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First published online November 19, 2004
Journal of Experimental Biology 207, 4463-4471 (2004)
Published by The Company of Biologists 2004
doi: 10.1242/jeb.01284

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The hyperoxic switch: assessing respiratory water loss rates in tracheate arthropods with continuous gas exchange

John R. B. Lighton^1,*, Pablo E. Schilman² and David A. Holway²

¹ University of Nevada at Las Vegas, Department of Biology, University of Nevada at Las Vegas, 4505 Maryland Parkway, NV 89154-4004 USA
² Section of Ecology, Behavior and Evolution, Division of Biological Sciences, University of California at San Diego, 9500 Gilman Drive, La Jolla, CA 92093-0116 USA

View larger version (28K): [in a new window]   Fig. 1. Simplified diagram of the respirometry system. Not to scale. Data acquisition system not shown. Oxygen and nitrogen tanks are at the bottom; each opens into a manifold through which oxygen or nitrogen flow can be controlled with a needle valve (NV). MFC, mass flow control valve (associated controller not shown). Dashed rectangle is temperature-controlled cabinet (Peltier effect; PE-temp). S, scrubber (H2O and CO2); EQ, equilibration coil; RC, respirometry chamber; T, thermocouple; H2O, water vapor analyzer; CO2, carbon dioxide analyzer. See text for details.

View larger version (20K): [in a new window]   Fig. 2. Typical recording of a hyperoxic switch recording of Drosophila melanogaster. Eleven flies, total mass 9.41 mg, at 20°C and 40 ml min–1 STP. The recording begins and ends with baselines. Two water excretion events can be seen at 20–30 min into the recording. The large dip in CO2 that follows hyperoxia is plainly visible at 65 min. A modest drop in H2O coincides with the drop in CO2. To minimize the influence of long-term drift on our measurements, we used only the magnitude of the H2O drop immediately coinciding with the CO2 drop. Following the introduction of nitrogen, a rapid rise in both H2O and CO2 are evident. CO2 rapidly declines to near baseline levels, but H2O plateaus at an intermediate level; see text.

View larger version (21K): [in a new window]   Fig. 3. Typical recording of a hyperoxic switch recording of Forelius mccooki. Ten ants, total mass 3.28 mg, at 20°C and 20 ml min–1 STP. The recording begins and ends with baselines. Intermittent water excretion events can be seen near the start of the recording and at 60 min. The large dip in CO2 that follows hyperoxia is plainly visible at 50 min. The drop in H2O coincides with the drop in CO2 and immediately precedes a small excretion event. We noticed that water excretion events often occurred 5–20 min after initiation of hyperoxia in all species. Because we used only the magnitude of the H2O drop immediately coinciding with the CO2 drop, these events, though annoying, usually did not interfere with our measurements. Following the introduction of nitrogen, a rapid rise in both H2O and CO2 are evident. CO2 rapidly declines to near baseline levels, but H2O starts to plateau at an intermediate level; see text.

View larger version (19K): [in a new window]   Fig. 4. Typical recording of a hyperoxic switch recording of Pogonomyrmex californicus. One ant, mass 8.25 mg, at 40°C and 20 ml min–1 STP. The recording begins and ends with baselines. The large dip in CO2 that follows hyperoxia is plainly visible. The drop in H2O coincides with the drop in CO2. Following the introduction of nitrogen, a rapid rise in both H2O and CO2 are evident. CO2 rapidly declines to near baseline levels, but H2O plateaus at an intermediate level; see text.