<b>Postnatal development in the cold render bird mitochondria more susceptible to heat stress</b>

Research on birds suggests that extreme weather events during development may have long-lasting consequences on form and function. The underlying cellular mechanisms mediating such phenotypic effects are poorly studied. We raised Japanese quail in warm (30°C) or cold (10°C) temperatures from hatching until adulthood and then measured mitochondrial metabolism in intact blood cells at representative normothermic body temperature (41°C) and a hyperthermic temperature (45°C), that quail commonly attain when heat stressed. To investigate whether any postnatal developmental effects were reversible, half of the cold- and warm-acclimated birds were assigned to a common garden (20°C) 3 weeks before the measurements. Across groups, hyperthermia was associated with increased proton leak but decreased phosphorylating respiration (where ATP is produced) and maximal working capacity of the mitochondria. Cold-reared birds were more strongly affected by heat stress: the increase in proton leak was 1.6-fold higher compared to warm-acclimated birds. This did not reflect developmental programming, as the difference did not remain in the common-garden birds. Our study describes the cellular consequences of overheating and suggests that cold acclimation during postnatal development is traded off against heat tolerance at the level of cellular metabolism. These findings have potential implications for understanding avian responses to climate change.

针对鸟类的研究显示，个体发育阶段遭遇的极端天气事件，可能会对其形态与功能造成长期影响。然而，介导此类表型效应的潜在细胞机制尚未得到充分研究。
我们将日本鹌鹑（Japanese quail）从孵化直至成年的整个阶段，分别饲养于温暖（30℃）或寒冷（10℃）环境中。随后，在代表性的正常体温（41℃）以及鹌鹑热应激时通常会达到的高热体温（45℃）下，检测其完整血细胞中的线粒体代谢水平。
为探究产后发育产生的效应是否可逆，我们在检测前3周，将半数冷驯化与温驯化的鹌鹑安置于统一饲养环境（common garden，20℃）中。
整体来看，各组实验对象在高热状态下均表现为质子渗漏增强，但磷酸化呼吸（即ATP生成过程）与线粒体最大工作能力出现下降。其中，冷驯化饲养的鹌鹑受热应激的影响更为显著：其质子渗漏的增幅较温驯化鹌鹑高出1.6倍。该现象并未体现发育编程效应，因为在统一饲养环境下饲养的鹌鹑不再保留该差异。
本研究阐明了过热产生的细胞层面后果，并表明产后发育阶段的冷驯化会在细胞代谢层面与热耐受性形成权衡取舍。上述发现对于理解鸟类应对气候变化的响应具有潜在参考价值。