The tails of two invasive species: genetic responses to acute and chronic bottlenecks

Genetic diversity can affect population viability and can be reduced by both acute and chronic mechanisms. Using the history of the establishment and management of two invasive rat species on Tetiaroa atoll, French Polynesia, we investigated the intensity and longevity of contrasting population bottleneck mechanisms on genetic diversity and bottleneck signal. Using microsatellite loci we show how both a chronic reduction over approximately 50 years of a Rattus exulans population caused by the arrival of its competitor R. rattus, and an acute reduction in a R. rattus population caused by a failed eradication approximately 10 years ago, caused similar magnitudes of genetic diversity loss. Furthermore, these strong bottleneck signals were in addition to the lasting signal from initial colonisation by each species many decades to centuries earlier, characterising a genetic paradox of biological invasion. These findings have implications for the study of population genetics of invasive species, and underscore how important historical context of population dynamics is when interpreting snapshots of genetic diversity.