The color of wolves mysteriously changes across America. We finally know why: ScienceAlert

Guessing the coat color of a gray wolf seems like a no-brainer. But canids, whose habitats are spread across North America and Eurasia, are not always gray.

On the North American continent, specifically, the further south you go, the more dark and black coated wolves there are. The phenomenon went unexplained for a long time, but scientists have now determined that the culprit is one of the biggest drivers of natural selection: disease.

An international team led by ecologist Sarah Cubaynes of the University of Montpellier in France has determined that the often deadly canine distemper virus is the trigger that produces greater numbers of black-haired wolves (Canis lupus).

“In most parts of the world, black wolves are absent or very rare, but in North America they are common in some areas and absent in others,” says biologist Tim Coulson from the University of Oxford. .

“Scientists have long wondered why. We now have an explanation based on wolf surveys across North America and modeling driven by extraordinary data collected by co-authors working in Yellowstone.”

Evolutionary pressure can lead to particular consequences, especially when it comes to diseases. Some people may be more likely to survive due to the presence of genes that confer resistance to this disease. Survivors then produce offspring with these genetic variations, and the genetic profile of a population can change over time.

However, the genetic configurations that confer resistance do not always have a single function. As we have recently learned, the genetic variants that confer resistance to the Black Death also increase susceptibility to autoimmune diseases such as rheumatoid arthritis, meaning we are still feeling its effects centuries later.

In the case of these wolves, coat color is determined by a gene called CPD103, which has historically turned their coats gray. However, a CPD103 mutation appeared in dogs and passed to wolves, producing a black coat.

Each wolf has two copies of CPD103, one inherited from each parent. Unlike red hair in humans, however, it only takes one copy of the black coat gene to produce a black coat.

Scientists suspect that the distemper virus may play a role in the number of black-haired wolves in North America because the region of DNA in which CPD103 resides is also involved in coding a protein that protects against lung infections such as distemper.

This would mean that while black-coated wolves are more likely to survive the disease, they will breed and pass on their CPD103 variant to their young.

The team therefore set out to test this hypothesis. Researchers analyzed 12 wolf populations across North America to see if the presence of distemper antibodies – a sign of having had and surviving the virus – was strongly correlated with black-haired wolves. .

They found that antibody-carrying wolves were indeed more likely to have black coats, especially in older wolves. Black wolves were also more common in areas where outbreaks had occurred.

Next, the team studied 20 years of wolf population data from Yellowstone National Park, where wolves were reintroduced in the 1990s.

There, the population consists of 55% gray wolves and 45% black wolves. Of these black wolves, only 5% had two copies of the black-coated CPD103 variant. This suggests that wolves that choose mates of the opposite color have a better chance of reproductive success and that their offspring survive distemper.

However, this only works in areas that have had outbreaks of canine distemper. According to the team’s mathematical modeling, the competitive advantage of choosing an opposite-colored mate disappears if distemper isn’t an issue.

The research not only provides a fascinating reason for the greater prevalence of black wolves in some areas, but it also offers a tool to study historical distemper outbreaks, as well as disease resistance.

The team notes that their results are likely to apply to a wide range of species. In a wide range of insects, mammals, amphibians, reptiles, and birds, color variation may be associated with disease resistance; this coloration can act as a signal to help animals choose mates that will give their offspring a survival advantage.

“When coloration is genetically determined and disease resistance is inherited and associated with coloration, a preference for a mate of a specific color will improve fitness by maximizing the chance of producing resistant offspring in environments with agents sufficiently frequent and virulent pathogens”, write the researchers in their paper.

“It is possible that we have greatly underestimated the role of pathogens in generating the diversity of morphological and behavioral traits observed in nature.”

Isn’t that an intriguing notion?

The research has been published in Science.

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