IDENTIFICATION OF FEMALE TUATARA IN OVULATORY CONDITION USING PLASMA SEX STEROID CONCENTRATIONS

Female tuatara (Sphenodon punctatus) are long-lived reptiles that do not nest each year. Identification of gravid females (those carrying oviducal eggs) has in the past been achieved only with radiography or laparoscopy. Both techniques require considerable equipment and/or operator skill, and both pose an unquantified degree of risk to tuatara. For these reasons, we sought to develop a blood test for identifying females destined to nest in a given year. We observed that on Stephens Island, New Zealand, those females that nested in a given year had significantly higher plasma concentrations of oestradiol, testosterone, and progesterone at the time of mating-ovulation (February-March) than in those females that did not ovulate and nest that year. Used in conjunction, the criteria of a testosterone concentration greater-than-or-equal-to 2.0 ng/ml or a progesterone concentration greater-than-or-equal-to 5.8 ng/ml in plasma, obtained within 3 h of capture in February-March, can be used to distinguish females destined to nest that year from those that do not nest. These criteria may prove useful for comparing nesting frequencies among years on Stephens Island, for comparing nesting frequencies among different islands, and for monitoring reproduction in captivity. To our knowledge, this is the first time that plasma hormone concentrations have been used to identify nesting females in reptiles that do not nest each year.