Phylogenomics resolves the invasion history of Acacia auriculiformis in Florida

Aim: Understanding the genetic structure of plants in their native range is crucial when reconstructing the invasion history of weeds. This information allows researchers to pin-point the provenance of invasive plants, and to test the importance of genetic admixture in facilitating invasion success. We assessed genetic structuring across the native range of A. auriculiformis, to determine whether genetic admixture contributes to the success of this weed in its introduced range, and test for rapid adaptation to environmental conditions in the invasive lineage. Location: Australia, Papua New Guinea, Florida Taxon: Acacia auriculiformis Methods: We sampled A. auriculiformis from across its entire native distribution (northern Australia, Papua New Guinea) and its invasive range in Florida, and used Genotyping-by-sequencing (GBS) to assess population structuring. Results: Principal component analysis, based on 9,591 SNPs, indicated significant differentiation among samples from Papua New Guinea, the Northern Territory (Australia), and north Queensland (Australia). Florida samples also formed a distinct cluster, with these samples most closely related to samples from the Northern Territory. These results indicate that the Florida A. auriculiformis lineage most likely originates from the Northern Territory, with no evidence that plants were introduced from different parts of the native range. We found evidence of allelic shifts in the Florida population, suggesting rapid adaptation to environmental conditions may contribute the success of the invasive lineage. Main conclusions: Two well-known biogeographic barriers – the Carpentaria Gap and Torres Strait – have caused genome-wide divergence among A. auriculiformis plants from north Queensland, Northern Territory, and Papua New Guinea. The taxonomic status of these allopatric populations should be further assessed. As the Florida lineage originated in the Northern Territory the search for potential biological control agents should be focused in this region. Our results also demonstrate how artificial selection and strong genetic drift may cause introduced plants to have a unique genetic make-up not found in the native range