Enzymatic analysis of the American locust jumping muscle during development

Abstract

Insects have the highest mass‐specific metabolic rates among animals due in part to their tracheal respiratory system. However, it has been hypothesized that larger/older insects may have greater oxygen delivery problems than smaller/younger insects because longer tracheae may be less efficient. This effect of size on oxygen delivery may be most dramatic during development or locomotion when oxygen demands are greatest. We tested this hypothesis by comparing the metabolic profile of the jumping muscle during development in the American locust (Schistocerca americana). Developing grasshoppers increase their body mass over 200 times from 1st instar juveniles to adults. To determine whether there is a developmental shift in the metabolic profile of the jumping muscle, we compared how enzymatic markers for aerobic (citrate synthase) and anaerobic metabolism (lactate dehydrogenase) varied in 2nd, 4th, and 6th instar as well as adult grasshoppers. Lactate dehydrogenase increased 2.8 fold with age from the 2nd instar to the adult. In contrast, citrate synthase decreased 1.9 fold with age from the 2nd instar to the adult. These findings support the hypothesis that the metabolic profile of S. americana jumping muscle gradually increases its reliance on anaerobic metabolism with development. Our research supports previous findings that larger/older grasshoppers produce more powerful jumps that result in greater lactic acid production than smaller/younger grasshoppers.