| Symposium proposal | |
| Organizer: | Dr. Cédric Finet (National University of Singapore) |
| Structural coloration, as opposed to pigment coloration, is the production of color by selective light scattering, either incoherent or coherent, by integumentary nanostructures. In animals, famous vivid examples are for instance the metallic blue color on butterfly wings and the iridescent colors of peacock tail feathers. But these few examples should not hide the huge diversity of structural color and associated biophotonic structures across animals. Over the last decade, structural coloration has drawn the attention of a broad range of scientists, leading to the emergence of a new field of investigation in itself. On the one hand, biophysical studies have produced a wealth of data describing the nanostructures and physics involved in their coloration. On the other hand, evolutionary studies have aimed at unraveling the biological function(s) of structural colors, as well as at identifying how the biophotonic structures are produced during development. Last, engineers are interested in such natural structures with optical properties to develop bio-inspired new materials. | |
S17-1
Physics, fossils, and color evolution in birds
Chad M Eliason1
1Field Museum
Color is a striking features of birds, varying not only in spectral properties like hue and brightness, but also in where and how it is produced on the body. Although the fitness benefits of color in terms of display or crypsis play a clear role in shaping color diversity among bird species, understanding color mechanisms might be crucial for predicting response to selection. Recent advances in computational techniques have enabled rigorous examination of color mechanisms in nature. I will discuss the diversity of color mechanisms in birds, examine interactions between physical processes and macroevolutionary patterns of color diversity, and then review analytical approaches for tackling longstanding questions within animal communication. I will demonstrate that variation in color mechanisms influences rates of color evolution, both among species and across the body, and emphasize a key role for physics in addressing fundamental questions within animal communication. I will incorporate these ideas in a multivariate comparative and paleontological framework, highlighting the interplay between proximate and ultimate causes of color evolution in birds.
S17-2
Wing transparency in butterflies and moths: from structural diversity to ecological relevance
Doris Gomez1, Marianne Elias2, Christine Andraud6, Serge Berthier3, Monica Arias1, Charline Pinna2, Jonathan Pairraire3, Willy Daney de Marcillac3, Aaron Pomerantz5, Nipam Patel4
1CEFE, Univ Montpellier, CNRS, EPHE, IRD, Montpellier, France
2ISYEB, UMR 7205, CNRS, MNHN, Sorbonne University, EPHE, France
3INSP, Sorbonne University, CNRS, Paris, France
4Marine Biological Laboratory, Woods Hole, Massachusetts, USA
5Department Integrative Biology, University of California Berkeley, Berkeley, USA
6CRC, MNHN, Paris, France
2ISYEB, UMR 7205, CNRS, MNHN, Sorbonne University, EPHE, France
3INSP, Sorbonne University, CNRS, Paris, France
4Marine Biological Laboratory, Woods Hole, Massachusetts, USA
5Department Integrative Biology, University of California Berkeley, Berkeley, USA
6CRC, MNHN, Paris, France
Butterflies and moths represent an outstanding group to investigate transparency on land, as species typically harbour opaque wings covered with coloured scales, a key multifunctional innovation. Yet, many Lepidoptera species have evolved partially or fully transparent wings. At the interface between physics and biology, the present study investigates wing transparency in 123 Lepidoptera species (from 31 families) for its structural basis, optical properties and biological relevance in relation to visual detection (concealment), hydrophobicity, thermoregulation, and protection against UV. Our results suggest that transparency has likely evolved multiple times independently. Efficiency at transmitting light is largely determined by clear wing macrostructure and microstructure (scale shape, insertion, colouration, dimensions and density). Transparency appears highly relevant for concealment, and its variation with latitude are consistent with a potential role in thermoregulation but not for UV protection. Altogether, our results shed new light on the physical and ecological processes driving the evolution of transparency on land and underline that transparency is a more complex colouration strategy than previously thought.
S17-3
The evolution of iridescent structural colour in Heliconius butterflies
Nicola Nadeau1, Andrew Parnell1, Emma Curran1, Melanie Brien1, Victoria Lloyd1, Juan Enciso Romero1
1The University of Sheffield
Some of the brightest and most striking colours found in nature are produced not by pigments but through coherent scattering of light by nano-scale structures. Despite the importance of these colours for animal and plant signalling and communication, and their application in man-made products, very little is known about their developmental control in natural systems. We are using genetically controlled within-species variation in iridescent blue structural colour in the Heliconius butterflies in order to study the genetic and developmental basis of these colours. Populations of the co-mimetic butterflies H. erato and H. melpomene on the Western slope of the Andes in Ecuador and Colombia have an iridescent blue colour that is absent from all other populations of these species. Using a combination of genetic mapping, differential gene expression analyses and fluorescence imaging through development, we are beginning to understand the genetic mechanisms controlling structural colour formation.
S17-4
A proposed gene regulatory network controlling metallic wing scale development in Bicyclus anynana butterflies
Anupama Prakash1, Cedric Finet1, Vinodkumar Saranathan1,2, Antonia Monteiro1,2
1National University of Singapore
2Yale-NUS College, Singapore
2Yale-NUS College, Singapore
Butterfly wing scales are the pointillistic sources of color on the wings that can produce structural colors via nano-morphologies. Silver and gold broadband metallic reflections are a category of structural colors produced by ultrastructural modifications of the scales to induce spatial color mixing. To address the yet unexplored genetic basis of metallic scale development, we leveraged existing crispants in the butterfly Bicyclus anynana, where knockouts of five genes – apterous A (apA), Ultrabithorax (Ubx), doublesex (dsx), Antennapedia (Antp) and optix – showed mosaic ectopic silver scale development or loss of silver reflectances. We characterized five silver scale types across the fore- and hindwings of wildtype and, the ectopic silver or brown scales from the crispants using scanning electron microscopy (SEM), focused ion beam SEM (FIB-SEM), theoretical modeling and microspectrophotometry (MSP). All silver reflectors in wildtype exhibited the most common scale ultrastructural modification for metallic reflectance, i.e., an undulatory thin-film created by the lower lamina and a closed upper lamina enclosing a variable air gap layer. Different amounts of pigmentation modulated the intensity of broadband reflectance. Ectopic silver scales resembled wildtype silver scales via the gain of a non-perforated upper lamina, reduced lower lamina thickness and reduced pigmentation. The reverse was seen when silver scales became brown. On the forewings, Antp was identified as the top selector gene for silver scale development, while its absence on the hindwing suggests that hindwing metallic scale development is regulated by a different gene regulatory network (GRN). Based on the results we propose a GRN for fore- and hindwing metallic scales in B. anynana.
S17-5
Structural colors in jewel beetles: analytical methods, tools, and future directions
Nathan P. Lord1, Hannah I. Weller2
1Dept. of Entomology, LSU AgCenter, Louisiana State University
2Dept. of Ecology and Evolutionary Biology, Brown University
2Dept. of Ecology and Evolutionary Biology, Brown University
Throughout the animal kingdom, color and pattern are known to play a major role in natural history, behavior, and evolution of numerous species and lineages. Structural color is also well understood, however the biological utility of some forms, particularly iridescence, are still debated. Amongst the speciose insects, the jewel beetles (Coleoptera: Buprestidae) are exceptions in not only their diversity (~15,000 spp.), but in their predominantly iridescent coloration. This research focuses on 1) the color production mechanisms from an ultrastructural to organismal level (e.g., TEM, SEM, digital imaging), 2) the signals produced (e.g., pattern, reflectance, scattering, and 3) the potential for biological utility (e.g., visual system sensitivity, signal (dis)similarity). Here we demonstrate current methods and tools being used to understand these elements, including workflows for color-accurate digital imaging and spectral analyses and the utilization of unsupervised machine learning for analyzing perceptual similarity. In addition to analytical pipelines, we introduce the Insect Color Database (ICDB), an online web portal for color data storage and analysis. These components are serving as the foundation for color studies that relate to optical physics, taxonomy and systematics, visual ecology, and evolutionary biology.
