Sexual dimorphism in the Moorish gecko (Tarentola mauritanica, Gekkota, Phyllodactylidae): body size and head shape characteristics

Two main adaptive hypotheses are invoked for the evolution of SD: sexual selection and natural selection. In snakes SD is generally interpreted as the adaptation of the two sexes to different ecological niches, whereas in lizards sexual and ecological causes may work simultaneously, with different outcomes according to taxonomic group. Surprisingly, geckos have been almost ignored in the general debate over the evolution of SD, despite their being an extremely diversified taxon with over 1300 species showing a wide range of variability in SD. The Moorish gecko is one of those species whose dimorphism is poorly studied. We took an integrated approach using a linear (biometrical) analysis on head and body size of 157 geckos and a relatively new analytical approach (geometric morphometry) to assess head size of 38 geckos from central Italy. Males were, on average, larger and heavier than females, and body size relationships differed between age classes showing a significant SD between sexes. When controlling for snout to vent length, sexes differed only in body mass and eye diameter (larger in males). Head shape, on the contrary, showed differences according to age classes, with deep differences in hatchlings compared to adults and, among adults, between sexes. However, the growth trajectories did not differ among sexes, and SD of head shape is probably due to a more prolonged growth of the males with respect to the females. The male-biased pattern of SD in this species is most parsimoniously interpreted as the result of sexual selection, whereby larger head and body size probably confer a greater advantage to males during combats and courtship, rather than conferring independent adaptations to different ecological pressures to each sex.