Disorder in convergent floral nanostructures enhances signalling to bees.

Abstract

In nature diverse nanoscale architectures generate structural colour and play signalling roles within and between species. Structural colour results from interference of light from approximately regular periodic structures, but some structural disorder is inevitable in biological organisms. Is this disorder functional and subject to evolutionary selection or is it simply an unavoidable outcome of developmental processes? We show that disordered nanostructures enable flowers to produce salient visual signals to bees. These disordered nanostructures, identified in most major lineages of angiosperms, have distinct anatomies but convergent optical properties, which all produce an angle-dependent scattered light predominantly at short wavelengths (ultraviolet and blue). We manufactured samples with tailored disorder to investigate how foraging bumblebees respond to this optical effect. We conclude that floral nanostructures have independently evolved an effective degree of relative spatial disorder that generates a strongly insect-salient photonic signature.