Hypobaria enhances oxygen delivery in grasshoppers

Abstract

Hypobaric hypoxia (altitude) theoretically poses less of a challenge to oxygen delivery than normobaric hypoxia for animals with significant diffusive exchange in the gas phase, as increases in the diffusion coefficient match decreases in PO2 as barometric pressure decreases. However hypobaria could have separate stressful effects on collapsible structures. Here we tested the effect of hypobaric hypoxia, normobaric hypoxia, and hypobaric normoxia (constant PO2) on respiratory responses of adult American locusts, Schistocerca americana. Hypobaric and normobaric hypoxia stimulated ventilation frequency, limb movements (escape behavior) and CO2 emission rates. Multiple results supported the importance of aerial diffusion in resting gas exchange of grasshoppers. First, animals in hypobaric hypoxia struggled less than those in normobaric hypoxia at equivalent PO2's. Second, ventilation and CO2 emission rates decreased as barometric pressure decreased at constant PO2. These data indicate that gas‐phase diffusion is an important mechanism of gas exchange in these large insects that exhibit prominent abdominal pumping, and that insects are likely to perform better at altitude than predicted by tests performed in normobaric hypoxia. This research was supported by IBN‐9985857 and IBN 0419704 to JFH.