Guessing the color of a gray wolf’s coat seems like a no-brainer. But the canines, whose habitats are spread across North America and Eurasia, are not always gray either.
In the North American continent, especially the further south you go, there are more wolves with black coats, with dark discolourations. The fact was unknown for a long time, but now scientists have decided that it is one of the most important drivers of natural selection: disease.
An international team led by ecologist Sarah Cubaynes of the University of Montispessulani in France has determined that the often fatal canine distemper virus is the trigger that produces a greater number of black wolves (Wolf dog).
“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 wondered for a long time. Now we have an explanation that spans wolves across North America, and models using extraordinary data from co-authors who work in Yellowstone.”
The pressure of development can result in some unique consequences, especially when it comes to disease. Some people are more likely to survive depending on the presence of genes that confer resistance to that disease. The rest then produce offspring with those genetic variations and the genetic makeup of the population can change over time.
The genetic patterns that confer resistance, however, do not always have a single function. As we recently learned, genetic variants that contributed to resistance against the Black Plague also increase susceptibility to autoimmune disorders such as rheumatoid arthritis, the effects of which we still feel centuries later.
In these wolves, coat color is determined by CPD103, which historically made their coats gray. But the CPD103 mutation appeared in dogs and crossed over to wolves, producing a black coat.
Each wolf has two copies of CPD103, one from each parent. Unlike red hair in humans, though, it only takes one copy of the black coat gene to produce a black coat.
Scientists have suspected that the canine distemper virus may be playing a role in the soaring numbers of black wolves across North America, since the region of DNA in which CPD103 resides is also involved in the transcription of a protein that protects against lung infections such as canine distemper.
This means that if wolves with black coats are more likely to survive the disease, they produce and pass on the CPD103 variant to their pups.
So, the team set out to test this hypothesis. Researchers analyzed a dozen populations of wolves across North America to see if the presence of canine distemper antibodies — a marker of having and surviving the virus — was strongly correlated with black wolves.
Wolves with the elements were found to actually have more black coats, especially in older wolves. Black wolves were also more frequent in the areas where the riots took place.
Next, the team studied 20 years worth of wolf populations from Yellowstone National Park, where wolves were introduced in the 1990s.
There, 55 percent of the population is gray wolves and 45 percent black wolves. Of those black wolves, only 5 percent, in two copies of the black-loric CPD103 variant. This suggests that wolves choosing mates of the opposite color have a better chance of reproductive success, and their offspring survive canine disease.
But it only works in areas that have experienced canine motion sickness. According to the team’s mathematical model, the competitive advantage of choosing a different color disappears if the dog’s health is not a problem.
The research not only provides a compelling case for the greater prevalence of black wolves in certain areas, but also provides a tool for studying historical canine disease outbreaks as well as resistance.
The team notes that they will have their results in a wide variety of ways. In a wide range of insects, mammals, amphibians, reptiles and birds, color variation can be associated with disease resistance; this coloration can act as a signal to help animals choose mates who will give their offspring a survival advantage.
“Since coloration is genetically determined and disease resistance is heritable and associated with coloration, we would prefer to approach the second color of the species, which maximizes the chances of producing resistant offspring in environments with frequent and virulent pathogens,” the researchers write in their paper.
“It is possible that the role of pathogens in generating the diversity of morphological and behavioral characteristics observed in nature has been significantly underestimated.”
Is it an ambitious concept?
The research was published in Science.
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