Youngblood Jacob P, da Silva Carmen R B, Angilletta Michael J, VandenBrooks John M
Physiol Biochem Zool. 2019 Nov/Dec;92(6):567-572. doi: 10.1086/705439.
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 () on the second and seventh days of the sixth instar, in either a normoxic or a hypoxic atmosphere (21% or 10% O, 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.
随着生物体的生长和发育，热生理会发生变化，但我们并不清楚是什么导致了这些个体发育转变。根据氧和容量限制热耐受性理论，生物体的耐热性应在整个个体发育过程中随着其输送氧气能力的变化而改变。随着昆虫在一个龄期内生长，它们的代谢需求增加，而向组织供应氧气的气管大小却没有成比例增加。如果氧气输送限制了耐热性，那么供需之间的不匹配应该会使昆虫在一个龄期内更容易受到高温和低氧的影响。我们通过测量六龄期第二天和第七天的蝗虫（）在常氧或低氧环境（分别为21%或10% O）中的耐热性来检验这一假设。正如预期的那样，随着蝗虫体型变大，耐热性下降。然而，与预期相反，低氧对所有阶段和体型的耐热性均无影响。尽管随着蝗虫生长耐热性会下降，但这种模式必定源于氧气限制以外的其他机制。
