Meeting Abstract
38.4 Jan. 5 Does body size affect the safety margin for oxygen delivery in flying dragonflies? HENRY, J.R.*; HARRISON, J.F.; Arizona State University; Arizona State University Joanna.Henry@asu.edu
It has been widely hypothesized that the evolution of insect gigantism during the late Paleozoic was permitted due to increased atmospheric oxygen levels at the time. One mechanism by which increased atmospheric oxygen levels might facilitate evolution of larger insects would be by enabling more efficient delivery of oxygen to tissues in larger animals. According to this hypothesis, larger extant insects should have a lower safety margin for oxygen delivery. Nevertheless, recent studies have shown that safety margins for oxygen delivery neither decrease with size in resting or hopping grasshoppers, nor with feeding Manduca caterpillars. However, perhaps these prior negative results occurred because they did not test insects during the conditions of maximal oxygen consumption�-namely flight. We measured the oxygen-sensitivity of take-off capacity and flight metabolic rate for 12 species of dragonflies that vary by an order of magnitude in body size. Flight metabolic rates and flight times were measured in 2.5, 5, 7.5, 10, 15, 21 and 30% O2 balanced with N2 or helium. Atmospheric oxygen levels strongly affected flight metabolism and times, and hypodense atmospheres increased flight metabolic rates. However, data suggest that large body size is not correlated with a reduced safety margins for oxygen delivery. These results and other studies consistently suggest that insects match oxygen delivery capacity to need across size changes, due to morphological (increased tracheal densities) and physiological (increased convection) changes. Simple diffusive models of gas exchange that postulate a need for higher oxygen to enable oxygen delivery in larger insects should be abandoned. This research was funded by NSF grant IBN-0419704 awarded to JFH.
