Meeting Abstract

31.1  Wednesday, Jan. 5  The Role of Atmospheric Oxygen in the Evolution of Insect Body Size VANDENBROOKS, John M.*; MUNOZ, Elyse E.; WEED, Michael D.; HARRISON, Jon F.; Arizona State University; Arizona State University; Arizona State University; Arizona State University jvandenb@asu.edu

While not all models agree, most estimate that over the last 500 million years atmospheric oxygen has varied from 12% to 31%. The giant insects of the late Paleozoic occurred when atmospheric PO2 (aPO2) was hyperoxic, hinting at a role of oxygen in the evolution of insect body size. However, the paucity of the insect fossil record and the complex interactions between oxygen levels, organisms and communities have made it difficult to definitively accept or reject a historical oxygen-size link. We’ve carried out a unique combination of modern rearing and fossil studies to test this link. The results of our rearing studies support a link between oxygen and size: 1) most insects develop smaller body sizes in hypoxia, and some develop and evolve larger sizes in hyperoxia; 2) insects developmentally and evolutionarily reduce their proportional investment in the tracheal system when living in higher aPO2; and 3) larger insects invest more of their body in the tracheal system, potentially leading to greater effects of aPO2 on large insects. These provide mechanisms by which tracheal oxygen delivery may be involved in the small size of modern insects and hyperoxia-enabled Paleozoic gigantism. The results of our fossil studies also support the oxygen-size link: 1) the maximal and average size of Protodonata and Paleodictyoptera fossils correlate positively with modeled atmospheric oxygen, 2) Blattodea fossils showed little variation in maximum size, but average size was correlated with atmospheric oxygen, and 3) the giant arthropods, such as Arthropleura , are outliers to an overall pattern of oxygen-mediated body size change. These results strengthen the argument that atmospheric oxygen has played a role in the evolution of insect body size. Supported by NSF EAR 0746352.