Thermal physiology changes as organisms grow and develop, but we do not understand what causes these ontogenetic shifts. According to the theory of oxygen- and capacity-limited thermal tolerance, an organism's heat tolerance should change throughout ontogeny as its ability to deliver oxygen varies. As insects grow during an instar, their metabolic demand increases without a proportional increase in the size of tracheae that supply oxygen to the tissues. If oxygen delivery limits heat tolerance, the mismatch between supply and demand should make insects more susceptible to heat and hypoxia as they progress through an instar. We tested this hypothesis by measuring the heat tolerance of grasshoppers (Schistocerca americana) on the second and seventh days of the sixth instar, in either a normoxic or a hypoxic atmosphere (21% or 10% O2, respectively). As expected, heat tolerance decreased as grasshoppers grew larger. Yet contrary to expectation, hypoxia had no effect on heat tolerance across all stages and sizes. Although heat tolerance declines as grasshoppers grow, this pattern must stem from a mechanism other than oxygen limitation.

中文翻译：

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在发育过程中，氧气含量的限制不会导致蚱Grass的耐热性下降。

热生理学随着生物体的生长和发展而变化，但是我们不了解是什么原因导致这些个体发生变化。根据氧气和容量限制的热耐受性理论，生物体的耐热性应在整个个体发育中随着其输送氧气的能力而变化。当昆虫在幼虫期生长时，它们的代谢需求增加，而向组织供氧的气管的大小却没有成比例的增加。如果氧气的输送限制了耐热性，则供需之间的不匹配应使昆虫在经过幼虫时更容易受热和缺氧。我们通过在常氧或低氧环境（21％或10％的O2）中测量蝗虫在第六龄第二天和第七天的耐热性来验证这一假设 分别）。正如预期的那样，随着蚱grew的生长，耐热性下降。然而与预期相反，缺氧对所有阶段和大小的耐热性均没有影响。尽管耐热性会随着蚱grow的生长而下降，但这种模式必须源自除氧气限制以外的其他机制。