Reproductive cycles of male and female tuatara (Sphenodon punctatus) on Stephens Island, New Zealand

Abstract

Cycles in gonadal activity and plasma sex steroid concentrations were investigated in wild female and male tuatara on Stephens Island, New Zealand. Females nest once every four years on average. Vitellogenesis is spread over the first three years, and mating, ovulation and nesting occur in the fourth. Oviducal eggs are carried for6–8 months before nesting. Although the length of this ovarian cycle is unparalleled among oviparous reptiles, the associated cycles in plasma concentrations of sex steroids are similar to those in other reptiles. Mean plasma concentrations of oestradiol increase during vitellogenesis, peak at mating, fall rapidly before or around ovulation, are low during most of gravidity, and rise slightly during late gravidity‐nesting. Plasma concentrations of testosterone show a similarcycle. Mean plasma concentrations of progesterone are low during vitellogenesis and peak around ovulation. This periovulatory surge falls within1–2 months, and mean concentrations are low during the final 5–6 months of gravidity. Male tuatara show an annual, pre‐nuptial reproductive cycle. Mean plasma concentrations of testosterone are low during winter, rise during spring, peak during midsummer‐early autumn, when pre‐nuptial displays and mating occur, and fall in mid autumn. Limited histological data indicate that spermiogenesis occurs during midsummer‐early autumn, and also support a previous study suggesting that there may be no period of complete testicular and epididymal regression. In comparison with the pre‐nuptial cycles of other temperate‐zone reptiles, the cycle in male tuatara shows a more prolonged duration of testicular activity and of rising or elevated plasma testosterone concentrations. The prolonged reproductive cycles of male and female tuatara may be adaptations to a temperate environment with cool summers and cool, but not freezing, winters.

Identification of female tuatara in ovulatory condition using plasma sex steroid concentrations

“…We observed previously that it was not possible to distinguish gravid from nongravid females on the basis of plasma concentrations of oestradiol, progesterone, testosterone, calcium or total protein, or the presence or absence of plasma vitellogenin, during the month before nesting in spring (Cree et al 1991). However, we also observed that plasma concentrations of oestmdiol, progesterone, and testosterone were generally elevated in late summer-autumn around the time of mating and/or ovulation (Cree et al 1992). In the present study, we determined whether plasma concentrations of these sex hormones were significantly higher in late summer-autumn in females that ovulated that year than in those that did not.…”

“…The elevated levels of oestradiol and testosterone probably help stimulate mating behaviour, oviducal hypertrophy, and the completion of vitellogenesis, as reported for other reptiles (Yaron 1972;Botte 1974;McNicol & Crews 1979;Ho et al 1981;Licht 1984;Ho 1987). The elevation in progesterone is probably associated with P<0.OO1 1Hz = oestradiol, P = progesterone, T = testosterone 423 ovulation, which occurs between March and April within about a month of mating (Cree et al 1991(Cree et al , 1992. High plasma concentrations of progesterone are seen in other reptiles around ovulation and are associated with the formation of corpora lutea (van Wyk 1984;Xavier 1987).…”

“…In this population, mating occurs during January-March, ovulation between March and April, and nesting during OctoberDecember (Cree & Thompson 1988;Cree et al 1991Cree et al ,1992). Blood samples (1 ml) were obtained in a heparinised syringe from the tail within 3 h of capture.…”

“…The females were then released at their capture site. The results from blood sampling, X-mying, or laparoscopy of some females have also been used in other studies (Cree et al 1991(Cree et al , 1992. Although as mentioned above, neither X-mying nor laparoscopy is regarded as suitable for widespread use in tuatara, they were the only techniques available to us at the time to confirm the gravidity of females.…”

“…Thus, only those females caught in the process of nest construction can be assumed to be gravid. Radiography (Newman & Watson 1985) and laparoscopy (Cree et al 1990a(Cree et al , 1991(Cree et al , 1992 have been used to identify gravid female tuatara on Stephens Island (40040'E, 174°00'S), but these techniques are not ideal for widespread use on all tuatara populations.…”