Cyclic gas exchange in the giant burrowing cockroach, Macropanesthia rhinoceros: Effect of oxygen tension and temperature

The giant burrowing cockroach, Macropanesthia rhinoceros, is endemic to north-eastern Australia and excavates a permanent burrow up to 1 m deep into soil. Using flow-through respirometry, we investigated gas exchange and water loss at three different oxygen tensions (21%, 10% and 2% at 20 °C) and temperatures (10, 20 and 30 °C at 21% oxygen). M. rhinoceros employ cyclic gas exchange (CGE) making the species by far the largest insect known to engage in discontinuous ventilation. CGE featured rhythmic bursts of CO2 dispersed among inter-burst periods of reduced output. CGE was most commonly observed at 20 °C and degraded at <10% oxygen. Mild hypoxia (10% oxygen) resulted in a lengthening of the burst period by approximately two-fold; this result is complementary to oxygen consumption data that suggests that the burst period is important in oxygen uptake. When exposed to severe hypoxia (2% oxygen), CGE was degraded to a more erratic continuous pattern. Also, during severe hypoxia, total water loss increased significantly, although CO2 release was maintained at the same level as in 21% oxygen. During CGE, an increase in temperature from 10 to 20 °C caused both water loss and CO2 output to double; from 20 to 30 °C, CO2 output again doubled but water loss increased by only 31%.