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Wolf-Dog Mating Led to Darker Wolves

Christine Dell'Amore
National Geographic News
February 5, 2009
 
The black wolves that haunt scary stories would have been mere fiction were it not for domestic dogs.

A recent study surprised scientists by revealing that the gene for darker coats in gray wolves, at least in North America, originated in our best furry friends.

Although it's well known that dogs descended from wolves, the new finding implies that some genetic material moved backward in the evolutionary chain.

(From wolf to woof: see pictures of dogs' evolution from wolves.)

This isn't to say that darker wolves resemble dogs, said study co-author Greg Barsh, a geneticist at Stanford University in California.

"It's quite clear that black wolves are just as much wolf as a non-black wolf," Barsh said. But this small amount of dog genes may have given black-coated wolves a selective advantage.

Native American Dogs

Among the gray wolves in North America, the number of dark wolves in a given population can range from 10 to 70 percent. Worldwide, the only other wolves known to have darker coats are in Italy.

Scientists know there are particular gene receptors that cause dark colors in animals as diverse as birds, fish, and rabbits.

But when Barsh and colleagues looked at variations of those genes in wolves and coyotes, the researchers found that those variations didn't affect the color of the canines' fur.

Instead, a more unique gene that darkens fur in dogs was found in dark wolves and coyotes from Wyoming's Yellowstone National Park and the Canadian Arctic.

(See photos of dogs submitted by National Geographic magazine readers.)

Thousands of years ago, the researchers suggest, a few wolves mated with dogs—possibly kept as pets by Native Americans—creating hybrid animals that passed on their genes.

The study appears in this week's issue of the journal Science.

Unknown Benefit

The new work's genetic data is "as good as it gets," said Marc Bekoff, an ecological and evolutionary biologist at the University of Colorado at Boulder who was not involved in the study.

But the research can't answer some of the larger questions, including why darker wolves tend to live in forests.

"It does seem natural to say, Oh, well there's more black wolves in the forest because that helps them blend into their environment," study author Barsh said.

But wolves don't depend on camouflage to hunt, biologists have found, suggesting that the benefit of being genetically coded for dark fur might not be related to color.

"That's an intriguing idea, because it turns out [the same] gene is involved in humans in helping bolster the immune system to fight off infection," Barsh said.

Who's a Wolf?

The new study may also help conservation biologists think beyond traditional views on genetic diversity, Barsh added.

"There is sometimes one school of thought that to preserve species diversity is to keep the natural population pure," he said.

"This is an example where preserving genetic diversity has in fact been facilitated by a hybridization event with a domesticated animal."

The newly identified dog gene may also "ask us to consider who's a wolf," Colorado's Bekoff added.

"It's going to ask us to revise what we think about what is wild and natural [in animals], and how we protect those species."
 

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