Growth within an instar reduces jumping performance in American locusts (Schistocera americana)

Abstract

In developing vertebrates, morphological changes that alter behavior, ecological patterns, and physiological processes are well known. However, the effect of ontogenetic structural changes on insect life‐history are not well understood. During development, American locust grasshoppers (Schistocerca americana) exhibit dramatic increases in body size both across and within instars. We have shown previously that as grasshoppers develop across instars, older animals have reduced jump endurance and increased lactic acid production in the jumping muscle. Within an instar, juvenile grasshoppers nearly double their body mass; however, since respiratory structures only increase during intermolt periods, oxygen delivery may be reduced. We show here that older grasshoppers have a reduced whole body air volume, yet femoral air volume is maintained through structural changes to the leg. In addition, older juveniles within an instar hop less frequently and produce more lactic acid during repeated jumping. We conclude that morphological changes during development may decrease convective oxygen delivery to the jumping muscle resulting in increased anaerobic metabolism and locomotory fatigue. These ontogenetic changes significantly alter the life‐history of juvenile grasshoppers. This research was partially supported by NSF IBN‐0104959 to SDK and JFH and the Union College IEF fund.