Exaggeration and suppression of iridescence: the evolution of two-dimensional butterfly structural colours

Abstract

Many butterfly species possess 'structural' colour, where colour is due to optical microstructures found in the wing scales. A number of such structures have been identified in butterfly scales, including three variations on a simple multi-layer structure. In this study, we optically characterize examples of all three types of multi-layer structure, as found in 10 species. The optical mechanism of the suppression and exaggeration of the angle-dependent optical properties (iridescence) of these structures is described. In addition, we consider the phylogeny of the butterflies, and are thus able to relate the optical properties of the structures to their evolutionary development. By applying two different types of analysis, the mechanism of adaptation is addressed. A simple parsimony analysis, in which all evolutionary changes are given an equal weighting, suggests convergent evolution of one structure. A Dollo parsimony analysis, in which the evolutionary 'cost' of losing a structure is less than that of gaining it, implies that 'latent' structures can be reused.

Artificial selection for structural color on butterfly wings and comparison with natural evolution

“…Structural colors play major roles in natural and sexual selection in many species (1) and have a broad range of applications in color display, paint, cosmetics, and textile industries (2). Structural color surveys across widely divergent species have revealed a large diversity of color-producing mechanisms (3)(4)(5)(6)(7)(8)(9). However, there has been a lack of systematic study and comparison of how different colors from closely related species or within populations of a single species evolve, even though these colors can vary dramatically.…”

A protean palette: colour materials and mixing in birds and butterflies

“…Other pigments with more complex wavelengthdependent absorption profiles, such as pterins, carotenoids and ommochromes, are also found in structural colour patterns (Schmidt & Paulus 1970;Fox 1976;Steinbrecht et al 1985;Rutowski et al 2005;Wickham et al 2006). The contributions of these pigments to the optical properties of colour patterns are various.…”

“…In some instances, they shape the colour of light reflected from broadband reflectors, such as the chirped multilayers in butterfly pupae (Steinbrecht et al 1985), the reflective scales of fish (Denton & Land 1971;Land 1972) and the skin of cephalopods (Mathger & Hanlon 2007). In other cases, they influence the scattering of light wavelengths not reflected by nearby optical structures, resulting in novel and complex colour phenotypes (Mason 1923(Mason , 1926Schmidt & Paulus 1970;Prum & Torres 2003;Stavenga et al 2006;Wickham et al 2006). In even more specific instances, pigments may absorb extraneous light in wavelengths reflected by optical nanostructures while transmitting light in other wavelengths, thus creating a complex colour element that simultaneously showcases both the structural and pigment-based components of the colour trait (Rutowski et al 2005).…”

Photonic Structures in Biology: A Possible Blueprint for Nanotechnology

“…The development of photonic structures involved a gradual increase in complexity and colouration, from scutes (patterned, hardened external parts of insect wing scales) to multilayer structures, diffraction gratings and, finally, to the complex cubic structures we find in some insects today. [41][42][43] The earliest multilayer systems and gratings in the fossil record were discovered within the hairs and spines of beetles ( Figure 5) found in the Burgess shale fossils from the Cambrian, 515 million years ago (mya). 41 Within the spines, the diffraction gratings were aligned in the same direction regardless of the turns and twists of the spines, indicating that these periodic structures were not simply a product of fossilization.…”