Sexual size dimorphism in amphibians: an overview

Abstract This chapter reviews patterns of sexual dimorphism in amphibians and discusses their proximal causes and possible adaptive significance. Amphibians are diverse organisms that live in aquatic or terrestrial ecosystems. Female-biased sexual size dimorphism (SSD) is the common pattern in frogs and salamanders, and male-biased SSD is only present in few lineages. Preliminary SSD data for caecilians indicate that many are monomorphic in body size, while others exhibit female-biased dimorphism. The typical female-biased SSD may be partly explained by sex-specific growth trajectories and delayed maturity of females. Male-biased SSD is associated with sexual selection for large males through territoriality and male-male combat. In comparison with other vertebrates, our understanding of SSD in amphibians is still incomplete. Phylogenetic comparative analyses are needed to describe more fully the evolutionary patterns of amphibian SSD and to test hypotheses based on fecundity and sexual selection, life history theory, and ecological divergence.