Meeting Abstract
141.3 Monday, Jan. 7 Fluctuations in Historical Oxygen Levels Impacted Insect Body Size and Physiology VANDENBROOKS, J.M.*; MUNOZ, E.E.; WEED, M.D.; HARRISON, J.F.; Arizona State University; Penn State University; University of Arizona; Arizona State University jvandenb@asu.edu
Fluctuations in atmospheric oxygen over the last 500 million years have been hypothesized to have driven a number of evolutionary changes, including Paleozoic insect gigantism. However, the fact that not all insect groups exhibited gigantism coupled with the paucity of the fossil record and the complex interactions between oxygen, organisms and communities makes it difficult to definitively accept or reject the oxygen-size link. Yet, evidence from a series of modern insect rearing experiments does support this link: 1) dragonflies and other insects develop larger body sizes in hyperoxia, 2) almost all insects develop smaller body sizes in hypoxia, 3) tracheal system investment is inversely correlated with rearing oxygen, and 4) rearing oxygen affects insect physiology including growth, development, and fecundity even in insects that show no increase in body size. These results point to not just an effect of oxygen on maximum size, but a strong effect on average body size and insect physiology. Therefore, we have carried out a series of fossil studies focused on average body size across geologic times of both high and low oxygen levels. The results of these studies further support the link between fluctuations in oxygen and insect evolution: 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 Triassic hypoxic event appears to have a larger impact on insect body size than the Paleozoic hyperoxic event. The results from this combination of modern and fossil studies suggest that historical fluctuations in atmospheric oxygen would have influenced insect size, physiology and fitness. Supported by NSF EAR 0746352.
