Buzz-Pollinated Plants: Their Chemical and Behavioural Ecology

This thesis explores how scent influences the attraction and behaviour of bees and, consequently, the ecology of flowers with a specialised pollination mechanism: buzz pollination. Pollen of approximately 6% of flowering plant species is contained within specialised flowers and is most effectively extracted using vibrations. These buzz-pollinated plants are primarily pollinated by bees. Floral scent is a complex phenotype widely known to mediate plant-pollinator interactions, which has recently been implicated in stimulating floral vibration production in bees visiting buzz-pollinated flowers. Yet the role of scent in regulating plant-pollinator interactions during buzz pollination is poorly understood. Firstly, I characterised how scent and sight signals of buzz-pollinated plants vary within a flower and assessed how these scent signals influenced foraging bees. Secondly, I explored how flowers with concealed pollinator rewards, for example pollen within buzz-pollinated flowers, might reliably indicate reward presence using scent. Thirdly, I investigated how scent informs decision making in pollen foraging bees. Fourthly, I explored the interactions between buzz-pollinated plants and their floral visitors in their natural environment. I found floral scent of buzz-pollinated plants to be a dynamic trait. Scent emission varied both in space and in time: between floral organs and with pollen presence, respectively. I also demonstrated that bees use scent to inform decision making when foraging for pollen. However, how bees learn to associate signals with rewards may differ when foraging for different resources, i.e., pollen and nectar. Buzzing behaviour was stimulated in bees by the complex scents produced by flowers as well as a single volatile chemical: linalool. Finally, I demonstrated that buzz-pollinated plants are regularly visited by bees which do not produce floral buzzes. These non-buzzing bees often damage flowers while collecting pollen and are expected to reduce reproductive success. Overall, these results show buzz-pollination to be a highly specialised exchange between plants and pollinators. The coordination of signals acting on multiple senses stimulates the attraction, positioning, and behaviour of bees necessary for effective pollination. Buzz-pollination has been hypothesised to select for effective pollinators, yet in natural ecosystems I found it to be regularly bypassed by pollen thieves. These findings highlight floral scent as a spatially and temporally dynamic signal used by plants to influence pollinator behaviour and learning, as well as providing novel insight into the globally important field of pollen foraging.