Maternal corticosterone is transferred to avian yolk and may alter offspring growth and adult phenotype.

Many environmental perturbations may elevate plasma corticosterone in laying birds, including disease, poor body condition, high predator density, anthropogenic disturbance, and/or food scarcity. When adverse conditions are not dire enough to dictate foregoing reproduction, maternal corticosterone in egg yolk may phenotypically engineer offspring so as to maximize success under the constraints of the local environment. We tested the hypotheses that corticosterone in avian egg yolk should correlate with corticosterone in maternal circulation at the time of laying, and that high corticosterone in yolk should then influence offspring development and adult phenotype. We implanted female Japanese quail (Coturnix coturnix japonica) with corticosterone-filled or empty implants and measured concentrations of corticosterone in the yolk of their eggs. Then we incubated the eggs and raised the chicks to test for effects on growth and hypothalamo-pituitary-adrenal response to capture and restraint in adult offspring. We found that corticosterone implants significantly increased corticosterone in yolk. Furthermore, chicks of corticosterone-implanted mothers grew more slowly than controls and showed higher activity of the hypothalamo-adrenal axis in response to capture and restraint as adults. These results suggest that stress experienced by a laying bird has significant effects on offspring development and adult phenotype, possibly mediated by the transfer of maternal corticosterone to yolk.