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
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 receptors for CORT also change seasonally. If so, this would
indicate that there is a physiological consequence to 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.