Mystery of North American Black Wolves Solved

Two wolves from the Druid Peak pack play in Yellowstone National Park. The gray colored wolf (left) represents the homozygous gray phenotype, while the black colored wolf on the right represents the black K-locus phenotype.

Outbreaks of distemper have influenced the coat color of wolves in North America, British and American scientists show.

A particular phenomenon is observed in packs on the North American continent: the number of black wolves increases compared to that of gray wolves as one moves along the Rocky Mountains, from the Canadian Arctic towards the national park of Yellowstone, USA.

The black wolf is non-existent or very rare virtually anywhere in the world, but is quite common in parts of North America, including Yellowstone , explains in a press release Professor Tim Coulson of the Department of Biology at the University of Oxford.

To help understand this anomaly, Dr. Coulson, his team and colleagues at Pennsylvania State University analyzed genetic data from twelve North American wolf populations collected over 20 years.

Many wolves in the Druid Peak pack are black.

• The coat color of wolves (Canis lupus) is determined by the CPD103 gene. Depending on which gene variant a wolf has, its coat may be black or gray.
• The ancestral version of the gene determines a gray coat. A mutation that appeared in domestic dogs and then crossed with wolves determines a black color.
• The dog-associated mutation was likely introduced to the North American wolf population in the past 7,250 years, when humans migrated across the Bering Strait with dogs carrying the gene.
• Cubs inherit two copies of CPD103 (one from each parent), but inheriting one copy of the black variant is not enough to show a dark coat.
• Distemper (VMC) is believed to have emerged in the 1730s from a bovine virus introduced to North America by settlers from Europe.

Analysis of genetic data showed that black-mantled wolves had greater immunity to distemper, since they had antibodies that protected them against respiratory viruses.

Unsurprisingly, black wolves were more likely to survive outbreaks of distemper than gray wolves.

In addition, the researchers also determined that the more black wolves there are in an area, the more that area has been hit by distemper outbreaks in the past.

About half of Druid Peak's pack are black.

The researchers also found that black and gray wolves were more likely to mate together in areas where distemper outbreaks are common. However, this competitive advantage disappears in disease-free areas.

We found that wolves can signal their resistance to canine distemper virus by their coat color, which could allow individuals to identify mates capable of providing them with healthier offspring, said Peter Hudson, professor of biology at Pennsylvania State University

Fascinatingly, the disease protection gene came from domestic dogs that accompanied the first humans to North America, and the disease virus appeared on the continent many thousands of years later, yet another times from dogs, notes Peter Hudson, professor of biology at the University of Pennsylvania.

According to the authors of this work published in the journal Science, other animal species, including insects, amphibians, birds, and mammals, certainly show associations between color and disease resistance.

Furthermore, it is highly likely that the presence of a disease, and its frequency of occurrence, is an important factor influencing the color of a mating partner.