Data and code from: Evolution of brilliant iridescent feather nanostructures

The brilliant iridescent plumage of birds creates some of the most
stunning color displays known in the natural world. Iridescent plumage
colors are produced by nanostructures in feathers and have evolved in a
wide variety of birds. The building blocks of these structures—melanosomes
(melanin-filled organelles)—come in a variety of forms, yet how these
different forms contribute to color production across birds remains
unclear. Here, we leverage evolutionary analyses, optical simulations and
reflectance spectrophotometry to uncover general principles that govern
the production of brilliant iridescence. We find that a key feature that
unites all melanosome forms in brilliant iridescent structures is thin
melanin layers. Birds have achieved this in multiple ways: by decreasing
the size of the melanosome directly, by hollowing out the interior, or by
flattening the melanosome into a platelet. The evolution of thin melanin
layers unlocks color-producing possibilities, more than doubling the range
of colors that can be produced with a thick melanin layer and
simultaneously increasing brightness. We discuss the implications of these
findings for the evolution of iridescent structures in birds and propose
two evolutionary paths to brilliant iridescence.