Figure 3.

Within-individual plasticity in CORT and clutch size generates a within-individual correlation between CORT and a fitness metric. In this hypothetical example, selection has favoured CORT to increase plastically within one individual in response to a decline in her nutritional state (a). In that same individual, clutch size plastically responds to nutritional state in the opposite direction, increasing when resources are abundant (b). Because of these two plastic responses (a and b), which are both adaptive, CORT and clutch size will be negatively correlated within this individual across multiple breeding bouts with varying nutritional states (c). This correlation (c) arises because nutritional state influences both CORT levels and fitness within individuals.