PRUM, Richard O. ; University of Kansas: Phylogenetic Fourier Analyses of the Biophysics and Evolution of Avian Structural Colors

The nanostructures that produce the structural colors used in intersexual communication signals provide a fascinating insight into the evolutionary consequences of visual mate preferences. There are three physical classes of coherently scattering color producing arrays: laminar, crystal-like, and quasi-ordered. Traditionally, color production by laminar and crystal-like arrays was analyzed by thin film optics and Bragg’s Law, respectively. We have developed a new Fourier analysis method to analyze coherent scattering by quasi-ordered arrays. This Fourier tool provides accurate predictions of the shape of the reflectance spectrum and iridescence (i.e. changes in hue with angle of observation) from all three classes of structurally colored tissues. Comparative phylogenetic analyses of structurally colored avian tissues documents evolutionary transitions among the three classes of spatial organization in structurally colored bird feathers and skin: e.g. quasi-ordered to crystal-like. The Fourier method constitutes the first available method to investigate evolution among nanostructure classes and optical function within clades. Combined with phylogenetic hypotheses, the Fourier method permits us to investigate the evolution of structural color and nanostructure as a consequence of intersexual selection through female visual preferences within clades of polygynous birds.