Postnatal developmental temperature affects the ontogeny of heat- and cold tolerance

Thermoregulatory precision is key to maintaining fitness in thermally unstable environments. Previous research found that development in the warmth renders birds better able to handle mild heat stress, while cold postnatal development gives no apparent benefit upon mild cold exposure. It is still not known how developmental temperature affects maximal heat tolerance limits, or if there is a physiological trade-off between heat and cold tolerance. We investigated how postnatal developmental under simulated cold snap- or heatwave-like conditions from hatching until reproductive maturity impacted the ontogeny of maximal heat- and cold tolerance in Japanese quail (Coturnix japonica). To study if any such effects were reversible or permanently programmed, we transferred half of each treatment group to intermediate common garden conditions once reproductive maturity was reached and repeated the measurements several weeks later. Development in heatwave-like conditions increased evaporative water loss rate and moved heat tolerance limits upwards, whereas cold snap-like development rendered more thermogenic birds with improved cold tolerance limits. However, we found no evidence for a trade-off between thermogenic performance and evaporative cooling capacity. The common garden birds converged in nearly all thermoregulatory traits at the end of the study, suggesting that the prior emergence of temperature-dependent phenotypes reflected reversible plasticity. We suggest that improved temperature tolerance limits improve performance in matched thermal conditions, reducing the rate at which thermal injury accrues. Yet, in the short term, we found markedly lower capacity to acclimate heat tolerance compared to cold tolerance, with possible implications for life in a warming world.