Data from: Gradual pollen release in a buzz pollinated plant: Investigating pollen presentation theory under bee visitation

The rate at which flowers dispense pollen across successive pollinator
visits is a key functional trait influencing male reproductive success.
Pollen presentation theory (PPT) predicts that when pollinators are
abundant and actively groom their bodies to collect pollen, plants should
evolve gradual pollen release. Despite its intuitive appeal and
generality, PPT has rarely been tested empirically using real bee visits,
especially in buzz pollinated plants where pollen dispensing is controlled
mechanically. Buzz pollinated plants are ideal to study PPT because they
are often nectarless and rely on pollen-grooming bees, which must apply
vibrations to specialised tube-like or poricidal anthers to release
pollen. The vibrations generated by some bees directly determine pollen
release and thus yield a direct mapping between bee behaviour and floral
function. Here, we provide the first quantitative assessment of pollen
dispensing in a buzz pollinated plant, Solanum rostratum, using real
bumblebee (Bombus terrestris) visits. We conducted 80 trials with
individual bees and measured over 2,000 pollination buzzes to estimate the
relationship between total buzzing time and pollen dosing. For each trial
we measured the total time spent buzzing and the amount of pollen
remaining in the flower after visitation. We also characterised the
properties (frequency and duration) of individual buzzes. Individual
pollination buzzes had a fundamental frequency of 340 ± 26 Hz (mean ± SD)
and were relatively short in duration (0.748 ± 0.604 s). We found that S.
rostratum shows a strong pattern of gradual pollen release with flowers
dispensing on average 2-4% of the available pollen grains for each buzzing
second. Our study links an ecologically relevant pollinator behaviour to a
key floral functional trait that affects male fitness, offering empirical
support for PPT in a buzz pollinated system.