Disorder in convergent floral nanostructures enhances signalling to bees

• Published in: Nature (London) 2017-10, Vol.550 (7677), p.469-474
• Main Authors: Moyroud, Edwige, Wenzel, Tobias, Middleton, Rox, Rudall, Paula J., Banks, Hannah, Reed, Alison, Mellers, Greg, Killoran, Patrick, Westwood, M. Murphy, Steiner, Ullrich, Vignolini, Silvia, Glover, Beverley J.
• Format: Article
• Language: English
• Subjects: 631/158/857; 631/181/2481; 631/449/2669; 639/301/357; 639/624/399; Angiosperms; Bees; Behavior; Biological activity; Biological evolution; Bombus; Bombus terrestris; Bumblebees; Color; Convergence; Environmental aspects; Flowers; Flowers & plants; Forage; Foraging (Animal feeding behavior); Hibiscus trionum; Humanities and Social Sciences; multidisciplinary; Optical properties; Periodic structures; Photonics; Phylogenetics; Pollinators; Science; Signal transduction; Signaling; Visual signals; Wavelengths; Zoological research
• ISSN: 0028-0836; 1476-4687
• DOI: 10.1038/nature24285

Diverse forms of nanoscale architecture generate structural colour and perform signalling functions within and between species. Structural colour is the result of the interference of light from approximately regular periodic structures; some structural disorder is, however, inevitable in biological organisms. Is this disorder functional and subject to evolutionary selection, or is it simply an unavoidable outcome of biological developmental processes? Here we show that disordered nanostructures enable flowers to produce visual signals that are salient to bees. These disordered nanostructures (identified in most major lineages of angiosperms) have distinct anatomies but convergent optical properties; they all produce angle-dependent scattered light, predominantly at short wavelengths (ultraviolet and blue). We manufactured artificial flowers with nanoscale structures that possessed tailored levels of disorder in order to investigate how foraging bumblebees respond to this optical effect. We conclude that floral nanostructures have evolved, on multiple independent occasions, an effective degree of relative spatial disorder that generates a photonic signature that is highly salient to insect pollinators. Disordered nanoscale striations on petals, tepals and bracts have evolved multiple times among flowering plants and provide a salient visual signal to foraging bumblebees ( Bombus terrestris ). Pretty orderly disorder The natural world is always a bit fuzzy at the edges, but the fuzziness has a purpose. The surfaces of petals of many flowers have striations or ridges, which scatter light. But these arrays of ridges are not always arranged in a regimental order. In this paper, Beverley Glover and colleagues find that all of the flowering plants that they examined whose petals have such striations always display the same degree of disorder. This creates a 'blue halo' around the petals that pollinators find attractive. The authors find that similarly disorderly conduct happens in all flowering plants that are pollinated by insects or other animals, whereas the most primitive flowers, which are not pollinated by animals, seem not to have this capacity for orderly disorder.