Analysis of the optical properties of the silvery spots on the wings of the Gulf Fritillary, Dione vanillae

Abstract

The ventral face of the wings of the butterfly Dione vanillae is covered with bright and shiny silvery spots. These areas contain densely packed ground- and coverscales with a bright metallic appearance reflecting more than 50% of light uniformly over the visible range. Our analysis shows that this optically attractive feature is caused by the inner microstructure of the scales located in these areas. Electron microscopy of cross sections through the scales shows that upper and lower lamina, supporting trabeculae, and topping ridges can be approximated by a ‘circus tent’-like geometry. By simulating its optical properties, we show that a moderate disorder of this geometry is important for the uniform reflection of light resulting in the silvery appearance.

Antennapedia and optix regulate metallic silver wing scale development and cell shape in Bicyclus anynana butterflies

“…This creates an undulatory air layer sandwiched by the lower and upper laminas whose thicknesses also vary spatially. Broadband reflectance is achieved by additive color mixing that occurs due to local spatial variation or disorder in the scale ultrastructure (D'Alba et al, 2019;Dolinko et al, 2021;Ren et al, 2020;Vukusic et al, 2009;Wilts et al, 2013). This means that a single silver scale, when observed at very high resolution, is made up of many small patches of distinct colors, such as blues, greens, oranges, and pinks.…”

“…These examples suggest that the regulatory networks that create a metallic scale type must involve regulation of scale ultrastructure dimensions, perhaps along with pigmentation. Although the optical origin of broadband silvery colors from thin-film and chirped multilayer reflectors in the arthropod integument is well understood (D'Alba et al, 2019;Dolinko et al, 2021;Neville, 1977;Steinbrecht et al, 1985;Vukusic et al, 2009;Wilts et al, 2013), the necessity of a bilaminate airfilled nanostructure, the relative contributions of air gap layer versus upper and lower laminas, and the genetic circuits that create these broadband metallic reflectors in butterfly wing scales remain unclear despite a number of studies on silvery butterfly scales (Dolinko et al, 2021;Ren et al, 2020;Vukusic et al, 2009;Wilts et al, 2013).…”

Multilayer subwavelength gratings or sandwiches with periodic structure shape light reflection in the tapetum lucidum of taxonomically diverse vertebrate animals

“…Throughout their scientific history, studies of the reflective properties of vertebrate eye mirrors have relied heavily on diffraction principles. If conventional optical components control light using gradual phase accumulation through propagation in refractive materials, diffracting devices rely on local phase shifts induced by subwavelength‐scale optical components, in a field that is now termed “nano‐optics.” It has been reported that the reflection of light by fish scales, as well as reflection by butterfly wings, chameleon skin or cuttlefish, uses the same diffraction‐based principle [69–73]. Appreciation of the unconventionality of eye reflection came earlier.…”

Antennapedia and optix regulate metallic silver wing scale development and cell shape in Bicyclus anynana butterflies

“…This creates an undulatory air layer sandwiched by the lower and upper laminas whose thicknesses also vary spatially. Broadband reflectance is achieved by additive color mixing that occurs due to local spatial variation or disorder in the scale ultrastructure (10,21,23,24,26). The broadband metallic reflectors seen in fossil moths (23,27), in extant moths (22), and in springtails (28), however, utilize thin film interference from a single chitin layer, resulting from fused scales.…”

“…These examples suggest that the regulatory networks that create a metallic scale type must involve regulation of scale ultrastructure dimensions perhaps along with pigmentation. While the optical origin of broadband silvery colors from thin-film and chirped multi-layer reflectors in the arthropod integument is well understood (3,10,19,21,23,26), the necessity of a bilaminate air-filled nanostructure, the relative contributions of air gap layer vs upper and lower laminas, and the genetic circuits that create these broadband metallic reflectors in butterfly wing scales remain unclear, despite a number of studies on silvery butterfly scales (10,21,24,26) We have begun to explore the genetic basis of silver scale development with a series of CRISPR experiments performed in the nymphalid butterfly B. anynana. This species exhibits different subtypes of broadband reflecting metallic scales on both fore-and hindwings (34).…”