Plasma levels of estradiol during vitellogenesis and early gestation in oviparous and viviparous Lacerta (Zootoca) vivipara

Abstract

The evolution of viviparity in lizards and snakes is always associated with a reduction of the eggshell membrane. There is strong evidence indicating that estradiol is the primary factor involved in seasonal development of the uterine glands in preparation for eggshelling. However, the hypothesis that the thinner eggshells of viviparous species could be the consequence of lower pre-ovulatory levels of circulating estradiol has not been tested. In a previous histological study we showed that the pre-ovulatory growth of the uterine shell glands is significantly more pronounced in oviparous than in viviparous females of the lizard Lacerta (Zootoca) vivipara. During the current study we assayed plasma levels of estradiol before and during vitellogenesis and during early gestation. We did not find any significant difference of estradiol concentrations between oviparous and viviparous females. In both reproductive forms the plasma estradiol concentration was significantly higher during late vitellogenesis than during early gestation. Future research should address whether variation in the growth of the uterine shell glands could be predominantly mediated by modification affecting estrogen receptors of the uterus rather than by concentration of the circulating hormone. © 2008 Brill Academic Publishers.