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The first dog-fox hybrid points to the growing risk to wild animals of domestic species

Next time you see a fox when out walking with your dog, pause for a moment and ponder their relatedness. Dogs and foxes are .

Until recently, scientists thought it was impossible for them to breed. However, the discovery of a dog-fox hybrid in Brazil suggests that "The Fox and the Hound" might sometimes be a little more "Lady and the Tramp."

The known as a "dogxim" (a cross between dog and graxaim-do-campo, the Portuguese name for pampas fox) in Brazil also raises concerns about the impact that our pet dogs might have on .

This female, dog-like creature was first noticed when she was she was hit by a car and taken to a wildlife rehabilitation facility. The staff at the wildlife center noticed she had a strange mix of .

Her pricked ears and preference for eating small mammals seemed fox-like, but her barking was more reminiscent of a dog. Throughout the centuries there have been of fox-dog hybrids, but none have been confirmed before with genetic testing.

Genetic testing revealed that she was a hybrid between a female pampas fox () and a male domestic dog . This is the first documented case of a dog-fox hybrid. Genetic analysis revealed she had a total of 76 chromosomes, compared to the 78 chromosomes of the domestic dog and 74 of the pampas fox.

What is a hybrid?

Hybridization is when . Normally, animals only mate with members of their own species.

(the structure in which DNA is packaged within the cell nucleus) often make species genetically incompatible with each other. Mating behavior and courtship rituals tend to be individual to a species, , as is reproductive anatomy and physiology.

Many well-known hybrids, such as , , are a result of human intervention. A lion and tiger would never meet naturally in the wild, as their native ranges are too far apart.

The more closely related (and thus genetically alike) two species are, the higher the chance of successful hybridisation. For example, only diverged between 11,000 and 35,000 years ago. are because their genetics, reproductive anatomy and behavior are still fairly similar.

Most hybrids are sterile, meaning they are biological dead-ends. Even if differences in chromosome don't prevent two species from producing young, it may .

How common are hybrids?

Hybrids are more widespread than you might think—they are all around us in the plant world, both natural and as a result of human intervention.

Research suggests that approximately have been affected by interbreeding in the wild.

Many domesticated species can breed with their too. In Poland, a 2018 study found high numbers of free-living wild boars had domestic genes, for example.

Hybrid offspring are not always infertile, and some people are concerned about how this affects the long-term survival and purity of individual species. Hybrids their parent species. For endangered species with small, fragile populations, this is a serious threat. In the case of the dogxim, her fertility was not verified. Sadly, , so we will probably never know.

Why are hybrids controversial?

Hybridization is important in the evolution of species, allowing populations to . Early humans are widely recognized in science to have , helping our ancestors survive in some harsh environments. Long term, hybrids can lead to the .

But there are also negative consequences. including changes to skull, dental and horn structures, .

Hybridization is also a problem for , leading to reduced fitness and therefore the survival of individuals and even whole populations. The Scottish wildcat wild population, for instance, is now wildcat-domestic cat hybrids.

What does the dog-fox hybrid tell us?

The dog-pampas fox hybrid strongly suggests that contact between wild and domestic species is increasing, possibly because of on wild habitats. This can also .

The dogxim might well be a warning of the destructive impact humans and domesticated animals are having on biodiversity. We don't know how many other hybrids may be living in the wild. Although the , this example of hybridisation between a domestic and wild species signals the importance of monitoring interactions between different species, .

It is important to note that the pampas fox species is very different to the . We probably do not need to worry about creating dog-fox hybrids on our daily dog walks, because of the genetic distance between the two. However, the dogxim should warn us that our dogs' interactions with nature can have unexpected consequences.