Download new world wolves and coyotes owe debt to dogs

New World Wolves and Coyotes Owe Debt to Dogs
By Mark Derr, The New York Times
February 5, 2009
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Researchers have determined that black-coated wolves, like these in Yellowstone
National Park, got their distinctive color from dogs.
In a bit of genetic sleuthing, a team of researchers has determined that black wolves and
coyotes in North America got their distinctive color from dogs that carried a gene
mutation to the New World.
The finding presents a rare instance in which a genetic mutation from a domesticated
animal has benefited wild animals by enriching their “genetic legacy,” the scientists write
in Thursday’s Science Express, the online edition of the journal Science. Because black
wolves are more common in forested areas than on the tundra, the researchers
concluded that melanism — the pigmentation that resulted from the mutation — must
give those animals an adaptive advantage.
Although common in many species, melanism in dogs follows a unique genetic pathway,
said Dr. Gregory S. Barsh, a professor of genetics and pediatrics at the Stanford
University School of Medicine and the senior author of the paper.
Last year, Dr. Barsh and his laboratory identified a gene mutation responsible for the
protein beta-defensin 3, which regulates melanism in dogs. After finding that the same
mutation was responsible for black wolves and black coyotes in North America, and for
black wolves from the Italian Apennines where wolves have recently hybridized with
free-ranging dogs, the researchers set out to discover where and when the mutation
evolved.
Comparing large sections of wolf, dog and coyote genomes, Dr. Barsh and his
colleagues concluded that the mutation arose in dogs 12,779 to 121,182 years ago, with
a preferred date of 46,886 years ago. Because the first domesticated dogs are estimated
to date back just 15,000 to 40,000 years ago in East Asia, the researchers said that they
could not determine with certainty whether the mutation arose first in wolves that predate
that time, or in dogs at an early date in their domestication.
Robert K. Wayne, an evolutionary biologist at the University of California, Los Angeles,
who studies canine evolution and is a co-author on the Science paper, said in an
interview that he believed the mutation occurred first in dogs. But even if it arose first in
wolves, he said, it was passed on to dogs who brought it to the New World and then
passed it to wolves and coyotes soon after their arrival.
Dr. Wayne and his colleagues have dated the presence of dogs in Alaska to about
14,000 years ago and are now checking ancient dog remains from across the Americas
for the mutation.
The researchers concluded that the mutation is subject to positive selection, meaning
that it serves some adaptive purpose. Cross-breeding produces offspring with one set of
genes from each parent, in this case a dog and a wolf. If all subsequent breeding takes
place among wolves, the dog genes eventually vanish, unless one or more of them
helps the organism survive.
Scientists have not yet identified the mutation’s purpose, but they suggested that its
association with forested habitats meant the prevalence of melanism should increase as
forests expand northward.
In an interview, Dr. Barsh observed that beta-defensin is involved in providing immunity
to viral and bacterial skin infections, which might be more common in forested, warmer
environments.
Marc Bekoff, a behavioral ethologist from the University of Colorado, who was not
involved in the project, said more work was needed to show what adaptive advantage
black coats might provide. But, Dr. Bekoff added, “This is an important paper that among
other things should make us revisit and likely revise what we mean by a ‘pure’ species.”
The Big Black Wolf Is a Legacy from Dogs, Study Finds
By Thomas H. Maugh II, Los Angeles Times
February 7, 2009
The fur color was bred into dogs by humans, then introduced into wild wolves and
coyotes, researchers say. It appears almost exclusively in North America.
Black wolves and coyotes are often the villains of cartoons and children's fairy tales, but
it now appears that they inherited their color from a much more warm and fuzzy animal -the dog.
True, dogs are descended from wolves, but research Friday in the journal Science
indicates that black fur was bred into dogs by humans, then inadvertently introduced into
the wild species.
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The trait shows up in the wild primarily in North America, and it was probably brought to
the continent about 15,000 years ago when the first immigrants crossed over the Bering
land bridge, bringing their dogs with them.
The fact that the mutation has stayed in the wild population for so long suggests that it is
beneficial in some way.
The gene responsible for the color, called beta-defensin, was discovered in 2007 by
geneticist Greg Barsh of Stanford University.
It belongs to a family of genes thought to be involved in fighting infections.
When the gene appears in its normal form, the animal has a light or yellow-colored coat.
But when one copy of the gene is missing three nucleotides, the animal develops a black
coat.
Studying genes from a large number of wolves, coyotes and dogs, Barsh and his
colleagues concluded that the current mutation first appeared in dogs about 50,000
years ago.
It may also have appeared in wild animals, then disappeared again, the researchers
speculated.
They also concluded that the mutation appeared in wolves and coyotes some time after
the first humans reached North America.
Its almost exclusive appearance in the New World is probably because it was much
easier for dogs to mingle with the wild animals here than in Europe, said Barsh's
graduate student Tovi Anderson.
Black coats occur in about 62% of wolves in the forested areas of the Canadian Arctic,
compared with about 7% in the icy tundra. Researchers agree that the coat does not
camouflage the animals from predators, but it may help them sneak up on prey.
The mutated gene might also provide a better immune defense against infectious agents
that occur primarily in the warmer forests, Barsh said.
[email protected]
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