Australian Rabbit Plague Puzzle Solved With DNA Profiling

According to a recent DNA analysis, Thomas Austin's estate Barwon Park, located close to Geelong in Victoria, is where the "rabbit pandemic" in Australia started.

When five domestic animals arrived in Sydney on the First Fleet in 1788, the first rabbits were brought to mainland Australia. Before 1859, there would be at least 90 more importations, but none of these populations would spread. However, rabbits would expand throughout the entire continent in 50 years at a rate of 100 km (62 miles) per year. The rate of colonization for an introduced mammal has never been faster than this. What then altered and how did the invasion start after 1859?

Long believed to have started at Thomas Austin's farm Barwon Park, close to Geelong in Victoria, the "rabbit plague" of Australia is believed by historians and the general public to have originated there. An international team of researchers led by the University of Cambridge and CIBIO Institute in Portugal finally offers genetic evidence for this version of events in a paper published today in the Proceedings of the National Academy of Sciences. It also puts to rest the question of whether a single introduction or a number of separate ones led to the invasion.

William, Austin's brother, sent some domestic and wild rabbits on the ship Lightning on October 6, 1859. The bunnies were collected on the family's estate in Baltonsborough, Somerset. 24 rabbits arrived in Melbourne on Christmas Day and were sent to Barwon Park. According to Austin and the local newspaper, "Austin rabbits" proliferated into the thousands in three years.

The researchers examined historical records and fresh genetic data from 187 "European rabbits," the majority of which were wild-caught in Australia, Tasmania, New Zealand, Britain, and France between 1865 and 2018, to determine where Australia's invasive rabbits originated. They sought to ascertain whether the invasion resulted from a single introduction or several, how they moved throughout the nation, and whether there was a genetic basis for their success in comparison to previous imported rabbit populations.

The European rabbit traveled from the Iberian Peninsula to Australia and New Zealand during its colonization phase. Thanks to Joel Alves

Recent investigations argued that invasive rabbits evolved from multiple distinct imports, disputing the single-origin idea. They did not, however, take samples from ancestor European and domestic populations, which was necessary to determine where Australia's rabbits came from. Dr. Joel Alves, the study's lead author and a researcher at the CIBIO Institute and the University of Oxford, said:

"We were able to pinpoint the South-West of England, where Austin's family had collected the rabbits in 1859, as the origin of Australia's invasion population.

Our research demonstrates that despite repeated introductions into Australia, a single batch of English rabbits was the catalyst for this catastrophic biological invasion, the consequences of which may still be seen today.

The researchers discovered that when the rabbits traveled farther from Barwon Park, their genetic diversity decreased and their occurrence of uncommon genetic variants that are common in quickly expanding populations increased.

Rabbits continue to be a severe danger to native flora and animals in Australia despite deliberate introduction of the myxoma virus, construction of rabbit-proof fences, and other interventions. They are predicted to cost the agricultural industry $200 million annually.

Previous research has revealed that a number of variables, such as the population size, the number of introductions, and environmental changes, have a role in biological invasions. According to the results of the recent study, those animals' genetic makeup may have just as much, if not more, influence.

The researchers note that numerous local rabbit populations would have likely increased if an environmental change, such as the creation of significant pastoral regions by human settlers, had been the cause of the invasion. The genetic results of the investigation and the failure of pre-1859 rabbits to establish themselves as invasive species cast doubt on this hypothesis.

Instead, the scientists looked into the idea that a specific genetic trait's appearance served as the invasion's catalyst, which would help to explain the genetic data's overwhelming support for a single introduction.

Before 1859, rabbits were brought to Australia, and they were frequently noted for their friendliness, elaborate coat patterns, and floppy ears. These are characteristics of domestic breeds, yet they are typically lacking in wild animals. The DNA results of the new study demonstrate that at least some of Austin's rabbits were truly wild, despite the fact that they were once described as wild-caught.

Feral domestic rabbits may exhibit a variety of characteristics that render them ill suited to surviving in the wild, but it's also probable that they lacked the genetic diversity needed to adapt to Australia's arid and semi-arid climate.

"Australian rabbits have evolved new body shapes to help them regulate their body temperature in order to cope with this. Therefore, it's possible that Thomas Austin's wild rabbits—as well as their progeny—had a genetic advantage when it came to adapting to these circumstances.

Joan Palmer recounted in the 20th century that her grandfather William Austin had had to find Thomas the animals since "wild rabbits were by no means numerous around Baltonsborough. Six were obtained only after tremendous effort; these were half-grown individuals that had been captured from their nests and domesticated. He purchased seven grey rabbits that the locals had maintained in hutches, either as pets or for food, to round up the number.

Joan Palmer asserts that the wild and domestic rabbits in the shipment bred before or during their 80-day journey, which would account for why more rabbits arrived than were sent. Alves and Jiggins discovered that the invasive rabbits descended from Austin's imports contained a significant element of domestic ancestry, which they contend supports Palmer's claim.

These findings are important, according to Dr. Alves, because biological invasions pose a serious threat to the world's biodiversity and are difficult to stop without an understanding of their mechanisms.

Despite the fact that environmental change may have left Australia more open to invasion, one of the most famous biological invasions in history was actually sparked by a tiny group of wild rabbits.

This serves as a warning that even a single person's or a small group of people's activities can have a catastrophic effect on the ecosystem.

Reference: Joel M. Alves, Miguel Carneiro, Jonathan P. Day, John J. Welch, Janine A. Duckworth, Tarnya E. Cox, Mike Letnic, Tanja Strive, Nuno Ferrand, and Francis M. Jiggins, "A Single Introduction of Wild Rabbits Triggered the Biological Invasion of Australia," Proceedings of the National Academy of Sciences, 22 August 2022.

By UNIVERSITY OF CAMBRIDGE