Animals that grow a white coat in winter are at risk from predators as summers lengthen and snow cover retreats. But they could evolve faster than you might expect, according to a new study.
Our planet's northerly climes undergo extreme seasonal change — from round-the-clock darkness to midnight sun, and from barren icescapes to verdant meadows and lush forest.
Animals must take extreme measures to survive there. Some head south once summer's abundance is past. Some hibernate. And some make it through the winter with a costume change.
Swapping dull brown fur for a luxurious white winter coat means animals can stay camouflaged all year, helping them avoid predators or keep hidden as they stalk their prey.
But as the climate changes, they're being caught in inappropriate attire for the season. Longer summers and reduced snow cover mean bright white fur or feathers can stand out like a beacon against an unseasonably snow-free habitat.
A team of scientists led by L. Scott Mills, a professor of wildlife biology at the University of Montana, studied the impact of this mismatch on the snowshoe hare, and came to the conclusion that the animal's population numbers were already falling.
"What was certain from our research is being white on a brown background kills," Mills told DW.
The artic fox is famous for its luxurious white coat, but its summer attire might be more practical in the long run
But there is hope, the researchers state in their study that was published in the journal Science on Thursday. The hare's seasonal transformation is a genetic trait carried only by certain members of the species. There are also populations in warmer climates that keep their brown coat all year.
Evolutionary hot spots
"This is a genetically adapted trait," Mills explained. "They are evolved to turn white in the north, and at the high elevations where there's snow — predictable seasonal snow — and they remain brown in the south and at the lower elevations."
Most importantly, there are "polymorphic zones" where both strains live side by side. Mills and his team hope this will allow interbreeding to help the hare evolve out of its dangerous winter-white trait.
"These areas where there's both brown and white together — these polymorphic zones where brown and white individuals are in the same population — those we expect to be evolutionary hot spots," Mills said.
The research team identified such hot spots for various species of rabbit, hare and weasel on the North American continent.
Predators and prey
They also reviewed population data on other winter-white animals, like the Arctic fox, and found evidence of their ranges retreating north. Now, the researchers intend to delve deeper and see if they can show that color mismatch is a factor.
The scientists found overlap between the territories of brown weasels and their more seasonally attuned cousins
Arctic foxes, Mills points out, don't just use camouflage to keep a low profile while stalking smaller animals. The wrong color can make a fox a prime target for eagles in snowless winters.
"They are interesting because they have double benefits of camouflage both as prey and predators," Mills said.
Of course, it would be a shame to lose the striking sight of these Arctic species in all their winter glory, and Mills is keen to stress that the priority is to cut emissions and slow climate change.
But identifying and protecting areas where these animals have the best chance of evolutionary adaptation could provide another line of defense.
"This idea that evolution could rescue animal species from extinction due to climate change may seem radical, but that's because we still tend to think that evolution only happens on the time scale of fossils, over millions of years," Mills said.
"The fact is, over the last couple decades, science has shown without doubt that under the right conditions, meaningful adaptive changes can happen fast — more in the range of tens of years."