Why are Rare Black Wolves Common in Yellowstone Park?

Researchers at the University of Oxford and Penn State University may may have found an explanation for why black wolf prevalence increases southward along the Rocky Mountain crest, a phenomena that has long intrigued wildlife biologists.

The black wolf color phase is rare or completely absent in other regions of the world yet somewhat common in the American West, especially in Yellowstone National Park, and a study published in the journal Science strongly suggests that genetics, mating behavior and regular outbreaks of canine distemper in the park may be the reason.

Canine coat color is determined by a gene, and the ancestral version of that gene codes for a gray coat. Black coats can be traced to a single mutation of the gene that occurred between 1,598 and 7,248 years ago. The mutation did not occur in North American wolves but in domestic dogs overseas. The gene entered the American wolf pool when people brought black dogs to America and wild wolves mated with them. Wolves get one color gene from each parent and only need to inherit one black-variant gene to have a black coat.

There is no geographical barrier to prevent the gene flowing north or south. The researchers instead postulated that there is a link with canine distemper, which occurs more frequently in the southern Rockies. The genetics that predispose to black coats might also help a wolf survive distemper because the DNA region that contains the color gene also encodes for a protein that plays a role in defending against infections in the lungs.

They predicted that black coats could be associated with the ability to survive distemper and while analyzing more than 20 years of carefully collected data from the wolf population at Yellowstone Park, they found that the black wolves were, indeed, more likely esearchers at the University of Oxford and Penn State Univer to have survived distemper (indicated by antibodies in their blood).