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.