A genomic analysis has helped to show that Australia’s invasive rabbit population probably originated from a shipment of two dozen wild English rabbits that arrived near Melbourne on Christmas Day 1859. The study1 also finds that the herd’s wild ancestry probably gave it an advantage over previous arrivals.
Rabbits have invaded most of the Australian continent and have had a disastrous impact on ecosystems, threatening some 300 species of plant and animal, and causing hundreds of millions of dollars’ worth of damage to the agriculture industry each year. “That single event triggered this enormous catastrophe, ecologically and economically, in Australia,” says Francis Jiggins, an evolutionary geneticist at the University of Cambridge, UK, and a co-author of the study.
Breeding like rabbits
Historical records suggest that the first European rabbits (Oryctolagus cuniculus) in Australia arrived in Sydney in 1788, with the first colonizers. Ships bringing rabbits continued to dock along the coast for decades, but it wasn’t until the second half of the nineteenth century that the population expanded significantly, spreading across the country at a rate of 100 kilometers a year.
Historical records also suggest that the rabbit expansion came after a shipment of animals that arrived for a certain Thomas Austin at Barwon Park, southwest of what is now Melbourne. His brother had trapped them around their family property in Baltonsborough in southwest England.
Joel Alves, an evolutionary geneticist at the University of Oxford, UK, and his colleagues wanted to find out whether genomic data corroborated the records. They analyzed genetic data from 179 wild rabbits caught across Australia and in New Zealand, France and the United Kingdom, as well as 8 domestic rabbits of different breeds.
They found that most rabbits in mainland Australia were genetically similar, with mixed wild and domestic ancestry. Australian rabbits also shared more rare alleles with rabbits from southwest England than with those from elsewhere in the United Kingdom, suggesting that they originated in Baltonsborough. Looking specifically at mitochondrial DNA, which is inherited from the mother, the researchers concluded that most mainland Australian rabbits descended from about five females, introduced from Europe.
The researchers also found that the rabbits’ genetic diversity declined the farther from Barwon Park the animals were caught, and that alleles that are rare or absent in wild rabbits increased. The researchers say these patterns are consistent with the idea that most rabbits across Australia originated from Barwon Park. The team report their findings in the Proceedings of the National Academy of Sciences on 22 Aug1.
“This is a very exciting paper on a very important and well-studied topic,” says Martin Nuñez, who researches ecological invasions at the University of Houston in Texas. Using genetics to understand how unwanted animal invasions start can help to predict future invasions, he says.
Overall, the team says that the rabbits’ wild ancestry was an important factor in triggering their invasion of the continent. “Wild rabbits are different,” says Alves. They exhibit traits such as fleeing stressful environments and burrow-digging, meaning that they were probably better at evading predators and surviving in difficult terrain than are domestic rabbits, he says. Historical records suggest that Austin requested wild rabbits, and that previous arrivals were largely domestic breeds.
The expansion of Australian pastoral lands and widespread suppression of predators around that time would have also helped their expansion. “It was like a perfect storm,” says Alves. “You have the right rabbits in the right place at the right time, with the right changes in the environment.”
“The genetic analyzes appear very sound,” says rabbit geneticist Amy Iannella, a consultant based in Adelaide, Australia. She adds that although the country’s rabbit populations probably originated in Barwon Park, their rapid expansion might have been aided by people transporting the animals to other parts of the country, where they also began spreading. Rabbits are typically communal animals that rely on shelter for survival and juveniles rarely travel farther than 1 kilometer, she says. “The idea of rabbits moving fast enough at the invasion front to colonize Australia so quickly from a single release, well that feels extreme to me, given what we know about rabbit ecology.”