Phylogenies and Physiological Processes—The Evolution of Sexual Dimorphism in Southeast Asian Frogs

Abstract

There are a number of species of Southeast Asian Rana that are characterized by an unusual suite of sexually dimorphic features and derived reproductive modes. These frogs lack the usual secondary sexual characteristics of ranid frogs: nuptial pads, vocal sacs, and enlarged flexor muscles. Secondary sexual characteristics in frogs are under androgenic control. Phyloge- netic analyses using morphological and molecular data indicate that a drop in androgen level and/or a shift in androgen sensitivity may have been involved in the evolution of male parental care and the loss of the common suite of secondary sexual characteristics in these Asian frogs. Phylogenetic analyses also provide important information on experimental design by indicating the most appropriate taxa to use in the exploration of physiological processes controlling the expression of sexual dimorphism. This work is an example of how emergent properties from phylogenetic analyses can be used to formulate and test hypotheses of process and pattern of evolutionary change. (Frog; Rana; hormone; sexual dimorphism; parental care.)