North American red and eastern wolves are probably not distinct species, but are instead hybrid mixes between gray wolves and coyotes, according to a new study in the 27 July issue of Science Advances.
The animals' surprising genetic history could affect how they are protected under the U.S. Endangered Species Act (ESA), which does not have any provisions for protecting genetically mixed populations.
"The Endangered Species Act is a remarkable document that has allowed for the recovery of critical species, and preserved their environments. Our results suggest that in addition to 'pure' species and populations, hybrids between protected animals and non-protected ones may deserve protection," said Robert Wayne, a biologist at University of California Los Angeles and senior author of the study.
Two well-accepted species of wolf-like canid animals inhabit North America: the gray wolf — currently listed as endangered — and the widespread coyote. Red and eastern wolves have been recognized more recently as evolutionarily distinct species, though some researchers consider the two to be hybrids between coyotes and gray wolves.
The U.S. Fish and Wildlife Service has accepted the eastern wolf of the Great Lakes region as a distinct species, and has proposed removing the gray wolf in the eastern United States from endangered species protection. They suggest that the eastern U.S. is the historical range of the eastern wolf, and not the gray wolf as previously thought.
Meanwhile, the red wolf from the southeastern United States remains protected by the ESA. The red wolf was listed as an endangered species in 1973, initiating a captive breeding program by the U.S. Fish and Wildlife Service. Under the program, a small group of carefully selected types of red wolves, considered to be pure red wolves based on their appearance and the lack of "coyote-like" traits in their offspring, were bred through mating in controlled environments.
Since then, several hundred red wolves have been born in the captive breeding program and reintroduced into the wild in eastern North Carolina.
Fast forward several decades, and scientists are now equipped with the advanced genomic technology needed to explore a species' evolutionary history at an unprecedented level, leading to new questions that challenge current definitions of what constitutes a species and which species deserve protection.
Wayne, along with Princeton University researcher Bridgett vonHoldt and colleagues, sequenced the genomes of 28 different wolves and coyotes and found that there is little evidence that the red wolves selected for the 1970s captive breeding program have a distinct ancestry. Instead, the red wolf genome is made up of about 25% gray wolf and 75% coyote ancestry.
"The Endangered Species Act is a remarkable document that has allowed for the recovery of critical species, and preserved their environments. Our results suggest that in addition to 'pure' species and populations, hybrids between protected animals and non-protected ones may deserve protection."
In contrast, the eastern wolf is mostly gray wolf, with about 50% to 75% of its genome assigned to that species. This difference reflects the more recent arrival of coyotes to the Great Lakes area about 100 years ago, and that unlike in the American South, pure gray wolves still persist in the Great Lakes area.
"We were surprised by the results, because we expected a substantial fraction of the genome of the red wolf and eastern wolf, maybe 20% to 30%, would be derived from a long-distinct species, much as about 1% to 4% of [human] Eurasian genomes derive from Neanderthals," said Wayne.
The researchers found only a very small proportion of the red and eastern wolves' genomes to be unique. Instead, the vast majority of the genome was derived from coyotes or gray wolves, suggesting that the red wolf and eastern wolf are mixtures of those two species.
"It is likely in the case of the red wolf and the Great Lakes [eastern] wolf that mixture with coyotes was caused by human actions, wolf control, and habitat destruction, which allowed coyote numbers to increase. And as wolves were so rare, they had few options but to breed with coyotes," Wayne explained.
Rather than focus on the strict application of species identification to support endangered species status, Wayne and vonHoldt argue that the preservation of evolutionary and ecological processes is of greater importance. Genetic mixing is one critical example of a process that may enhance the adaptation and evolution of a species in the rapidly changing environment of the modern world.
This more dynamic view of conservation, which allows for species' adaptation to human-altered habitats and changing climates, may be a way to maintain a portion of endangered genetic ancestry, the scientists suggest.
"We have a mandate and a responsibility to restore the genetic landscape of North American wolves to what it was historically, before the arrival of coyotes," said Wayne.