Flies Avoid Current Atmospheric CO(2) Concentrations

CO(2) differs from most other odors by being ubiquitously present in the air animals inhale. CO(2) levels of the atmosphere, however, are subject to change. Depending on the landscape, temperature, and time of the year, CO(2) levels can change even on shortest time scales. In addition, since the 18th century the CO(2) baseline keeps increasing due to the intensive fossil fuel usage. However, we do not know whether this change is significant for animals, and if yes whether and how animals adapt to this change. Most insects possess olfactory receptors to detect the gaseous molecule, and CO(2) is one of the key odorants for insects such as the vinegar fly Drosophila melanogaster to find food sources and to warn con-specifics. So far, CO(2) and its sensory system have been studied in the context of rotting fruit and other CO(2)-emitting sources to investigate flies’ response to significantly elevated levels of CO(2). However, it has not been addressed whether flies detect and potentially react to atmospheric levels of CO(2). By using behavioral experiments, here we show that flies can detect atmospheric CO(2) concentrations and, if given the choice, prefer air with sub-atmospheric levels of the molecule. Blocking the synaptic release from CO(2) receptor neurons abolishes this choice. Based on electrophysiological recordings, we hypothesize that CO(2) receptors, similar to ambient temperature receptors, actively sample environmental CO(2) concentrations close to atmospheric levels. Based on recent findings and our data, we hypothesize that Gr-dependent CO(2) receptors do not primarily serve as a cue detector to find food sources or avoid danger, instead they function as sensors for preferred environmental conditions.