Frequency of visits and efficiency of pollination by diurnal and nocturnal lepidopterans for the dioecious tree Randia itatiaiae (Rubiaceae)

Abstract

In plants pollinated by different groups of animals, the most frequent visitors may not be the most effective for fitness because of their differential efficiency in pollen transfer. We addressed this question by studying a rare dioecious species of Rubiaceae in Brazil. The flowers of Randia itatiaiae are gender-heteromorphic and hypocrateriform with greenish corolla tubes ~2 cm long, and exhale a strong sweet scent during the entire period of anthesis, which starts at sunset for female flowers. Sucrose was the dominant or co-dominant nectar sugar for both genders. In spite of these typical sphingophilous-phalaenophilous traits, the flowers last for 6 days, and nectar was available in both diurnal and nocturnal assessments. Moreover, the flowering of R. itatiaiae did not overlap the phenodynamics of the Sphingidae community. Accordingly, two functional groups of Lepidoptera – Hesperiidae during the day and Sphingidae and Noctuidae at night – visited the flowers. Visits by either group resulted in equivalent fruit set and seed number per fruit, although the frequency of visits to flowers was higher during the day than at night. Diurnal and nocturnal lepidopterans may exert similar pressures on floral morphology, in addition to divergent pressures on other characters, such as the temporal dynamics of anthesis and nectar production. The pollination system of R. itatiaiae is specialised at the coarse scale, because its floral morphology precludes pollination by animals other than lepidopterans; however, its floral phenotype also represents a generalist compromise between the conflicting pressures exerted by diurnal and nocturnal groups of lepidopterans.