Adaptive respiration patterns by antlion larvae support the chthonic hypothesis for discontinuous gas exchange cycles

Insects display various respiration patterns using a respiratory system composed of valve-like spiracles and branching conduit-like tracheae. However, the adaptive value of discontinuous gas exchange cycles (DGCs), a respiratory pattern with unique gas exchange sequences, remains unanswered. Here, we used flow-through respirometry to study respiration patterns of antlion larvae, Myrmeleon crudelis, an insect that resides in pits constructed in soil, a possibly hypoxic-hypercapnic environment. Exposed antlions displayed continuous respiration patterns; however, antlion larvae inside pits switch to DGC, despite no changes in environmental parameters. Furthermore, transpiration rates did not differ between treatments. Investigations with confocal and scanning electron microscopy of tracheae revealed a hydrophobic chemistry that likely reduces water vapor permeability from hemolymph and an inner hierarchical topography that would enable efficient gas exchange. These findings show that the occurrence of DGCs in M. crudelis is associated with burrowing underground, suggesting it is a respiratory adaptation for hypoxic-hypercapnic subterranean environments.