Rabbits were first introduced to Australia in the 18th century. None of the 90 subsequent importations became invaders. Within 50 years, rabbits would spread across the entire continent, making this the fastest colonization rate for an introduced mammal. What happened after 1859 and how did the invaders start?
The country's "rabbit plague" is thought to have started at Barwon Park, the estate of Thomas Austin. In a study published today in PNAS, an international team led by the University of Cambridge and CIBIO Institute in Portugal provides genetic proof for this version of events and settles a debate about whether the invasion came from a single or several independent introductions.
Austin's brother, William, sent a group of wild rabbits and some domestic rabbits on a ship. The rabbits were dispatched to Barwon Park. According to a local newspaper report, the "Austin rabbits" had grown into thousands within three years.
The researchers studied historical records alongside new genetic data collected from 187 European rabbits to find out where Australia's rabbits came from.
The single origin hypothesis was disputed by recent studies. They didn't sample ancestral European and domestic populations, which is important to find the source of Australia's rabbits. The lead author of the book is a researcher at the University of Oxford.
Austin's family collected rabbits from the South-West of England in the 19th century.
Despite the numerous introductions across Australia, it was a single bunch of English rabbits that triggered this devastating biological invasion.
The researchers found that as the rabbits moved further away from Barwon Park, genetic diversity declined and rare genetic variant became more frequent.
rabbits are one of the major invaders in Australia threatening native flora and fauna and costing the agricultural sector an estimated $200 million per year.
Several factors contribute to biological invasions, including the number of individuals, the number of introductions, and the environment. According to the new findings, the genetics of those animals can be influential.
If environmental change, such as the development of large pastoral areas by humans, triggered the invasion, multiple local rabbit populations would likely have expanded. This possibility was undermined by the study's findings and the failure of pre-1859 rabbits to become invaders.
The team explored the possibility that the invasion was caused by specific genetic traits, something which would explain the overwhelming genetic evidence for a single introduction.
The rabbits introduced to Australia before 1859 were often described as showing tameness, fancy coat colors and floppy ears, but not found in wild animals. The new study shows that at least some of the rabbits in Austin were actually wild.
It is possible that rabbits lacking the genetic variation required to adapt to Australia's arid and semi-arid climate are not adapted to survive in the wild.
Australia's rabbits have evolved to control their temperature. It is possible that Thomas Austin's wild rabbits and their offspring had a genetic advantage.
In the 20th century, Joan Palmer said that her grandfather William Austin was unable to find animals for Thomas as wild rabbits were not common around Baltonsborough. He only got six because they were half grown and were taken from their nest. He bought seven gray rabbits for the villagers to keep as pets or to eat.
Joan Palmer's claim that more rabbits arrived than were sent is supported by the fact that the rabbits descended from Austin's imports contained a substantial element of domestic ancestry.
If you want to prevent biological invasions from taking place you need to understand what makes them succeed.
The genetic makeup of a small group of rabbits sparked one of the most famous biological invasions of all time.
The actions of just one person, or a few people, can have a negative impact on the environment.
More information: A single introduction of wild rabbits triggered the biological invasion of Australia, Proceedings of the National Academy of Sciences (2022). doi.org/10.1073/pnas.2122734119 Journal information: Proceedings of the National Academy of Sciences
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