The evolution of iridescent plumage in the Galliformes: Proximate mechanisms and ultimate functions

Iridescence is a specialized type of structural colouration that produces some of the most spectacular visual displays found in animals. However, the proximate mechanisms and ultimate functions that shape the evolution of iridescent colouration remain poorly studied. The Galliformes comprise a diverse order of birds with multiple sexually dimorphic traits thought to have evolved by sexual selection. Using a phylogenetic approach, I model the evolution of iridescent plumage and its corresponding barbule nanostructures in Galliformes. I show that nanostructural innovations have allowed iridescent colouration to evolve multiple times in Galliformes, allowing them to produce a much broader range of colours. I also show that visually modelled spectral dichromatism and size dimorphism are related to mating system and paternal care in this group. My research suggests that iridescence is a highly labile trait that is likely influenced by a complex combination of selective pressures.