The Australia-wide rabbit invasion from a single introduction of just 24 animals in 1859, new research has confirmed.
Using historical and genetic data, scientists have pinpointed the origins of what they call “the fastest colonization rate for an introduced mammal ever recorded”.
New research, published in the Proceedings of the National Academy of Scienceshas confirmed what historians have long suspected: that the country’s bunny infestation originated from Barwon Park, the estate of Thomas Austin, near Geelong in Victoria.
The European Rabbit, Oryctolagus cuniculuswas originally introduced to mainland Australia on the first fleet in 1788, when five domestic rabbits were brought to Sydney.
But despite at least 90 subsequent importations, populations only exploded in the latter half of the 19th century – rabbits then spread across the entire Australian continent within 50 years, at a rate of 100km a year.
In 1859, Austin received a consignment of 24 wild and domestic rabbits from his brother in Baltonsborough, in south-west England. Within three years, the animals had multiplied into the thousands.
Scientists now say the continent-wide rabbit invasion from this single importation, rather than previous multiple introductions.
In addition to historical records, they analyzed genetic material from 187 European rabbits caught across mainland Australia, Tasmania, New Zealand, Great Britain and France between 1865 and 2018.
The research team, led by the University of Cambridge and the CIBIO Institute in Portugal, found that mainland Australian rabbits were most genetically similar to populations found in the south-west of England, near Baltonsborough.
The prevalence of rare gene variants in Australian rabbits also increased with distance from Barwon Park, a process known to occur in geographically expanding populations.
The researchers traced DNA found in the mitochondria of cells – which is inherited from the mother – and estimated that “the mainland Australian rabbits in our dataset trace their maternal ancestry back to five females that were introduced from Europe”.
The analysis also found evidence of other rabbit introductions that led to surviving populations, but without wide geographical spread. Two groups of rabbits – one in Sydney, and one in Cattai national park, to the city’s north-west – had distinct ancestry, the study showed.
The researchers hypothesise the Barwon Park rabbits were likely more successful in spreading because of their wild ancestry. Many previous introductions had involved rabbits with domestic origins, with reports of “tameness, fancy coat colors and floppy ears” as traits.
Study co-author Prof Mike Letnic, of the University of New South Wales, said the wild rabbits introduced to Barwon Park may have had genetic traits that made them more likely to survive in the Australian wilderness.
“If animals are bred for domestication, one of the things they lack is predators,” he said. “Anti-predator behavior is both learned and also evolved … the genes that you carry that might make you nervous or jumpy end up being junk and they get lost in domestication.”
The Barwon Park rabbits had “invaded many different environments across the country”, Letnic said. “There’s rabbits that live in relatively cool and comparatively moist areas of Australia, and then there’s rabbits that live in the middle of the desert.”
The damage wreaked by rabbits to agricultural crops is an estimated $200m yearly.
An unappreciated impact of the pests is that they have amplified predation pressures across the continent, Letnic said. “The numbers of foxes and cats and dingoes tend to be much higher in areas where there’s lots of rabbits, and that means that it makes it harder for other animals to live because there’s more predators.”
“It highlights that whatever we do, we need to avoid … bringing [wild animals] into this country and having them escape.”
In Tasmania and New Zealand, rabbits also became a pest decades after their introduction. The researchers found that Tasmanian rabbits had mixed domestic British and mainland Australian ancestry, while New Zealand rabbits had a mix of wild and domestic British, and mainland Australian ancestry.