Hereditary Character of Photonics Structure in Pachyrhynchus sarcitis Weevils: Color Changes via One Generation Hybridization

Abstract

Pachyrhynchus sarcitis weevils are flightless weevils characterized by colored patches of scales on their dark elytra. The vivid colors of such patches result from the reflection of differently oriented 3D photonic crystals within their scales. The results show that hybrid P. sarcitis, the first filial generation of two P. sarcitis populations from Lanyu Island (Taiwan) and Babuyan Island (Philippines), mixes the color of its ancestors by tuning the photonic structure in its scales. A careful spectroscopical and anatomical analysis of the weevils in the phylogeny reveals the hereditary characteristics of the photonic crystals within their scales in terms of lattice constant, orientation and domain size. Monitoring how structural coloration is inherited by offspring highlights the versatility of photonic structures to completely redesign the optical response of living organisms. Such finding sheds light onto the evolution and development mechanisms of structural coloration in Pachyrhynchus weevils and provides inspiration for the design of visual appearance in artificial photonic materials.

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

“…Polycrystalline diamonds are common in beetles scales and have been observed through a wide range of species to generate various colors (8,9,23,34). In particular, these results are consistent with previous work on Pachyrhynchus weevil scales, where the structure within these scales was identified as a single-diamond network of chitin and air (30,31). The main parameters that influence the observed color of biological 3DPCs are (i) its local orientation, (ii) its lattice parameter and (iii) its solid filling fraction (13,30).…”

“…In this work, we examine the full 3D structure in the elytral scales of the Pachyrhynchus congestus mirabilis weevil and link it to the optical appearance of the scales. Previous work on Pachyrhynchus weevils has discussed either single colored spots or rainbow-colored spots on jet-black elytra (9,30,31). These studies found an ordered single-network diamond structure (space group F d 3m) in their scales (30,31), with color variations resulting from changes in the lattice constant, chitin filling fraction and/or domain orientation.…”

“…Previous work on Pachyrhynchus weevils has discussed either single colored spots or rainbow-colored spots on jet-black elytra (9,30,31). These studies found an ordered single-network diamond structure (space group F d 3m) in their scales (30,31), with color variations resulting from changes in the lattice constant, chitin filling fraction and/or domain orientation. Through FIB-SEM 3D reconstructions of the photonic networks within the wing scales of P. c. mirabilis and by using a novel Pt-based deposition technique, this study demonstrates the origin of color from ordered and seemingly amorphous PC structures.…”

Light in correlated disordered media

“…(c) Pachyrhynchus sarcitis Weevils, the blue colored spot in the weevil exoskeleton are the results of a polydomain diamond photonic structures, shown in the SEM image on (d). Adapted with permission from (Chang et al, 2020). (e) Kingfisher, the angular independent blue coloration of the bird feather is the result of a correlated 3D structure, which is shown in the SEM image in (f).…”

“…In these cases, polydomains provide a more angular independent response which might again be functional for signalling and camouflaging (Michielsen and Stavenga, 2007). Examples are the diamond-like structures observed inside the scales of the weevils Lamprocyphus augustus (Galusha et al, 2008) and Entimus imperialis (Wilts et al, 2012) and Pachyrhynchus weevils (Chang et al, 2020). Similarly, gyroid structures are found in many lycaenid and papilionid butterflies by (Michielsen and Stavenga, 2007) and in various species such as C. rubi (Michielsen et al, 2009;Schröder-Turk et al, 2011), C. remus, P. sesostris (Wilts et al, 2011), and T. opisena (Wilts et al, 2017).…”