Meeting Abstract

54.1  Thursday, Jan. 5  Developmental and fossil evidence that changes in atmospheric oxygen drove historical patterns in insect body size VANDENBROOKS, John M. *; MUNOZ, Elyse E.; WEED, Michael D; HARRISON, Jon F.; Arizona State University; Penn State University; Arizona State University; Arizona State University jvandenb@asu.edu

Recent geochemical models predict that over the last 500 million years atmospheric oxygen has varied from 12% to 31%. The major rise in oxygen during the late Paleozoic has been correlated with the evolution of insect gigantism. However, the correlation between oxygen and insect body size has never been rigorously tested and not all groups of insects exhibit gigantism. We’ve carried out a unique combination of modern rearing and fossil studies to test this link. The results of our fossil studies 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. Given the variation in responses of modern insects to oxygen, our rearing studies have focused on groups related to Paleozoic insects – dragonflies, related to the giant Protodanta and cockroaches, a group with no known giant fossils. The results were that: 1) dragonflies grew larger in hyperoxia and smaller in hypoxia, 2) cockroaches showed only a mild effect of hyperoxia on size, while hypoxia reduced size, 3) development, growth, and fecundity of the cockroaches were affected by oxygen and 4) cockroach tracheal volumes were inversely proportional to rearing oxygen. These results show that Paleozoic oxygen could have influenced insect size, physiology and fitness, even in groups that exhibit no gigantism, strengthening the link between oxygen and insect evolution. Supported by NSF EAR 0746352.