ANT BREATHING - TESTING REGULATION AND MECHANISM HYPOTHESES WITH HYPOXIA

Using normoxic and hypoxic flow-through respirometry, we investigated the regulation of the closed-spiracle (C) and the nature of the flutte ring-spiracle (F) phases of the discontinuous gas-exchange cycle (DGC) of the ant Camponotus vicinus. We predicted that as ambient O-2 conce ntrations declined, DGC frequency would increase, because C phase dura tion would decrease (reflecting earlier hypoxic initiation of the F ph ase) and F phase duration would shorten (reflecting nitrogen accumulat ion), if convective mass inflow caused by a negative pressure gradient across the spiracles, rather than by diffusion, is the dominant F pha se gas-exchange mechanism. C phase duration decreased with declining a mbient O-2 concentrations, as predicted, In contrast, DGC frequency de creased and F phase duration increased with decreasing ambient O-2 con centrations, This was opposite to the expected trend if gas exchange i n the F phase was mediated by convection, as is generally hypothesized , We therefore cannot disprove that F phase gas exchange was largely o r purely diffusion-based, In addition, our data show equivalent molar rates of H2O and CO2 emission during the F phase. In contrast, during the open-spiracle phase, the duration of which was not affected by amb ient O-2 concentration, far more H2O than CO2 was lost. We discuss the se findings and suggest that current hypotheses of F phase gas-exchang e mechanisms and function in reducing respiratory water loss in adult insects may require revision.