Validation of manometric microrespirometers for measuring oxygen consumption in small arthropods

Scientists have used numerous techniques to measure organismal metabolic rate, including assays of oxygen (O₂) consumption and carbon dioxide (CO₂) production. Relatively few studies have directly compared estimates of metabolic rate on the same groups of animals as determined by different assay methods. This study directly compared measures of the metabolic rate of three lines of Drosophila simulans as determined either from direct measures of CO₂ production using infrared gas analysis (IRGA), or from estimates of O₂ consumption based on manometeric techniques. Determinations of metabolic rate of the same cohorts of flies using these two methods produced results that often differed widely. Typically metabolic rate as determined by the manometric method was significantly greater than that determined by CO₂ output. These differences are difficult to explain by simple biotic or abiotic factor(s). Because of the idiosyncratic nature of these differences it is not possible to use a simple factor to convert from metabolic rate measurements done using manometric techniques to those expected from direct measures of CO₂ output or O₂ consumption. Although manometric devices are simple to construct and use, measurements of metabolic rate made with this method can vary significantly from measurements made by directly assaying CO₂ production or O₂ consumption.