Yolk hormone levels in the synchronously developing eggs ofParoedura picta, a gecko with genetic sex determination

Sex steroid hormones of presumably maternal origin have been found in yolk of many oviparous vertebrates. Their effects on behavioural or physiological traits are well documented in birds, but until now are largely unknown in reptiles. The investigations of yolk steroids in reptiles have been focused mainly on species with temperature-dependent sex determination, where steroid levels are suggested to determine the sex of progeny. Here we report initial oestradiol (E2) and testosterone (T) levels in the yolk of the Madagascar ground gecko, Paroedura picta (Peters, 1854), a species with genetic sex determination. The yolk concentration was 0.39 ± 0.02 ng/g (mean ± SE) in E2, whereas the concentration of T was much higher (1.48 ± 0.06 ng/g, mean ± SE). Geckos usually lay two exceptionally large eggs per clutch; vitellogenesis and ovulation of both eggs proceed in phase. Individual two-egg clutches differed considerably in E2 and T levels. A clutch mean of E2 levels varied from 0.22 to 0.53 ng/g, whereas T levels varied from a clutch mean of 1.02 to 1.99 ng/g. Both eggs in a clutch possessed very similar levels of E2 and T. Initial yolk steroid levels thus presumably reflect maternal conditions during egg formation rather than differential allocation of hormones according to offspring sex.