Figure 3.

Reaction norms from different perspectives. (a) A neuroendocrinological perspective: the neuroendocrinological system integrates information and signals to the rest of the organism. The genotype determines how the neuroendocrinological system is configured, and hence the resulting relationship between the trait value and the environment. Different genotypes therefore produce different reaction norms. (b) An ecological perspective: Selection pressures and functional constraints vary between environments, so that the optimal values of traits (T₁, T₂, T₃, …) vary across environments (E₁, E₂, E₃, …). The optimal reaction norm represents the optimal trait values across a range of environments and is the reaction norm that would give the organism highest fitness.