Endocrinology of Oviposition in the Tuatara (Sphenodon Punctatus): I. Plasma Steroids and Prostaglandins during Natural Nesting12

Plasma concentrations of estradiol, progesterone, prostaglandin (PG) E2 and PGF were measured during three stages of the natural nesting cycle of the tuatara (Sphenodon punctatus), a rare New Zealand reptile. Specifically, we tested whether nesting activity in this species is correlated with significant modifications in plasma concentrations of these hormones. Tuatara dig a nest over a period of several nights, oviposit a complete clutch on a single night, and then guard that nest for several nights. We observed no significant changes in mean plasma concentrations of estradiol or progesterone among the different stages of nesting. In contrast, PGE2 was elevated during nest digging and oviposition but declined significantly during nest guarding. Plasma PGF was elevated during nest digging, rose significantly during oviposition, and declined to basal levels during nest guarding. These data indicate that oviposition in reptiles is associated with elevated plasma concentrations of PGs, suggesting that these hormones function in causing oviducal contractions and/or luteolysis. Moreover, these data suggest that the role of PGs in oviducal function may have been conserved throughout evolution of the amniote vertebrates.