Sexual Dimorphism in the Limb Bones of Asiatic Toad (Bufo gargarizans) in Relation to Sexual Selection

SIMPLE SUMMARY: In this study, the sexual dimorphism of the limb bones of the Asiatic toad was investigated. Despite male toads having smaller body lengths than females, they possess longer upper arms, forearms, thighs, calves, and feet. Additionally, the humerus and radioulna bones of males are heavier compared to females, and the protrusions on the humerus and femur of males are longer and higher than females. However, female toads have significantly longer hands than males. These sexual differences in limb morphology are believed to be adaptations to specific reproductive behaviors. We propose that the sexual dimorphism in the limb morphology of the Asiatic toad may be attributed to amplexus and male–male competition during the long process of adaptive evolution. ABSTRACT: Sexual dimorphism is often considered to be the result of differences in the intensity of sexual selection between sexes. From this point of view, the sexual dimorphism of the limb bones of the Bufo gargarizans in southwest China was studied. Results showed that the fore- and hindlimb skeletons of this species were sexually dimorphic in anatomy. The humerus, radioulna, and total lengths of the forelimb skeleton of males were substantially longer than those of females, but the hand length of males was smaller than that of females. Several other features of males, such as deltoid and medial crest areas and humerus and radioulnar weights, were also significantly larger than those of females. The femoris, tibiofibula, talus–calcaneus, and foot lengths; total hindlimb skeleton length; and femoral upper crest areas of males were significantly greater than those of females. However, no significant intersexual difference in femoris and tibiofibular weights was observed. These findings suggested that robust forelimb bones and long hindlimb bones could contribute to the mating success of males; if so, sexual selection promotes the evolution of sexual size and shape dimorphism in the limb bones of the B. gargarizans.