Meeting Abstract
Iridescent bird coloration produces some of the most spectacular color displays in the natural world, yet much of how these colors evolve remains enigmatic. Birds often produce iridescence in their feathers by layering pigment-filled organelles (melanosomes) and keratin in the feather filaments, effectively creating a photonic crystal that reflects only certain colors of light. Typically, melanosomes are solid and cylindrical, but in some iridescent species novel types of melanosomes have evolved, including hollow (air-filled) and flattened morphologies. These derived morphologies have evolved independently multiple times in birds, and likely affect color production. Yet, the interplay between nanostructural diversity and color diversity has never been tested on a large scale. Here, we test the hypothesis that novel melanosome morphologies allow birds to produce a greater diversity of colors. We collected spectral data on 72 iridescent bird species spanning 11 orders and encompassing all types of melanosome morphologies. We combined these empirical data with an optical modelling approach to estimate what colors could theoretically be produced with each morphology, varying a range of optically important parameters. Our results show that birds with derived melanosome morphologies tend to produce brighter and more saturated colors than birds with solid cylindrical melanosomes, which results in a greater possible color diversity. The main evolutionary forces driving the repeated evolution of derived melanosome morphologies might therefore be related to a paired brightness and saturation advantage, compared to the ancestral form.
