How domestic rabbits become feral in the wild

The study, published in Nature Ecology and Evolution, helps answer the question of how normally tame rabbits -- which have many natural predators -- can become a force of ecological destruction when purposefully or accidentally reintroduced to the wild.

Here Comes Peter Cottontail

Every gardener knows how much of a nuisance rabbits can be, but many people may not realize the magnitude of ecological destruction that rabbits are capable of.

"The classic example is Australia, which was colonized by rabbits to the point that it caused one of the largest environmental disasters in history," said Dr. Leif Andersson, a professor in the VMBS' Department of Veterinary Integrative Biosciences and a professor at Uppsala University in Sweden. "In 1859, an Englishman named Thomas Austin released 24 European rabbits onto his estate as game animals, but the population of rabbits exploded, causing an infestation that continues to cause millions of dollars' worth of crop damage each year.

"What is interesting is that rabbits had already been introduced to Australia in 1788. Why did Austin's rabbit release cause such a population explosion and not the earlier release?" he said.

Thanks to the recent study, scientists now believe that they have the answer.

"After sequencing the genomes of nearly 300 rabbits from Europe, South America, and Oceania, we found that all of them had a mix of feral and domestic DNA," Andersson said. "This was not what we had expected to find -- we expected that feral rabbits were domestic rabbits that have somehow relearned how to live in the wild. But our findings show us that these rabbits already had a portion of wild DNA helping them survive in nature."

Andersson's discovery explains why the 24 rabbits introduced to the Australian landscape in 1859 were so quick to adapt to living in the wild -- they already possessed the right genetic traits that would help them thrive.

Rewilding Domestic Rabbits

But returning a species to the wild after centuries of domestication isn't a simple process. For example, domestic rabbits have been bred by humans to be more docile and trusting than their wild counterparts. They are also often bred to have certain coat colors that humans find attractive -- like all-black or all-white coats -- that would make them easier for predators to spot in the wild.

"During the rewilding process, natural selection removes many of these domestic traits because they are maladaptive -- or unhelpful for survival -- in the wild," Andersson explained. "But it's not just coat colors that change. We also observed that many of the genetic variants removed during natural selection are related to behavior, like tameness. This brings back the wild flight instinct that is important for eluding predators."

The entire process appears to depend on whether the rabbits already have wild genes in their DNA as a sort of foundation for the rewilding process.

"We hope that this study will help lawmakers understand the importance of preventing domestic animals from being released into the wild," Andersson said. "This project has helped us understand not only how rabbits become feral but also how other species like pigs and cats can become feral nuisances."

The study is a collaboration with the Research Center in Biodiversity and Genetic Resources (CIBIO), a Portuguese research organization.