Microsatellite matrix of Poa annua

Comparative studies of invasive species in human-inhabited versus truly uninhabited habitats, particularly on their genetic structure, remain scarce. Sub-Antarctic islands provide an ideal system to study invasions in such contrasting environments as they represent semi-pristine conditions in highly remote areas that are accessible only through a small number of introduction routes. Here we studied the invasion genetics of annual bluegrass Poa annua on the Prince Edward Islands (PEI) that include the inhabited Marion Island and the uninhabited Prince Edward Island. We analysed variation at nuclear microsatellite loci and performed flow cytometry analyses to compare the genetic diversity and structure of this widespread invasive grass. We also used ecological niche models to estimate currently suitable habitat in these islands. We found high levels of genetic diversity and evidence for extensive admixture between genetically distinct groups of P. annua on Marion Island. In contrast, Prince Edward Island populations showed low levels of genetic diversity and no apparent admixture. Higher genetic diversity was apparent at the human entry points and around human settlements on both islands, suggesting that these areas received multiple introductions and acted as both initial introduction sites and secondary sources for invasive populations within the archipelago. Over 70 years of continuous human activity on Marion Island have led to the invasive spread of this species around human settlements and along footpaths, facilitating ongoing gene flow among geographically separated populations. In contrast, this was not the case for Prince Edward Island. The high levels of genetic variation, admixture, and habitat suitability in invasive P. annua facilitated by human actions, may increase the adaptive potential of the species, which could further enhance the species' invasiveness.