Oxygen limitation is not the cause of death during lethal heat exposure in an insect

Oxygen- and capacity-limited thermal tolerance (OCLTT) is a controversial hypothesis claiming to explain variation in, and mechanistically determine, animal thermal limits. The lack of support from Insecta is typically argued to be a consequence of their high-performance respiratory systems. However, no studies have reported internal body oxygen levels during thermal ramping so it is unclear if changes in ambient gas are partially or fully offset by a compensatory respiratory system. Here we provide such an assessment by simultaneously recording haemolymph oxygen (pO2) levels – as an approximation of tissue oxygenation - while experimentally manipulating ambient oxygen and subjecting organisms to thermal extremes in a series of thermolimit respirometry experiments using pupae of the butterfly Pieris napi. The main results are that while P. napi undergo large changes in haemolymph pO2 that are positively correlated with experimental oxygen levels, haemolymph pO2 is similar pre- and post-...氧与容量限制的热耐受假说（Oxygen- and capacity-limited thermal tolerance, OCLTT）是一项颇具争议的假说，旨在解释动物热耐受极限的变异特征，并从机制层面阐明动物热耐受极限的决定逻辑。学界普遍认为，昆虫纲（Insecta）未能为该假说提供支持，这一现象通常被归因于其拥有高性能的呼吸系统。然而，目前尚无研究报道动物在热升温过程中的体内氧水平，因此尚不清楚环境气体的变化是否可通过代偿性呼吸系统得到部分或完全抵消。 本研究以菜粉蝶（Pieris napi）蛹为实验材料，开展一系列热极限呼吸测定实验（thermolimit respirometry experiments），在人为调控环境氧浓度的同时，同步记录血淋巴（haemolymph）氧分压（pO2）——以此作为组织氧合状态的近似指标——并将实验生物体暴露于极端温度条件下，从而完成上述评估。研究的主要结果显示，尽管菜粉蝶蛹的血淋巴氧分压会随实验氧浓度发生显著变化且呈正相关关系，但其实验前后的血淋巴氧分压较为相似——