Flower movement increases pollinator preference for flowers with better grip

1.Conical cells in the petal epidermis are common across many diverse flowering plant species, and it was recently shown that in difficult-to-handle flowers, pollinators prefer conical cells because they increase grip. However, this does not explain the prevalence of conical cells amongst other, simpler, flowers. 2.The movement of objects is an integral part of the world and is of particular importance to bees because the relative motion of objects is essential to a bee's 3D vision. The motion of flowers can increase pollinator attraction; however, it also makes flowers more difficult for a bee to handle. This makes foraging more metabolically expensive. To explore whether conical petal cells make handling moving flowers easier, we tested bumblebee (Bombus terrestris) preference for conical- or flat-celled Petunia (Petunia hybrida) flowers under different conditions of motion. We also used differently coloured Petunia flowers to test how colour and visibility interact with tactile cues to form a pollinator's preferences. 3.Bees preferred to visit conical-celled Petunia flowers except when the conical-celled flowers were harder to detect visually. The bees then favoured flowers that were easier to detect. But when flowers were moving and more difficult to handle, bees always learned to favour conical-celled flowers, irrespective of visual difficulty. 4.By providing easier handling through better grip from conical cells, the plant can benefit from the natural visual attractant of flowers moving in the wind without losing pollinator preference for easier-to-handle flowers. Bee preference for conical-celled flowers when flowers are moving shows how plants can use conical petal cells to take advantage of an attractant that would otherwise decrease pollinator preference by making handling difficult (movement). The selective pressure from pollinators choosing conical-celled flowers when flowers are moving in the wind provides an explanation for the persistence of conical cells in so many diverse angiosperm species across evolutionary time.