Focus on Arts and Ecology

Researchers analyzed hundreds of spotted skunk specimens to classify the animals.

Spotted skunks are tiny acrobats. Weighing in at less than two pounds, they plant their front paws firmly on the ground, throw their hind legs into the air and let their tail splay out like garland on a Christmas tree, balancing in a handstand as a final warning before they spray.

It’s an exaggerated version of a defense mechanism they share with their much larger striped cousins, and one that makes them tricky to catch and, as a result, to study.

And not being able to catch them has created a problem. Without a wide range of specimens to study, scientists haven’t been able to conduct genetic analysis to determine how many species exist. Over the years, researchers have thought as many as 14 and as few as two existed. Most recently, they agreed there were four.

But now, a group of scientists have made a remarkable new discovery: seven species of spotted skunk exist. In a new paper in Molecular Phylogenetics and Evolution, a team of researchers describes how it analyzed the DNA of 203 skunk specimens—some victims of wildlife-vehicle collisions and others from museum collections—to determine what should be considered a species and what should be a subspecies.

What they found came as a shock.

“We expected to either validate the four species hypothesis or invalidate it and make it three, not actually expand it to seven,” says Adam Ferguson, an evolutionary ecologist at Chicago’s Field Museum and one of the paper’s coauthors.

Prior to the new study, researchers tended to differentiate spotted skunk species by looking at their morphology—things like differences in spotting patterns, as well as cranial and dental measurements. But those factors are so similar among some of the seven species that they were thought to be the same type of spotted skunk.

The lack of genetic data that was analyzed among the species made Ferguson want to look more closely at spotted skunk diversity. But collecting enough specimens to carry out a complete DNA study on the wide-ranging genus, which can be found throughout North and Central America, was no easy task.

It would take years to amass enough specimens—Ferguson started collecting them while he was still working on his master’s degree, which he completed in 2008. Some specimens would come to him after they were killed in wildlife-vehicle collisions across the United States, but he still needed more. Without any tissue samples from Central America or the Yucatan, he and his team couldn’t look at the full history of the spotted skunk’s evolution, a crucial component to understanding the species that exist today.

So they turned to museum collections to fill those holes. Century-old museum samples led Molly McDonough, a biology professor at Chicago State University and another of the paper’s coauthors, to identify the Yucatan spotted skunk, a previously unrecognized species endemic to the Yucatan Peninsula. The team also used museum specimens to determine that the Plains spotted skunk, which calls the Great Plains its home, is its own species, and not a subspecies as previously thought.

“That’s the beauty of museums,” says Ferguson. “The person who collected a skunk 40 years ago had no idea it would be used in a paper today.”

But what surprised the scientists most was how much the two species have in common.

Despite being geographically distant, the researchers found that the Yucatan spotted skunk is more closely related to species living in the eastern U.S., like the Plains spotted skunk, than it is to other species living in closer proximity to it, like those in Tabasco, Mexico. Up until now, most research has focused on spotted skunks in the western and eastern U.S. Understanding the similarities between these newly identified species could help open doors for more research into spotted skunks in other regions.

“One of the things I hope will happen is that this will encourage people to look at the ecology of the species in their own backyard,” says Ferguson.

Knowing each individual species’ habitat range and barriers, diet and reproductive capabilities will prepare scientists to protect them if, in the future, one of the populations declines.

The Plains spotted skunk already knows this struggle. Previously designated a subspecies, it has suffered dramatic declines in its population over the last century.

Experts petitioned for it to be included in the Endangered Species Act while it was a subspecies, but it has yet to be added to the list. Protection of a species, says Ferguson, is often considered more important “because of the evolutionary distinctiveness.”

“It’s taken a little more seriously,” he says, “because it requires a bit more rigorous evidence to document that it’s a species and not just a subspecies or a variation on a more widely spread species.”

Now that proof exists that the Plains spotted skunk is its own species and not a subspecies of the eastern spotted skunk, it has a better chance of getting the protection it needs.

“If the spotted skunk in the Plains was considered a subspecies you could argue that, well it’s doing terrible in the Great Plains, but it’s doing great in Appalachia,” says Ferguson. But knowing it is its own species and only lives on the Great Plains makes it clear that its population is struggling and needs better protection.

Jerry W. Dragoo, a mephitologist—a.k.a. skunk expert—and assistant research professor of biology at the University of New Mexico, says habitat boundaries can and should now be studied further.

“[The paper authors] describe a lot of features that can separate these populations and keep these populations isolated,” says Dragoo, who was not involved in the study. “Once you understand that, you can look to see what happens when they interact.”

Ferguson agrees. In a previous paper from the research team published in 2017, they described how the Rio Grande was historically considered a barrier that limited gene flow by keeping spotted skunk populations separate from each other. Now, in more recent specimens, they’ve seen genetic interchange across the river. They suspect the cause is that the river has started to dry and become smaller, allowing animals that wouldn’t historically cross the water to make the trip to the other side. “That’s directly tied to both irrigation—from draining the river—and changing climate as well,” Ferguson says.

By looking at the genome of spotted skunks, the researchers were able to determine that another era of climate change—this time during the Ice Age—is what pushed them to split into different species. Glacial expansion may have created different environments where they survived. Once those glaciers retreated and the habitat became one again, the species were brought back into contact with one another, but had already evolved separately.

The redrawing of the spotted skunk’s family tree is an early step scientists have taken to better understand the species, but an important one that will help with management decisions for their conservation.

“[This paper] gives us a better idea of how these things are evolving,” says Dragoo. “And you need to understand the ecology and the past history of these animals in order to try to protect them.”

(Sources: Smithsonian Magazine)