A method for studying the metabolic activity of individual tardigrades by measuring oxygen uptake using micro-respirometry

Studies of tardigrade biology have been severely limited by the sparsity of appropriate quantitative techniques, informative on a single-organism level. Therefore, many studies rely on motility-based survival scoring and quantifying reproductive success. Measurements of O2 respiration rates, as an integrating expression of the metabolic activity of single tardigrades, would provide a more comprehensive insight into how an individual tardigrade is responding to specific environmental factors or changes in life stages. Here we present and validate a new method for determining the O2 respiration rate (nmol O2 mg-1 hour-1) of single tardigrades under steady state, using O2-microsensors. As an example, we show that the O2 respiration rate determined in MilliQ water for individuals of Richtersius coronifer and of Macrobiotus macrocalix at 22 °C was 10.8±1.8 nmol O2 mg-1 hour-1 and 13.1±2.3 nmol O2 mg-1 hour-1, respectively.