Insects are the most evolutionarily successful animals in part due to their air-filled tracheal respiratory system. The tracheal system is an intricate network of tubes that exchange gases between the atmosphere and tissues. Some insects, including grasshoppers, also have air sacs that enhance convective airflow. During intermolt periods, the American locust (Schistocerca americana) doubles their body mass, which may compress the tracheae. In a recent study, late-stage grasshoppers had reduced air sac ventilation frequency, decreased convective capabilities, and less of their body dedicated to their respiratory system. We hypothesized that these developmental changes may reduce both oxygen delivery and jump performance. We forced early-stage (day 2) and late-stage (day 8) 6th instar grasshoppers to jump in artificial oxygen atmospheres (5%, 10%, 21%, 40% oxygen: balance nitrogen) in a 100 L gloved box. After jumping, grasshoppers were immediately frozen in liquid nitrogen for a fluorometric lactate assay. We predicted that if oxygen delivery is compromised during development, then late-stage grasshopper jump rate and lactate production would correlate with oxygen level.
Within the first one to two minutes of jumping, there were no significant differences in jump rate between early- and late-stage grasshoppers at any oxygen level. This result was not surprising since previous work has shown that the first two minutes of jumping is fueled primarily by anaerobic ATP production. At moderate hypoxia (10% O2) and normoxia (21% O2), there were no differences in jump rate between early- and late-stage grasshoppers. In extreme hypoxia (5% O2), there was no difference in jump performance for the first two minutes, but late-stage grasshoppers had a 1.6-fold lower average jump rate in minutes three through five. In hyperoxia (40% O2), jump performance was similar during the first minute, and late-instar grasshoppers jump rates increased on average by 1.4-fold in minutes two through five.
Late-instar grasshopper muscles produced significantly greater lactate regardless of oxygen level. Within each group, oxygen level did not significantly affect jumping muscle lactate production. However, late-stage grasshoppers produced 26.3% significantly more lactate in 5% oxygen than 40% oxygen (post-hoc Student’s t; p<0.04). Future research will examine how age and oxygen level impact HIF-1 expression in grasshoppers. Since late-stage grasshoppers have lower jump rates and increased lactate production, we predict they will also have elevated HIF-1 protein levels.
This research was funded in part by the Arnold & Mabel Beckman Foundation and Union College.