Arizona Game and Fish Department

Mexican wolf.

The endangered Mexican gray wolf (Canis lupus baileyi) has weathered challenges from near extinction to political wrangling. Now, a genetic study settles whether the wolves might have interbred with dogs.

The Journal of Heredity study could affect future conservation and management of the wolves.

Once distributed across the southwestern U.S. and northern Mexico, Mexican wolves were hunted, trapped and poisoned to the brink of extinction by 1976, when the federal government listed them as a protected species under the U.S. Endangered Species Act.

Since then, captive breeding programs have taken Mexican wolves from three captive groups totaling seven genetic "founders" to a population of around 100, reintroduced into Arizona and New Mexico recovery zones.

But reestablishment and protection have faced opposition from ranchers and their political allies, who view the wolves as a danger to livestock.

Following attempts to lump Mexican wolves in with their more populous cousin, the gray wolf (which is itself listed as endangered and threatened in certain areas), researchers established that the Mexican wolf is its own subspecies, eligible for protection.

More recently, jurisdictions like Apache County have justified removing some of those protections by arguing the wolves have interbred with dogs, producing a "wolf-dog hybrid."

"There were some anecdotal reports about, they may be mixed with domestic dogs, and they had certain traits that looked like they may be domestic dogs. So that was kind of always in the back of everyone's mind," said Bob Fitak, now a postdoctoral researcher at Duke University, who performed the research as part of his dissertation at University of Arizona.

Mexican wolves are smaller than other North American wolves. Their skulls are different, and their coats are distinctive. Earlier studies examining these factors, combined with smaller-scale genetic testing, already suggested that no interbreeding had occurred.

Now, by analyzing 172,000 single nucleotide polymorphisms — simple, one-letter changes in DNA bases that scientists use as biomarkers and for establishing heredity — Fitak and his colleagues believe they have settled the question.

"It's not that we don't find any genetic variation that looks like it could be from dog. The question is, what we do find that looks like dog is probably just due to sharing a dog ancestor, you know, several thousand years ago."