Meeting Abstract
39.3 Tuesday, Jan. 5 Atmospheric Oxygen Influences on the Size of Modern and Fossil Insects VANDENBROOKS, John M.*; HARRISON, Jon F.; Arizona State University; Arizona State University jvandenb@asu.edu
Recent modeling has estimated that over the last 500 million years atmospheric oxygen has varied from as low as 12% in the Triassic to as high as 31% in the Permian. While there have been many hypotheses linking oxygen variation to evolutionary events (i.e. insect gigantism, extinctions, and dispersals), the majority of evidence is correlational. To test the effects of oxygen on physiology and evolution and move from correlation to causation, we have reared a wide variety of insects under historical oxygen levels including beetles, cockroaches, moths, fruitflies, grasshoppers and dragonflies. What has become evident is the wide diversity of responses of insect body size to variation in rearing oxygen. While the majority of species show decreased body sizes in hypoxia, the responses to hyperoxia are quite variable. For example, the body size of Schistocerca grasshoppers were unaffected by hyperoxia, while Blatella cockroaches were progressively smaller with hyperoxia. Manduca moths showed no effect of mild hyperoxia, but were smaller at high levels of hyperoxia, yet Zophobas beetles showed increased body sizes under hyperoxia up to a threshold value beyond which they decreased in size. Throughout all the species, atmospheric oxygen affected not just maximum body size, but also strongly influenced average body size. When we begin to examine the fossil record, we also see that certain groups have responded more strongly to historical variation in oxygen. While taxa such as Protodonata, Paleodictyoptera, and Arthropleura exhibited gigantism, Blattodea show little variation in maximum size, but do show shifts in average size. Here we examine the differential responses in modern organisms and the implications for the fossil record. This research was supported by NSF EAR 0746352 and DOD 3000654843 subcontract to JFH.
