Genetic Variation for Thermal Adaptation in a Cosmopolitan Stored Product Pest

Ectotherms' ability to adapt to climate warming depends on the availability of genetic variation. This is particularly important for insect pests because adaptation to warming could lead to greater crop damage and food shortages. We quantified genetic variation in the thermal reaction norms of life history traits in the bean beetle Callosobruchus maculatus, a stored product pest with a cosmopolitan distribution. We used these data to measure genetic variation in fitness, as quantified by the temperature response of the intrinsic growth rate. We find that the maturation rate, a trait subject to strong biochemical control, exhibits the least amount of genetic variation, while the birth rate, subject to regulatory feedback processes, exhibits the greatest amount. As a result, genetic variation in fitness is constrained by genetic variability in the thermal reaction norm for maturation, suggesting that maturation may be the key limiting factor in ectotherms' adaptation to climate warming.