Sex determination. Viviparous lizard selects sex of embryos.

No one suspected that temperature-dependent sex determination (TSD), whereby the sex of embryos depends on the temperature at which they develop, might occur in viviparous (live-bearing) reptiles, because thermoregulation in the mother results in relatively stable, raised gestation temperatures. But here we show that developing embryos of the actively thermoregulating viviparous skink Eulamprus tympanum are subject to TSD, offering the mother the chance to select the sex of her offspring and a mechanism to help to balance sex ratios in wild populations.