Nevard, L. | bioRxiv Science

bioRxiv2021

Transmission of vibrations in buzz-pollinated plant species with disparate floral morphologies

In buzz-pollinated plants, bees apply vibrations produced by their thoracic muscles to the flower, causing pollen release from anthers, often through small apical pores. During floral buzzing, bees grasp one or more anthers with their mandibles, and vibrations are transmitted to the focal anther(s), adjacent anthers, and the whole flower. Because pollen release depends on the vibrations experienced by the anther, the transmission of vibrations through flowers with different morphologies may determine patterns of release, affecting both bee foraging and plant fitness. Anther morphology and intra-floral arrangement varies widely among buzz-pollinated plants. Here, we compare the transmission of vibrations among focal and non-focal anthers in four species with contrasting anther morphologies: Cyclamen persicum (Primulaceae), Exacum affine (Gentianaceae), Solanum dulcamara and S. houstonii (Solanaceae). We used a mechanical transducer to apply bee-like artificial vibrations to focal anthers, and simultaneously measured the vibration frequency and displacement amplitude at the tips of focal and non-focal anthers using high-speed video analysis (6,000 frames per second). In flowers in which anthers are tightly held together (C. persicum and S. dulcamara), vibrations in focal and non-focal anthers are indistinguishable in both frequency and displacement amplitude. In contrast, flowers with loosely arranged anthers (E. affine) including those in which stamens are morphologically differentiated within the same flower (heterantherous S. houstonii), show the same frequency but higher displacement amplitude in non-focal anthers compared to focal anthers. Our results suggest that stamen arrangement affects vibration transmission with potential consequences for pollen release and bee behaviour.

biophysics↗

bioRxiv2020

Are flowers tuned to buzzing pollinators? Variation in the natural frequency of stamens with different morphologies and its relationship to bee vibrations

During buzz pollination, bees use vibrations to remove pollen from flowers. Vibrations at the natural frequency of pollen-carrying stamens are amplified through resonance, resulting in higher-amplitude vibrations. Because pollen release depends on vibration amplitude, bees could increase pollen removal by vibrating at the natural frequency of stamens. Yet, few studies have characterized the natural frequencies of stamens and compared them to frequencies of buzz-pollinating bees. Here we use laser Doppler vibrometry to characterise natural frequencies of stamens of six buzz-pollinated Solanum taxa of contrasting stamen morphology. We also compare the fundamental frequency of bumblebee buzzes produced on two Solanum species with different natural frequencies. We found that stamen morphology and plant identity explain variation in natural frequency of stamens. Our results show that medium-sized pollinators, such as bumblebees, produce buzzes of frequencies higher than the natural frequency of most (5/6) of the Solanum species we studied. However, the observed natural frequency of Solanum stamens is at the low end of the range of frequencies produced by other buzz-pollinating bees. Thus, our findings suggest that in some buzz pollination interactions, but not others, stamen resonance may play a role in mediating pollen release.

biophysics↗