Sophora tomentosa and Crotalaria vitellina (Fabaceae): reproductive biology and interactions with bees in the restinga of Ubatuba, São Paulo

Abstract

The study of plant-pollinator interactions is a major tool for conservation biology of fragmented habitats like the Atlantic Rain Forest and for the study of evolutionary traits that rule these interactions. Information on reproductive biology and floral visitor interactions of Sophora tomentosa and Crotalaria vitellina (Fabaceae) is presented in this study. Both species are common in the restinga formation of the Atlantic Rain Forest in the Núcleo Picinguaba, Parque Estadual da Serra do Mar, Ubatuba - São Paulo. These species occur in the same areas, the flowering period is the same for both and they have yellow flowers that offer nectar as the major reward. Both are self-compatible, although fruit and seed set depend on the pollinators. Xylocopa brasilianorum and Megachile sp.1 were pollinators of S. tomentosa, whereas C. vitellina was pollinated by both the aforementioned bees and Bombus morio, Centris labrosa and two separate species of Megachile. All these bees have long tongues and are able to reach nectar at the bottom of the nectar chamber by legitimate visits. The inflorescences of S. tomentosa received more visits (0,62 visits/inflorescence/day) than the inflorescences of C. vitellina (0,37 visits/inflorescence/day). However, the fruit set of S. tomentosa (33%) is similar to that of C. vitellina (42%) in natural conditions, probably due to different pollinator efficiency. Having shorter tongues, Trigona and Augochlora bees have no access to the nectar chamber by means of legitimate visits. Hence, the dimensions of the nectar chamber of S. tomentosa and C. vitellina act as a selective barrier to short-tongued bees, thus guaranteeing more nectar to the long-tongued visitors. These legume pollinators are very common in the restinga forest, and they act as pollen vectors of other species in this ecosystem as well. The preservation of these legume plants is important to the diversity of bees and essential to the plant community.