In gray wolves, the K locus, a β-defensin gene, causes black coat color via a dominantly inherited KB allele. The allele is derived from dog-wolf hybridization and is at high frequency in North American wolf populations.

 Gray Wolf-Black Color Phase

We designed a DNA capture array to probe the geographic origin, age, and number of introgression events of the KB allele in a panel of 331 wolves and 20 dogs. We found low diversity in KB, but not ancestral ky, wolf haplotypes consistent with a selective sweep of the black haplotype across North America.

 Further, North American wolf KB haplotypes are monophyletic, suggesting that a single adaptive introgression from dogs to wolves most likely occurred in the Northwest Territories or Yukon. We use a new analytical approach to date the origin of the KB allele in Yukon wolves to between 1598 to 7248 years ago, suggesting that introgression with early Native American dogs was the source.

Gray Wolf-Black Color Phase

 Using population genetic simulations, we show that the K locus is undergoing natural selection in four wolf populations. We find evidence for balancing selection, specifically in Yellowstone wolves, which could be a result of selection for enhanced immunity in response to distemper. With these data, we demonstrate how the spread of an adaptive variant may have occurred across a species geographic range.

Molecular and Evolutionary History of Melanism in North American Gray Wolves

March 6, 2009
*To whom correspondence should be addressed. ude.drofnats@hsrab


Morphological diversity within closely related species is an essential aspect of evolution and adaptation. Mutations in the Melanocortin 1 receptor (Mc1r) gene contribute to pigmentary diversity in natural populations of fish, birds, and many mammals. 

Eastern Coyote-Black Color Phase

However, melanism in the gray wolf, Canis lupus, is caused by a different melanocortin pathway component, the K locus, that encodes a beta-defensin protein that acts as an alternative ligand for Mc1r. We show that the melanistic K locus mutation in North American wolves derives from past hybridization with domestic dogs, has risen to high frequency in forested habitats, and exhibits a molecular signature of positive selection.
The dog was domesticated between 15,000 and 40,000 years ago in East Asia from gray wolves (), and we estimate that KB is at least 46,886 years old (95% confidence limit: 12,779 to 121,182 years); therefore, we cannot distinguish whether KB arose before or after domestication. However, if KB arose in Old World wolves before domestication, our data indicate that it must have been lost from the gene pool and reacquired in North America, perhaps from Native American dogs that accompanied humans across the Bering Strait 12,000 to 14,000 years ago

Eastern Coyote-Black Color Phase

The same mutation also causes melanism in the coyote, Canis latrans, and in Italian gray wolves, and hence our results demonstrate how traits selected in domesticated species can influence the morphological diversity of their wild relatives.