Learning to handle flowers increases pollen collection benefits for bees but does not affect pollination success for plants

Cooperation and conflict are common in plant-pollinator interactions.
Flowering plants often entice pollinators to visit by offering floral food
rewards, thereby facilitating pollination. However, pollinators such as
bees can learn to improve their collection of floral rewards (such as
pollen), changing how they interact with the flower’s reproductive organs,
which together could reduce pollination success. Consequently, complex
flowers that slow pollinator learning might benefit the plant. Yet how
pollinator learning and flower complexity interact to affect pollination
success is unknown. We therefore asked how differences in complexity of
four flower types (Phacelia campanularia, Exacum affine, Solanum
elaeagnifolium, and Erythranthe guttata) affected learning by
pollen-foraging generalist bumble bees (Bombus impatiens) and how learning
affected pollen collection and pollen deposition on these flowers. We
found that bees generally learned how to efficiently handle more complex
flower types more slowly. Bees that required more visits to become
efficient foragers collected less pollen, with no effect on pollen
deposition. Except for the simplest flower type, learning also involved
development of motor routines unique to each flower type. Experienced bees
overall collected more pollen, but individual differences in motor
routines did not affect pollen collection. Conversely, individual
differences in motor routines affected pollen deposition, but there was no
overall effect of experience. Thus, even though learning overall benefits
the bee, it does not alter female (and potentially male) fitness benefits
for the plant. We discuss potential reasons for these patterns and
consequences for bee behavior and flower evolution.