A new approach for measuring temperature inside turtle eggs

For turtles, the thermal environment experienced during development plays critical roles in many biological processes. While the temperature inside an egg is assumed to match the substrate temperature, many factors such as evaporative cooling, metabolic heating and the insulating properties of extra-embryonic components can lead to thermal differences. However, no method developed to date has allowed for measurement of the embryonic temperature in live chelonian eggs. We designed a thermocouple-based technique to measure embryonic temperature, achieving 94% survival in Trachemys scripta This methodology may be applicable to other reptile species. We found that, while the temperature in the substrate adjacent to the eggshell accurately reflects the internal egg temperature, it differs from air temperature (∼2°C) in a moisture-dependent manner. Our results demonstrate that external egg temperature, but not air temperature, is suitable for assessing the effects of temperature on biological processes, which could be critical when considering that processes such as temperature-dependent sex determination in turtles occurs within a 4°C window.