Evolution of sexual dimorphism in semi-fossorial lizards: a case study with Ablepharus kitaibelii

Abstract

Sexual size dimorphism (SSD) in lizards is often explained through two main evolutionary strategies: fecundity selection in females reflected in differences in abdomen length (being bigger in females) and male–male competition reflected in differences in head and body size (greater in males). However, in lizards with fossorial lifestyles, sexual dimorphism is often lacking or reduced, likely due to the constraints imposed by burrowing. In the present study, we studied the sexual size and shape dimorphism in the small semi-fossorial skink Ablepharus kitaibelii. Our results show a significant size dimorphism with females being larger than males in all subspecies examined. Moreover, we found differences between sexes in both relative head and abdomen size reflecting both fecundity selection and male–male competition. Females have more elongate and wider abdomens, allowing them to carry up to 5 large eggs, whereas males have bigger heads likely related to male–male aggression and territoriality. Overall, our results suggest that despite the possible constraints imposed by burrowing, in semi-fossorial species, the SSD can evolve. Future studies on other semi-fossorial and fossorial species are needed to test the generality of these results.