Meeting Abstract

83.3  Sunday, Jan. 6  Optics and evolution of iridescence in the wings of ducks ELIASON, C.M.*; MAIA, R.; SHAWKEY, M.D.; University of Akron; University of Akron; University of Akron cme16@zips.uakron.edu

The colors of birds are diverse but limited relative to what they can perceive. This mismatch may be partially caused by the properties of their color-producing mechanisms. Aside from pigments, several classes of highly ordered nanostructures (e.g., thin films, multilayers, photonic crystals) can produce a range of colors. However, the variability of any single nanostructural class has rarely been explored. Dabbling ducks are a speciose clade with substantial interspecific variation in the iridescent coloration of their wing patches (specula). We used electron microscopy, spectrophotometry, refractive index-matching experiments, optical modeling and phylogenetic comparative methods to investigate the mechanism and evolution of these colors. We show that color is produced by a complex nanostructure consisting of a thin film of keratin and hexagonally arranged melanin rods (melanosomes) within feather barbules. Although the range of potential variation of this nanostructure is theoretically broad, only relatively close-packed, energetically stable variants producing more saturated colors were observed, suggesting that ducks are either physically constrained to these configurations or are under selection for the colors that they produce. Thus, we further tested how functionally independent components of this nanostructure evolve within this limited region of morphospace and found that melanosome diameter and spacing evolve at different rates, but species explore available morphospace uniformly. Taken together, these results reveal a previously undescribed color-producing nanostructure and suggest that both physical variability and constraints within single nanostructural classes may help explain the broader patterns of color across Aves.