DISSERTATION RESEARCH: Effect of Body Size and Development on Gas Exchange Mechanisms in Insects: Diffusion vs. Convection

论文研究：身体大小和发育对昆虫气体交换机制的影响：扩散与转化乔恩·F·哈里森·肯德拉·J·格林利生物体中氧气的输送通过两种基本机制进行：对流和扩散。确定这些机制的相对重要性是理解任何生物体内气体交换的基础。当呼吸肌产生的压力导致空气大量流动时，就会发生对流。扩散是通过氧分子从高浓度区到低浓度区的被动运动而发生的。对于昆虫来说，对流和扩散在气体交换中的相对作用存在很大争议。过去的证据支持这样一种观点，即一些昆虫可以仅通过扩散氧气来维持其能量需求。然而，许多昆虫表现出产生压力的行为，例如蝗虫的腹部泵动。特别是，人们认为对流的相对重要性可能会随着昆虫身体的大小而增加。在这项研究中，扩散和对流对昆虫气体交换的相对重要性将通过操纵氧气使用不同载气扩散的能力来量化。一般来说，空气中含有21%的氧气和79%的氮。用氦或六氟化硫代替氮会改变氧的扩散系数，使氧更容易或更难通过扩散来移动。蝗虫对氧气水平降低的代谢反应将在所有三种载气中进行测量。如果蝗虫通过扩散呼吸，它们的新陈代谢反应应该会受到这些操作的强烈影响。相反，如果蝗虫通过对流呼吸，它们对缺氧的新陈代谢反应不会受到载气变化的影响。为了测试扩散和对流的相对重要性是否随大小而变化，这些实验将在幼年(小型)和成年(大型)蝗虫身上进行。为了进一步测试昆虫中扩散和对流的重要性，将用氯胺酮麻醉蝗虫，以防止腹部泵血运动。如果对流确实在较大的昆虫中变得越来越重要，那么氯胺酮预计对较大的蝗虫的低氧代谢反应有更强的影响。总而言之，这些实验将首次对不同大小昆虫体内扩散和对流的相对重要性进行实验测试。

DISSERTATION RESEAERCH: Effect of Body Size and Development on Gas Exchange Mechanisms in Insects: Diffusion vs. ConvectionJon F. HarrisonKendra J. GreenleeDelivery of oxygen in organisms occurs by two basic mechanisms, convection and diffusion. Determining the relative importance of these mechanisms is fundamental to understanding gas exchange in any organism. Convection occurs when pressure generated by respiratory muscles causes bulk movement of air. Diffusion occurs by passive movement of oxygen molecules from areas of high concentration to areas of lower concentration. For insects, the relative role of convection and diffusion in gas exchange is highly controversial. Past evidence supports the notion that some insects can sustain their energy demands through diffusion of oxygen alone. However, many insects exhibit pressure-generating behaviors, such as abdominal pumping in grasshoppers. In particular, it is thought that the relative importance of convection may increase with insect body size. In this study, the relative importance of diffusion and convection to insect gas exchange will be quantified by manipulating the ability of oxygen to diffuse using different carrier gases. Generally, air contains 21% oxygen and 79% nitrogen. Substituting helium or sulfur hexaflouride for nitrogen alters the oxygen diffusion coefficient, making it easier or more difficult, respectively, for oxygen to move by diffusion. The grasshoppers' metabolic response to lowered oxygen levels will be measured in all three carrier gases. If grasshoppers are breathing by diffusion, their metabolic responses should be strongly affected by these manipulations. Conversely, if grasshoppers breathe by convection, their metabolic responses to hypoxia will not be affected by variations in carrier gas. To test whether the relative importance of diffusion and convection varies with size, these experiments will be performed with juvenile (small) and adult (large) grasshoppers. To further test the importance of diffusion and convection in insects, grasshoppers will be anesthetized with ketamine to prevent abdominal pumping movements. If convection does become increasingly important in larger insects, ketamine is predicted to have a much stronger effect on metabolic responses to hypoxia in larger grasshoppers. Together, these experiments will provide the first empirical tests of the relative importance of diffusion and convection in insects of different sizes.