Handstanding Skunks' DNA Shaped by Ancient Climate Change

Western spotted skunks — striped skunks' smaller cousins that stand on their "hands" to blast their smelly defensive spray — are helping scientists piece together a picture of how ancient climate change shaped animal populations millions of years ago, and could provide clues for how present climate change may affect animals alive today.

Image: skeeze-272447/Pixabay

These endearing and widely distributed skunks have been around for about 1 million years and live in a range of habitats across western North America. But even though the skunks all belong to one species, Spilogale gracilis, genetic differences divide them into three distinct groups that are known as clades, and scientists have puzzled over what might have driven these changes in the skunks' DNA.

Researchers investigating these adorable little stinkers recently discovered the likely scenario that led to these genetic divisions — ancient climate change during the Pleistocene ice age, as glaciers divided skunk populations into habitats isolated from each other.

Unlike the bold bands of white fur lining the black backs of striped skunks, western spotted skunks' markings curve and twine like the walls of a maze, with a single large spot marking the center of their heads. They are the smallest of the North American skunks, with males measuring about 16 inches (41 centimeters) in length and weighing about 22 ounces (630 grams), according to a species description by the Montana Natural Heritage Program and Montana Fish, Wildlife and Parks.

Western spotted skunks perform "handstands" just before they spray. | Credit: Copyright Jerry W. Dragoo

Because their distribution is so broad — from British Columbia to northern Mexico, and from California to the central Great Plains — groups of skunks could potentially be separated from each other by many natural geographical barriers, such are rivers and mountain ranges. Scientists wanted to know whether geography could explain how skunk populations separated from each other and evolved unique genetic signatures, or if other land-shaping factors might have played a part, study lead author Adam Ferguson, collection manager of mammals at the Field Museum of Natural History, told Live Science.

"We were interested in whether we would see if genetic breaks are associated with older events — major biogeographic events, like the Sierra, the Rockies, the Rio Grande — or with climate change," Ferguson explained.

Stinky study subjects

In general, skunks aren't well-studied, probably because working with them comes with an odious olfactory price — "even their tissues stink," Ferguson said. In fact, during each season of fieldwork, he puts aside what will be "the skunk clothes," an outfit that sometimes must be permanently retired when the season ends, he said.

Study lead author Adam Fergusun wearing impromptu Kleenex nose plugs — not to block the smell of his study subject, but because he had a cold. | Credit: Courtesy of Adam Fergusun

For the study, the scientists sampled genetic data from 97 skunks representing a range of habitats and climates in the southwestern U.S. But the genetic differences that separated them didn't map to geographic features. For example, two skunk populations divided by mountains were mostly identical on a genetic level, the study authors found.

By modeling climate conditions during the ice age glacial maximum — the period when ice covered the most land mass — the researchers discovered that advancing glaciers could have effectively isolated habitat "refuges" from each other, allowing genetic differences to evolve in separated animal groups.

Their findings help to fill in the picture of how ancient climate change affected not only the western spotted skunks, but possibly other animals as well — large and small — that shared the skunks' habitats across the southwestern U.S. And this could help scientists predict how ecosystems and their inhabitants might be affected by present-day climate change, Ferguson said.

"If we have data from rodents, bats, small carnivores, large carnivores, reptiles, birds, we can say, 'How as a whole would the Sonoran Desert community respond potentially to climate change across the board?' You can make these general predictions of how climate change might affect an entire community — not just a single species," he told Live Science.

The findings were published online today (May 3) in the journal Ecology and Evolution.

SOURCE: LiveScience