A hybridisation headache hinders control of invasive Prosopis species

Biological invasions are a major threat to biodiversity, ecosystem services and human well-being. With modern-day globalisation, the number of species being translocated, intentionally or accidently, is ever increasing. Accurate taxonomic identification of invasive alien plant species is crucial to implementing timely management options.

The legume genus Prosopis, commonly known as mesquite, includes some of the world’s worst woody invasive species. Alien Prosopis species are now present in 103 countries and are considered invasive in 49 of these. Globally, the taxonomy of Prosopis species is problematic due to misidentification and extensive hybridization. Large scale biogeographic studies, including both native and non-native ranges, could provide valuable information about the genetic diversity and differentiation of invasive Prosopis, the occurrence of hybridization, and may help clarify taxonomic uncertainties.

In their new study published in AoBP, Castillo et al. used population genetic data to clarify the taxonomic placement of selected invasive Prosopis populations. They found tetraploid P. juliflora to be highly differentiated from all other diploid species of the genus. Diploid species, on the other hand, had low genetic differentiation, supporting anecdotal evidence that suggests these species often form hybrid swarms in their non-native ranges.

The authors conclude that, for regulatory purposes, all invasive diploid Prosopis taxa should be treated as a single taxonomic unit. Their findings may also have implications for the management of Prosopis invasions, particularly when we consider that most biological control agents have been tested on diploid Prosopis species in Australia and South Africa, rather than hybrid species in Eastern Africa. Hybridisation between Prosopis species may reduce the likelihood of finding effective biological control agents against any particular taxon.

Researcher highlight

María Loreto Castillo obtained a PhD in Botany from the Centre for Invasion Biology (CIB) – Stellenbosch University, South Africa. Her PhD study formed part of an international project: “Woody invasive alien species in Eastern Africa: assessing and mitigating their negative impact on ecosystem services and rural livelihoods”, under the auspices of the Centre for Agriculture and Bioscience International (CABI). María Loreto currently is a researcher of the Lab. of Geographic Ecology, University of Chile and Research Associate of the Lab of Biological Invasions (LIB), University of Concepción, Chile. She is also a IPBES fellow for the Global Assessment of Invasive Alien Species and their Control.

María Loreto is interested in the study of the direct drivers of biodiversity and ecosystem change, such as biological invasions. Her work includes eco-evolutionary dynamics across plant populations, and for different taxa, from local to global scales; studies of niche requirements and potential habitats of species, population demographic responses, patterns of variation in life history traits along environmental gradients and effect of landscape and dispersal abilities on species’ range expansions. She has extensive field experience in South America and Eastern Africa.