Atmospheric Oxygen Effects on Insect Body Size and Tracheal Function

据推测，古生代晚期的巨型昆虫可能是由高大气含氧量造成的，而目前昆虫的体型受到大气含氧量21%的限制。本研究将通过一系列实验来验证这一假设，研究单代和多代暴露于不同大气O2水平对昆虫大小、发育速度、气管结构和功能的影响。这些实验大多使用果蝇（Drosophila melanogaster），但一项广泛的比较研究包括16种昆虫对大气O2水平变化的发育可塑性的响应。本研究的第一个目标是测试黑腹d.m anogaster在实验室中是否会随着大气O2水平（10,20,40% O2）的变化而进化出不同的体型。第二个目标是通过在不同的氧气环境中选择大体型来确定大气中的氧气水平是否可以作为黑腹龙大体型进化的约束。第三个目标是测试氧气输送限制，以及果蝇呼吸系统对大气氧气水平变化的潜在代偿反应。具体来说，这些实验将检查在10%、20%和40%的氧气条件下饲养一代、多代或选择大尺寸苍蝇时的呼吸反应。大气O2对气管系统输送氧气能力的影响将通过电子显微镜进行形态学测量，并通过测量允许正常代谢率的最低O2水平进行生理学测量。第四个目标是测试为什么饲养氧气水平会影响果蝇个体大小的三个非替代假设：1)直接氧气限制（DOL）假说认为，增加氧气利用率可以通过增加营养摄取量来提高幼虫的生长速度；2)氧气提示（OC）假说认为，增加氧气水平可以通过推迟换羽开始来延长发育速度；3)细胞大小假说认为，在细胞数量不变的情况下，较高的氧气水平可以通过增加细胞大小来增加苍蝇的大小。最后，我们将测试饲养O2水平对昆虫大小和发育速度的普遍性。这项对16个物种的比较研究还将测试氧气对这些变量的影响是否受到昆虫大小、发育模式或栖息地的影响。这个项目涉及一个独特的系统，在这个系统中，我们可以量化主要生活史特征（体型、发育速度）进化的生理约束程度（氧气可用性），因此将引起广泛的进化生物学家、生理学家和生态学家的兴趣。此外，大气中氧气对昆虫大小（以及历史上的昆虫巨体症）的可能控制引起了包括古地质学家、环境科学家和普通公众在内的许多非生物学家的极大兴趣。研究结果将通过生理和进化期刊以及《科学美国人》或《自然历史》等更广泛的渠道广泛传播。将建立一个关于昆虫呼吸生理学和氧气对昆虫大小影响的网站，并与昆虫生理学在线网站（http://lamar.colostate.edu/%7Einsects/index.html）相连。最后，该奖项还将资助博士后、研究生和本科生培训项目，为目前在生物学专业中代表性不足的群体提供培训。

It has been hypothesized that the giant insects of the late Paleozoic were made possible by high atmospheric oxygen levels, and that current insect body sizes are constrained by our atmospheric oxygen level of 21%. This research will test this hypothesis with a series of experiments that examine the effect of single- and multi-generation exposure to different atmospheric O2 levels on insect size, developmental rate, tracheal structure and function. Most of these experiments use fruitflies (Drosophila melanogaster), but one broad comparative study of the developmental plasticity of 16 insect species in response to variation in atmospheric O2 levels is included. The first goal of this research is to test whether D. melanogaster evolve different body sizes in response to variation in atmospheric O2 level (10, 20, 40% O2) in the lab. A second goal is to determine whether atmospheric O2 level can serve as a constraint on the evolution of large body size in D. melanogaster by selecting for large size in different O2 atmospheres. A third goal is to test for O2 delivery limitations, and potential compensatory responses of the respiratory system to variation in atmospheric oxygen level in fruitflies. Specifically these experiments will examine respiratory responses to rearing flies in 10, 20 and 40% O2 for one generation, multiple generations, or when selecting for large size. Atmospheric O2 effects on the capacity of the tracheal system to deliver oxygen will be measured morphologically with electron microscopy, and physiologically by measuring the lowest O2 level that permits normal metabolic rate. A fourth goal is to test three non-alternative hypotheses for why rearing O2 level affects individual fruitfly size: 1) The Direct O2 Limitation (DOL) Hypothesis that increasing O2 availability increases larval growth rates by increasing nutrient intake rates, 2) The O2 Cue (OC) Hypothesis, that increasing oxygen levels extend development rate by delaying the initiation of molting, and 3) The Cell Size (CS) hypothesis, that higher O2 levels increase fly size by increasing cell size at constant cell number. Finally, we will test for the generality of rearing O2 level on insect size and development rate. This comparative study of 16 species will also test whether O2 effects on these variables are influenced by insect size, developmental pattern, or habitat. This project involves a unique system in which we can quantify the degree of physiological constraint (O2 availability) on the evolution of major life history traits (body size, developmental rate), and thus will be of interest to a wide array of evolutionary biologists, physiologists and ecologists. In addition, the possible control of atmospheric O2 on insect size (and historical insect gigantism) is of substantial interest to many non-biologists including paleogeologists, environmental scientists and the general public. Results will be widely disseminated through reviewed scientific papers in physiological and evolutionary journals as well as more general outlets such as Scientific American or Natural History. A web site on insect respiratory physiology and oxygen effects on insect size will be created and linked to the Insect Physiology On-line web site (http://lamar.colostate.edu/%7Einsects/index.html). Finally, this award will also fund postdoctoral, graduate, and undergraduate training programs for individuals from groups currently under-represented among biology professions.