Jon F. Harrison1,*, Alexander Kaiser2 and John M. VandenBrooks1
-Author Affiliations
1School of Life Sciences, Arizona State University, Tempe, AZ 85287-4501, USA
2Department of Biochemistry, Midwestern University, Glendale, AZ 85308, USA
* Author for correspondence (j.harrison@asu.edu).
Abstract
Insects are small relative to vertebrates, possibly owing to limitations or costs associated with their blind-ended tracheal respiratory system. The giant insects of the late Palaeozoic occurred when atmospheric PO2 (aPO2) was hyperoxic, supporting a role for oxygen in the evolution of insect body size. The paucity of the insect fossil record and the complex interactions between atmospheric oxygen level, organisms and their communities makes it impossible to definitively accept or reject the historical oxygen-size link, and multiple alternative hypotheses exist. However, a variety of recent empirical findings support a link between oxygen and insect size, including: (i) most insects develop smaller body sizes in hypoxia, and some develop and evolve larger sizes in hyperoxia; (ii) insects developmentally and evolutionarily reduce their proportional investment in the tracheal system when living in higher aPO2, suggesting that there are significant costs associated with tracheal system structure and function; and (iii) larger insects invest more of their body in the tracheal system, potentially leading to greater effects of aPO2 on larger insects. Together, these provide a wealth of plausible mechanisms by which tracheal oxygen delivery may be centrally involved in setting the relatively small size of insects and for hyperoxia-enabled Palaeozoic gigantism.
body size evolution oxygen gigantism
Footnotes
Received January 7, 2010.
Accepted February 19, 2010.
© 2010 The Royal Society
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