Tradeoffs and the evolution of thermal reaction norms

Tradeoffs have played a prominent role in the development of theories describing the evolution of reaction norms. Different classes of tradeoffs are known to constrain the evolution of phenotypes, but current theories incorporate only a subset of these tradeoffs. Consequently, these theories cannot account for some of the variation in reaction norms that has been observed within and among species. Empirical studies of thermal reaction norms for physiological and life historical traits have shown that different proximate mechanisms can produce similar reaction norms. As a consequence, certain tradeoffs can be circumvented when the fitness costs imposed by these tradeoffs are severe. We argue that a unified theory that includes all classes of tradeoffs would provide a better understanding of the mechanisms that drive the evolution of reaction norms.