Abstracts (first author)
Evolutionary pathways to convergence in plumage pattern phenotypes
Convergence in animal phenotypes is a central theme in evolution. Bird plumage patterns are an emerging model system due to the hierarchical nature of feather growth and spectacular within-feather pigmentation. Although birds are visually diverse, at the level of individual feathers there are just three major types of regularly repeating patterns: scales, bars and spots. Previous studies of avian pattern phenotypes have predominantly been adaptationist, focusing on camouflage and/or communication. In contrast, developmental constraint in plumage pattern convergence is relatively unexplored. A biologically realistic model of within-feather pattern formation (Prum & Williamson 2002) relies on a reaction-diffusion based mechanism. According to this model, scales require the least stringent regulation, bars require a higher rate of activation decay than scales, and spots require simultaneous spatial and temporal differentiation. Thus, development may constraint scales to evolve first, followed by bars and finally spots. Here, we use Bayesian phylogenetic modeling to reconstruct the evolutionary pathways to plumage pattern convergence, in the two avian clades with the most spectacular plumage patterns – waterfowl (Anseriformes – 118 species), and gamebirds (Galliformes – 170 species). Plumage pattern evolution was allowed to evolve independently in six feather tracts over the body, in each group separately. We found that for each tract, in both groups, scales predominantly evolve first, followed by barred and spotted plumage. Interestingly, we found that spotted plumage is more likely to evolve from scaled than barred plumage in gamebirds, but not in waterfowl. Together our results demonstrate directionality in plumage pattern evolution, providing support for developmental constraint that may be mediated by reaction-diffusion dynamics. These results underscore the importance of considering selection in the context of development in studies of phenotypic evolution.