Selection of the intrinsic polarization properties of animal optical materials creates enhanced structural reflectivity and camouflage

Abstract

Many animals use structural coloration to create bright and conspicuous visual signals. Selection of the size and shape of the optical structures animals use defines both the colour and intensity of the light reflected. The material used to create these reflectors is also important; however, animals are restricted to a limited number of materials: commonly chitin, guanine and the protein, reflectin. In this work we highlight that a particular set of material properties can also be under selection in order to increase the optical functionality of structural reflectors. Specifically, polarization properties, such as birefringence (the difference between the refractive indices of a material) and chirality (which relates to molecular asymmetry) are both under selection to create enhanced structural reflectivity. We demonstrate that the structural coloration of the gold beetle Chrysina resplendens and silvery reflective sides of the Atlantic herring, Clupea harengus are two examples of this phenomenon. Importantly, these polarization properties are not selected to control the polarization of the reflected light as a source of visual information per se. Instead, by creating higher levels of reflectivity than are otherwise possible, such internal polarization properties improve intensity-matching camouflage.This article is part of the themed issue ‘Animal coloration: production, perception, function and application’.

The current and future state of animal coloration research

“…There are now large numbers of papers on reflectance spectra, including humans [10,11]. New discoveries in animal communication have led to work on fluorescence [12] and polarization [13][14][15], which can significantly enhance simultaneous communication and camouflage. Also expanding is work on colour change [16], and relationships among coloration, colour change and thermoregulation [17,18].…”

Mathematical modeling of the protective coloration of animals with usage of parameters of diversity and evenness

“…A certain statement conrmed in (Endler and Mappes, 2017;Johnsen et al, 2014;Marshall and Johnsen, 2017;Feller et al, 2017;Lind et al, 2017;Shawkey and D'Alba, 2017;San-Jose and Roulin, 2017;Merilaita et al, 2017;Duarte et al, 2017;Nothdurft, 2018) appears to be well-grounded. It means the following.…”

“…In the work (Feller et al, 2017), the authors present the results of using neural networks for the study of the performance of the protective coloration of animals. In this work, it is noted that in the case of usage of neural networks the requirements for the initial data are not so strict as for Big Data, but still quite serious.…”

“…The mechanisms that marine animals use for masking bioluminescence and polarization of light are described in (Marshall and Johnsen, 2017;Feller et al, 2017).…”

Anderson localization and Brewster anomaly of electromagnetic waves in randomly-stratified anisotropic media

“…We focus especially on the unique phenomenon called Brewster anomaly (BA), which is the delocalization of p-polarized electromagnetic waves in randomly-stratified media at a special incident angle [9,10,11,12,13,14,15]. Understanding the mechanism of this phenomenon in anisotropic media, which can be encountered frequently among both naturally-occurring media and fabricated metamaterials, is crucial in the development of polarization-insensitive reflectors and polarization-sensitive optical devices, as well as in understanding some bio-optical properties [16,17,18,19,20,21,22,23].…”