Impacts of Paleo-Oxygen Levels on the Size, Development, Reproduction, and Tracheal Systems of Blatella germanica

Atmospheric oxygen has varied substantially over the Phanerozoic (the last 500 million years) with periods of both hyperoxia and hypoxia relative to today. Unlike some insect groups, cockroaches have not been reported to exhibit gigantism during the late Paleozoic period of hyperoxia. Studies with modern insects have shown a diversity of developmental responses to oxygen, suggesting that evaluation of historical hypotheses should focus on groups most closely related to those present in the Paleozoic. Here we investigated the impacts of Paleozoic oxygen levels (12-31%) on the development of Blatella germanica cockroaches. Body size decreased strongly in hypoxia, but was only mildly affected by hyperoxia. Development time, growth rate and fecundity were negatively impacted by both hypoxia and hyperoxia. Tracheal volumes were inversely proportional to rearing oxygen, suggesting developmental responses aimed at regulating internal oxygen level. The results of these experiments on a modern species are consistent with the fossil record and suggest that changes in atmospheric oxygen would be challenging for many insects, despite plastic compensatory responses in the tracheal system.