HAYWARD, LS; EBEL, N; WINGFIELD, JC; Univ. of Washington; Univ. of Washington; Univ. of Washington: Elevated yolk corticosterone and cooling prior to hatch significantly alter maze performance in two-day old chicks

Exposure to elevated glucocorticoids early in development has been shown to reduce learning ability in vertebrates. We tested the effects of elevated yolk corticosterone (B) and elevated endogenous embryonic B on Japanese quail chick performance in a simple maze. By injecting eggs with a physiologically relevant amount of B prior to incubation we mimicked the elevated yolk B found in eggs of female quail with high plasma B. We also cooled eggs just prior to hatch to induce elevations of the embryos� own circulating B. Chicks exposed to high B (B-injected, B-injected and cooled and control-injected and cooled) tended not to fail on first trial as often as control chicks, and chicks from eggs injected with a low dose of B finished the maze significantly faster than controls during their first trial. However, control chicks were significantly faster at maze completion in the second trial than they had been in their first and chicks from other treatment groups were not. This suggests that exposure to high B (either maternal or embryonic) prior to hatch impairs leaning in an avian system. We propose that the seemingly detrimental effects of high B on learning are countered by better ability to solve a novel task, and may be part of a modified behavioral strategy by which an individual can maximize fitness under suboptimal conditions.