Pollinator specificity and convergence in fly-pollinated Pleurothallis (Orchidaceae) species: A multiple population approach

Abstract

We studied the floral biology of 12 populations of five rupicolous Pleurothallis (Orchidaceae) species occurring in campo rupestre vegetation at nine localities in Brazil. All of these species are pollinated by flies belonging to the families Chloropidae and Phoridae. In the five Pleurothallis species studied, all conspecific populations attracted the same pollinator species. All pollinators were females; they laid eggs in flowers of the two nectarless species, but never in the flowers of nectar-presenting species. The two pairs of Pleurothallis species with similar flower morphologies and odours attracted the same pollinators: P. johannensis-P. fabiobarrosii, pollinated by Tricimba sp. (Chloropidae) and P. teres-P. ochreata pollinated by Megaselia spp. (Phoridae). There was no overlap in the distribution of the Pleurothallis species that shared pollinators. Despite similarities in floral morphology and odour, genetic data show that these species pairs are not each other's closest relatives. We hypothesize that these similarities are due to convergence in allopatric species that evolved similar pollination mechanisms. Conversely, there are reasons to believe that adaptation to different pollination mechanisms occurred in the closely related species P. johannensis and P. teres. © 2001 Annals of Botany Company.