The impact of sand moisture on the temperature-sex ratio responses of developing loggerhead (Caretta caretta) sea turtles

All species of sea turtles exhibit a cooler male/warmer female temperature-sex ratio response. Field and experimental studies on loggerhead sea turtle sex ratios suggest that increased sand moisture impacts sea turtle sex ratios with, and perhaps beyond, a cooling effect. This study examines how varying sand moisture impacts the embryo's response to temperature. Across three years, loggerhead (Caretta caretta) sea turtle eggs were incubated at temperatures ranging from 28.0 degrees C to 33.0 degrees C. Groups of eggs were incubated in one of three volumetric moisture contents: low, medium, or high. Temperatures inside the group of eggs were recorded throughout incubation. Hatchlings were raised for 2-3 months and sex was identified laparoscopically. We calculated temperature response curves for groups of eggs incubated at each moisture level. Pivotal temperatures did not different among eggs incubated in different sand moistures. The transitional ranges of temperatures (TRT) for eggs incubated in high moisture and low moisture were narrower than the TRT for eggs incubated in medium moisture. The results of this study are crucial for understanding how sea turtle embryos respond to temperature directly or indirectly under different moisture conditions. Current sex ratio predictions rely on the embryos response to temperature only and may inaccurately estimate sex ratios especially during periods of heavy rainfall or drought.