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Spotted skunk evolution driven by climate change, suggest researchers

Ice Age climate change played a bigger role in skunk genetics than geological barriers

Climate plays a key role in determining what animals can live where. And while human-induced climate change has been causing major problems for wildlife as of late, changes in Earth’s climate have impacted evolution for millions of years — offering tantalizing clues into how to protect animals facing climate change today. In a new paper in Ecology and Evolution, scientists have delved into the effects of Ice Age climate change upon the evolution of tiny, hand-standing skunks.

“By analyzing western spotted skunk DNA, we learned that Ice Age climate change played a crucial role in their evolution,” says lead author Adam Ferguson, Collections Manager of Mammals at The Field Museum in Chicago and affiliate of Texas Tech University. “Over the past million years, changing climates isolated groups of spotted skunks in regions with suitable abiotic conditions, giving rise to genetic sub-divisions that we still see today.”

Western spotted skunks are really stinkin’ cute — at two pounds, they’re smaller than the striped Pepe Le Pew variety, their coats are an almost maze-like pattern of black and white swirls, and when they spray, they often do a hand-stand, hind legs and fluffy tail in the air as they unleash smelly chemicals to ward off predators. They’re found throughout the Western US and Mexico, in a wide variety of climates — they thrive everywhere from Oregon’s temperate rainforests to the Sonoran, the hottest desert in Mexico.

There are three genetic sub-groups, called clades, of western spotted skunks. Often, clades develop when a species is split up by geography. If a species is separated by, say, a mountain range, the groups on either side of the mountain may wind up splitting off from each other genetically. However, the division of the skunks into three clades doesn’t seem to have been driven solely by geographical barriers — populations separated by mountains are more or less genetically identical. Instead, the skunks vary genetically from one historic climate region to another, due to Ice Age climate change.

“Western spotted skunks have been around for a million years, since the Pleistocene Ice Age,” explains Ferguson. “During the Ice Age, western North America was mostly covered by glaciers, and there were patches of suitable climates for the skunks separated by patches of unsuitable climates. These regions are called climate refugia. When we analyzed the DNA of spotted skunks living today, we found three groups that correspond to three different climate refugia.”

“That means that for spotted skunk evolution, climate change appears to have been a more important factor than geographical barriers,” says Ferguson.

In the study, scientists used DNA samples from 97 skunks from a variety of regions and climates in the American Southwest. Upon sequencing the DNA, the scientists were surprised to see that the skunks split into three clades based on pockets of suitable climate present during the Pleistocene.

“Small carnivores like skunks haven’t been well-studied when it comes to historical climate change,” says Ferguson. “We know how small mammals like rodents respond to changing climates, and we know how bigger carnivores like wolves respond, but this study helps bridge the gap between them.”

Ferguson also notes that skunks don’t deserve the bad rap they get. “Skunks are a really interesting family of North American carnivores — they’re well-known, but not well-studied. And studying them comes with a cost — they stink, even their tissues stink, and you run the risk of getting sprayed. But they’re important to their ecosystems — for example, they eat insects and rodents that damage our crops,” he says.

Moreover, Ferguson says, the study can illuminate the bigger picture of biodiversity in the face of climate change — an issue that grows increasingly relevant as human-driven climate change affects more and more of the world’s animals.

“What we know about the past can inform what we expect to see in the future,” says Ferguson. “Understanding these genetic subdivisions that happened as a result of changing climatic conditions can help us conserve skunks and other animals in the future.”

Before working at The Field Museum, Adam Ferguson was affiliated with Texas Tech University and completed this research there. Ferguson’s co-authors are affiliated with Angelo State University, the National Museum of Natural History, the National Zoological Park, the US Fish and Wildlife Service, and the University of New Mexico.

Climate plays a key role in determining what animals can live where. And while human-induced climate change has been causing major problems for wildlife as of late, changes in the Earth’s climate have impacted evolution for millions of years — offering tantalizing clues into how to protect animals facing climate change today. In a new paper, scientists have delved into the effects of Ice Age climate change upon the evolution of tiny, hand-standing skunks.

The Fascinating Evolution of the World’s Most Charming Skunk

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After so many years in the public eye, skunks have lost their pizzazz. It’s not their fault, it’s just that we’ve all forgotten how bizarre they are. Very few animals can fire sulphurous fluids out of their bums to incapacitate their foes, after all. Very few. But good on skunks, really, for keeping it weird.

One particular variety, the western spotted skunk—which balances on its front legs before it sprays you, as if that’s a charming consolation—just got even weirder. In a study published today in the journal Ecology and Evolution, researchers report that the two-pound terror has evolved into three genetically distinct groups, called clades, in an intriguing way: not with geological isolation (the classical impetus for getting populations to diverge genetically) but with climatic isolation. That is, dramatic climate change led to a genetic splintering of the species.

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It’s actually fairly easy to get a new species. Just run a river or a mountain range through a population, splitting it in two. In their isolation, the groups will eventually grow so genetically distinct that they can no longer mate and produce offspring. Boom, two new species. The spotted skunk is kind of up to the same thing, though it hasn’t diverged enough to become new species, but instead three clades: western (California, Nevada, Baja California), Arizona, and east-central (Texas and Mexico). Though the clades existed in different geographical areas, they weren’t necessarily cordoned off from each other by geological boundaries.

By melding climate models and genetic work that showed when the spotted skunk began diverging, the researchers determined that the three clades likely got stuck in isolated pockets of actually habitable habitat during the Pleistocene Ice Age. “The idea is that these suitable conditions would contract when glaciers were expanding—it was cooler periods—and then expand during the interglacial periods,” says mammalogist and study co-author Adam Ferguson of the Field Museum.

The spotted skunk’s divergence began about 1 million years ago, and continued as glaciers in North America expanded and contracted over millennia. “Unlike the anthropogenically induced climate change we are experiencing today, the change in temperatures and rainfall patterns was more gradual,” Ferguson says, “occurring over thousands to tens of thousands of years.” These fluctuations as the glaciers moved in and out probably created suitable wooded habitats for skunks, and destroyed others, as groups of the creatures evolved in isolation.

Really, it’s not hard to see how this could come about. Say a forested area started drying out, and grasslands took over for dying trees. “The western spotted skunks really depend on cover and thick areas for protection from aerial predators,” Ferguson says, “and so crossing these open grasslands might not have been possible for them per se.” Western America’s newfound plains were just as restrictive for the skunk as new rivers or mountain ranges would have been.

The beauty of it all is that scientists can use this data to get a better picture of a disorderly climatic future. “By projecting into the past and understanding what happened to this species, it could give us an idea of how changing climates of the future could potentially change at least the distribution of suitable areas for this species,” Ferguson says.

The spotted skunk’s evolutionary journey is also a reminder that climate change affects different creatures in different ways. Warming oceans are definitely bad for coral, for instance. But other species will adapt to a planet in flux, like the spotted skunk did during the Pleistocene.

Problem is, it’s not just human-made climate change that’s the issue, but human-made everything. Urban development in particular threatens mammals all over the world. “If there’s bigger freeways, and all these other things dividing up the land, it’s going to be harder for small populations to persist,” says ecologist Craig Benkman.

But here’s to the continued survival of the spotted skunk. I for one am glad it got its groove back.

The two-pound terror has evolved into three genetically distinct groups, called clades, in an intriguing way.