Structural Diversity with Varying Disorder Enables the Multicolored Display in the Longhorn Beetle Sulawesiella rafaelae

Abstract

Summary Light control through layered photonic nanostructures enables the strikingly colored displays of many beetles, birds, and butterflies. To achieve different reflected colors, natural organisms mainly rely on refractive index variations or scaling of a fixed structure design, as opposed to varying the type of structure. Here, we describe the presence of distinct coloration mechanisms in the longhorn beetle Sulawesiella rafaelae , which exhibits turquoise, yellow-green, and orange colors, each with a variable iridescence. By optical and electron microscopy, we show that the colors originate from multilayered architectures in hair-like scales with varying amounts of structural disorder. Structural characterizations and optical modeling show that the disorder strongly influences the optical properties of the scales, allowing an independent adjustment of the optical response. Our results shed light on the interplay of disorder in multilayered photonic structures and their biological significance, and could potentially inspire new ecological research and the development of novel optical components.

Optical costs and benefits of disorder in biological photonic crystals

“…Other structures in beetle scales have also been identied, including gyroids, close-packed spheres, perforated multilayers and inverse columns. 28,52,[110][111][112][113][114][115] These structures also exhibit various ranges of disorder. For instance, Bermúdez-Ureña et al highlighted the presence of various extents of disorder in structurally coloured scales of the Sulawesiella rafaelae longhorn beetle.…”

“…For instance, Bermúdez-Ureña et al highlighted the presence of various extents of disorder in structurally coloured scales of the Sulawesiella rafaelae longhorn beetle. 52 This beetle displays green, orange and turquoise hues due to perforated multilayer structures ( Fig. 4A-C).…”

“…Studies conrm that various degrees of disorder prevail, sometimes concurrently, among a range of biological systems. 45,[49][50][51][52] Unexpectedly, disordered structures can also enhance reectance. 53,54 One example is the silvery appearance of the skins of certain shes, which is due to guanine platelets in the cytoplasm of cells called iridophores.…”

“…36,50,74,75 Many aspects of disorder can be characterised using a statistical approach relying on measurements of physical features, for example: the distances between scattering centres, their sizes and shapes (e.g., number of sides or ellipticity), or their orientations, radial distribution functions or structure factors. 32,[52][53][54][76][77][78] In this paper, we suggest that the distributions of these measured quantities represent a useful measure of the extent of a system's disorder. For some systems, a measure of structural entropy has been dened.…”

3D tomographic analysis of the order-disorder interplay in the Pachyrhynchus congestus mirabilis weevil

“…The produced color is more diffuse, less saturated and angle-independent compared to colors produced by highly ordered PCs. Partially disordered bicontinuous structures are a less common mechanism to generate color in nature and observations have so far been limited to blue coloration, mainly in beetle scales and bird feathers (21)(22)(23)(24)(25)(26)(27)(28). So far, studies of amorphous structures in biological systems have predominantly relied on 2D data collection from crosssectional electron microscopy (21,22,25) , or small-angle x-ray scattering studies (29).…”