Meeting Abstract
Temperature influences both development rate and growth rate in ectothermic vertebrates, but it is unclear whether both processes have similar thermal sensitivity. To determine whether growth and development rates parallel one another at different temperatures, we incubated snapping turtle eggs under four different thermal regimes: a constant 25°C, a fluctuating temperature of 12h at 29°C and 12h at 21°C (constant temperature equivalent [CTE] = 26.6°C), a constant 30°C, and a fluctuating temperature of 12h at 34 C and 12h at 26°C (CTE = 31.1°C). We used a model developed by Rollinson et al. (2018, J. Therm. Biol.) to estimate the time needed for the embryos at different temperatures to develop to particular development stages corresponding to the end of neurulation (Yntema stage 12), organogenesis (Yntema stage 15), and early growth (Yntema stage 18). At stage 12, embryos in the 25±0°C treatment had the largest head lengths, eye diameters, and dry masses, whereas those incubated at 30±0°C were the smallest. Similar differences in size measures among thermal treatments were present at stage 15 and stage 18. Hatching occurred earliest in the eggs incubated at 30±0°C and was latest in those incubated at 25±0°C and 25±4°C. Live mass, linear measurements, dry yolk sac mass, and dry yolk-free carcass mass at Day 7 post-hatching were generally similar among treatments. The findings suggest that embryonic growth rate may be less sensitive to variation in temperature than is embryonic development rate, enabling embryos at lower temperatures to grow to larger sizes at a given developmental stage. However, the size of the hatchlings appears to be relatively independent of temperature. Rather, egg size appears to be the main factor determining size at hatching.
