Prenatal Motor Development Affects Observed Motor Behavior for Different Incubation Periods in Domestic Chick

INTRODUCTION The length of incubation and thus, the time to hatch, significantly vary in chick embryos (Gallus gallus) with light exposure conditions. Continuous incubation in the dark throughout embryogenesis (24D) delays hatching by 1-2 days (~5-10% of total gestation), as compared to incubation in daily periodic light (12 hours of light, 12L) or continuous bright light (24L). Do such light-induced changes during prenatal development impact postnatal motor skill? Our null hypothesis is that, regardless of incubation conditions, chicks adapt and hatch equally ready to cope with the postnatal environment. In agreement with this, a recent study of global gait parameters found no differences in body weight, leg length or locomotor competence across these 3 conditions [1]. However, unconstrained overground locomotion is a highly variable behavior, and the global gait parameters may not have been sufficiently sensitive to detect group differences, if they existed. Thus, in this study we investigate postural control of sway during quiet stance, by examining center of pressure (COP) dynamics, as a more sensitive measure of motor skill [2]. Our results identify significant differences across incubation conditions for several postural metrics, suggesting that length of incubation impacts motor behavior on the day of hatching.