Seasonal Variation in Stress Responses

Winter is energetically demanding; thermogenic requirements are high and resources are scarce. This prolonged imbalance in energy intake and expenditure causes a stress response and glucocorticoid release. A chronic stress response typically results in pathology, but anticipation of seasonal stressors allows for the reorganization of endocrine, metabolic, immune, and neural processes to reduce energetic requirements. These trade-offs are mediated by differential investment in immune function and reproduction during times of low (fall and winter) and high (spring and summer) energy availability, respectively. Many nontropical animals monitor day length (i.e., photoperiod), in order to coordinate these seasonal adaptations. Much of the photoperiodic signal is transduced by pineal melatonin, as it is secreted inversely proportional to the absolute day length. This chapter will discuss seasonal changes in glucocorticoid release, binding globulin capacity, and receptor expression and their ultimate contributions to differential stress responses