Conical cells in the petal epidermis are a common trait across the angiosperms, and influence pollinator behaviour and pollination success. This work explores two key aspects of conical cell evolution: firstly, why conical cells are so prevalent across many diverse species, and secondly, why some species have lost conical petal cells.

Using Petunia flowers to test bee preferences under conditions of motion, we investigate whether the tactile advantage of conical petal cells on complicated flowers can also benefit simple flowers with low inherent tactile difficulty. We find that flower movement increases bee preference for conical-celled flowers. Since motion increases flower attractiveness, a tactile benefit under motion may explain why conical cells have persisted throughout evolution across many diverse flower morphologies.

The major focus of this work is an exploration of conical cell loss using the buzzpollinated genus Solanum. Phylogenetic, molecular developmental and bee behavioural approaches were used to develop an integrated understanding of the frequency, mechanisms and possible causes of conical cell losses. We provide evidence of multiple independent losses of conical petal cells in Solanum. We find that two of these losses have occurred through similar molecular means, that of a change in the expression patterns of regulatory Subgroup 9A (Mixta-Like) R2R3 MYB genes. Bumblebee behavioural experiments show that bees do not display a preference in favour of either conical- or flat-celled flowers while buzz pollinating. These results show that conical cells are a trait under more than a single simple selective pressure, as bumblebee preferences in Petunia, and previously shown in Antirrhinum, differ from those identified by this study in the buzz-pollinated genus Solanum.

These results help expand our understanding of the complex pressures that can act on a single multifunctional trait, as well as providing evidence for the repeatability of evolution on a molecular level.