| Scaling relationships provide great predictive value for understanding ecological patterns and functional consequences of animal design. In this thesis, I investigated how both ontogenetic and interspecific body size changes affect locomotory performance and metabolism in jumping grasshoppers.; In developmental studies using the American locust (Schistocerca americana), I forced various aged grasshoppers to jump until exhaustion and measured jump performance, morphology, lactate production, oxygen consumption, carbon dioxide production, and oxygen sensitivity. Power outputs during initial jumps increased with age due to increased leg length, energy storage, and muscle lactate production. Ontogeny was also associated with a strong decrease in endurance, which may be linked with the increased reliance on anaerobic metabolism. However, older grasshoppers also had higher jumping muscle mass-specific aerobic rates and whole-body aerobic scopes. The jump performance of older grasshoppers was also more oxygen sensitive during the first minute of jumping, suggesting that older grasshoppers have lower safety margins for oxygen delivery. In contrast to the common ontogenetic pattern for vertebrate performance, grasshoppers appear to develop from low-power, high-endurance juveniles to high-power, low-endurance adults. Changes in locomotory performance appear to reflect life history, as the adult leg appears to be adapted for the high power output required to initiate flight but with a consequential loss of endurance.; To separate developmental changes from body size effects, jump performance and lactate production were also examined across twenty-two grasshopper species over a 38-fold body mass range. A prominent hypothesis suggests that increased atmospheric oxygen levels (35%) during the late Paleozoic facilitated the evolution of gigantic taxa including insects. Therefore, I predicted that larger grasshoppers would have reduced locomotory endurance and increased lactate production because of increasing size-related problems with oxygen delivery. This hypothesis was not supported, as jumping endurance was unrelated to size and lactate production rates actually decreased with size. However, an unexpected scaling pattern emerged. Smaller grasshoppers had increased proportions of jumping muscle mass and jumped proportionally farther, suggesting stronger selection for locomotory performance in smaller animals. |
