Genetic insights into the globally invasive and taxonomically problematic tree genus Prosopis

<p class="MsoCommentText"><span><span><span><span><span><span><span><span><span><span><span>Accurate taxonomic identification of alien species is crucial to detect new incursions, prevent or reduce the arrival of new invaders and implement management options such as biological control. Globally, the taxonomy of non-native <i>Prosopis </i>species<i> </i>is problematic due to misidentification and extensive hybridization. We performed a genetic analysis on several <i>Prosopis</i> species, and their putative hybrids, including both native and non-native populations, with a special focus on <i>Prosopis</i> invasions in Eastern Africa (Ethiopia, Kenya and Tanzania). We aimed to clarify the taxonomic placement of non-native populations and to infer the introduction histories of <i>Prosopis</i> in Eastern Africa. DNA sequencing data from nuclear and<b> </b>chloroplast markers showed high homology (almost 100%) between most species analysed. Analyses based on seven nuclear microsatellites confirmed weak population genetic structure among <i>Prosopis </i>species. Hybrids and polyploid individuals were recorded in both native and non-native populations. Invasive genotypes of <i>P. juliflora</i> in Kenya and Ethiopia could have a similar native Mexican origin, while Tanzanian genotypes likely are from a different source. Native Peruvian <i>Prosopis pallida</i> genotypes showed high similarity with non-invasive genotypes from Kenya. Levels of introduced genetic diversity, relative to native populations, suggest that multiple introductions of <i>P. juliflora</i> and <i>P. pallida</i> occurred to Eastern Africa. Polyploidy may explain the successful invasion of <i>P. juliflora </i>in Eastern Africa. The polyploid <i>Prosopis juliflora</i> was highly differentiated from the rest of the (diploid) species within the genus. The lack of genetic differentiation between most diploid species in their native ranges supports the notion that hybridization between allopatric species may occur frequently when they are co-introduced into non-native areas. For regulatory purposes, we propose to treat diploid <i>Prosopis</i> taxa from the Americas as a single taxonomic unit in non-native ranges.</span></span></span></span></span></span></span></span></span></span></span></p>