Stress response during development predicts fitness in a wild, long lived vertebrate

Abstract

Short-term elevation of circulating glucocorticosteroids (GCs) in vertebrates facilitates the adoption of a distinct emergency life history state, which allows individuals to cope with perturbations and recover homeostasis at the expense of temporarily suppressing nonessential activities. Although GC responses are viewed as a major evolutionary mechanism to maximize fitness through stress management, phenotypic variability exists within animal populations, and it remains unclear whether interindividual differences in stress physiology can explain variance in unequivocal components of fitness. We show that the magnitude of the adrenocortical response to a standardized perturbation during development is negatively related to survival and recruitment in a wild population of long lived birds. Our results provide empirical evidence for a link between stress response, not exposure to stressors, and fitness in a vertebrate under natural conditions. Recent studies suggest that variability in the adrenocortical response to stress may be maintained if high and low GC responders represent alternative coping strategies, with differential adaptive value depending on environmental conditions. Increased fitness among low GC responders, having a proactive personality, is predicted under elevated population density and availability of food resources, conditions that characterize our study population.

Fig. 1.

Probability of survival to adulthood as a function of stress-induced corticosterone and body condition during development. (Top and Bottom) The actual recorded levels of stress-induced corticosterone in individuals that survived and did not survive, respectively (shaded bars indicate mean ± SEM corticosterone, and open dots represent individual values). (Middle) The predicted survival function according to the statistical model. The model predictions have been generated for a range of body condition estimates (maximum, minimum, and average condition scores according to study sample) to illustrate the simultaneous effects of both stress-induced response and body condition on survival probability. The probability of survival decreases as stress-induced corticosterone levels increase; however, for a given level of corticosterone, the survival probability is higher when the bird is in good condition.

Fig. 2.

Probability of recruitment into the breeding population as a function of stress-induced corticosterone and nestling age (in days) at sampling. (Top and Bottom) The actual recorded levels of stress-induced corticosterone in recruited and nonrecruited individuals, respectively (shaded bars indicate mean ± SEM corticosterone, and open dots represent individual values). (Middle) The predicted probability of recruitment according to the statistical model. The model predictions have been generated for a range of ages to illustrate the simultaneous effects of both stress-induced response and nestling age on recruitment probability.