Atmospheric Oxygen Effects on Insect Body Size and Tracheal Function

有人假设，古生代晚期的巨型昆虫是由于大气中的高含氧量而成为可能的，而目前的昆虫身体大小受到我们21%的大气含氧量的限制。 这项研究将通过一系列实验来验证这一假设，这些实验检查单代和多代暴露于不同的大气O2水平对昆虫大小、发育速率、气管结构和功能的影响。 大多数这些实验使用果蝇（果蝇），但一个广泛的比较研究的16种昆虫的发育可塑性在大气中的O2水平的变化。 本研究的第一个目的是检验D.在实验室条件下，黑腹果蝇对不同浓度O2（10、20、40%O2）的反应是不同的。 第二个目标是确定大气中的O2水平是否可以作为一个约束的发展大型机构在D。黑腹果蝇在不同的O2气氛中选择大尺寸。 第三个目标是测试O2输送限制，以及呼吸系统对果蝇大气氧含量变化的潜在补偿反应。 具体而言，这些实验将检查呼吸反应饲养苍蝇在10，20和40%的O2为一代，多代，或当选择大尺寸。 大气O2对气管系统供氧能力的影响将通过电子显微镜在形态学上进行测量，并通过测量允许正常代谢率的最低O2水平在生理学上进行测量。 第四个目标是测试为什么饲养O2水平影响个体果蝇大小的三个非替代假设：1）直接O2限制（DOL）假说，即增加O2可用性通过增加营养摄入速率来增加幼虫生长速率，2）O2线索（OC）假说，即增加氧水平通过延迟蜕皮的开始来延长发育速率，3）细胞大小（CS）假说，即较高的O2水平通过在恒定的细胞数量下增加细胞大小来增加苍蝇大小。 最后，我们将测试饲养O2水平对昆虫大小和发育速率的通用性。 16个物种的比较研究还将测试是否O2对这些变量的影响是由昆虫的大小，发育模式，或栖息地。 该项目涉及一个独特的系统，在该系统中，我们可以量化生理约束（O2可用性）对主要生活史特征（体型，发育率）进化的程度，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O2对昆虫大小的可能控制（以及历史上的昆虫寄生）引起了许多非生物学家的极大兴趣，包括古地质学家，环境科学家和公众。 研究结果将通过生理学和进化学期刊上的综述性科学论文以及《科学美国人》或《自然历史》等更一般的媒体广泛传播。 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，并将其与昆虫生理学在线网站（http：//lamar.colostate.edu/%7Einsects/index.html）链接。 最后，该奖项还将资助博士后，研究生和本科生培训计划，为目前生物专业中代表性不足的群体提供个人。

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.