Asynchronous Male and Female Gonadal Cycles and Plasma Steroid Concentrations in a Viviparous Lizard,Niveoscincus ocellatus(Scincidae), from Tasmania

Abstract

The reproductive cycle in males of the skink,Niveoscincus ocellatus,is characterised by testicular development during summer, followed by mating in autumn. Plasma testosterone concentrations show a bimodal seasonal cycle, with the major peak (18.6±1.2 ng/ml) in late summer/autumn and a minor peak (7.4±1.0 ng/ml) at spring emergence. In contrast to the males, the females have a gonadal cycle in which mating is temporally dissociated from peak development of the gonads: ovulation occurs in spring and the young are born in summer. Fresh mating marks on females in spring indicate that at least part of the population mates for a second time after spring emergence. In females, plasma estradiol concentrations are significantly elevated (956±214 pg/ml) through vitellogenesis and are highest (1241±175 pg/ml) during the preovulatory phase. Plasma progesterone concentrations rise during gestation to 6.5 ± 1.5 ng/ml, but fall in the final stage of gestation to 1.6 ± 0.2 ng/ml. There is minimal atresia of vitellogenic follicles, suggesting that clutch size is determined when the follicles are recruited for vitellogenesis.