Insects are tracheate arthropods and employ direct transfer of respiratory gases to and from their sites of use and generation via the tracheal system. Those gases flow through the tracheal system via convective and/or diffusive processes. The interface between the tracheal system and the outside world, the spiracles, requires stringent control to minimize the otherwise rapid loss of body water by evaporation and to facilitate gas exchange. The normal functioning of water-conserving spiracular control is critically dependent on the production of large partial pressure gradients which may be accompanied by negative endotracheal pressures that serve to retard the egress of water vapor. These factors result in a discontinuous gas exchange cycle or DGC. The DGC is vitally important in the "bottleneck" state of ant colony reproduction, the claustral phase of female alate ants, during which hypoxia and hypercapnia may occur, and during which energy and water management are vital components of fitness. Here we report (in intact female alates of Camponotus vicinus) the hygric correlates of manipulation of oxygen partial pressure gradients as measured with simultaneous water vapor detection using state of the art flow-through respirometry. The resulting distortion and finally complete disruption of spiracular control as oxygen partial pressure gradients fall below critical values, and respiratory water losses reach maximal values, are analyzed in the light of current theories of discontinuous gas exchange in insects and their evolutionary relevance to the selective genesis of the DGC.
Species 1: Hymenoptera Formicidae Camponotus vicinus (Carpenter ant)
Keywords: Hypoxia, water loss
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