Bees and other pollinators can find flowers more easily due to a blue halo generated by nanoscale patterns on the petals, shows a study in Nature this week. This study shows that these signals are present in most groups of extant flowering plants, but that they may have evolved independently across lineages.
Some flowers possess striations on their petals that scatter light to produce structural colour, which generates signals that are visible pollinators. These nanoscale striations display a degree of disorder, that is, variation in the size and spacing within the patterns of a single flower. Beverley Glover and colleagues analysed these patterns in a range of flowering plants, and show that, despite this variation in the nanostructures, the patterns all display a similar degree of disorder. Regardless of the underlying pigment colour, these disordered structures all generate ultraviolet-to-blue haloes when hit by rays of sunlight.
Bees have been shown to be drawn to the colour blue, so to determine whether the blue halo is a visual signature that is attractive to bees, the authors made synthetic flowers with or without the nanoscale surface patterns seen in natural flowers. Behavioural experiments then demonstrated that bumblebees could find synthetic flowers that produced a blue halo more quickly than flowers that did not. The authors conclude that, although the varying nanostructures may have evolved independently, they all converge on producing the same striking visual signals that are striking to the pollinator's eye.