Sick Grays: Disease Outbreaks Affect Wolf Color in North America

New research from the University of Oxford, Yellowstone National Park and Penn State, published today in the journal Sciencemay have finally solved why wolves change color on the North American continent.

If you were to travel from Arctic Canada and head south through the Rocky Mountains to the US toward Mexico, the further south you go, the more black wolves there are. The reasons why have long puzzled scientists.

Professor Tim Coulson of the University of Oxford’s Department of Biology, who led the work, explains: ‘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. Scientists have long wondered why. We now have an explanation based on wolf surveys in North America and modeling motivated by extraordinary data collected by co-authors working in Yellowstone.”

Coat color in wolves (Wolf) is determined by a gene called CPD103

. Depending on the variant of the gene a wolf has, its fur can be black or gray.

The researchers suggested that this gene also plays a role in protecting against respiratory diseases such as canine distemper virus (CDV). This is because the region of DNA containing the gene also codes for a protein that plays a role in defense against infection in the mammalian lungs. They predicted that having a black coat would be associated with wolves’ ability to survive an infection with CDV.

To test this idea, they analyzed 12 wolf populations from North America to investigate whether the probability of a wolf being black was predicted by the presence of CDV antibodies. If a wolf has CDV antibodies, it has caught and survived CDV in the past. They found that wolves with CDV antibodies were black rather than gray. They also found that black wolves were more common in areas where CDV outbreaks occurred.

The researchers analyzed more than 20 years of wolf population data in Yellowstone National Park. They found that black wolves were more likely to survive CDV outbreaks than gray wolves. These results led them to hypothesize that in areas where canine distemper outbreaks occur, wolves should choose mates with the opposite coat color to maximize the chance that their cubs would have black coats.

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They used a simple mathematical model to test this idea. Excitingly, their model’s predictions closely matched observations that black and gray wolves were more likely to mate in areas where CDV outbreaks are common. This competitive advantage is lost in areas where CDV outbreaks do not occur.

These results are consistent with the idea that the frequency of CDV outbreaks in North America is responsible for the spread of black wolves, as having the gene for black fur may also provide protection against the virus. It also explains why couples in Yellowstone, where canine distemper outbreaks occur, are usually black-gray.

Peter Hudson, Willaman Professor of Biology, Penn State said: “Intriguingly, the gene for protection against CDV came from domestic dogs brought in by the first humans to enter North America, and the CDV disease virus appeared for many thousands of years. later in North America, once again from dogs.’

‘What I love about this study is how we’ve been able to bring together experts from so many fields and a range of approaches to show how disease can have a remarkable impact on wolf morphology and behavior. We are learning that disease is an important evolutionary driver that affects so many aspects of animal populations.’

The researchers speculate that other species may follow a similar pattern to wolves. Many insects, amphibians, birds and non-human mammals have associations between color and disease resistance. It may be that the presence of a disease, or how often a disease outbreak occurs, is a major factor influencing the color of the mate an animal prefers.

black jackets

The black coat color in North American wolves can be traced to a single mutation that occurred between 1,598 and 7,248 years ago. Until now, it has been a mystery why the frequency of black wolves in North America varies, despite there being no geographic barriers to prevent gene transfer.

These findings are inconclusive and none of the analyzes on their own provides conclusive support for the hypothesis that the frequency of black wolves in North America is determined by the frequency of CDV outbreaks. Together, the complementary lines of evidence provide strong support.


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