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First published online August 14, 2009
Journal of Experimental Biology 212, 2773-2780 (2009)
Published by The Company of Biologists 2009
doi: 10.1242/jeb.031310

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Cockroaches breathe discontinuously to reduce respiratory water loss

Natalie G. Schimpf^*, Philip G. D. Matthews, Robbie S. Wilson and Craig R. White

School of Biological Sciences, Faculty of Biological and Chemical Sciences, University of Queensland, Brisbane 4000, Australia

^* Author for correspondence (e-mail: n.schimpf{at}uq.edu.au)

Accepted 8 June 2009

The reasons why many insects breathe discontinuously at rest are poorly understood and hotly debated. Three adaptive hypotheses attempt to explain the significance of these discontinuous gas exchange cycles (DGCs), whether it be to save water, to facilitate gas exchange in underground environments or to limit oxidative damage. Comparative studies favour the water saving hypothesis and mechanistic studies are equivocal but no study has examined the acclimation responses of adult insects chronically exposed to a range of respiratory environments. The present research is the first manipulative study of such chronic exposure to take a strong-inference approach to evaluating the competing hypotheses according to the explicit predictions stemming from them. Adult cockroaches (Nauphoeta cinerea) were chronically exposed to various treatments of different respiratory gas compositions (O₂, CO₂ and humidity) and the DGC responses were interpreted in light of the a priori predictions stemming from the competing hypotheses. Rates of mass loss during respirometry were also measured for animals acclimated to a range of humidity conditions. The results refute the hypotheses of oxidative damage and underground gas exchange, and provide evidence supporting the hypothesis that DGCs serve to reduce respiratory water loss: cockroaches exposed to low humidity conditions exchange respiratory gases for shorter durations during each DGC and showed lower rates of body mass loss during respirometry than cockroaches exposed to high humidity conditions.

Key words: DGC, discontinuous gas exchange, hygric, chthonic, oxidative damage, Nauphoeta cinerea

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