Corticosterone exposure during development has sustained but not lifelong effects on body size and total and free corticosterone responses in the zebra finch

• Developmental CORT increased total/free CORT responses in birds 30 days post-hatch.
• CORT treatment did not affect total/free CORT responses 60 or 90 days post-hatch.
• CORT treatment decreased body size at 30, but not 60 or 90 days post-hatch.
• Clutch size had sustained effects on body size.
• Birds from medium sized clutches were the largest.

Animals exposed to stress during development experience sustained morphological, physiological, neurological, and behavioral consequences. For example, elevated glucocorticoids (GCs) during development can increase GC secretion in adults. Studies have examined the sustained effects of elevated developmental GCs on total GC responses, but no study to date has examined the effect of developmental stress on corticosteroid binding globulin (CBG). CBG is a protein which binds to GCs and facilitates their transportation in blood. When bound to CBG, GCs are unavailable to interact with target tissues. Exposure to stress can decrease CBG capacity and, thus, increase free GCs (the portion of unbound GCs). We examined the long-term effects of elevated corticosterone (CORT) during development (12–28 days post-hatch) on acute stress responses, negative feedback, and CBG capacity at 30, 60, and 90 days post-hatch in zebra finches. Additionally, we evaluated the effect of CORT treatment on body size and condition at 28, 60, and 90 days post-hatch. CORT exposed birds had higher acute stress responses at 30 days post-hatch compared to control birds. However, there was no treatment effect at 60 or 90 days post-hatch. CBG levels were not affected by treatment, and so free CORT estimations reflected patterns in total CORT. CORT treatment decreased growth and condition in zebra finches at 28 days post-hatch, but these differences were not present at later life history stages. However, brood size had a sustained effect on body size such that birds reared in medium sized broods were larger at 28, 60, and 90 days post-hatch. These results demonstrate the complexity of early environmental effects on adult phenotype and suggest that some conditions may have stronger programmatic effects than others.