Wolves are mysteriously changing color across America. We finally know why

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

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

An international team led by ecologist Sarah Coppinis of the University of Montpellier in France has determined that the often deadly canine lineage virus is the driver that produces more black-coated wolves (the gray wolf).

“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,” explains biologist Tim Coulson of 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 the extraordinary data collected by co-authors working on Yellowstone.”

Evolutionary pressure can lead to some strange results, especially when it comes to disease. Certain individuals may be at increased risk of survival based on the presence of genes that confer resistance to this disease. The survivors then produce offspring with these genetic differences, and the population’s genetic profile can change over time.

However, the genetic configurations that confer resistance do not always have only one function. As we recently learned, the genetic variants that conferred resistance to the black plague also increase susceptibility to autoimmune disorders like rheumatoid arthritis, which means we can still feel its effects centuries later.

In the case of these wolves, coat color is determined by a gene called CPD103, which has historically made coats gray. However, the CPD103 mutation appeared in dogs and was crossed into wolves, resulting in the production of a black coat.

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

Scientists suspected that the canine strain virus may be playing a role in the population of black-coated wolves across North America because the region of DNA that CPD103 resides in is also involved in encoding a protein that protects against lung infections such as canine tuberculosis.

This means that if wolves with black coats are likely to survive the disease, they will reproduce and pass their CPD103 variant on to their cubs.

Therefore, the team set out to test this hypothesis. The researchers analyzed 12 packs of wolves across North America to see if the presence of antibodies in dogs — a sign of virus presence and survival — correlated more closely with black-coated wolves.

They found that the wolves carrying the antibodies were actually more likely to have black coats — especially in older wolves. Blackflies were also more common in areas where infestations 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 is made up of 55 percent gray wolves and 45 percent black wolves. Of these black wolves, only 5 percent had two copies of the black-cased CPD103 variant. This indicates that wolves that choose mates of the opposite color have a better chance of succeeding in breeding, and that their surviving offspring are defective.

However, it only works in areas that have experienced canine disease outbreaks. According to the team’s mathematical modeling, the competitive advantage of choosing an opposite-colored mate disappears if canine imbalance is not an issue.

Not only does the research give a fascinating reason why blackflies are more common in some areas, but it also provides a tool for studying historical canine tuberculosis outbreaks, as well as disease resistance.

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

“When coloration is genetically determined and disease resistance is genetic and correlated with coloration, preference for a mate of a particular color will enhance fitness by maximizing the chances of producing resistant offspring in environments with sufficiently frequent and virulent pathogens,” the researchers write. their paper.

“It is possible that we have greatly underestimated the pathogen’s role in generating the diversity in morphological and behavioral traits that have been observed in nature.”

Isn’t that an interesting idea?

Research published in science.

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