The effects of pre-hatch elevated corticosterone and post-hatch restrictive food availability on the HPA axis development of mallard ducks (Anas platyrhynchos)

Environmental changes can be stressors (altered habitat and food supply, climate change, etc.) to wild animals. Stressors trigger the hypothalamic pituitary adrenal (HPA) axis to release corticosterone (CORT) which modifies energy homeostasis. During nesting, stressed females can deposit increased concentrations of CORT into eggs, altering egg viability and offspring characteristics, constituting a significant mechanism regulating population productivity in subsequent generations. In this study, increased maternal disposition of CORT was mimicked through a 15 ng/g in ovo injection of CORT into mallard duck eggs. Growth and HPA axis function were measured during post-hatch development. For growth, changes in mass were compared at hatch, 7 weeks and 11 weeks. The HPA axis was assessed at seven weeks by measuring CORT at baseline, followed by restraint stress, dexamethasone (negative feedback) and ACTH (maximal adrenal capacity) challenges. At eleven weeks of age, ducks were subjected to a 6-day 25% feed reduction to simulate a poor quality environment to evaluate response to a chronic stressor by comparing CORT at baseline and after restraint stress. Growth and CORT concentration did not differ between treatments at seven weeks or after feed restriction (11 weeks). The CORT dosage administered did not appear to affect HPA axis development in ducklings. Mallards are a highly adaptable species and may have overcome any early alterations to their phenotype. Further research is needed to determine the effects of increased maternal CORT on growth and the development of the HPA axis in ducks.Summary statement: This study examines how maternal stress (simulated through elevated corticosterone in ovo) and post-hatch chronic stressors (food restriction) affect the development of the HPA axis in a precocial bird.