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Britt Heidinger
Ph.D. Student
Dissertation Research
The influence of age on the glucocorticoid stress response in common terns Sterna hirundo
Life-history theory predicts reproductive effort will increase with age. Although empirical studies generally support this prediction, the physiological mechanisms underlying variation in reproductive effort are poorly understood. In vertebrates, the glucocorticoid stress response is regulated by the hypothalamic-pituitary-adrenal (HPA) axis and may be an endocrine mechanism mediating the trade-off between investment in current reproduction versus future reproduction and survival. Research suggests, when the value of current reproduction is high, the glucocorticoid stress response is attenuated so critical resources are not diverted away from reproduction. Relating this to age, older adults would be expected to suppress their response to stressors and to be less likely to reduce parental behavior when glucocorticoid levels are elevated. However, this hypothesis has yet to be tested. My dissertation will address the following questions: 1) Do older adults respond less strongly to stressors? 2) Are older adults equally capable of secreting glucocorticoids in response to stressors? 3) Are older adults less likely to suppress parental behavior when glucocorticoid levels are experimentally elevated?
I am conducting this research on a known age population of common terns that breed on Bird Island in Buzzards Bay, MA in collaboration with Dr. Ian Nisbet who has been studying their reproductive biology for over thirty years. This study will provide the first test of the hypothesis that changes in the HPA axis mediate age-related changes in parental performance and will enhance our understanding of the physiological mechanisms underlying life-history trade-offs.