Despite being a keystone species in the native range ( 12), rabbits are considered pests in most introduced locations, responsible for damage to agriculture, habitat degradation, and endangerment of native species ( 13). During the Middle Ages, rabbits were extensively translocated by humans and today rabbits are one of the most widespread mammals, with a presence across multiple continents and in hundreds of islands spread around the globe ( 10, 11). For most of its existence, the European rabbit ( Oryctolagus cuniculus) was restricted to the Iberian Peninsula and the South of France ( 8, 9). To understand the role of genetic factors in biological invasions, we combined genetic data and historical records to investigate one of the most iconic and thoroughly recorded biological invasions in history, the rabbit colonization of Australia. Alternatively, high propagule pressure can also increase the probability that an invasive adaptive genotype will be introduced ( 4, 7). One mechanism by which this can occur is introducing greater genetic variation, which may reduce inbreeding depression or provide the genetic variation that natural selection can act on to adapt the population to the new environment ( 3, 4). However, it has also been argued that high propagule pressure may allow established but localized populations to become invasive by altering the genetic makeup of the introduced population ( 4). More recently, it has become apparent that propagule pressure-the number of introductions and the number of individuals introduced-plays a key role by helping overcome stochastic processes that can lead to population extinction ( 3, 4). The genetics of invasive populations has also been shown to play an important role in the outcome of these processes ( 6). Due to this devastating and often irreversible impact, the reason why some introductions lead to biological invasions, but others do not, has attracted considerable attention ( 3, 4).Įcological factors are critical for biological invasions, with the properties of certain species making them successful invaders and the properties of some environments making them vulnerable to invasion ( 5). In an increasingly cosmopolitan world where human activity and climate change are moving species beyond their native range at ever-increasing rates, the risk of biological invasions has never been higher. These events, known as biological invasions, are a major cause of environmental ( 1) and economic disruption, with an estimated global cost of US$1.288 trillion over the last 50 y ( 2). However, occasionally exotic species proliferate and outcompete well-adapted native species. When organisms spread beyond their native range, they often either establish localized populations or do not survive. These findings demonstrate how the genetic composition of invasive individuals can determine the success of an introduction and provide a mechanism by which multiple introductions can be required for a biological invasion. We argue that the common denominator of these invasions was the arrival of a new genotype that was better adapted to the natural environment. In New Zealand and Tasmania, rabbits also became a pest several decades after being introduced. Combining genomic and historical data we show that, contrary to the earlier introductions, which consisted mostly of domestic animals, the invasive rabbits had wild ancestry. We also find evidence of additional introductions that established local populations but have not spread geographically. We found genetic support for historical accounts that these were English rabbits imported in 1859 by a settler named Thomas Austin and traced the origin of the invasive population back to his birthplace in England. Here, we show that despite numerous introductions over a 70-y period, this invasion was triggered by a single release of a few animals that spread thousands of kilometers across the continent. The colonization of Australia by the European rabbit is one of the most iconic and devastating biological invasions in recorded history. While ecological factors are key determinants of their success, the role of genetics has been more challenging to demonstrate. Biological invasions are a major cause of environmental and economic disruption.
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