The Mystery of North America's Black Wolves

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Despite their name, gray wolves (Canis lupus) are not always just gray. These canids can also have black or white coats; the ones with black coats are referred to, logically enough, as black wolves.

The frequencies of the various coat shades and colors prevailing within a wolf population often vary with habitat. For example, wolf packs that live in open tundra consist mostly of light-colored individuals; the pale coats of these wolves allow them to blend in with their surroundings and conceal themselves when pursuing caribou, their primary prey. On the other hand, wolf packs living in boreal forests contain higher proportions of dark-colored individuals, as their murky habitat enables darker-colored individuals to blend in.

Of all the color variations in Canis lupus, the black individuals are the most intriguing. Black wolves are so colored because of a genetic mutation in their K locus gene. This mutation causes a condition known as melanism, an increased presence of dark pigmentation which causes an individual to be colored black (or nearly black). Black wolves are also intriguing because of their distribution; there are significantly more black wolves in North America than there are in Europe.  

To better understand the genetic underpinnings of black wolves, a team of scientists from Stanford University, UCLA, Sweden, Canada and Italy recently assembled under the leadership of Stanford's Dr. Gregory Barsh; this group analyzed the DNA sequences of 150 wolves (about half of which were black) from Yellowstone National Park. They wound up piecing together a surprising genetic story, stretching back tens of thousands of years to a time when early humans were breeding domestic canines in favor of darker varieties.

It turns out that the presence of black individuals in Yellowstone's wolf packs is the result of deep historical mating between black domestic dogs and gray wolves. In the distant past, humans bred dogs in favor of darker, melanistic individuals, thus increasing the abundance of melanism in domestic dog populations. When domestic dogs interbred with wild wolves, they helped to bolster melanism in wolf populations as well.

Unraveling the deep genetic past of any animal is a tricky business. Molecular analysis provides scientists with a way to estimate when genetic shifts could have occurred in the past, but it's usually impossible to attach a firm date to such events. Based on genetic analysis, Dr Barsh's team estimated that the melanism mutation in canids arose sometime between 13,000 and 120,00 years ago (with the most likely date being about 47,000 years ago). Since dogs were domesticated around 40,000 years ago, this evidence fails to confirm whether the melanism mutation arose first in wolves or in domestic dogs.

But the story does not end there. Because melanism is far more prevalent in North American wolf populations than it is in European wolf populations, this suggests that the cross between domestic dogs populations (rich in melanistic forms) likely occurred in North America. Using the data collected, study co-author Dr. Robert Wayne has dated the presence of domestic dogs in Alaska to about 14,000 years ago. He and his colleagues are now investigating ancient dog remains from that time and location to determine whether (and to what degree) melanism was present in those ancient domestic dogs.

Edited on February 7, 2017 by Bob Strauss