Hypotheses regarding the discontinuous gas exchange cycle (DGC) of insects

• Insects produce three distinct patterns of gas exchange.
• The function and evolutionary significance of these patterns has been the topic of numerous studies.
• We review current hypotheses regarding the evolutionary significance of the DGC.
• We conclude that the DGC arose primarily to regulate respiratory gas exchange.
• The DGC may also serve as an exaptation that provides additional adaptive benefits.

The evolutionary origin of the insect respiratory pattern referred to as the discontinuous gas exchange cycle (DGC) has been a topic of extensive discussion among insect physiologists for at least 50 years. This pattern has often been thought to reduce respiratory water loss (RWL). However, because this pattern does not consistently conserve water among all taxa, other hypotheses have been proposed to try and explain the significance of the DGC. In this review we briefly describe the different hypotheses postulated to date. We conclude that the DGC is primarily a respiratory pattern deriving from the simultaneous regulation of O2 and CO2. It may nonetheless have additional adaptive functions in insects.