Check out this recent and extremely interesting paper by Andrew Hugall and Devi Stuart-Fox just published in Nature! In it, Andrew and Devi use species-level molecular phylogenies from five families of non-passerine birds (i.e. falcons, owls, nightjars, accipitrids and pheasants) to show that colour polymorphism is associated with accelerated speciation rates in the three groups where colour-polymorphism is more prevalent. Their study included more than 700 hundred taxa, which is very impressive! Finally, they corroborated the generality of their finding using a species-level molecular phylogeny of passerines (the largest order of birds including more than half of all bird species), incorporating 4,128 (66.5%) extant species, to show that polymorphic species tend to be younger than monomorphic species. Their article provides definitive empirical proof for the idea that where colour polymorphism does occur, processes generating and maintaining it can promote speciation, and is bound to become a citation classic!
