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Respiration by mangrove ants Camponotus anderseni during nest submersion associated with tidal inundation in Northern Australia

Abstract.  The ant Camponotus anderseni lives exclusively in twigs of the mangrove tree Sonneratia alba, which forms the fringe at the wettest part of the mangrove zone. During inundation, which can last up to 3 h, the entrance hole to the nest cavity is blocked with a soldier's head that effectively prevents flooding, but simultaneously blocks gas exchange with the surroundings. The ants and brood, together with their mutualistic Coccid, Myzolecanium sp. 1, occupy an average of 23% of the volume of the nest cavities (maximum of 50%). Measurements of CO2 production in the laboratory indicate respiratory rates of 1.90 and 0.41 µL CO2 h−1 mg−1 live mass at 25 °C for workers and larvae, respectively. Measurements of sealed natural nests show that mean respiratory rates decrease to 18.9% and 1.8% of the normoxic rate at CO2 concentrations of 10% and 25%, respectively. In artificial nests where the initial CO2 is elevated, the respiratory rates after 1 h are reduced to 48% and 2.3% of the normoxic rate when exposed to CO2 concentrations of 10% and 25%, respectively. Air samples from natural nests in the field taken more than 12 h after inundation have mean CO2 concentrations of up to 4–5%, which means that the CO2 concentration in the parts farthest from the entrance must be much higher. In sealed nests in the laboratory, the O2 concentration after 1 h decreases by 6.8% and, in the same period, the CO2 concentration increases by 12.1%, which suggests that the ants have partly switched to anaerobic respiration. The rapid and extreme depression of the respiratory rates of C. anderseni represents an outstanding physiological adaptation that allows their survival under the extreme conditions of tidal inundation.