Genetic and thermal variation influence adaptation to fluctuating temperature in the seed beetle, Callosobruchus maculatus

Summary Climate change is associated with both the increase in mean and variability of thermal conditions. The use of more realistic thermal regimes is therefore the most appropriate laboratory method to correctly predict population responses to thermal heterogeneity. However, both the long- and short-term implications of evolving under such conditions are not well understood. Here, we examined the effect of fluctuating daily temperatures on several key life history traits in the seed beetle, Callosobruchus maculatus , that was exposed to a short-term thermal switch into a novel environment. Populations were kept for 19 generations at one of two temperatures: constant control temperature (T=29°C) or a fluctuating daily cycle (T mean =33°C, T max =40°C, and T min =26°C) and were subsequently exposed to a switch to the opposite condition. We found that beetles that had evolved in stressful environments were smaller in size when switched to a constant 29°C and had far greater reproductive fitness compared to beetles from both the constant control and continuously stressful 33°C environments. This suggests that beetles raised in environments with stressful fluctuating temperatures were more phenotypically plastic and had greater genetic variability than control treatment beetles and indicates that populations that experience fluctuations in temperature may be better able to respond to short-term changes in environmental conditions.