Pollen dispensing schedules in buzz-pollinated plants: Experimental comparison of species with contrasting floral morphologies

Abstract

O_LIIn buzz-pollinated plants, bees apply vibrations to remove pollen from anthers that have small apical pores or slits. These poricidal anthers potentially function as mechanism to stagger pollen release, but this has rarely been tested across plant species differing in anther morphology. C_LIO_LIIn Solanum section Androceras, three pairs of buzz-pollinated Solanum species have undergone independent evolutionary shifts between large- and small-flowered taxa. These shifts in flower size are accompanied by replicate changes in anther morphology, and we used these shifts in anther morphology to characterise the association between anther morphology and pollen dispensing schedules. We characterised pollen dispensing schedules by applying simulated bee-like vibrations directly to anthers to elicit pollen release. We then compared pollen dispensing schedules across anther morphologies, and we further investigated how vibration velocity affects pollen release. Finally, we assessed whether particular anther traits, presented in the Buchmann-Hurley model, can predict pollen dispensing schedules. C_LIO_LIWe show that replicate transitions in Solanum anther morphology are associated with consistent changes in pollen dispensing schedules. We found that small-flowered taxa with small anthers release their pollen at higher rates than their large-flowered counterparts, showing an association between general anther morphology and pollen dispensing. Further, higher vibration velocities resulted in quicker pollen dispensing and more total pollen released, which suggested that bees that produce high-energy vibrations can access more reward than bees producing low-energy vibrations. Finally, both the pollen dispensing rate and the amount of pollen released in the first vibration were negatively related to anther wall area, but, surprisingly, we did not observe any association between pore size and pollen dispensing. C_LIO_LIOur results provide the first empirical demonstration that the pollen dispensing properties of poricidal anthers depend on both floral characteristics and bee vibration properties, and suggest that morphological modification of anthers could provide a mechanism to exploit different pollination environments. C_LI