Effect of Diurnal Incubation Temperature Fluctuation on Hatch, Size, and Motility in Green and Loggerhead Turtles

Sea turtle incubation temperature is an important environmental factor that can alter the hatchling phenotype and impact their survival. Turtle eggs naturally experience diurnal temperature fluctuations, but climate change is expected to intensify their impact on the eggs. Southwestern Japan encompasses the northern and southern limits of green turtle and loggerhead turtle nesting areas in the western North Pacific and is considered to be where the impacts of climate change are most evident. We investigated how the diurnal variation of fluctuating incubation temperature affects the hatching success, size and swimming performance in green and loggerhead turtle hatchlings. We collected eggs of both species from five nests each laid on beaches. Eggs from each nest were divided into three treatments based on the sand temperatures measured in natural beaches. One treatment group was held at a constant temperature of 29.0°C, while the other two groups were kept at a mean 29.0°C with daily fluctuations of ±1.0°C or ±2.0°C. For loggerhead turtles, hatching success was highest in the group with ±1.0°C fluctuation. For both species, swimming thrusts were higher in the ±1.0°C fluctuations and constant-temperature groups than in the ±2.0°C fluctuations group. Our study suggests that for the traits surveyed, incubation regimes that mimic the natural daily temperature fluctuations of each species result in better hatchling outcomes. Therefore, when translocating eggs, maintaining them under conditions that reflect the natural temperature fluctuation is ideal. These findings provide valuable guidance for improving the success of hatching programs.