Red wolves, Mexican gray wolves are valid taxonomic species, researchers say

Evidence uncovered during a yearlong study chaired by a Florida State University professor indicates the red wolf is a distinct species in the wolf family and the Mexican gray is a distinct subspecies of the gray wolf.Additional genomic evidence from historical red wolf specimens, however, could change the finding about this species.

These conclusions were published today in the consensus report “Evaluating the Taxonomic Status of the Mexican Gray Wolf and the Red Wolf" by the National Academies of Science. ​

Joe Travis, Robert O. Lawton Distinguished Professor in the Florida State University Department of Biological Science, served as the research committee’s chair. He said enough prevailing genomic evidence existed to question the taxonomic status of these animals, given both types of wolves had been driven to near extinction in the wild and that questions had been raised about whether the remaining individuals were the product of hybridizations with other species.

The study was commissioned in 2018 by the U.S. Fish and Wildlife Service in order to develop an independent assessment. Travis briefed federal officials on the findings Wednesday.

“The current extant populations of Mexican gray wolves and red wolves are based on captive breeding colonies that were established for each species, and members of which have been released into the wild in North Carolina, so there’s reason to investigate this question, since we’re looking at a population based on a small number of founders,” Travis said.

Concluding the Mexican gray wolf (canis lupus baileyi) is a valid subspecies, in fact the most distinctive wolf subspecies in North America, was relatively straightforward, Travis said, referring to the animals’ unique size, coloration, shape and genetics.“There was no evidence of hybridization with coyotes, no evidence of any past introgression of genes from domestic dogs,” Travis said. “We know the extant wolves are descendants of the historical wolves because they were the last remaining Mexican gray wolves were taken from Mexico and used as breeding stock. You can show the genetic continuity.”

The red-wolf debate

Until now, the taxonomic status of red wolves (canis rufus) has been a subject of controversy due to intermingling of gray wolf and coyote traits through cross-species mating. Part of the challenge for the group was the relative dearth of a historical, paleontological record for these particular wolves: There are only a handful of specimens that represent what a red wolf would have looked like prior to the European colonization of America.

Scientifically, there is no doubt that red wolves contain significant genetic material from both gray wolves and coyotes, and that they are more closely related to coyotes than they are to gray wolves. However, the committee’s findings indicate there truly was a historical red wolf.

“The first red wolf specimen dates to 10,000 years ago and was found here in Florida,” Travis said. “If you look at the genes in the managed population in North Carolina, those wolves share these specific red-wolf genes with a previously undiscovered group of red wolves living on Galveston Island, in Texas.”

The key takeaway for the red wolves is they have unique alleles not shared with coyotes or wolves, something that only happens if the animals are a species descended from a canid that lived between 10,000 and 100,000 years ago. It’s just not possible for today’s red wolves to be only a combination of coyotes and gray wolves, he said.

The right science for the right questions

An additional reason for the controversy surrounding the taxonomic status of these two types of wolves is that while current methods for describing and analyzing genomes are the most sophisticated in history, these methods do not always deliver an unambiguous picture for groups that are evolving rapidly or have some level of mating between species, known as admixture.

“We emphasized that, because the genomic work is at the limits of its resolution, you have to consider all the data,” Travis said. “Look at the historical record, the ecology of the animals today, their mating behavior, their genetics, everything, because, in fact, what we call definitions of species and subspecies really involve all those types of data.”

Putting a premium on genetic data to the exclusion of other types of data would be a mistake, just as it would be to put emphasis on the ecological data without examining the genetic data, he explained.

Some may indicate red wolves are a distinct species, but do not reveal how much of the genome is shared by coyotes. Other methods may show red wolves are distinct, but not how long it has been since they diverged from other species. Still other methods may indicate that hybridization has occurred, but not how long ago.All of these data are subject to the same challenge: the lack of reference DNA from ancient red wolves.

“You can’t estimate accurately the proportion of genes in red wolves that come from coyotes and red wolves, because you don’t know what the original red wolf genome looked like,” Travis said. “If you don’t have the right reference population, you can draw a misleading conclusion, and it has proven extremely difficult to extract genomic DNA from the handful of red wolf specimens that predate European colonization.”

Mating and behavioral activity are also important considerations in the committee’s determinations and deliver more insight into reasons for red-wolf hybridization. Wolves mate assertively; if a breeding pair is disrupted, the other animal will seek another mate from within its own species. If one is unavailable, it will mate with a different species.

“Looking into the behavioral data in the context of wolf habitat, the habitat has changed dramatically,” Travis said. “Many places in North Carolina, at the edge of the protected area, the habitat is farmland, which is neither coyote habitat nor wolf habitat. That’s where you see hybrids and why you see them in that location.”

Along with the habitat alteration, wolves have been hunted heavily and their populations declined dramatically, making it difficult to reconstruct the original distribution of these species. While some is known, controversy still exists, for example, surrounding the original range of the Mexican gray wolf.

A study unlike any other

What differentiates this study from others is that it overlays these different methods of data capture to provide a full-spectrum view. To aid in the assessment, the committee — composed of Travis, an ecologist and evolutionary biologist, along with population geneticist Fred Allendorf, wolf behavioral biologist Diane Boyd, mammalian hybridization and genetics expert Lori Eggert, canid geneticist Diane Genereux, evolutionary genomics expert Michael Lynch, mammalian geneticists Jesús Maldonado and Liliana Ortiz, and computational genomicist Rasmus Nielson — looked at all the materials they could get their hands on.

“The study is groundbreaking because it extended beyond a purely genomic study and integrated all available evidence. We read all the literature, invited people to come and speak to us, and conducted webinars,” Travis said. “And through the generosity of other scientists who shared unpublished manuscripts, we were even able to review unpublished data. We digested and assimilated all of it to write this report.”

The committee was able to use the right methods to ask the right questions, he said, noting that even work that has been eclipsed by new methods can sometimes offer a result that would have been invisible any other way.

“Part of what we relied on were traditional investigations into cranial morphology. One of the key references is ‘Quaternary Canis of North America,’ published in 1950,” he said. “If you want to know what’s known about the historic red wolves and Mexican gray wolves, that’s the reference. While the statistical methods the authors used aren’t what we would use today, sometimes old science is still relevant to the questions we’re asking.”