Distinctions blur between wolf species

Wolves are having something of an identity crisis. Gray wolves and coyotes might be the only pure wild canine species in North America, a new genetic analysis suggests. Other wolves — like red wolves and eastern wolves — appear to be blends of gray wolf and coyote ancestry instead of their own distinct lineages.

Red wolves contain about 75 percent coyote genes and 25 percent wolf genes, an international team of scientists reports online July 27 in Science Advances. Eastern wolves have about 25 to 50 percent coyote ancestry.

That finding adds another twist to the ongoing battle over wolf protection and regulation in the United States: how to protect a population that’s not its own species but carries valuable genetic information.

Gray wolves used to roam much of North America — until they were hunted to near-extinction. Protection under the Endangered Species Act has helped them to rebound, but their current range is still far smaller than it used to be. Red wolves, found in the southeastern United States, and eastern wolves, found in the Great Lakes region, look similar to gray wolves but are often treated as distinct species. The two groups occupy territory where gray wolves are now scarcer (in the Great Lakes area) or completely gone (in the southeast).

The new study examined the entire genetic makeup, or genome, of 23 wild canines from around North America. The researchers compared the mixed genomes to those from pure coyotes and Eurasian wolves to figure out what percent of each animal’s genetic material came from the wolf and what part came from the coyote.

Red and eastern wolves have historically mated with coyotes, the team found. But gray wolves have recent coyote ancestry too, and neither eastern wolves nor red wolves differ genetically from gray wolves any more than from other individuals of their species. That suggests that these different groups of wolves are more evolutionarily intertwined than previously believed, says Robert Wayne, a biologist at UCLA who coauthored the study

Red wolves and eastern wolves probably arose when gray wolf populations in the eastern United States were hunted by early settlers, says Doug Smith, a biologist who leads the Wolf Restoration Program in Yellowstone National Park. That created room for coyotes to move east, where the struggling wolves bred with them. Mixing genes with coyotes probably helped wolves survive in lean times.

While their coyote genes make red wolves and eastern wolves look slightly different from gray wolves, “we don’t find anything incredibly unique in the red wolf that you can’t find in other canines,” says Bridgett vonHoldt, a biologist at Princeton University who worked with Wayne and collaborators. But they’re still important to protect, because “the wolf part of their genome might actually represent the last of the southeastern gray wolf.” It’s a similar story for the eastern wolf.

Blended species like these are hard to label, Smith says, because traditional species definitions assume clear boundaries that prevent gene sharing.

“Nothing isolates a wolf,” says Smith. “They’re just so capable of moving around.”

Right now, wolves in the United States are managed through a patchwork of federal and state regulations. Red wolves are federally listed as endangered; gray wolves are listed as endangered in some parts of the country, including in the upper Midwest. Genetic mixing makes designing appropriate regulations even more challenging.

“These animals don’t walk around with little name tags on them in the field,” says vonHoldt. “So hybrids or admixed animals don’t always look very different from a pure coyote or pure wolf.”

The only way to ensure that wolf genes stick around in certain areas would be to prohibit killing of both wolves and coyotes, vonHoldt says. But such a restriction would be nearly impossible to implement.  

This study is an important step, but its conclusions aren’t definitive, says Paul Wilson, a biologist at Trent University in Ontario, Canada. His work still supports the idea that the eastern wolf is its own species. Comparison with DNA from ancient North American canids — before wolves and coyotes interbred at all — could help further clarify the debate, he says. 

---

Editor’s note: This story was updated July 28, 2016, to correct where gray wolves are listed as endangered.