KIRKTON, S.D.*; HARRISON, J.F.; Arizona St. University; Arizona St. University: Developmental and Interspecific Body Size Effects on Grasshopper Jumping Performance
Due to the increased length of their tracheal system, larger insects are believed to have reduced safety margins for oxygen delivery. The gigantic insects of the late Paleozoic may have overcome oxygen delivery problems due to the increased atmospheric oxygen levels (35%) at that time. To test the hypothesis that oxygen delivery problems increase for larger insects, we have studied the jumping performance of developing Schistocerca americana grasshoppers (0.02g to 2g). Throughout ontogeny anaerobic capacity increased and jumping endurance decreased. This reduced endurance was due to increased muscle power output during initial minutes of jumping and increased muscle lactate production, rather than a disproportionate increase in body mass relative to jumping muscle mass. Furthermore, older S. americana have significant problems with oxygen delivery during jumping as evidenced by decreased femur PO2. We also addressed the hypothesis by comparing jumping performance in adult grasshoppers of different species (0.04g to 7g). Our findings suggest that phylogeny greatly influences how body size affects jumping endurance. In most clades where the adults cannot fly, the smaller species had an increased jumping performance and much better endurance. These results support the hypothesis that larger grasshoppers may have more difficulty with oxygen delivery when the respiratory system is challenged during locomotion. However in clades with flying adults (specifically the Melanopline and the band-wing grasshoppers) the hypothesis was not supported. Flying grasshoppers maybe better able to convectively ventilate their entire tracheal system; improving their oxygen delivery capacity and reducing the effect of body size on jump performance.
