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

We studied the floral biology of 12 populations of five rupicolous Pleuroth allis (Orchidaceae) species occurring in campo rupestre vegetation at nine localities in Brazil. All of these species are pollinated by flies belongin g to the families Chloropidae and Phoridae. In the five Pleurothallis speci es studied, all conspecific populations attracted the same pollinator speci es. All pollinators were females; they laid eggs in flowers of the two nect arless species, but never in the flowers of nectar-presenting species. The two pairs of Pleurothallis species with similar flower morphologies and odo urs attracted the same pollinators: P. johannensis-P. fabiobarrosii, pollin ated by Tricimba sp. (Chloropidae) and P. teres-P. ochreata pollinated by M egaselia spp. (Phoridae). There was no overlap in the distribution of the P leurothallis species that shared pollinators. Despite similarities in flora l morphology and odour, generic 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 m echanisms. Conversely, there are reasons to believe that adaptation to diff erent pollination mechanisms occurred in the closely related species P. joh annensis and P. teres. (C) 2001 Annals of Botany Company.