Historical range contraction, and not taxonomy, explains the contemporary genetic structure of the Australian tree Acacia dealbata Link
Irrespective of its causes, strong population genetic structure indicates a lack of gene flow. Understanding the processes that underlie such structure, and the spatial patterns it causes, is valuable for conservation efforts such as restoration. On the other hand, when a species is invasive outside its native range, such information can aid management in the non-native range. Here we explored the genetic characteristics of the Australian tree Acacia dealbata in its native range. Two subspecies of A. dealbata have previously been described based on morphology and environmental requirements, but recent phylogeographic data raised questions regarding the validity of this taxonomic subdivision. The species has been widely planted within and outside its native Australian range and is also a highly successful invasive species in many parts of the world. We employed microsatellite markers to investigate the population genetic diversity and structure among 42 A. dealbata populations from across the species’ native range. We also tested whether environmental variables purportedly relevant for the putative separation of subspecies are linked with population genetic differentiation. We found no relationship between population genetic structure of A. dealbata in Australia and these environmental features. Rather, we identified two geographically distinct genetic clusters that corresponded with populations in the northeastern part of mainland Australia, and the southern mainland and Tasmanian range of the species. Our results do not support the taxonomic subdivision of the species into two distinct subspecies based on environmental features. We therefore assume that the observed morphological differences between the putative subspecies are plastic phenotypic responses. This study provides population genetic information that will be useful for the conservation of the species within Australia as well as to better understand the invasion dynamics of A. dealbata.
KeywordsBiological invasions Fabaceae Genetic diversity and structure Microsatellites Tree invasions
We thank M.J. Mathese and P.H. Du Preez for their assistance in the laboratory, L. Gallien for advice on statistical approaches, and C. Gairifo, J. Ndlovu, and J.R.U. Wilson for assistance with collecting and/or providing samples used in this study.
Funding for this study was provided by the DST-NRF Centre of Excellence for Invasion Biology and the Working for Water Programme through the collaborative research project “Integrated Management of invasive alien species in South Africa,” a Subcommittee B grant from Stellenbosch University (to JLR), and the Drakenstein Trust. Additional support was provided by the DST-NRF Centre of Excellence for Invasion Biology, Stellenbosch University, and the National Research Foundation of South Africa (grant 85417 to DMR).
Compliance with ethical standards
Conflict of interest
The authors declare that they have no conflict of interest.
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