Anther cones increase pollen release in buzz‐pollinated Solanum flowers

Abstract

The widespread evolution of tube-like anthers releasing pollen from apical pores is associated with buzz pollination, in which bees vibrate flowers to remove pollen. The mechanical connection among anthers in buzz-pollinated species varies from loosely held conformations, to anthers tightly held together with trichomes or bioadhesives forming a functionally joined conical structure (anther cone). Joined anther cones in buzz-pollinated species have evolved independently across plant families and via different genetic mechanisms, yet their functional significance remains mostly untested. We used experimental manipulations to compare vibrational and functional (pollen release) consequences of joined anther cones in three buzz-pollinated species of Solanum (Solanaceae). We applied bee-like vibrations to focal anthers in flowers with ("joined") and without ("free") experimentally created joined anther cones, and characterized vibrations transmitted to other anthers and the amount of pollen released. We found that joined anther architectures cause nonfocal anthers to vibrate at higher amplitudes than free architectures. Moreover, in the two species with naturally loosely held anthers, anther fusion increases pollen release, whereas in the species with a free but naturally compact architecture it does not. We discuss hypotheses for the adaptive significance of the convergent evolution of joined anther cones.

Hold tight or loosen up? Functional consequences of a shift in anther architecture depend substantially on bee body size

“…Prior studies have predicted that joined anther architecture evolved to more effectively release pollen and reward bees, and experimental work with simulated bee buzzes has found that joined anther architecture increases pollen release (Glover et al 2004;Vallejo-Marín et al 2022). In contrast, we nd that joined anther architecture overall decreases both pollen release from the anthers (by 34%) and pollen collection by the bee into its pollen baskets (by 23%).…”

“…plants, yet the functional signi cance of this variation is imperfectly understood (Faegri 1986;Vogel 1978; Glover et al 2004;Vallejo-Marín et al 2022). Such plants are pollinated by bees capable of generating powerful vibrations (' oral buzzing'; performed by an estimated 58% of bee species; Cardinal et al 2018), which expel pollen from the terminal pores of the tube-like poricidal anthers (Macior 1968;…”

“…Vallejo-Marín 2019; Brito et al 2020). Many of these buzz pollinated plant species possess owers whose anthers are spread apart and capable of relatively independent movement ('free anther architecture') (Glover et al 2004;Vallejo-Marín et al 2022). Yet many other buzz pollinated species across taxonomically diverse families have independently evolved a joined anther architecture, in which poricidal anthers are arranged and joined in the centre of the ower, resembling a cone (Fig.…”

Pollination service provided by honey bees to buzz-pollinated crops in the Neotropics

“…Less frequently, we saw AHB using the first two pair of legs to push the anthers by means of quick movements, what is defined as "striking" or "drumming" of the anther [49,50]. In addition, the anther cone structure of Solanum flowers increases pollen release, whereas this is more difficult in species with a free anther architecture [51]. Evidently, honey bees are capable of removing pollen from S. melongena and they can pollinate them.…”

Digest: Anther cones increase pollen release in buzz‐pollinated Solanum flowers*

“…Using three species of flowering plants of the genus Solanum with different anther conformations, Vallejo‐Marín et al. (2022) investigated this question by testing whether vibration transmission and subsequent pollen release rates differed between conical and free architectures. The researchers measured vibration transmission to distal anthers for flowers in their natural state and in an artificially glued anther state, testing vibration transmission in the cones.…”