Research on the Rana Frog Sexual Dichromatism: Natural Selection, Sexual Choice and Unexpected Diversity of Frogs

Sexual dichromatism is common in animals, a type of sexual dimorphism in which males and females vary in color, but it has been mainly studied in birds, fish and butterflies. Moreover, while there are many suggested evolutionary pathways for sexual dichromatism in vertebrates, few experiments have investigated this process outside the framework of sexual selection. The unusually high diversity of sexual dichromatism in frogs is defined here and a comparative context is developed to direct future studies of the evolution of these variations in sexual color. We discuss what is known about the evolution of color dimorphism in frogs, highlight alternate mechanisms that may lead to the evolution of variations in sexual color, and equate them with mechanisms that are involved in other large vertebrate classes. Sexual dichromatism can be complex in frogs (temporary change of color in males) or ontogenetic (permanent change of colour in males or females). The degree and length of variations in sexual color vary greatly between lines, and in the distribution of this feature we do not detect phylogenetic signal, so frogs offer an opportunity to explore the functions of natural and sexual selection across several separate derivations of sexual dichromatism.