Respiratory adaptations to a combination of oxygen deprivation and extreme carbon dioxide concentration in nematodes

To examine physiological adaptations to the two combined stressors O2 deprivation and extreme CO2 concentrations, we compared respiratory responses of two nematode species occurring in natural CO2 springs. The minimum O2 concentration allowing maintenance of respiration in both species was 0.0176 μmol O2 ml−1 (corresponds to 1.4% O2 in air). After exposure to anoxia, individuals resumed respiration immediately when O2 was added, but on a lower level compared to control and without showing a respiratory overshoot. A species-specific response was found in respiration rate during 20% CO2: the more tolerant species maintained respiration rates, whereas the sensitive species showed a decreased respiration rate as low as after anoxia. The results indicate that during 20% CO2 the sensitive species undergo a survival state. We conclude, that the ability to maintain respiration even under low oxygen and high CO2 concentrations may allow the better adapted species to occupy an ecological niche in the field, where others cannot exist.