Temperature selection by juvenile tuatara (Sphenodon punctatus) is not influenced by temperatures experienced as...

Most reptiles thermoregulate to achieve body temperatures needed for biological processes, such as digestion and growth. Temperatures experienced during embryogenesis may also influence post-hatching growth rate, potentially through influencing post-hatching choice of temperatures. We investigated in laboratory settings whether embryonic temperatures (constant 18°C, 21°C and 22°C) influence selected body temperatures (T_sel) of juvenile tuatara (Sphenodon punctatus), providing a possible mechanism for differences in growth rates. We found that incubation temperature does not influence T_sel. Although the average daily mean T_sel was 21.6 ± 0.3°C, we recorded individual T_sel values up to 33.5°C in juvenile tuatara, which is higher than expected and above the panting threshold of 31-33°C reported for adults. We found diel patterns of T_sel of juvenile tuatara, observing a general pattern of two apparent peaks and troughs per day, with T_sel being significantly lower around dawn and at 1500h than any other time. When comparing our results with other studies on tuatara there is a remarkable consistency in mean T_sel of ~ 21°C across tuatara of different ages, sizes and acclimatization histories. The ability of juvenile tuatara to withstand a wide range of temperatures supports their former widespread distribution throughout New Zealand and warrants further investigation into their plasticity to withstand climate warming, particularly where they have choices of habitat and the ability to thermoregulate.