Evolutionary tinkering allows buzz pollinated plants to escape from an adaptive dead-end

Abstract

Buzz pollination is a type of pollination in which animal visitors use vibrations to extract pollen from flowers with specialized morphologies, incidentally transferring pollen to the stigma. In buzz‐pollinated flowers, pollen is kept tightly locked inside anthers that dehisce only through small pores or slits, usually at the tip of the anther (Buchmann, 1983). Species with so‐called poricidal anthers are usually nectar‐less and provide pollen as the principal reward to attract pollinators (Vallejo‐Marín et al., 2010). Although pollen can be extracted from these poricidal anthers through different mechanisms (e.g. chewing the anther wall, or by probing the anther pores), the most efficient way to extract it is, by far, through ‘buzzing’ (De Luca & Vallejo‐Marín, 2013). In this context, buzzing refers to the complex behaviour performed by bees to generate vibrations using their thoracic muscles to remove pollen from anthers. These vibrations are transmitted from the bee to the anthers, causing pollen grains to become expelled through the anther pores and onto the bee's body. The only animals known to use vibrations to remove pollen from flowers are bees, although, for reasons still unknown, not all bees are capable of buzz pollination (Cardinal et al., 2018). Buzz‐pollinated flowers with poricidal anthers have evolved independently multiple times through the history of angiosperms and occur in c. 6% of species (Buchmann, 1983; De Luca & Vallejo‐Marín, 2013; Cardinal et al., 2018). In some cases, poricidal anthers and buzz pollination characterize large groups of closely related species such as in the > 1500 species of Solanum (Solanaceae) and among the majority of species in the Melastomataceae. The stereotypical floral morphology of some buzz‐pollinated groups (e.g. Solanum) as well as the fact that buzzing is restricted to some species of bees, has led to the suggestion that buzz pollination represents an adaptive peak (Renner, 1989), and that the evolution of buzz‐pollinated flowers towards a different type of pollination is relatively constrained. In this issue of New Phytologist, Dellinger et al. (2019, pp. 1136–1149) provide the best‐documented example to date of the evolution of new pollination syndromes from a buzz‐pollinated ancestor.