Phenology, abundance and efficiency of pollinators drive the reproductive success of Sarcoglottis acaulis (Orchidaceae) at the Atlantic Forest

Abstract

Male euglossine bees (Euglossine: Apidae) pollinate flowers of as many as 1,000 Neotropical plant species and there is evidence that blooming in these plants is synchronized with the seasonality of euglossine pollinators. The present study aimed to monitor for two years the phenology of Sarcoglottis acaulis (Orchidaceae -Spiranthinae subtribe) and the seasonality of its pollinators at three Atlantic Forest fragments, two of which surrounded by urban anthropized areas. Phenologies in the three areas were related to abiotic factors, suggesting that precipitation on months prior to the beginning of the flowering period influenced the fructification rates of S. acaulis. Additionally, water shortage during the driest months resulted in vegetative dormancy. Sarcoglottis acaulis sets only a low number of fruits by self-pollination, and the plant's reproductive success depended on the frequency of its main pollinator, i.e., the male euglossine bees Eulaema atleticana. Lower rates of pollinia removal were observed in areas where this bee is less frequent and, consequently, less fruits were formed, suggesting a high dependency on this pollinator.