The color of wolves is mysteriously changing across America. We finally know why: ScienceAlert
Guessing the color of a gray wolf’s fur seems like a good idea. But the canines, whose habitats are scattered across North America and Eurasia, aren’t always actually gray.
Particularly on the North American continent, the further south you go, the more wolves there are with dark, black-tinted coats. The phenomenon remained unexplained for a long time, but now scientists have 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 found that it often has deadly consequences distemper virus is the trigger that produces a greater number of black-coated wolves (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 not in others.” explains biologist Tim Coulson from the University of Oxford.
“Scientists have long wondered why. We now have an explanation based on wolf surveys in North America and models inspired by extraordinary data collected by co-authors working in Yellowstone.”
Evolutionary pressures can have some peculiar consequences, especially when it comes to disease. Some individuals may be more likely to survive based on the presence of genes that confer resistance to that disease. The survivors then produce offspring with those genetic variations, and a population’s genetic profile can change over time.
However, the genetic configurations that confer resistance do not always serve only one function. As we recently learnedgenetic variants that conferred black plague resistance also increase susceptibility to autoimmune diseases like rheumatoid arthritis, meaning we’re still feeling its effects centuries later.
In the case of these wolves, coat color is determined by a gene called CPD103, which traditionally made their coats gray. However, a CPD103 mutation arose in dogs and it passed to wolves, producing black fur.
Each wolf has two copies of CPD103, one inherited from each parent. in contrast to red hair in humanshowever, only one copy of the black coat gene is needed to produce a black coat.
Scientists suspected that the distemper virus may play a role in the number of black-coated wolves in North America, as the DNA region in which CPD103 resides is also involved in encoding a protein that protects against lung infections such as distemper.
This would mean that if wolves with black coats are more likely to survive the disease, they will reproduce and pass on their CPD103 variant to their cubs.
So the team started testing this hypothesis. Researchers analyzed 12 wolf populations in North America to see if distemper was present antibodies — a sign of having had and surviving the virus — was highly correlated with black-coated wolves.
They found that wolves with the antibodies 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 percent gray wolves and 45 percent black wolves. Of those black wolves, only 5 percent had two copies of the black-coated CPD103 variant. This suggests that wolves that choose mates of the opposite color have a higher chance of reproductive success and their offspring surviving distemper.
However, it only works in regions with distemper outbreaks. According to the team’s mathematical modeling, if distemper isn’t an issue, the competitive advantage of choosing a mate of the opposite color disappears.
The research not only provides a fascinating rationale for the greater prevalence of black wolves in some areas, but also provides a resource for studying historical outbreaks of distemper, as well as disease resistance.
The team notes that their results likely apply to a wide range of species. In a wide variety of insects, mammals, amphibians, reptiles and birds, color variation may be associated with disease resistance; this color can serve as a signal to help animals choose mates that will give their offspring a survival advantage.
“When coloration is genetic and disease resistance is inherited and associated with coloration, a preference for a mate of a specific color will improve the condition by maximizing the chances of producing resistant offspring in environments with frequent and virulent enough pathogens.” write the researchers in their paper.
“It is possible that we have significantly underestimated the role of pathogens in generating the diversity of morphological and behavioral traits observed in nature.”
Isn’t that an intriguing thought?
The research has been published in Science.
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