Population genomics reveal multiple introductions and admixture of Sonchus oleraceus in Australia

Aim: The goal of this study was to investigate the invasion history of the weed Sonchus oleraceus in Australia by comparing the population genetic structure of individuals at different locations in Australia, and in the most likely areas of origin in the native range. Location: Samples were collected in Europe and Morocco, North Africa (27 locations), and Australia (17 locations). Methods: We performed population genetic analyses using a large dataset comprising 2883 single nucleotide polymorphism markers from 547 plant samples and investigated the invasion history of S. oleraceus with Approximate Bayesian Computation and Random Forest classification algorithms. We compared single and multiple invasion scenarios considering admixture having occurred before and after introduction. Results: Our results revealed high levels of inbreeding within sampling locations in the two ranges. Analyses also showed that S. oleraceus was possibly introduced to Australia at least twice: a first introduction around 1000years ago before British settlement and a more recent introduction (similar to 65 years ago) from Europe and North Africa. We also found evidence of post-introduction admixture and a potential reintroduction of S. oleraceus from Australia back to its native range. Main conclusions: We conclude that the invasion history of S. oleraceus into Australia is probably historic (i.e. prior to British settlements) and complex showing recent evidence of post-introduction admixture. The complex invasion history of S. oleraceus in Australia poses challenges for the search of potential biological control agents.