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 substrate temperature, many factors like evaporative cooling, metabolic heating, and insulating properties of extra-embryonic components can lead to thermal differences. However, no method, to date, allowed for measurement of embryonic temperature in live chelonian eggs. We designed a thermocouple-based technique to measure embryonic temperature achieving 94 percent survival in Trachemys scripta. This methodology may be applicable to other reptile species. We found that, while temperature in the substrate adjacent to the eggshell accurately reflects internal egg temperature, it differs from air temperature (∼ 2 °C) in a moisture-dependent manner. Our results demonstrate that external egg, but not air temperature is suitable for assessing the effects of temperature on biological processes, critical when considering that the TSD mechanism in turtles occur within a 4° C window.