Phenotypic Effects of Thermal Means and Variances on Smooth Softshell Turtle (apalone Mutica) Embryos and Hatchlings

Temperature is a crucial factor in the development of oviparous organisms. Under natural conditions, the eggs of many species are subjected to changing thermal environments, but most laboratory studies have incubated eggs at constant temperatures. To evaluate the phenotypic effects of different thermal means and variances and to separate temperature effects from maternal effects, eggs from 10 clutches of smooth softshell turtles (Apalone mutica) were equally distributed among six temperature treatments that reflect thermal conditions observed in natural nests: two eggs each at a mean of 28.5 or 32.5 C, with ranges of 6 0, 2, and 4 C. In addition to embryonic traits (change in egg mass, hatching success, and incubation length), we measured and evaluated body size, swimming performance, and righting time of the hatchlings. The interaction between mean temperature and temperature fluctuation exerted a significant influence on eight of the ten traits we measured, indicating that fluctuating temperatures do not have equivalent phenotypic effects at different mean temperatures. Clutch of origin also was responsible for explaining a large fraction of the variation for nearly all but two of the traits. Altogether, these results suggests that clutch effects are pervasive and that thermal effects during embryonic development are complex and deserve further investigation.