Centre for Invasion Biology, Department of Conservation Ecology and Entomology, Stellenbosch University, Stellenbosch, South Africa; Department of Zoology, Stockholm University, Sweden.
Centre for Invasion Biology, Department of Conservation Ecology and Entomology, Stellenbosch University, Stellenbosch, South Africa.
J Insect Physiol. 2021 Apr;130:104199. doi: 10.1016/j.jinsphys.2021.104199. Epub 2021 Feb 5.
How respiratory structures vary with, or are constrained by, an animal's environment is of central importance to diverse evolutionary and comparative physiology hypotheses. To date, quantifying insect respiratory structures and their variation has remained challenging due to their microscopic size, hence only a handful of species have been examined. Several methods for imaging insect respiratory systems are available, in many cases however, the analytical process is lethal, destructive, time consuming and labour intensive. Here, we explore and test a different approach to measuring tracheal volume using X-ray micro-tomography (µCT) scanning (at 15 µm resolution) on living, sedated larvae of the cerambycid beetle Cacosceles newmannii across a range of body sizes at two points in development. We provide novel data on resistance of the larvae to the radiation dose absorbed during µCT scanning, repeatability of imaging analyses both within and between time-points and, structural tracheal trait differences provided by different image segmentation methods. By comparing how tracheal dimension (reflecting metabolic supply) and basal metabolic rate (reflecting metabolic demand) increase with mass, we show that tracheal oxygen supply capacity increases during development at a comparable, or even higher rate than metabolic demand. Given that abundant gas delivery capacity in the insect respiratory system may be costly (due to e.g. oxygen toxicity or space restrictions), there are probably balancing factors requiring such a capacity that are not linked to direct tissue oxygen demand and that have not been thoroughly elucidated to date, including CO efflux. Our study provides methodological insights and novel biological data on key issues in rapidly quantifying insect respiratory anatomy on live insects.
动物的呼吸结构如何随其环境而变化，或受其环境制约，这对各种进化和比较生理学假说都至关重要。迄今为止，由于昆虫呼吸结构的体积微小，对其进行量化及其变化的研究一直具有挑战性，因此仅对少数几种昆虫进行了研究。有几种昆虫呼吸系统的成像方法，但在许多情况下，分析过程是致命的、破坏性的、耗时且劳动密集型的。在这里，我们探索并测试了一种不同的方法，即在两个发育阶段，使用 X 射线微断层扫描（µCT）（15 µm 分辨率）对生活在麻醉状态下的拟步甲科甲虫 Cacosceles newmannii 的幼虫的气管体积进行测量。我们提供了关于幼虫对µCT 扫描过程中吸收的辐射剂量的抗性的新数据，在不同时间点内和之间，成像分析的重复性，以及不同图像分割方法提供的结构气管特征差异。通过比较气管尺寸（反映代谢供应）和基础代谢率（反映代谢需求）如何随质量增加，我们表明，在发育过程中，气管的氧供应能力以可比甚至更高的速度增加。鉴于昆虫呼吸系统中丰富的气体输送能力可能是昂贵的（由于例如氧气毒性或空间限制），因此可能存在与直接组织氧气需求无关但尚未彻底阐明的平衡因素，包括 CO 排放。我们的研究为快速量化活体昆虫的昆虫呼吸解剖结构提供了方法学见解和新的生物学数据。
