Department of Physiology, Midwestern University, Glendale, AZ 85308, USA.
College of Veterinary Medicine, Midwestern University, Glendale, AZ 85308, USA.
J Insect Physiol. 2018 Apr;106(Pt 3):217-223. doi: 10.1016/j.jinsphys.2017.11.001. Epub 2017 Nov 6.
Atmospheric oxygen is one of the most important atmospheric component for all terrestrial organisms. Variation in atmospheric oxygen has wide ranging effects on animal physiology, development, and evolution. This variation in oxygen has the potential to affect both respiratory systems (the supply side) and mitochondrial networks (the demand side) in animals. Insect respiratory systems supplying oxygen to tissues in the gas phase through blind ended tracheal systems are particularly susceptible to this variation. While the large conducting tracheae have previously been shown to respond developmentally to changes in rearing oxygen, the effect of oxygen on the tracheolar network has been relatively unexplored, especially in adult insects. Similarly, mitochondrial networks that meet energy demand in insects and other animals are dynamic and their enzyme activities have been shown to vary in the presence of oxygen. These two systems together should be under selective pressure to meet the aerobic metabolic requirements of insects. To test this hypothesis, we reared Mito-YFP Drosophila under three different oxygen concentrations hypoxia (12%), normoxia (21%), and hyperoxia (31%) and imaged their tracheolar and mitochondrial networks within their flight muscle using confocal microscopy. In terms of oxygen supply, hypoxia increased mean (mid-length) tracheolar diameters, tracheolar tip diameters, the number of tracheoles per main branch and affected tracheal branching patterns, while the opposite was observed in hyperoxia. In terms of oxygen demand, hypoxia increased mitochondrial investment and mitochondrial to tracheolar volume ratios; while the opposite was observed in hyperoxia. Generally, hypoxia had a stronger effect on both systems than hyperoxia. These results show that insects are capable of developmentally changing investment in both their supply and demand networks to increase overall fitness.
大气中的氧气是所有陆地生物最重要的大气成分之一。大气氧气的变化对动物的生理、发育和进化有广泛的影响。这种氧气的变化有可能影响动物的呼吸系统（供应方）和线粒体网络（需求方）。通过盲端气管系统将氧气输送到组织的昆虫呼吸系统对这种变化特别敏感。虽然以前已经表明大型导气管在发育过程中会对饲养氧气的变化做出反应，但氧气对气管网络的影响相对来说还没有被探索过，尤其是在成年昆虫中。同样，满足昆虫和其他动物能量需求的线粒体网络是动态的，它们的酶活性在存在氧气的情况下会发生变化。这两个系统应该一起受到选择性压力的影响，以满足昆虫的需氧代谢需求。为了验证这一假设，我们在三种不同的氧气浓度（缺氧、常氧和高氧）下饲养了带有 Mito-YFP 的果蝇，并使用共聚焦显微镜在其飞行肌肉内对它们的气管和线粒体网络进行成像。在氧气供应方面，缺氧增加了平均（中长）气管直径、气管末端直径、每个主分支的气管数量并影响了气管分支模式，而高氧则相反。在氧气需求方面，缺氧增加了线粒体的投资和线粒体与气管的体积比；而高氧则相反。一般来说，缺氧对这两个系统的影响都比高氧强。这些结果表明，昆虫能够在其供应和需求网络中进行发育性投资，以增加整体适应性。
