Evidence for diurnal bee pollination in the ancestrally hawkmoth-pollinated genus Crinum (Amaryllidaceae)

Abstract

Shifts between diurnal and nocturnal pollination systems have been important in the radiation of the angiosperms. Here we examined the pollination ecology of Crinum campanulatum (Amaryllidaceae), an aquatic geophyte. Although visits by noctuid moths were observed in the evening, the flowers of C. campanulatum were visited mainly by honeybees and carpenter bees. The species was found to be self-incompatible, and flowers exposed to only diurnal visitors produced a higher number of fruits and seeds than those exposed to only nocturnal visitors. Overall seed production was not pollen limited. The floral scent was found to be dominated by aromatic compounds, including many with functional groups containing nitrogen. The chemical composition of scent did not differ between day and night samples, but floral scent emissions during the day were ~8-fold greater than those at night. Flower colour changes from white to a dark pink over four days from anthesis, which is associated with increased conspicuousness to bees. Ancestral state reconstruction revealed that long-tubed flowers pollinated by hawkmoths are ancestral and widespread in Crinum. These results are indicative of a shift from nocturnal to diurnal pollination in Crinum that is associated with a reduction in flower size and an increase in diurnal scent emission.