March 28, 2019
WASHINGTON — Current evidence supports the classification of the contemporary red wolf as a distinct species of wolf, although additional genomic evidence from historic wolf specimens could change that assessment, says Evaluating the Taxonomic Status of the Mexican Gray Wolf and the Red Wolf, a new report from the National Academies of Sciences, Engineering, and Medicine. The report also concludes that the Mexican gray wolf is a valid subspecies of gray wolf.
Scientists strive to develop clear rules for taxonomy — the naming and grouping of living organisms — but these classifications are often highly debated, since it can be difficult to determine whether the evolutionary history or future of a population is distinct enough to designate it as a unique species. There has been substantial controversy regarding the taxonomic status of red wolves and Mexican gray wolves. At the direction of Congress, the U.S. Fish and Wildlife Service (FWS) asked the National Academies for an independent assessment of the taxonomic validity of the Mexican gray wolf and the red wolf. FWS currently considers the red wolf to be a valid taxonomic species and the Mexican gray wolf to be a valid taxonomic subspecies. Both wolves are listed as endangered under the U.S. Endangered Species Act.
Mexican Gray Wolf
The Mexican gray wolf, whose range includes the Southwestern U.S. and Mexico, was largely driven extinct from the wild in the U.S. in the mid-1970s. Then 20 years ago the wolves were reintroduced, amid much controversy, into a small portion of their former range. Their designation as a subspecies has been controversial because there has been speculation that they are not physically or genetically distinct enough to justify that status. There has also been speculation that the current Mexican gray wolf population may have included ancestry from dogs or coyotes.
Whether the Mexican gray wolf is a valid subspecies hinges on the strength of the evidence for distinctiveness from other North American wolf populations, and the evidence for continuity between the historic Mexican gray wolf lineage and the contemporary population.
The report concludes that the Mexican gray wolf is a valid taxonomic subspecies of the gray wolf. The Mexican gray wolf’s size, morphology (physical characteristics such as head shape), and color distinguish it from other North American wolves. Genetic and genomic analyses confirm that the Mexican gray wolf is the most genetically distinct subspecies of gray wolf in North America. The Mexican gray wolf represents a smaller form of the gray wolf and inhabits a more arid ecosystem than the gray wolf. Furthermore, the current managed population of Mexican gray wolves are direct descendants of the last remaining wild Mexican gray wolves; the known history of current Mexican gray wolves suggests that there is continuity between them and the historic lineage. There is no evidence that the genome of the Mexican gray wolf includes DNA from domestic dogs, the report adds.
The red wolf historically inhabited much of the Eastern United States, but during the 20th century, populations were driven to very low numbers by habitat loss and predator eradication programs. Red wolves were largely replaced by coyotes that spread eastward from their original range in the western U.S. A few remaining specimens with red wolf morphology — physical characteristics long associated with red wolves — were captured in Texas and Louisiana before the red wolf went extinct in the wild and were used to establish a breeding program. The descendants of these animals were reintroduced in North Carolina and are now a managed population in the wild. The red wolf’s species status has been controversial because the individuals used to establish the breeding program were captured from a region where there had already been substantial interbreeding between red wolves and coyotes and gray wolves.
Whether the red wolf is a valid species hinges on whether there is evidence that the historic population of red wolves has a distinct lineage, evidence that contemporary red wolf populations are distinct from gray wolves and coyotes, and evidence for continuity between the historic red wolf population and the contemporary one.
The evidence currently available supports the classification of the contemporary red wolf as a distinct species, the report says. Contemporary red wolves are distinct from gray wolves and coyotes. In addition, available evidence suggests that the historic red wolves constituted a valid species, and that contemporary red wolves trace some of their ancestry from these historic red wolves. However, genetic continuity between contemporary red wolves and the historic population cannot be firmly established without genomic data from ancient specimens.
Genomic DNA from historic specimens could help clarify this issue regarding continuity, the report says. In addition, more precise genetic analysis might help determine the exact proportion of the red wolf genome that has been replaced through historic interbreeding with coyotes and wolves.
The study — undertaken by the Committee on Assessing the Taxonomic Status of the Red Wolf and the Mexican Gray Wolf — was sponsored by the U.S. Fish and Wildlife Service. The National Academies are private, nonprofit institutions that provide independent, objective analysis and advice to the nation to solve complex problems and inform public policy decisions related to science, technology, and medicine. They operate under an 1863 congressional charter to the National Academy of Sciences, signed by President Lincoln. For more information, visit nationalacademies.org.