Tracking energy expenditure in insect flight: from the contractile proteins to the animal's wake

昆虫是地球上最多样化、最成功和经济上最重要的目之一，飞行是它们成功的关键。飞行是能量消耗最大的运动方式之一，昆虫的生态、行为和生理几乎没有不受其能量需求影响的方面。在所有运动模式中，肌肉将化学能（最终来自食物）转化为机械功，最终转移到环境中产生运动。理想情况下，为了全面了解该系统，我们需要能够追踪从收缩蛋白质到转移到动物唤醒的动量的所有组织水平之间的能量转移，并将其与动物的运动性能，形态学和生态学联系起来。这还没有在任何运动模式中实现。然而，通过结合利兹的肌肉生理学和运动能量学以及牛津大学的流体动力学的研究专长，昆虫飞行是可以实现的。这项拟议研究的总体目标是使用一种综合的，多学科的方法来确定，在昆虫飞行，从生化势能的能量转移，通过肌肉，周围的空气。这将通过量化以下内容来跟踪能量的转换来实现。首先，我们将通过在风洞中测量系留飞行期间的氧气消耗率和二氧化碳产生率来确定整个生物体的代谢率。其次，我们将通过测量收缩期间的总焓来测量肌肉的代谢率-这是由飞行肌肉产生的机械功和由于收缩效率低下而释放的热量的总和。肌肉产生的机械功将通过模拟飞行过程中肌肉长度变化和活动模式来确定。与此同时，我们将使用热电堆来测量收缩期间和收缩后释放的热量，并确定横桥的效率，线粒体通过氧化磷酸化重新合成ATP的效率以及由于肌肉激活成本而产生的效率低下。最后，我们将确定机翼将飞行肌肉产生的功转化为空气中有用能量的效率。这将使用一种称为粒子图像测速（PIV）的技术来完成，该技术允许量化机翼周围和尾流中的空气流动速度。通过选择具有同步或异步飞行肌肉的昆虫，具有不同生态的密切相关的物种，表现出收敛的生态和形态进化的不相关物种以及在一系列身体大小上几何相似的物种，我们将确定运动效率差异的主要原因或原因。我们将能够解释运动的整体效率差异的基本过程：过桥的效率，线粒体重新合成ATP的效率，翅膀的空气动力学效率和肌肉弹性储存能量的能力差异。总之，我们的研究结果将提供一个前所未有的了解能源消耗在这个多样化和生态重要的群体。

Insects are amongst the most diverse, successful and economically important orders on earth and flight is key to their success. Flight is one of the most energetically expensive modes of locomotion and there are few aspects of an insect's ecology, behaviour and physiology that are not affected by its energetic demands. During all modes of locomotion, muscles convert chemical energy (ultimately derived from food) into mechanical work that is ultimately transferred to the environment to produce movement. Ideally, to achieve a full understanding of the system, we need to be able to trace the transfer of energy between all levels of organisation from the contractile proteins to the momentum transferred to the animal's wake and relate this to the animal's locomotor performance, morphology and ecology. This has not yet been achieved for any mode of locomotion. However, by combining research expertise in muscle physiology and locomotor energetics at Leeds and fluid dynamics at Oxford it is achievable in insect flight. The overall aim of this proposed research is to use an integrative, multidisciplinary approach to determine, in insect flight, the transfer of energy from biochemical potential energy, through the muscles, to the surrounding air. This will be achieved by tracking the transduction of energy by quantifying the following. First, we will determine the whole organism metabolic rate by measuring the rates of oxygen consumption and carbon dioxide production during tethered flight in a wind tunnel. Second, we will measure the muscle's metabolic rate by measuring the total enthalpy during contraction - this is the sum of the mechanical work generated by the flight muscles and the heat that is liberated due to the inefficiencies of the contraction. The mechanical work generated by the muscles will be determined by simulating the muscle length change and activity pattern during flight. At the same time, we will use a thermopile to measure the heat liberated both during and after the contraction and determine the efficiency of the crossbridges, the efficiency with which the mitochondria re-synthesise ATP by oxidative phosphorylation and the inefficiencies arising due to the costs of muscle activation. Finally we will determine the efficiency of the wings in transferring the work generated by the flight muscles into useful energy in the air. This will be done using a technique called Particle Image Velocimetry (PIV) that allows the velocities of air flowing around the wings and in the wake to be quantified. By selecting insects with either synchronous or asynchronous flight muscles, closely related species with different ecologies, unrelated species demonstrating convergent ecological and morphological evolution and geometrically similar species across a range of body sizes, we will identify the main cause or causes of differences in locomotor efficiency across a range of sizes, guilds and taxonomic groups. We will be able to explain differences in overall efficiency of locomotion in terms of the underlying processes: the efficiency of the crossbridges, the efficiency of the mitochondria in re-synthesising ATP, the aerodynamic efficiency of the wings and differences in the ability to store energy in muscle elasticity. Together, our results will provide an unprecedented understanding of energy expenditure in this diverse and ecologically important group.