Figure 18.8 Atmospheric Oxygen Concentrations and Body Size in Insects
Paleontologists have long wondered why giant insects are limited to the fossil record, disappearing at the end of the Permian. Given that Earth’s oxygen levels were also much higher during that time period, scientists have suggested that these higher levels of oxygen enabled the existence of these giant insects. In order to test the hypothesis that increased partial pressures of oxygen can result in selection for larger insects, Drosophila melanogaster were exposed to either normal control levels of oxygen given present atmospheric conditions (control) or an increased partial pressure of oxygen (hyperbaric) at the level thought to have occurred during the Carboniferous and Permian. Flies were reared for five generations under these conditions. Both lines of Drosophila were returned to normal control oxygen levels for the sixth generation to avoid any phenotypic differences due to environmentally induced plasticity. The mass of each fly from the sixth generation was determined and compared between the two treatments. Flies from parents exposed to the increased partial pressure of oxygen were significantly larger than the flies from parents reared in control atmospheric conditions. Thus, results show selection for larger flies with increased oxygen, supporting the explanation for the presence of giant insects during the Carboniferous and Permian. One constraint of this study was that increased atmospheric pressure and oxygen concentration were confounded; Dudley and Chai (1996) have demonstrated that these two variables can be varied independently by using combinations of oxygen, nitrogen, and noble gases such as helium and xenon. Using this method, this experiment could be rerun to determine whether increased atmospheric pressure or oxygen concentration is the true cause of increased body size.
Original Paper
Berner, R. A., D. J. Beerling, R. Dudley, J. M. Robinson, and R. A. Wildman, Jr. 2003. Phanerozoic atmospheric oxygen. Annual Review of Earth and Planetary Sciences 31: 105–134.
http://dx.doi.org/10.1146/annurev.earth.31.100901.141329
Links
Dudley, R., and P. Chai. 1996. Animal flight mechanics in physically variable gas mixtures. Journal of Experimental Biology 199: 1881–1885.
http://jeb.biologists.org/cgi/content/abstract/199/9/1881
Dudley, R. 1998. Atmospheric oxygen, giant Paleozoic insects and the evolution of aerial locomotor performance. Journal of Experimental Biology 201: 1043–1050.
http://jeb.biologists.org/cgi/content/short/201/8/1043
Frazier, M. R., H. A. Woods, and J. F. Harrison. 2001. Interactive Effects of Rearing Temperature and Oxygen on the Development of Drosophila Melanogaster. Physiological and Biochemical Zoology 74: 641–650.
http://www.journals.uchicago.edu/doi/abs/10.1086/322172
Harrison, J., M. R. Frazier, J. R. Henry, A. Kaiser, C. J. Kloka, and B. Rasc—n. 2006. Responses of terrestrial insects to hypoxia or hyperoxia. Respiratory Physiology & Neurobiology 154: 4–17.
http://dx.doi.org/10.1016/j.resp.2006.02.008
Klok, C. J., A. Kaiser, J. R. B. Lighton and J. F. Harrison. 2010. Critical oxygen partial pressures and maximal tracheal conductances for Drosophila melanogaster reared for multiple generations in hypoxia or hyperoxia. Journal of Insect Physiology 56: 461–469.
http://dx.doi.org/10.1016/j.jinsphys.2009.08.004
Klok, C. J., and J. F. Harrison. 2009. Atmospheric Hypoxia Limits Selection for Large Body Size in Insects. PLoS ONE 4(1): e3876.
http://dx.doi.org/10.1371/journal.pone.0003876
Arizona State University: Jon F. Harrison Lab
http://www.public.asu.edu/~icjfh/
Science Daily: Giant Insects Might Reign If Only There Was More Oxygen In The Air
http://www.sciencedaily.com/releases/2006/10/061012093716.htm
Arizona State University: ASU researchers link Paleozoic oxygen to insects’ size
http://asunews.asu.edu/20071004_insects
National Geographic: Giant Bugs a Thing of the Past, Study Suggests
http://news.nationalgeographic.com/news/2007/07/070730-giant-insects.html