In 2021, a dog-like animal was brought to an animal rehabilitation center in southern Brazil, after it was hit by a car. Soon after, veterinarians noticed unusual behavior.
The animal looked and barked like a dog—albeit one with long, pointed, foxlike ears—but it also climbed bushes, a behavior more typical of the local Pampas fox, and it refused common dog food, preferring to eat rats.
Caretakers began to wonder if it might be a hybrid—a mixture of domestic dog and some local wild canid, so they contacted geneticist Thales Renato Ochotorena de Freitas and Rafael Kretschmer from the Universidade Federal do Rio Grande do Sul who, last month, published a study confirming the animal was the world’s first documented fox-dog. The finding excited and intrigued experts in animal genetics.
“What a strange hybrid beast!” wrote Roland Kays, a biologist with North Carolina State University and the North Carolina Museum of Natural Sciences, on X (formerly Twitter), alongside a photo of the creature and link to the study.
He added that while cross-species hybridization is well known among more closely related animals like dogs and wolves, the domestic dog (canis lupis familiaris) and the Pampas fox (Lycalopex gymnocerus) belong to “two genera separated by 6.7 million years.”
“This is what one might expect to see in trees, but not vertebrates,” said Loren Reiseberg, a geneticist at the University of British Columbia. “It is like humans producing a viable hybrid with chimpanzees!”
The creature, a female, was named “Dogxim,” a cross between “dog” and “graxaim do campo,” the Portuguese name for Pampas fox. And while the first, it may not be the last of its kind. Environmental changes could possibly make more dog-fox hybrids in the future—a prospect that could have problematic consequences.
Discovering a hybrid
The first step in confirming the possibility that Dogxim was a hybrid was to determine the number of chromosomes in Dogxim’s cells. She had 76 in total, a clue scientists could use to determine her species because a single species will generally have a fixed number of chromosomes. The maned wolf (Chrysocyon brachyurus) is the only canid in the region with 76 chromosomes, but its appearance and behaviors ruled it out as a possible parent.
Scientists then reasoned that since a domestic dog has 39 chromosomes, and a Pampas fox has 37, the resulting 76 chromosomes found in Dogxim could indicate “the first evidence of the hybridization,” Kretschmer says.
Next, geneticists examined Dogxim’s mitochondrial DNA—the chromosomes inherited exclusively from its mother—and determined they came from a Pampas fox. They then looked at the nuclear DNA, which contains chromosomal information from both parents, and found a mixture of dog and Pampas fox. This genetic testing was completed over six months, during which time Dogxim healed from her vehicle strike injuries and was transferred to an animal preserve.
While foxes belong to the same biological family as wolves and dogs—Canidae—they don’t belong to the same smaller group, the genus Canis. Instead, over six million years ago, foxes diverged, eventually becoming distinct enough to now be considered the genus Vulpes—or, in the case of the Pampas fox native to South America, the genus Lycalopex.
“Generally, in mammals, species breed with their own kind,” explains Kays. “Sometimes, if they haven’t been separated by that long of an evolutionary time period, you can get different species breeding. We see this happen with coyotes and wolves, occasionally, but this tends to occur when one of the animals is very common in a region, and the other is very rare.”
Pampas foxes aren’t rare, but widespread throughout their range in South America. So how did this first-of-its kind hybridization occur, and what implications if any does it hold for possible fox-dogs of the future?
How a fox met a dog
Environmental disruptions likely contributed to Dogxim’s creation, says Kretschmer. The grassy plains of southern Brazil where Fampas foxes live are experiencing widespread habitat loss and development. Much of it is being converted to grazing pastures for cattle ranches and to human residences. While the populations of Pampas foxes have remained stable, their habitat is increasingly overlapping with the stomping grounds of domestic dogs, giving both more opportunities to mate.
Another factor, says Kretschmer’s study co-author Bruna Szunwelski, could be abandoned dogs.
“The practice of abandoning dogs is a crime in Brazil, but still happens frequently,” she says. “Pets and hunting dogs are often abandoned in natural areas by their owners, contributing to greater occurrence of dogs in natural habitats, including protected areas.
While an inter-species hybrid is typically an anomaly, unlikely to reproduce and launch a new population, it’s getting more difficult to predict how species might evolve as they’re forced to adapt more rapidly to the effects of climate change and other environmental disturbances.
“Data suggest hybridization has been much more common during the evolution of plants and animals than previously suspected, including between deeply divergent lineages,” Reiseberg notes.
Kay, however, thinks we’re unlikely to see more dog-foxes, in part because we only have one example in all the years that dogs and foxes have lived in proximity, and because it’s genetically risky.
“You’re more likely to have genes that are just not going to work together,” in a completely new creature like Dogxim, he says, rather than in a species that evolved over millions of years, through gradual mutations that proved advantageous to its survival.
Creatures created through hybridization often have health problems or other features that make them less likely to survive. Dogxim’s black fur, for example, contrasts with the typically paler shades of a Pampas fox’s coat, which are better camouflaged in the grasslands of its habitat.
Though reportedly healthy when transferred to state-run animal facility Mantenedouro São Braz in November of 2021, Dogxim died in March of 2023. Her cause of death still unknown. Kretchmer and others only learned of her demise this August when they called to request photos in advance of their study’s publication.
Per a statement from SEMA, Brazil’s Secretariat for the Environment and Infrastructure, the animal’s death is under investigation by the state.
Dogxim’s legacy
Whether or not Dogxim’s existence was a fluke occurrence, her discovery poses important questions.
“Hybridization between species with different evolutionary trajectories can be a powerful threat to wildlife conservation,” Kretcschmer and fellow authors explain in their study.
While Pampas foxes aren’t currently threatened in their native range, that could change. And hybrids like Dogxim could affect the native fox population, potentially introducing new diseases and genetic weaknesses, hindering their prospects for survival.
The complexities and mysteries surrounding Dogxim’s discovery merit further exploration, Kretschmer and colleagues note in their paper: studying the “consequences of hybridization on genetics, ecology, and behavior of wild populations will be essential to improve the conservation of this species.”
