Developmental Programming via Activation of the Hypothalamic–Pituitary–Adrenal Axis: A New Role for Acoustic Stimuli in Shaping Behavior?

Abstract

It has become increasingly evident that the conditions experienced during the prenatal period can have fundamental effects on a range of phenotypic traits that can persist into later developmental and adulthood stages. Indeed, prenatal environments can influence many behavioral strategies adopted by animals in postnatal life. There has been a great debate over the adaptive significance of this phenomenon of “developmental programming”; whether this represents a maternal strategy to maximize offspring survival under matching later conditions, or the effects merely reflect constraints placed on physiological systems. In this review, we will highlight the importance of prenatal conditions in shaping behavior in later life history stages, with a particular focus on the role of acoustic stimuli and the role of endocrine systems (the hypothalamic–pituitary–adrenal [HPA] axis) in mediating sustained programmed effects. While there is a great body of literature investigating several developmental factors that can cause long-term phenotypic effects, much less attention has been paid to the effects of sounds experienced during this developmental stage. However, there is a growing interest in this area, particularly in oviparous organisms. While we take a comparative approach here, much of the evidence will focus on avian species, due to the literature available for this taxa and the utility of external embryonic development when studying the embryonic responses to external stimuli. We will also highlight the important role that acoustic stimuli during development can have on later behaviors, and show the potential links between sound detection and activation of the HPA axis. Finally, we propose a novel hypothesis that the acoustic environment during prenatal development may program the HPA axis in such a way as to create phenotypes that cope better in certain environments in later life, and that acoustic signals could be a way of altering trajectories already put in place by maternal effects acting on the egg.