Prenatal sex ratios influence sexual dimorphism in a reptile.

The prenatal environment influences offspring traits in a variety of ways and in a wide range of taxa. For example, maternal allocation of steroids to the eggs influences offspring traits in birds, and in some mammals the intrauterine position influences morphological, behavioural, and physiological traits due to sex-related steroid transfer between sibling fetuses. We show that similar phenomena occur in the common lizard (Lacerta vivipara), a viviparous reptile. Females developing in male-biased clutches had a more masculine allometry (relatively larger heads) at parturition than females developing in female-biased clutches. Males were correspondingly feminized in female-biased clutches. The effects could either be due to diffusion of steroids produced by the offspring or by a general tendency for females to allocate steroids according to the sex ratio of her clutch. Subsequent to parturition, the sexes differed in their growth trajectories depending on sex ratio environment. In males, the difference in allometry between sex ratio environments remained over time, whereas in females the corresponding effect disappeared