Study

Support for a rare pattern of temperature-dependent sex determination in archaic reptiles: Evidence from two species of tuatara (Sphenodon)

  • Published source details Mitchell N.J., Nelson N.J., Cree A., Pledger S., Keall S.N. & Daugherty C.H. (2006) Support for a rare pattern of temperature-dependent sex determination in archaic reptiles: Evidence from two species of tuatara (Sphenodon). Frontiers in Zoology, 3, 1-12.

Actions

This study is summarised as evidence for the following.

Action Category

Alter incubation temperatures to achieve optimal/desired sex ratio: Tuatara

Action Link
Reptile Conservation

Use hormones and/or other drugs during captive-breeding programmes to induce reproduction/birth

Action Link
Reptile Conservation
  1. Alter incubation temperatures to achieve optimal/desired sex ratio: Tuatara

    A replicated, controlled study in a captive setting in Wellington, New Zealand (Mitchell et al. 2006) found that incubating eggs of two populations of tuatara (Sphenodon guntheri and Sphenodon punctatus) at higher temperatures produced more male hatchlings. Incubating eggs at higher temperatures resulted in more male offspring (22.1–24°C: 100% of 7–113 eggs produced males) compared to at lower temperatures (18–18.3°C: 0–8% of 12–105 eggs produced males). For one population (Sphenodon guntheri), males were produced above 21.6°C, and for the other population (Sphenodon punctatus), males were produced above 22.0°C. In 2000, a total of 71 Sphenodon guntheri eggs were collected from North Brother Island by inducing gravid females to lay eggs with oxytocin (49 eggs) or removing eggs from nests (22 eggs). Eggs were placed in moist vermiculite and randomly assigned to incubate at 18°C, 21°C, 22°C or 23°C. The sex of these hatchlings was determined via a surgical procedure (see paper for details). In 2003, fifteen eggs from a captive female (Sphenodon punctatus) were incubated at 18°C for seven weeks before being moved to 21.5°C (7 eggs) or 24.1°C (8 eggs). For eggs that failed to develop fully, sex could still be determined in some cases. Data from a number of other studies on incubation temperatures and sex ratios from 1989–1991 and 1999 were also included for comparison (see paper for details).

    (Summarised by: William Morgan)

  2. Use hormones and/or other drugs during captive-breeding programmes to induce reproduction/birth

    A study in 2000 on North Brother Island, New Zealand (Mitchell et al. 2006) reported that some tuatara (Sphenodon guntheri) could be induced to lay eggs using oxytocin. Nine of 21 females given oxytocin began to lay clutches of eggs (3–7 eggs/clutch) within 15–70 minutes of receiving the injection. However, eggs from two of those females were small and soft and did not develop successfully. The remaining 12 females did not respond to the oxytocin injection. In 2000, a total of 21 gravid female tuatara received an injection of oxytocin (Oxytocin-s,10 IU/mL) into the body cavity (details of total monitoring time not provided).

    (Summarised by: William Morgan)

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