The Mexican wolf (Canis lupus baileyi), also known as the lobo, is a subspecies of gray wolf native to southeastern Arizona and southern New Mexico in the United States, and northern Mexico. It once also ranged into western Texas. It is the smallest of North America's gray wolves, and is similar to the Great Plains wolf (C. l. nubilus), though it is distinguished by its smaller, narrower skull and its darker pelt, which is yellowish-gray and heavily clouded with black over the back and tail. Its ancestors were likely the first gray wolves to enter North America after the extinction of the Beringian wolf, as indicated by its southern range and basal physical and genetic characteristics.
Though once held in high regard in Pre-Columbian Mexico, it became the most endangered gray wolf subspecies in North America, having been extirpated in the wild during the mid-1900s through a combination of hunting, trapping, poisoning and digging pups from dens. After being listed under the Endangered Species Act in 1976, the United States and Mexico collaborated to capture all lobos remaining in the wild. This extreme measure forestalled their extinction. Five wild Mexican wolves (four males and one pregnant female) were captured alive in Mexico from 1977 to 1980 and used to start a captive breeding program. Through this program, captive-bred Mexican wolves were released into recovery areas in Arizona and New Mexico beginning in 1998 in order to recolonize the animals' historical range.
As of 2023, there are 241 wild Mexican wolves in the US and 45 in Mexico, and 380 in captive breeding programs, up from the 11 lobos that were released in Arizona in 1998. 2021 was the most successful year so far for the recovery program, resulting in the highest number of individuals, pups born, pups survived, and packs. Approximately 60% of the lobos were found in New Mexico and 40% in Arizona although historically both states have had similar amounts of wolves. In 2021, the U.S. population had nearly doubled over 5 years. These numbers represent a minimum since the survey only counts wolf sightings confirmed by Interagency Field Team staff.
Taxonomy
The Mexican wolf was first described as a distinct subspecies in 1929 by Edward Nelson and Edward Goldman on account of its small size, narrow skull and dark pelt. This wolf is recognized as a subspecies of Canis lupus in the taxonomic authority Mammal Species of the World (2005). In 2019, a literature review of previous studies was undertaken by the National Academies of Sciences, Engineering, and Medicine. The position of the National Academies is that the historic population of Mexican wolf represents a distinct evolutionary lineage of gray wolf, and that modern Mexican wolves are their direct descendants. It is a valid taxonomic subspecies classified as Canis lupus baileyi.
Lineage
Gray wolves (Canis lupus) migrated from Eurasia into North America 70,000–23,000 years ago and gave rise to at least two morphologically and genetically distinct groups. One group is represented by the extinct Beringian wolf and the other by the modern populations. One author proposes that the Mexican wolf's ancestors were likely the first gray wolves to cross the Bering Land Bridge into North America during the Late Pleistocene after the extinction of the Beringian wolf, colonizing most of the continent until pushed southwards by the newly arrived ancestors of the Great Plains wolf (C. l. nubilus).
A haplotype is a group of genes found in an organism that are inherited together from one of their parents. Mitochondrial DNA (mDNA) passes along the maternal line and can date back thousands of years. A 2005 study compared the mitochondrial DNA sequences of modern wolves with those from thirty-four specimens dated between 1856 and 1915. The historic population was found to possess twice the genetic diversity of modern wolves, which suggests that the mDNA diversity of the wolves eradicated from the western US was more than twice that of the modern population. Some haplotypes possessed by the Mexican wolf, the Great Plains wolf, and the extinct Southern Rocky Mountain wolf were found to form a unique "southern clade". All North American wolves group together with those from Eurasia, except for the southern clade which form a group exclusive to North America. The wide distribution area of the southern clade indicates that gene flow was extensive across the recognized limits of its subspecies.
In 2016, a study of mitochondrial DNA sequences of both modern and ancient wolves generated a phylogenetic tree which indicated that the two most basal North American haplotypes included the Mexican wolf and the Vancouver Island wolf.