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Disease has influenced wolf colors across North America

Scientists have long been puzzled by the fact that, across the North American continent, wolves tend to change their coat color: while in the Arctic Canada and other northern areas wolves tend to be grey, in the south, most of them are black. Now, a team of researchers led by the University of Oxford has found that patterns of infectious diseases can drive coat coloring in wolf populations. 

Coat color in wolves is determined by a gene called CPD103: depending on the variant of this gene that a specific wolf has, its coat can be either grey or black. By examining 12 wolf populations across North America, the scientists discovered that this gene also plays a major role in protecting against respiratory diseases such as the canine distemper virus (CDV) disease. The analyses revealed that most of the black wolves had CDV antibodies (suggesting that they contracted the disease in the past and survived), and that this coloring was more frequent in areas where CDV outbreaks occurred. Thus, black wolves appeared to be more likely to survive CDV outbreaks compared to grey wolves.

By analyzing 20 years-worth of data from the wolf population at the Yellowstone National Park, the scientists found that, in areas where CDV outbreaks occur, wolves would often choose mates of the opposite color in order to maximize the chance that their cubs would have black coats.

“It’s intriguing that the gene for protection against CDV came from domestic dogs brought by the first humans entering North America, and the CDV disease virus emerged in North America many thousands of years later, once again from dogs,” said study co-author Peter Hudson, a professor of Biology at the Pennsylvania State University.

“What I love about this study is how we have been able to bring together experts from so many fields and a range of approaches to show how disease can have remarkable impacts on wolf morphology and behavior. We are learning that disease is a major evolutionary driver that impacts so many aspect aspects of animal populations.”

According to the scientists, other animal species – such as insects, amphibians, birds, and some non-human mammals – may also have evolved associations between color patterns and disease resistance, leading them to conclude that the presence of a disease, or the frequency of disease outbreaks, are major factors affecting the color of mate an animal prefers.

The study is published in the journal Science.

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By Andrei Ionescu, Staff Writer

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