COMPETING EXPLANATIONS FOR SEXUAL DIMORPHISM IN A VOICELESS BORNEAN FROG

1. An unusual suite of sexually dimorphic features characterizing the voiceless Bornean frog, Rana blythi, could be the product of sexual selection or intraspecific niche dimorphism. 2. Males have enlarged heads, hypertrophied jaw muscles and bony processes or fangs in the lower jaw. Males are also larger than females. 3. Alternative explanations for the sexual dimorphism are explored by testing the predictions of a biomechanical model for trophic specialization and mapping the historical transformation of the sexually dimorphic characters on a phylogeny of voiceless frogs and their relatives. 4. The results of this analysis indicate that the unusual morphology is most likely the result of sexual selection. 5. The incorporation of approaches from functional morphology considerably strengthens our ability to discriminate between alternative hypotheses for the origin of sexually dimorphic characters.