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

论文研究：昆虫体型和发育对气体交换机制的影响：扩散与对流生物体内氧气的传递主要通过对流和扩散两种基本机制进行。确定这些机制的相对重要性是理解任何生物体中气体交换的基础。当呼吸肌产生的压力引起空气的大量运动时，对流就发生了。扩散是由氧分子从高浓度区域被动移动到低浓度区域而发生的。对昆虫来说，对流和扩散在气体交换中的相对作用是有很大争议的。过去的证据支持这样一种观点，即一些昆虫仅通过氧气的扩散就能维持它们的能量需求。然而，许多昆虫表现出产生压力的行为，比如蚱蜢的腹部抽水。特别是，人们认为对流的相对重要性可能随着昆虫体型的增大而增加。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%的氮气。用氦或六氟化硫代替氮会改变氧的扩散系数，分别使氧通过扩散移动变得更容易或更困难。蚱蜢对低氧水平的代谢反应将在所有三种载气中进行测量。如果蚱蜢是通过扩散呼吸，它们的代谢反应应该受到这些操作的强烈影响。相反，如果蚱蜢通过对流呼吸，它们对缺氧的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）和成年（大）蚱蜢身上进行。为了进一步测试扩散和对流对昆虫的重要性，蚱蜢将被氯胺酮麻醉，以防止腹部泵运动。如果对流在大型昆虫中变得越来越重要，预计氯胺酮对大型蚱蜢对缺氧的代谢反应有更强的影响。总之，这些实验将首次提供关于扩散和对流在不同大小昆虫中的相对重要性的经验检验。

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.