Meeting Abstract
Early life experiences can affect the function of the hypothalamo-pituitary-adrenal (HPA) axis of vertebrates, with the potential for fitness consequences later in life. In altricial species, for example, variations in parental behavior, e.g. brooding or feeding, can modulate HPA axis activation in young by altering their exposure to noxious stimuli during postnatal development. We have shown that a drop in the body temperature of eastern bluebird (Sialia sialis) chicks, such as occurs when females are away from the nest, can elevate their blood corticosterone (CORT) levels. Repeated cooling bouts also affect HPA responses to handling beyond the brooding period. Thus, variation in maternal behavior can shape HPA function in chicks. To better understand how maternal absence from the nest activates the HPA axis of bluebird chicks, we experimentally mimicked cooling induced by maternal absence, and investigated a) the age at which the HPA axis becomes capable of responding to cooling by increasing CORT secretion, b) whether prolonged cooling results in prolonged elevations of CORT, and c) whether fasting (also associated with prolonged maternal absence) interacts with cooling to affect CORT secretion. Cooling for 18 min significantly elevated circulating CORT levels of chicks as young as 4 days post-hatch, and the response increased with age thereafter. Cooling bouts of longer duration (up to 54 min) also produced significantly elevated CORT levels in chicks. A 1-hr period of fasting had no effect on CORT secretion, regardless of whether chicks were cooled or not. Collectively, these data demonstrate that variation in maternal brooding behavior can substantially modify CORT profiles during early postnatal development, and that chick temperature is likely the main driver of this.
