Behavioural responses to environmental hypercapnia in two eusocial species of African mole rats.

Damaraland and naked mole rat are eusocial mammals that live in crowded burrows in which CO is elevated. These species are thought to be highly tolerant of CO but their behavioural responses to hypercapnia are poorly understood. We hypothesized that Damaraland and naked mole rats would exhibit blunted behavioural responses to hypercapnia and predicted that their activity levels would be unaffected at low to moderate (2-5%) CO but increased at > 7% CO. To test this, we exposed Damaraland and naked mole rats to stepwise increases in environmental CO (0-10%) and measured activity, exploratory behaviour, and body temperature. Surprisingly, we found that both species exhibited no differences in movement velocity, distance travelled, zone transitions (exploration), or body temperature at any level of environmental hypercapnia. Conversely, when carbonic anhydrase was inhibited with acetazolamide (50 mg kg intraperitonially, to increase whole-animal acidosis), exploration was significantly elevated relative to hypercapnic controls in both species at all levels of inhaled CO, and naked mole rat body temperature decreased in > 7% CO. We conclude that both species are largely non-responsive to environmental CO, and that this tolerance may be dependent on bicarbonate buffering at the level of the kidney or within the blood.