Heidi Hirsch¹, David M. Richardson¹, Aníbal Pauchard^2,3 and Johannes J. Le Roux⁴

¹Centre for Invasion Biology, Department of Botany and Zoology, Stellenbosch University, Private Bag X1, Matieland, 7602, South Africa
²Laboratorio de Invasiones Biológicas, Facultad de Ciencias Forestales, Universidad de Concepción, Casilla 160-C, Concepción, Chile
³Institute of Ecology and Biodiversity (IEB), Las Palmeras 3425, Santiago, Chile
⁴Department of Biological Sciences, Macquarie University, Sydney, 2109, Australia

e-mail: heidihirsch71@gmail.com

Tracing the introduction routes of invasive populations is crucial to gain insight into a species’ introduction history, its invasion success, spread, evolutionary processes during the invasion process, and to explore biological control options. Acacia dealbata Link, also known as silver wattle or mimosa, is native to southeastern Australia and Tasmania and was introduced to several regions around the globe for multiple purposes (e.g. forestry, horticulture, perfume industry). In many of those regions, the species naturalized or became invasive, making it a globally important invader. In this study, we employed a combination genetic fingerprinting and genetic modelling approaches to compare the genetic diversity and structure between populations sampled across the species’ native and non-native ranges in Chile, Madagascar, New Zealand, Portugal, Reunion Island, South Africa and the United States, and to investigate the most likely introduction scenarios. Our comprehensive dataset comprised 1615 samples from 92 populations. Our results revealed that global introductions of A. dealbata are complex and cannot be generalized. For example, New Zealand invasions likely originated from a genetic cluster of A. dealbata in Tasmania, while Madagascan populations originated from the Australian mainland. South African invasions originated from an unknown (‘ghost’) source, which was also present in Reunion Island. Invasive populations in other regions, e.g. the United States and Chile, likely originated from multiple sources. We will discuss the implications of our findings in regard to effective management approaches of A. dealbata invasions.