Seasonal Variations in Stress Responses

One of the hallmarks of the stress response is the activation of the hypothalamic-pituitary-adrenal (HPA) axis, culminating in glucocorticoid release (either cortisol or corticosterone (CORT) — depending upon the species) several minutes after initiation of a stressful stimulus. CORT then induces a variety of behavioral and physiological effects.

Although CORT seems crucial for survival, we still have little idea how elevated CORT concentrations aid in survival. Work from the past 20 years has firmly established that many wild free-living species seasonally modulate CORT secretion. In other words, the magnitude of the stress response depends upon the time of year. An example is shown for white-crowned sparrows, but our lab has demonstrated this phenomenon in several species of birds, mammals, and salamanders. Modulation of CORT release has far-reaching implications for both the physiology of the stress response and the short-term survival of the individual animal. Several projects in our lab are exploring both how and why CORT release is modulated.

We now have two avian models that mimic seasonal CORT release in the laboratory, and combining experiments on these models with field studies will allow us to further explore both the physiological underpinnings of seasonal CORT release as well as begin to address the adaptive significance.

Current work is focusing on three aspects. First, we are exploring whether DNA damage, a consequence of stress (see "DNA Damage" section), changes seasonally. If so, this would indicate that there is a physiological consequence to seasonally varying CORT concentrations. Second, we have several recent papers testing whether the physiological process of molt in birds is negatively affected by CORT. Third, we continue to use the period of molt in birds as a natural experiment for periods of low stress reactivity. Our aim is eventually to have a broader idea of what role CORT plays in the stress response, and therefore the survival, of wild animals.

White-crowned Sparrow