Absence of daily cycles in plasma sex steroids in male and female tuatara ( Sphenodon punctatus), and the effects of acute capture stress on females

Abstract

The possible existence of daily cycles in plasma concentrations of sex steroids was examined in wild male and female tuatara ( Sphenodon punctatus). Samples were collected from freshly captured animals at dusk, middle of the night, dawn, and middle of the day in January (summer) and July (winter). Males showed daily cycles in mean body temperature ( T b) in both seasons but no daily cycle in mean plasma testosterone concentration in either season. Vitellogenic female tuatara in January and females in mixed reproductive condition in July also showed significant daily variation in T b. However, there were no daily cycles in mean plasma concentrations of estradiol, testosterone, or progesterone in either group of females. Vitellogenic female tuatara subjected to an acute capture stress (3-hr confinement) in January had mean plasma concentrations of estradiol and testosterone that did not differ from those of free-roaming females. However, progesterone and T b were significantly higher in captives than in free-roaming females. The elevation in progesterone may result from physical confinement, the difference in T b, or both. These data suggest that seasonal fluctuations in circulating concentrations of plasma sex steroids in tuatara can be determined using samples collected at different times of the 24-hr cycle. However, the effects of acute capture stress and/or changes in T b on plasma progesterone concentrations need to be considered in future studies on this and possibly other female reptiles.