Nymphaea pulchella (Nymphaeaceae) and Trigona spinipes (Apidae) interaction: From florivory to effective pollination in ponds surrounded by pasture

Abstract

Aquatic macrophytes that occur in isolated ponds in hostile pasture matrices may be subject to setbacks in the delicate balance of animal-plant interactions, such as pollination systems. In this work we took as a model Nymphaea pulchella DC., a species which occurs in isolated ponds in pastures in Northeast Brazil. We aimed to elucidate how complex pollination mechanisms can survive in human-dominated landscapes. We conducted studies involving floral biology to determine the morphological structure of the whorls and the anthesis sequence. We also analyzed behavior and frequency of floral visitors, as well as how the floral organs were used as resources, and tried to determine if there was pollinator dependence through pollen tube analyses and controlled pollination experiments. We recorded a gradient structure of floral organs and differences in the timing and extent of floral opening between days. Trigona spinipes consumes all floral whorls indiscriminately (configuring direct and indirect florivory). Despite the florivory, this bee was the most abundant floral visitor and was the only one confirmed effective pollinator. N. pulchella is autogamous with delayed self-pollination, but there were significantly more fruits formed in flowers exposed to bees than in spontaneous self-pollination, and even flowers with partially consumed ovaries produced fruits. Since interaction with T. spinipes contributes to greater fruit formation, we believe this supergeneralist native bee is an important factor in ensuring the success of N. pulchella in occupying the pasture matrix studied.