The Natural History of Cirrhaea and the Pollination System of Stanhopeinae (Orchidaceae)

Abstract

Premise of research. The relations between orchids and their pollinators are so specialized that the pollination of some of these flowers depends solely on specific groups of bees. Members of Stanhopeinae are pollinated exclusively by fragrance-collecting male euglossines. Although many studies have documented the pollination biology of various Stanhopeinae, data on the natural history of some genera (e.g., the Brazilian endemic Cirrhaea) are still lacking. In addition, few studies include molecular data on their pollination systems, and the Brazilian representatives of Stanhopeinae are rarely considered in phylogenies.Methodology. We documented the floral and reproductive biology of Cirrhaea through focal observations and experiments. We studied the interaction network between Stanhopeinae and Euglossini by reconstructing the phylogenies of both pollinators and orchids from molecular data.Pivotal results. Cirrhaea species present floral fragrances with different chemical compositions, are self-compatible, and are pollinated by two or more euglossine species. A single species of Cirrhaea can be pollinated by up to three bee species, and a single species of orchid bee can pollinate more than one species of Cirrhaea. Our data show that the relation between Cirrhaea and euglossines is not species specific and that orchids depend unilaterally on bees.Conclusions. The selection pressures of euglossine on flowers have promoted the production of divergent perfume bouquets. Moreover, they have favored the emergence of peculiar flower morphologies that have resulted in particular pollination mechanisms. This close relationship between flower and pollinator reduces pollen loss and promotes isolating mechanisms between sympatric interfertile species. The combination of the phylogeny of Stanhopeinae and Euglossini shows that species-specific relations between the evolution of plants and pollinators are rare.