Morphological and molecular characterization of a hybrid zone between Prosopis alba and P. nigra in the Chaco region of northwestern Argentina

Abstract

The Gran Chaco is the largest dry forest in South America. Oneof the key taxa of this biome is the genus Prosopis (Fabaceae)which contains several economically important species. One ofthe characteristics of this genus is its natural capacity toexchange genetic information among congeneric species,generating zones of high morphological and genetic variabilityat contact points. The study and management of these contactareas can contribute to the dynamic conservation of thesenative genetic resources. In this study, we analysed three siteswithin a gradient of land aridity, where P. nigra and P. alba growin sympatry and apparently hybridize. This is the first studyperformed in both, Prosopis pure sites and hybrid swarm,which includes a spatially explicit approach and simultaneouslyanalyses fruit and leaf morphological variation, togetherwith molecular information (microsatellites markers). We performeda multivariate morphological analysis, Bayesian geneticclustering and multivariate associations between geneticand morphological variability in the pure parental populationsand in the hybrid swarm, considering possible spatial autocorrelation.Bayesian cluster analysis revealed two distinct groupscorresponding to each species, differentiating the pure morphotypesfrom sites 1 and 2. Site 3, corresponding to the hybridswarm, was composed of pure P. alba and P. nigra trees andhybrid individuals. We found morphological and molecular evidenceof hybridization between P. alba and P. nigra, and detectednovel phenotypes in the hybrid site.