," the resulting offspring known as pizzly bears (sometimes called grolar bears). This hybrid phenomenon, at first only speculated to occur in the wild, is now becoming a somewhat regular occurrence. 

In 2006, an strange-looking polar bear was killed by an American hunter on Nelson Head, in the Northwest Territories of Canada. Later DNA testing confirmed that the bear was the first recorded pizzly found in the wild. Then, in 2010, a second strange-looking bear was shot. This second bear was confirmed to be an even greater surprise, as it was revealed to be a hybrid bear's offspring, making it a second-generation pizzly, according to Spiegel Online.

"It's important to recognize that polar bears branched off of grizzly bears rather recently in evolutionary terms," said Dr. Brendan Kelly, chief scientist and director of conservation research at the Monterey Bay Aquarium and long-time researcher of Alaskan ecology. "When a species splits into two it doesn't happen overnight. It takes a period of isolation for them to evolve differences, and it often takes an even greater period of isolation for them to become so different that they can't hybridize if they re-encounter one another."

Now, warmer climates and melting ice have forcing polar bears south, and grizzly bears north, causing the two to share a space much more frequently than they have, according to WBFO.

This hybrid breeding, although fascinating, may have extreme negative effects on the polar bear population, especially considering the specialization of the bear's evolution. Polar bears are adept hunters, with strong swimming skills and a camouflaged coat arguably more incredible than any other bear's.

"People often think of extinctions as, well, simply, a population becomes smaller and smaller and smaller until there's none left," Kelly said. "However, the reality is more complex. As the very specialized polar bear become increasingly likely to breed with the more generalized grizzly bear, the polar bear could eventually become consumed by this hybridization and effectively go extinct."

Polar bears aren't the only species that's shown signs of cross-breeding and hybridization. The North Pacific right whale stands the greatest threat for extinction, among cross-breeders, as their numbers have dropped to only 200, and unlike the pizzly, most of their hybrid offspring are infertile. There are other marine mammals going through hybridization, including narwhals and beluga whales, as well as bowhead whales and other species of right whales, according to Inhabitat.

"There's a lot of weird stuff going on in Alaska, and there's a lot of weird stuff going on in Siberia, Scandinavia, Canada as well," said David Biello, environment and energy editor for Scientific American.

The main danger posed to the hybrids themselves is that they aren't as well suited to their respective environments as their parents. Pizzly bears tend to hunt like polar bears, but lack the strong swimming skills of polar bears, and their grizzly bear-like claws prevent them from moving well on ice. 

It is expected that climate change and environmental degradation will bring about more hybridization. Polar ice melting is forcing polar bears onto dry land, while road construction and mining in southern Canada are pushing grizzlies north, according to Spiegel Online.

A 2010 essay in the journal Nature counted 34 species that could be affected, including: belugas with narwhals, largha seals with common seals, and Greenland whales with North Pacific right whales.

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