LIGHTON, JRB*; SCHILMAN, PE; Univ. of NV, Las Vegas; Univ. of CA, San Diego: What the Eleodes going on: Cyclic gas exchange in the xeric beetle, Eleodes armata

In insects, the discontinuous gas exchange cycle or DGC is now fairly well understood, though its selective correlates and evolutionary genesis remain elusive. Less well described and far less appreciated (in the sense of understood), cyclic gas exhange is a portmanteau term for patterns of gas exchange that involve a degree of active spiracular control, but do not allow for interpretation in terms of the triphasic DGC. CGE is not uncommon in insects and some studies suggest it may be the rule rather than the exception. Puzzlingly, although CGE should theoretically impose a repiratory water loss penalty, it is quite common among xeric insects. Here we describe the occurrence, nature and kinetics of the CGE in a common xeric arthropod, the darkling circus beetle Eleodes armata, a prominent inhabitant of deserts in the southwestern USA. We demonstrate that steady-state CGE regulates a constant endotracheal pO₂, and does so in the face of challenges in the form of changes in ambient pO₂. Moreover, CGE in is also characterized by intermittent and cyclic episodes of excess CO₂ emission, and the interaction between these events, the extent of hypoxic or hyperoxic challenge, and the role of the subelytral chamber, comprises an important part of this talk.