Floral adaptations to nocturnal moth pollination in Diplomorpha (Thymelaeaceae)

Many members of the family Thymelaeaceae are highly praised and economically important for the production of fragrant scent, but little is known about the ecological significance of their secondary metabolites. To explore the potential role that secondary metabolites play in pollination, we studied the pollination systems of five Diplomorpha species in Japan by investigating their floral morphology and flower-visiting insect fauna. We also analyzed the composition and temporal emission pattern of floral volatiles in one of the species to determine if there were any characteristics associated with the observed flower visitors. In Diplomorpha, anthesis began at dusk and various nocturnal moths were found visiting the flowers, often carrying numerous pollen grains on their proboscises. However, no hawkmoths were observed visiting Diplomorpha flowers. Diurnal insects visited the flowers less often, and most of them had short mouthparts and did not effectively contact the stigma. The floral scent of Diplomorpha sikokiana was released only at night when the moths were active and consisted mainly of monoterpenes and benzenoids, with a small amount of a sesquiterpene. The present study is the first to examine the pollination system of Diplomorpha and suggests that these plants exhibit a range of floral features associated with pollination by nocturnal moths. The single ovule in Diplomorpha flowers probably does not favor pollination by optimally foraging bees, which are more likely to cause intraplant pollen transfer, and might have facilitated adaptation to pollination by nocturnal moths, despite the lower number of pollen grains that are carried by these insects.