The Story Of Dogxim, The Fox-Dog Hybrid That Shouldn’t Have Existed

“What a strange hybrid beast!” tweeted Roland Kays, director of the Biodiversity Laboratory at the North Carolina Museum of Natural Sciences and a research associate professor at North Carolina State University, two years later. A case study of the animal had just been published, finally pinning down what species it was – and the answer was more confusing than anybody could have guessed.

“Cross-species hybridization is well known among the Canis (dogs/wolves/coyotes/jackals),” Kays wrote, “but I’ve never heard of CROSS-GENUS hybridization.”

Yet, that’s what this mysterious creature seemed to be. It was, the study had concluded, “a Dog [cross] Pampas fox hybrid from the wild,” Kays wrote – a mix of “two genera separated by 6.7 million [years].”

Her name was Dogxim – and her story was one nobody could have predicted.

Who was Dogxim?

Half dog, half graxaim-do-campo – the local term for a pampas fox – the name “Dogxim” was a hybrid made to perfectly match her genome. She was a funny-looking thing: rather like a fox, with pointed ears and a bushy tail, but with the dark coloring and unmistakable eyes of a domestic dog.

Her behavior was similarly muddled. She barked like a dog – but refused dog food, preferring to hunt rats. She climbed bushes like a pampas fox, but didn’t act aggressively like a wild canid would. “In some moments, she allowed herself to be touched and even caressed,” Flávia Ferrari, a conservationist who cared for Dogxim during her recovery, told The Telegraph in 2023. “[She] sometimes even play[ed] with toys.”

She was, in total, an enigma.

Luckily, this is the 21st century – and when the big picture doesn’t make sense, we have the ability to go deeper.

“The initial phase of our study involved determining the number of chromosomes and morphologies of [Dogxim],” wrote the Brazilian team charged with identifying the species of the mysterious canid. “We identified 76 autosomal chromosomes, all acrocentric, and the X chromosomes displaying submetacentric and metacentric morphologies.”

It was a sensible first step. Species usually have a fixed number of chromosomes, so counting them in Dogxim might yield a clue as to her heritage. But alas, no dice: the only other canid in Brazil with 76 chromosomes is the maned wolf, and “this species significantly differs in physical appearance” from Dogxim.

Perhaps a more lateral solution was needed. Rather than one creature with 76 chromosomes, perhaps the team could find two species whose chromosomes averaged 76?

In fact, they could: “dogs possess 2n = 78 [chromosomes],” the paper points out, “while pampas foxes have 2n = 74.”

More than that, Dogxim’s chromosomes looked like a mix of those two species. The mitochondrial DNA – the DNA only inherited from the mother of an individual – resembled that of a pampas fox; the nuclear DNA, which comes from both parents, seemed similar to a dog. Parts of the genome common to both dogs and pampas foxes were copied identically in Dogxim; in other places, each half of a chromosomal pair differed in ways specific to their original species.

Altogether, it was “the first evidence of the hybridization,” Rafael Kretschmer, a geneticist at the Universidade Federal de Pelotas in Brazil and one of the team behind the investigation, told National Geographic. But how on Earth did it happen?

How could it happen?

There’s a reason we don’t often see hybrid animals in the wild. “Generally, in mammals, species breed with their own kind,” Kays told National Geographic.

It makes sense – after all, you probably (hopefully) don’t find chimpanzees all that enticing as potential coparents. But there are some circumstances under which it can happen anyway: “Sometimes, if they haven’t been separated by that long of an evolutionary time period, you can get different species breeding,” Kays explained. “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.”

Dogxim, in contrast, was a mix of two very common species. So how did a dog meet and mate with a pampas fox?

The answer might be found in where Dogxim lived. “The geographic region where the hybrid was found belongs to the Atlantic Forest biome, the most anthropic biome in Brazil,” points out the paper. “The anthropization of the pampas fox habitat has caused this species to be tolerant of human disturbance, increasing overlapping ranges of this species with the domestic dog and may have facilitated the interspecific hybridization between these two taxa.”

In other words: we did it. Humans moved in, spread out, brought pets with them – and, depressingly often, abandoned those pets – and the local wild fauna had no choice but to adapt. For the pampas fox, that meant losing its fear of the incoming species – and, evidently in at least one case, becoming extremely comfortable with them.

“The practice of abandoning dogs is a crime in Brazil, but still happens frequently,” study co-author Bruna Szunwelski told National Geographic. “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.”

But that raises an interesting prospect. Let’s face it: despite the idea’s merits, humans aren’t likely to suddenly stop industrializing once-lush areas of natural biodiversity. So, are we going to see more weird hybrids like Dogxim turning up in the future?

The birth of a new species?

Dogxim passed away of unknown causes in 2023 – and, for all we know, that was the end of her “species”. But how certain can we be that we won’t see another like her in the future?

The answer seems to be: it’s unlikely, but not impossible. Usually, it’s very difficult for two species from different genera to reproduce together – when parents are too far apart on the evolutionary tree, “you’re more likely to have genes that are just not going to work together,” Kays told National Geographic. 

Even if mating is successful, the wildly different genetics at play make for an offspring that may be unhealthy, or simply ill-suited for either parent’s habitat or lifestyle. We can see that in Dogxim herself: her mother, the pampas fox, likely had a sandy-grey coat that allowed her to blend in with the surroundings, while Dogxim had the unmissably bold, black coat of a domestic dog. That would make hiding from prey and predators alike much more difficult – not very useful, as mutations go.

That said, we live in a rapidly changing world, and in the race to adapt to hotter temperatures and wildly different ecosystems, who knows what may happen? 

“This discovery implies that, although these species diverged about 6.7 million years ago and belong to different genera, they might still produce viable hybrids,” the researchers wrote. 

“Further studies are necessary to examine the frequency of hybridization,” they concluded, “and the potential for genetic introgression of dog genes into Pampas fox populations.”