Guessing the color of a wolf's coat is not difficult. The dogs, whose habitats are spread across North America and Europe, are not always gray.
The wolves with dark, black coats are more abundant in the south of the US. Disease is one of the biggest drivers of natural selection and the phenomenon was unexplained for a long while.
An international team led by Sarah Cubaynes of the University of Montpellier in France has determined the cause of the higher number of black-coated wolves.
In North America, black wolves are common in some areas and rare in others, but they are rare in most parts of the world.
Scientists have been wondering why. We now have an explanation that is based on surveys of wolves in North America.
When it comes to disease, evolutionary pressure can cause strange consequences. The presence of genes that confer resistance to a disease can increase survival. The genetics of a population can change over time.
Some genetic configurations have more than one function. We are still feeling the effects of the Black Plague centuries later because of the genetic variant that confers resistance to the disease.
The wolf's coat color is determined by a gene called CPD103, which has historically made their coats gray. Dogs and wolves produced a black coat due to the emergence of aCPD 103.
The wolves have two copies of the same book. It takes a single copy of the black coat genes to make a black coat.
Scientists suspected that the canine distemper virus may play a role in the number of black-coated wolves in North America since the DNA region in which CPD103 resides is also involved in protecting against lung infections.
If wolves with black coats are more likely to survive the disease, they will reproduce and pass on their variant of the disease to their pups.
The team decided to test this hypothesis. Researchers looked at 12 wolf populations across North America to see if there was a correlation between the canine distemper antibodies and the black coated wolves.
Black coats are more likely to be found in older wolves. In areas where there had been an outbreak, black wolves were more frequent.
The team studied 20 years' worth of data from the reintroduction of wolves in the 1990s.
The population is made up of 55 percent gray wolves and 45 percent black wolves. Only 5 percent of the black wolves had two copies of the black coat. This suggests that wolves have a better chance of reproductive success if they choose mates of the opposite color.
It only works in areas that have experienced distemper. If canine distemper isn't a problem, the competitive advantage of choosing an opposite color mate is gone.
The research gives a fascinating reason for the greater prevalence of black wolves in some areas, as well as a tool for studying the history of canine distemper.
Their results are likely to apply to a wide range of species. Color variation can be a signal to help animals choose mates that will give them a survival advantage.
A preference for a mate of a specific color will enhance fitness by maximizing the chances of producing resistant offspring in environments with frequent and virulent enough pathogens.
It is possible that we have underestimated the role of pathogens in generating the diversity of morphological and behavioral traits.
That is an intriguing idea.
The research has appeared in a journal.
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