Pollination of Aosa rupestris (Hook.) Weigend (Loasaceae): are stamen movements induced by pollinators?

Abstract

Inducement to stamen movement by oligolectic bees has been reported for some Loasaceae species; however, detailed research studies on the pollination ecology of species in the genus Aosa are absent. In this study, we analyzed the floral biology and breeding system of Aosa rupestris (Hook.) Weigend, focusing on the role of pollinators in inducing stamens’ movements. We described the anthesis, the behavior of floral visitors, and carried out reproductive experiments in a population in a dry forest (“caatinga”) area in Northeastern Brazil. We carried out four experiments and one control to establish whether the interval between the movements of two successive stamens is regulated by pollinator visits. Anthesis lasted for 3–4 days. Stamens (102 ± 12.57) remained with closed anther inside petals early in the anthesis, after which they moved to the center of the flower and presented its pollen (male phase). After all stamens have reached the center of the flower, the female phase started. Bicolletes nordestina Urban, 2006 was the only floral visitor to A. rupestris flowers, drinking nectar, collecting pollen, or sleeping on the flowers. Aosa rupestris was autogamous, but fruit set was higher under natural conditions. The interval between movements of two successive stamens was not different among experiments. Therefore, stamen movements were spontaneous and did not respond to pollinator visits, in contrast to the pattern of stamen movements observed in other Loasaceae species. Although A. rupestris is autogamous, floral structure and behavior of the oligolectic bee pollinator ensured the highest level of fruit set in this species.