Sexual Selection and Sexual Dimorphism in the Amphibia

Abstract

Published literature on amphibians is reviewed to examine predicted correlations between male combat and sexual dimorphism. Females grow larger than males in most species (61% of urodeles, 90% of anurans); males are often larger than females in species in which males engage in physical combat with each other. Although amphibian male combat has been reported only rarely (in 19% of urodeles and 5% of anurans), the association between male combat and male body size equal to or larger than female body size is highly significant within the urodele suborders Salamandroidea (n = 25 spp.) and Ambystomatoidea (n = 46), in the urodeles as a whole (n = 79), in the anuran Dendrobatidae (n = 34) and Ranidae (n = 149) and in the anurans as a whole (n = 589). Large male size and the occurrence of male combat are highly correlated in a comparison between several anuran families. Spines and tusks of male anurans may be adaptations to male combat. Combat, large male size and sexually dimorphic weapons appear to be most common in species that are relatively invulnerable to predation while fighting, by virtue of large body size or toxic skin secretions.