Hybridization and species boundaries between three sympatric bromeliads from the Brazilian Atlantic Forest

Recently diversified taxa commonly do not show complete reproductive isolation, and thus they represent an interesting model for studying the occurrence of hybridization and its influence on the integrity of species. In this study, we aim to elucidate the occurrence of hybridization and discuss species boundaries between three Aechmea spp. (Bromeliaceae) from southern Brazil. To achieve these aims, we used ten nuclear and six plastid microsatellite loci. We also investigated morphological and ecological differentiation and reproductive compatibility through interspecific cross-pollination experiments with these species. Molecular analyses confirmed the occurrence of hybridization between the three species, but interspecific gene flow was higher between A. comata and A. kertesziae than between A. comata and A. caudata. These Aechmea spp. showed morphological differentiation, and the results of the artificial interspecific crosses indicated that they can intercross. Aechmea caudata and A. kertesziae show distinct microhabitat preferences, whereas A. comata thrives in a microhabitat that is also inhabited by the other species. Despite the potential reproductive barriers being weak, especially those between A. comata and A. kertesziae, they may maintain the boundaries between these species and their integrity in sympatric populations.