Biomechanical properties of a buzz-pollinated flower

Abstract

Approximately half of all bee species use vibrations to remove pollen from plants with diverse floral morphologies. In many buzz-pollinated flowers, these mechanical vibrations generated by bees are transmitted through floral tissues, principally pollen-containing anthers, causing pollen to be ejected from small openings (pores or slits) at the tip of the stamen. Despite the importance of substrate-borne vibrations for both bees and plants, few studies to date have characterized the transmission properties of floral vibrations. In this study, we use contactless laser vibrometry to evaluate the transmission of vibrations in the corolla and anthers of buzz-pollinated flowers of Solanum rostratum , and measure vibrations in three spatial axes. We found that floral vibrations conserve their dominant frequency (300 Hz) as they are transmitted throughout the flower. We also found that vibration amplitude at anthers and petals can be up to greater than 400% higher than input amplitude applied at the receptacle at the base of the flower, and that anthers vibrate with a higher amplitude velocity than petals. Together, these results suggest that vibrations travel differently through floral structures and across different spatial axes. As pollen release is a function of vibration amplitude, we conjecture that bees might benefit from applying vibrations in the axes associated with higher vibration amplification.

Connective appendages in Huberia bradeana (Melastomataceae) affect pollen release during buzz pollination

“…Despite there still being no clue to the effect of the secondary harmonics in pollen release from buzz‐pollinated flowers, flower traits, such as mass, stiffness, geometry and other material properties of anthers and associated floral structures are expected to affect the transmission of vibrations and ultimately pollen release (Michelsen et al 1982; Vallejo‐Marín 2019; Brito et al . 2020). Moreover, it has already been discussed that the biomechanical structure of filaments can affect the transmission of vibrations by decreasing or increasing the amplitude produced by bees, potentially affecting pollen release (Buchmann & Hurley 1978; Harder & Barclay 1994; King & Buchmann 1996; Morgan et al 2016; Switzer & Combes 2017; Brito et al .…”

“…Moreover, it has already been discussed that the biomechanical structure of filaments can affect the transmission of vibrations by decreasing or increasing the amplitude produced by bees, potentially affecting pollen release (Buchmann & Hurley 1978; Harder & Barclay 1994; King & Buchmann 1996; Morgan et al 2016; Switzer & Combes 2017; Brito et al . 2020). However, it is important to note that the laser vibrometer used in this study is capable of measuring the vibration in only one of the three flower vibration axes, while we know that flowers can vibrate differently in different spatial axes (Vallejo‐Marín 2019, Brito et al .…”

“…However, it is important to note that the laser vibrometer used in this study is capable of measuring the vibration in only one of the three flower vibration axes, while we know that flowers can vibrate differently in different spatial axes (Vallejo‐Marín 2019, Brito et al . 2020).…”

“…After preparing each flower, we lightly touched the base of the stamens of each flower with a handmade vibrational device (a metal rod coupled to a metal plate sound speaker connected to a computer; see Brito et al . 2020). We set the values of frequency = 238 Hz and amplitude = −35.6 dB and generated a pure tone sine wave of 5 s. These values of vibration components used in the playback system were tuned and calibrated to simulate the same bee vibrations collected as the mean value of 20 Xylocopa cf.…”

“…Moreover, the optimal vibrational properties for maximum pollen release probably vary among plant species as a result of different floral structures, anther morphology and pollen properties (Buchmann 1983; Thorp 2000; Brito et al . 2020). Therefore, studying the structural and functional properties of poricidal anthers in relation to pollen release, as done in this study, has great potential to increase our understanding of the mechanisms underlying the evolution of buzz pollination.…”