Slow Estradiol-induced Vitellogenesis in the Tuatara, Sphenodon punctatus

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Abstract
The vitellogenic response to exogenous estradiol-17β in wild male and female tuatara (Sphenodon punctatus) is extremely slow to induce. Tuatara given slowrelease implants containing 4-11 μg estradiol/g body mass showed a marked elevation in plasma estradiol concentrations within 2 d (to levels of up to 2,967 pg/mL) but no marked increases in plasma concentrations of calcium, total protein, or inorganic phosphate within 11 d. A small increase in the amount of electrophoretically detectable vitellogenin in the plasma (expressed as a percentage of total plasma protein) was evident by 11 d. Plasma concentrations of progesterone in individual females and testosterone in individual males were low (<3. 7 ng/mL and <3.8 ng/mL, respectively) during the 11 d. Several individuals captured 4-9 mo after administration of implants showed very high plasma levels of vitellogenin (up to 59% of total plasma protein), calcium (up to 61 mmol/L), total protein (up to 108 g/L), and inorganic phosphate (up to 39 mmol/L); these concentrations are similar to those seen in other estrogen-treated reptiles within much shorter time periods. Estradiol-induced vitellogenesis in tuatara is slower to induce and may occur at a lower maximal rate than in other reptiles examined. These responses are probably explained by the cool body temperatures exhibited by tuatara and are consistent with the slow rate of natural vitellogenesis observed in wild female tuatara.

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