According to the maternal manipulation hypothesis, females manipulate the phenotypes of their offspring by selecting favourable incubation conditions. In oviparous black ratsnakes (Elaphe obsoleta Say in James, 1823), females manipulate offspring phenotype through nest-site selection. This study aimed to determine whether the thermal mean and variance of the incubation regime affect fitness-related traits in hatchlings. We incubated 136 eggs in a split-clutch design at two thermal means (26 and 29 °C) and variances (constant and ±3 °C). Hatchlings incubated at higher temperatures hatched earlier, were longer, faster, and less defensive. Hatchlings incubated at constant temperatures hatched earlier and were longer. For athletic performance, there was a significant interaction between temperature mean and variance: hatchlings incubated at 29 °C swam faster, had a lower muscular strength, and righted themselves equally fast when incubated at constant temperatures, whereas hatchlings incubated at 26 °C were stronger, swam faster, and righted themselves more slowly. Overall, constant incubation temperatures produced hatchlings with phenotypes favouring higher survival than fluctuating temperatures, but the effect of thermal variance was not as pronounced as the effect of thermal mean. Therefore, we found some support for the hypothesis that black ratsnakes prefer communal over single-female nests because communal nests have higher, more constant temperatures.
Collected eggs, hatched them and assessed their swimming speed, righting time and muscular strength