Effects of Periodic Cooling During Incubation on Lifelong Physiology in Zebra Finches

Abstract

Developmental stress can have long term consequences on phenotypes. In birds, incubation temperature is critically deterministic for a range of traits. When parents leave the nest to forage, developing embryos can be exposed to cooling events which can have long term effects on offspring development. To investigate the immediate and long-term consequences of periodic cooling on offspring development and physiology, we exposed zebra finch eggs to periodic cooling events 5 times a day for 30 minutes throughout the incubation period. Additionally, we incubated eggs at a constant optimum control temperature of 37.4C and at a constant low temperature of 36.4C. During embryonic development, we measured embryonic heart rates, embryonic mass change, duration of incubation, and survival to hatch. Post-hatch, we measured offspring growth as well as assessed adrenocortical function at baseline levels and in response to an acute stressor. We saw significant increases in embryonic heart rate early in development in periodically cooled and low temperature eggs while we only observed significant decreases in heart rates later development in the low treatment. Additionally, we saw increases in incubation duration in cooled and low temperature eggs, transient decreases in post-hatch growth in the cooling treatment, and significant differences between controls and the low constant temperature treatment in terms of the integrated adrenocortical response to an acute stressor. There were also differences in the stress induced adrenocortical response between and within treatments with age. These results indicate that periodic cooling during incubation significantly alters developmental metabolism, which has consequences on post-hatch growth and the ability to respond to a repeated acute stressor. Furthermore, the effect of constant low versus fluctuating incubation temperatures has different biological effects on both embryonic and post-hatch growth and physiology, which must be disentangled from one another to properly evaluate how organisms respond to temperature stress during early development.