Utilization of a Clark electrode device as a respirometer for small insects: A convincing test on ants allowing to detect discontinuous gas exchange

Respirometry provides a direct measure of an organism’s O₂ consumption rate (VO₂), which is a significant component of its metabolic rate (energy expenditure). Amongst ants, variations in lifespan between different social castes (such as workers and queens) can be substantial, varying depending on the species. As metabolic rate is higher in short-living species, we aimed to determine how VO₂ and longevity may have coevolved within ant casts. Measuring VO₂ in such tiny animal models can be challenging, and as a first methodological step, we validate the use of a Clark electrode, initially designed for measuring mitochondrial respiration control pathways, for assessing VO₂ in ants within a sealed chamber. This was done by comparing it with stop-flow VO₂ and CO₂ production, using a traditional indirect calorimetry device. The global aim is to provide a reliable protocol to conduct accurate comparisons of metabolic rates within and among ant species. As expected, using the Clark electrode entails high time resolution and revealed that queens and workers exhibited discontinuous gas exchange, with episodes of apnea lasting up to 20 min.