Variation in temperature of peak trait performance will constrain adaptation of arthropod populations to climatic warming.

The degree to which arthropod populations will be able to adapt to climatic warming is uncertain. Here, we report that arthropod thermal adaptation is likely to be constrained in two fundamental ways. First, maximization of population fitness with warming is predicted to be determined predominantly by the temperature of peak performance of juvenile development rate, followed by that of adult fecundity, juvenile mortality and adult mortality rates, in this specific order. Second, the differences among the temperature of peak performance of these four traits will constrain adaptation. By compiling a new global dataset of 61 diverse arthropod species, we show that contemporary populations have indeed evolved under these constraints. Our results provide a basis for using relatively feasible trait measurements to predict the adaptive capacity of arthropod populations to climatic warming. ### Competing Interest Statement The authors have declared no competing interest.