Sexual dimorphism in Scutiger boulengeri, an endemic toad from the Tibetan Plateau

Abstract

The evolution of sexual dimorphism has long fascinated evolutionary biologists and theory suggests that variation in sexual dimorphism is a consequence of selective forces acting differently on morphological traits in males versus females. Here, we analyzed sexual differences in size and shape of the Boulenger’s lazy toad, Scutiger boulengeri, based on the intersex variation pattern of sixteen morphometric traits including body size. The results suggested that sexual dimorphism was apparent in body size and some body shapes (e.g., head length and width, internasal space, interorbital space, diameter of lower arm and tibia width) of this toad. The bigger body size in females may be relevant to fecundity selection, a larger head in males as well as a broader internasal and interorbital space may be subject to male-male competition in combination with ecological selection, and both robust forelimbs and hindlimbs in males may be related to mating and competitive behaviors. These results are discussed with respect to the above selection procedures and possible sex differences in life history traits.