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First published online January 31, 2006
Journal of Experimental Biology 209, 748-765 (2006)
Published by The Company of Biologists 2006
doi: 10.1242/jeb.02051
Anatomically diverse butterfly scales all produce structural colours by coherent scattering
1 Department of Ecology and Evolutionary Biology, and Peabody Museum of
Natural History, Yale University, PO Box 208105, New Haven, Connecticut 06250,
USA
2 Department of Ecology and Evolutionary Biology, University of Kansas,
Lawrence, KS 66045, USA
3 Department of Mathematics, University of Kansas, Lawrence, KS 66045,
USA
* Author for correspondence (e-mail: richard.prum{at}yale.edu)
Accepted 20 December 2005
The structural colours of butterflies and moths (Lepidoptera) have been attributed to a diversity of physical mechanisms, including multilayer interference, diffraction, Bragg scattering, Tyndall scattering and Rayleigh scattering. We used fibre optic spectrophotometry, transmission electron microscopy (TEM) and 2D Fourier analysis to investigate the physical mechanisms of structural colour production in twelve lepidopteran species from four families, representing all of the previously proposed anatomical and optical classes of butterfly nanostructure. The 2D Fourier analyses of TEMs of colour producing butterfly scales document that all species are appropriately nanostructured to produce visible colours by coherent scattering, i.e. differential interference and reinforcement of scattered, visible wavelengths. Previously hypothesized to produce a blue colour by incoherent, Tyndall scattering, the scales of Papilio zalmoxis are not appropriately nanostructured for incoherent scattering. Rather, available data indicate that the blue of P. zalmoxis is a fluorescent pigmentary colour. Despite their nanoscale anatomical diversity, all structurally coloured butterfly scales share a single fundamental physical color production mechanism - coherent scattering. Recognition of this commonality provides a new perspective on how the nanostructure and optical properties of structurally coloured butterfly scales evolved and diversified among and within lepidopteran clades.
Key words: coherent scattering, structural colours, Fourier analysis, photonics, Lepidoptera, Callophrys, Celastrina, Morpho, Mitoura, Papilio, Parides, Parrhasius, Troides, Urania