Recently, a trail camera in northern Minnesota caught video of a pack of all-black wolves. The video has been viewed more than 950,000 times since it was uploaded in late December 2021. A greyish-brown wolf crosses the meadow in the shot, followed by three all-black wolves. People are fascinated. So, what affects animal coloration? And why are these wolves black?
First, although these wolves are black, they are still Canis lupus (commonly called the grey wolf). Naturally, wolves are red, brown, white, grey, black, and shades in between. These are the same colors we see available in nature in human hairs: black, brown, blonde, red, and grey/white. Other body coverings, such as scales and feathers, can be different colors due to the pigments available. Animals use color for camouflage, thermoregulation, and mating selection.
These are not the only black wolves known. In the 1960s, 3.6% of Minnesota’s wolves were black. Today, 1.5-2% of Minnesota’s wolves are black. In Yellowstone National Park, about half of the wolves (re-introduced to the park from Canada in 1995) are black.
Coat color genetics can be complicated. Three gene loci affect coat color: the A locus (beige and black/tan), the E locus (white, yellow, and red), and the K locus (black).
Black coat color is genetically dominant. It is thought that the gene for black coat color came from early domesticated black dogs, who then hybridized with wolves; thus, wolves now have the gene as well. But, this gene affects more than fur color — it also affects the immune system.
Black wolves seem to have lower mortality from Canine Distemper Virus (CDV) than grey wolves, although researchers have not found a change in immune response to support this statement. Canine distemper is highly contagious and has no cure, only supportive treatment. The first phase of canine distemper includes coughing, vomiting, fever, nasal or eye discharge, and lethargy. If the dog survives, its foot pads harden and swell up. Distemper then progresses into Stage 2, bringing new symptoms, such as seizures, convulsions, muscle twitching, and circling, which often cause death. Those who survive Stage 2 are saddled with permanent nervous system damage. Domestic dogs have a 50% mortality rate as adults and an 80% mortality rate as puppies. Other animals are affected by it as well; nearly all mustelids (ferrets, minks, martens, skunks) who get canine distemper die from it. There is a vaccine for distemper that the American Kennel Club recommends for domestic dogs.
There are negatives that come with black coat color as well. These fitness trade-offs seem to have affected mate choice. In Yellowstone, wolves tend to pick mates of a different coat color over mates with the same coat color. Interestingly, pups from female black wolves have a survival rate that is 25% lower than pups from female grey wolves. This preference for mates with different coat colors keeps multiple color genes in the pack, allowing the pack as a whole to benefit from both colors, have less susceptibility to canine distemper, and produce robust, surviving litters.
Will all wolves be black one day? We don’t know. But, it will be interesting to see what happens to the all-black pack in Minnesota, especially because a U.S. District Court just ruled to relist grey wolves (Canis lupus – which includes these black wolves) on the Endangered Species List (they were removed in 2020 in a decision widely-characterized as political).
Acknowledgements:
Dr. Douglas Knapp brought the trail camera footage to my attention.
Edited by Chloe Holden and Clara Boothby
Leave a Reply