Sexual size dimorphism in the lizard <i>Oplurus cuvieri cuvieri</i> (Squamata, Opluridae) from Madagascar

Abstract

Sexual size dimorphism in the medium-sized lizard Oplurus cuvieri cuvieri, which is endemic to the dry deciduous forest of Madagascar, is presented. Adults are  sexually dimorphic in body size, head size, and tail length. Males have a greater snout–vent length (SVL), head depth, head width, jaw length, tail length and body mass than females. Juvenile males have greater annual SVL growth rates than juvenile females, contributing to adult sexual size dimorphism. Moreover, the rates of increase in head depth and width differ significantly between the sexes after reaching maturity so that adult males have larger heads for a given body size than adult females. I suggest three proximate mechanisms that may cause sex-related differences in adult head size of O. c. cuvieri based on natural selection; to reduce intersexual food competition, sexual selection involving mate acquisition in males, and ontogenetic change of allometry to improve reproductive output in females.

Key words: sexual dimorphism, growth rates, lizards.