Stahler Yellowstone Wolves

If you peer into a pack of gray wolves, you might see a sea of ​​gray fur. However, you can also see a stunning array of silvers and soots and smoky blacks, as well as an assortment of additional hues from browns to beiges to whites.

Much more impressive than the colors themselves is their reason. In fact, according to a paper published in Science this fall some scientists believe that fur coloring patterns among North American wolves they are actually a sign of past illnesses.

Specifically, these scientists say that wolves’ colors signal the strength of their immunity to specific viruses, allowing individual wolves to identify which mates will provide them with resilient, virus-resistant pups.

Why wolves change colors

Wolves come in an assortment of colors, although they are generally gray and black in North America, with a greater prevalence of gray tones in the north and a greater prevalence of black tones in the south.

“In most parts of the world, black wolves are absent or very rare,” said Tim Coulson, study author and biologist at the University of Oxford, according to a press release. “In North America, they are common in some areas and absent in others.”

The source of these coat color variations, as well as their distribution patterns, have puzzled scientists for years, although they were not without their theories. For example, some toyed with the idea that variations in wolves’ fur meant theirs fitness as potential partnersan adaptable phenomenon seen through a abundance of plants and animals kinds.

And as it turns out, these specialists were on the right track.

A team of researchers decided to scrutinize the wolf fur “fitness” theory due to the realization that one of the same genes that influence wolf fur color, CBD103, could also inform their immune responses against various viruses.

Evaluating populations across North America, and specifically in Yellowstone National Park, the team found that black wolves retain stronger resistance to canine distemper virus (CDV), an acute and often fatal infection from the same family of viruses that causes measles and mumps. In addition to this, the results revealed that these shade-hued wolves are also particularly widespread in populations where CDV outbreaks are common.

Coat color and viral immunity

Starting with information from 12 separate North American populations, the team first investigated whether the presence of CDV antibodies among wolves — which would indicate which individuals had contracted and overcome CDV at some point in the past — was associated with particular coat colors. They soon found that individuals with these antibodies were black, suggesting a stronger ability to survive the disease among wolves with darker fur.

Not only that, the team also found that wolves with black fur, as opposed to gray fur, were much more common in areas with frequent CDV outbreaks, supporting the theory that these wolves are more immune to certain diseases.


Read more: Parasites can create wolf pack leaders in Yellowstone


To further solidify their findings, the researchers turned to Yellowstone National Park. There, their analysis of more than 20 years of information on wolf populations suggests that some wolves specifically choose their mates to maximize the likelihood that their pups will be black (and therefore immunologically prepared) in areas where CDV occurs and emerges regularly.

In fact, this selective mating manifests itself in a preference for black-gray pairs, which the team says are seen far more often in Yellowstone — where outbreaks occur at intervals of about five years — than in areas with fewer waves of disease.


Read more: The photos that saved Yellowstone


Ultimately, the team adds, these results are consistent with findings for a plethora of other animals, including insects, fish and birdswhose colors represent their ability or inability to resist disease.

“What I like about this study is how we were 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 coat color and behavior,” said Peter Hudson, another author. of the study and a biologist at Pennsylvania State University, according to a news release. “We’re learning that disease is a major evolutionary driver that affects so many aspects of animal populations.”

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