Intraspecific genetic and ecological differentiation in Australian Acacia species: insights from Acacia longifolia

Accurate taxonomic classifcation is the foundation of all biological organization and is crucial for biodiversity conservation and environmental management, including the control of invasive species. For example, different taxa may respond differently to management, such as biological control. Species distribution models (SDMs) are often used to predict the ecological niches of species and their potential geographic distributions, and are important tools in environmental management. SDMs rely on accurate taxonomy for high predictive power. However, these models assume that individual species are uniform entities, an assumption that is rarely met. For example, many invasive Acacia species ('wattles') show high intraspecifc variation that is sometimes formally recognized by their designation as different subspecies or varieties. This chapter provides an overview of genetic studies on invasive wattles that have investigated such taxonomic variation in the context of ecological/climate differentiation. We then provide new insights for A. longifolia, a species with two subspecies (subsp. longifolia and subsp. sophorae) that are known to hybridize where they co-occur, making accurate taxonomic identifcation diffcult. We tested the hypothesis that these two subspecies represent unique genetic lineages that occupy distinct bioclimatic niches in Australia. We found no support for our hypothesis, i.e. population genetic analyses and the SDMs failed to differentiate the two subspecies of A. longifolia. Thus, morphological characters currently used to differentiate these two subspecies may refect phenotypic plasticity rather than local genetically based adaptations. We conclude that the taxonomic classifcation of subspecies of A. longifolia requires revision, and that current taxonomic classifcation might be misleading for management efforts of invasive populations.