Meeting Abstract
In vertebrates, exposure to stressful stimuli or elevated glucocorticoids early in development may have fitness consequences later in life. In altricial species, parental brooding behavior may prevent temperature-induced elevations in glucocorticoid secretion by their chicks. To investigate this, we studied eastern bluebirds (Sialia sialis) with three goals. First, we measured the surface temperature of chicks during the first week post-hatch to determine the extent to which they cooled in the field. Second, we determined if a brief, experimental drop in body temperature within the range that occurs when a brooding female is off the nest was sufficient to stimulate glucocorticoid secretion in young chicks. And, third, we examined how experimentally induced bouts of cooling within an ecologically relevant range affected their hypothalamo-pituitary-adrenal (HPA) axis function in response to handling just prior to fledging. Chicks in 25% of broods experienced repeated, natural bouts of cooling in the nest, and experimental reduction of their surface temperatures within this cooling range significantly elevated their corticosterone secretion. Chicks that were experimentally subjected to four 20-min bouts of such cooling during the first week post-hatch had a reduced corticosterone response to restraint prior to fledging (more than 1 week later) compared to control chicks. Our data suggest that natural variation in maternal brooding patterns, and hence natural variation in chick temperature, can result in differential exposure of offspring to glucocorticoids early in development, with impacts on HPA function that extend well beyond the brooding period.
