Domestic Cats Could Breed Scottish Wildcats Out of Existence

Just a few decades of intermixing affected the DNA of all sampled modern wildcats, researchers say, suggesting the species may be “genomically extinct”

A wildcat pouncing
Wildcats appear very similar to domestic cats, but they are slightly larger with longer legs. NoodlePix via Getty Images

Despite living alongside house cats for more than 2,000 years, Scottish wildcats ignored the felines as potential breeding partners for centuries. But in just the last 70 or so years, the two groups began interbreeding, suggests research from a pair of new papers in Current Biology.

Now, scientists are concerned that this hybridization—spurred by habitat loss and other human activities—will breed the wildcats out of existence. 

“Not only are we at risk of losing a species from Britain, we’re potentially replacing it with hybrid and feral domestic cats that may be not as well adapted and may not perform the same ecological role in their habitat,” co-author Jo Howard-McCombe, a research scientist at the University of Bristol in England and the Royal Zoological Society of Scotland (RZSS), tells the Guardian’s Linda Geddes. “It is important to understand the history of this process, so that we can be better informed to manage that threat into the future.”

Wildcats (Felis silvestris) were once found all across Great Britain, but years of hunting and persecution—which also wiped out other large predators, including wolves, lynx and bears—confined the felines to Scotland. These critically endangered animals are now the last native cat species in Britain.

To pinpoint exactly when the felines began to mix, Howard-McCombe and her colleagues examined genomic sequences from wildcats and domestic cats, including 48 modern cats and 258 ancient samples spanning the last 8,500 years, collected from 85 archaeological sites, per a statement from the University of Oxford. Genetic analysis suggested the two species mostly kept to themselves for two millennia: Ancient European wildcats possessed little to no ancestry from domestic cats, one of the studies reported. 

But then came a sudden spike in interbreeding in the 1950s. Researchers found that all modern wildcats examined from between 1997 and 2018 showed evidence of interbreeding, and the proportion of ancestry traced to domestic cats ranged between 11 percent and 74 percent, per the other new study.

This shift may have occurred for a variety of reasons, including a rise in domestic cat ownership and habitat destruction. When humans deforested large patches of Scottish forest, wildcats were forced into environments closer to humans, where they were more likely to come in contact with a house cat, the authors write in the Conversation

“If you have a population of wildcats that’s being completely eradicated, those that are left are going to want to mate with something,” Greger Larson, an archaeologist at the University of Oxford and co-author of both studies, tells the Guardian. “If the only thing that’s around are domestic cats, that’s probably what they’re going to choose.”

a wildcat in greenery
A wildcat that is part of the breeding for release program in Scotland. Saving Wildcats

Though they’re closely related to domestic cats (Felis catus) and appear quite similar, wildcats are larger and longer-legged, with a bushy, blunt, black-tipped tail. Like house cats, wildcats prey on a variety of small animals, such as rabbits, rodents and birds. But now, because these animals’ genes are so heavily mixed with those of house cats, the researchers write that Scottish wildcats could be considered “genomically extinct.”

“It’s very intriguing work,” Shu-Jin Luo, a geneticist at Peking University who researches the DNA of wildcats in China and did not contribute to the new research, tells Science’s David Grimm. “The studies set a very good template for studying the interactions between domestic cats and wildcats around the world.”

Interestingly, this same interbreeding that is diluting wildcat genes might have actually saved the species from going extinct sooner—through genetic mixing, wildcats gained house cats’ ability to fight diseases such as feline leukemia and feline immunodeficiency virus, per Science. Still, the only reason they would have been exposed to those diseases in the first place would have been from house cats.

Now, the future of these felines may lie in programs that release captive wildcats into the Scottish Highlands. Established in 1960, the captive population’s earliest members would have had relatively little domestic cat ancestry. Their descendants today could add some much-needed genetic diversity to the wild population.

Recently, 19 of these animals were reintroduced into a Scottish pine forest to help boost the population. “It has been really positive, in the main,” Helen Senn, a biologist with RZSS who leads the reintroduction project, told the Guardian’s Severin Carrell last month. “We have seen evidence that the cats are able to hunt and fend for themselves. From that perspective, we’re really happy.”

The next hurdle will be surviving the winter, she adds to the publication. Two more releases of captive-bred wildcats are currently planned for 2024 and 2025.

“The last hope for Scottish wildcats is the captive wildcat population,” as Howard-McCombe tells Nature News’ Ewen Callaway.

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