Summary: Hugali & Stuart-Fox (2012)

Roulin (2004) defined a colour polymorphic species as one that possesses a colour trait that can be "easily classified into a limited number of morphs within one species suggesting a strong
genetic determinism." While colour polymorphism is widespread in a taxonomic sense, it is considered rare (occurring in only 3.5% of bird species for example). Hugali & Stuart-Fox (2012) suggested that the processes that generate and maintain colour polymorphism might also promote speciation. They found that colour polymorphism in three families of non-passerine bird species is linked to faster speciation rates. They also noted that rate of loss of colour polymorphism is much higher than the rate of gain. Hugali & Stuart-Fox (2012) suggest that the rarity of colour polymorphism, and its phylogenetic dispersion, is a result of an interaction between this higher rate of speciation and a greater transition rate between morphic types (poly- to monomorphism). Their results provide support for the general proposition that increased speciation rates can result from colour polymorphism.