HEIDINGER, Britt/J*; NISBET, Ian/CT; KETTERSON, Ellen/D; Indiana University; Indiana University: Attenuation of the stress response may mediate an increase in reproductive performance with age in the common tern Sterna hirundo

In many organisms, reproductive performance increases with age. However, we currently have little information about the physiological mechanisms underlying this commonly observed pattern. One physiological mechanism that may be important in mediating age-related differences in reproductive performance is the stress response. In response to stressors, vertebrates release glucocorticoids (CORT) which stimulate a physiological cascade that enhances survival, but concurrently inhibits reproduction and parental care behaviors. If modifications of the stress response underlie age-related changes in reproductive performance, the stress response should be attenuated with age. We tested this prediction in a free-living population of common terns Sterna hirundo using a standardized handling stress protocol. In addition, we investigated the effects of exogenously elevated CORT levels on parental behavior. We found that while baseline CORT levels did not vary with age, the magnitude and amount of CORT released throughout the stress response declined significantly with age. In addition, we found that adults that received CORT injections spent significantly less time incubating than adults given control oil injections. Taken together, these results suggest that an attenuation of the stress response may mediate an increase in reproductive performance with age.