A COLORFUL SURVIVAL STRATEGY

New research suggests that a darkening of coat colors was part of the prehistoric horse’s adaptation to changing environments and may have helped the species escape extinction.

For nearly a decade, researchers from academic institutions across Europe have been working with the Leibniz Institute for Zoo and Wildlife Research in Berlin, Germany, to study equine coat colors throughout history.

The group’s early findings showed that many coat colors and patterns arose only after domestication, under the influence of selective breeding. But there was a significant exception to that phenomenon: The black allele0, which produces darker coat colors, went from near zero frequency to greater than 75 percent of coat colors more than 1,000 years before the horse was domesticated. This led the researchers to hypothesize that an environmental event, such as a shift in habitat, led to natural selection for the coat color shift.

Through analysis of prehistoric equine DNA and pollen samples, the researchers linked the rise of the black coat allele to the transformation of open plains into forests across Europe at the end of the Ice Age.

The coat color change, says Arne Ludwig, PhD, would have been beneficial in camouflaging horses from predators in the darker, forested environment, contributing to the survival of the species. “These were likely the same predators---humans, wolves and bears---but their hunting strategy was different in open land versus forests,” he says.

Supporting this “adaptation to expanding forests” theory is the fact that at the same time, equine populations in parts of the world where forests were not emergent retained the lighter color that had been dominant in the species prior to the Ice Age. “In Asia, where open habitats exist even today, horses were dun brown, as seen in modern Przewalski’s horses,” says Ludwig.

Ludwig says that there’s no way to know why other species didn’t undergo similar color adaptations to their changing environments. “Probably mammoths and saber-toothed tigers had other problems,” he says. “Coat color adaptation is only one piece of the puzzle. Survival of a species depends on many things. If one fails, game over.”

Reference: “Coat color adaptation of post-glacial horses to increasing forest vegetation,” Nature Ecology & Evolution, October 2017