Meeting Abstract
90.8 Monday, Jan. 6 15:15 Grasshoppers defy gravity? Body position effects on hemolymph and air distribution in Schistocerca americana HARRISON, J.F.*; KLOK, C.J.; VANDENBROOKS, J.M.; DUELL, M.E.; CAMPBELL, J.B.; JIRJIES, S.; SOCHA, J.J.; Arizona State University; Arizona State University; Arizona State University; Arizona State University; Arizona State University; Arizona State University; Virginia Tech j.harrison@asu.edu
Gravity has strong effects on the fluid transport systems of terrestrial vertebrates and plants and should, in theory, be important for all terrestrial organisms. Insects retain the open circulatory system they evolved from aquatic crustacean ancestors, raising the question of how well their circulatory system copes with gravity. Air sacs of grasshoppers (Schistocerca americana) were visualized with synchrotron x-ray imaging at the Advanced Photon Source at Argonne National Laboratory. For adults in the head-up position, air sacs in the head expand whereas air sacs in the abdominal tip compress; the converse occurs in the head-down position. Similar changes occur when animals shift from supine to prone positions. Together, these changes demonstrate that the open body plan within the grasshopper can result in changes in the respiratory system in response to gravity, which may result from hydrostatic effects and/or the changes in flow of hemolymph. Nitrogen-paralysis accentuates these changes in the tracheal system, indicating that grasshoppers actively counter the effects of gravity on hemolymph distribution. Juveniles (third instar) showed reduced gravity effects on their air sacs, suggesting that gravity effects on hemolymph distribution may increase with size. Abdominal pumping (related to ventilation) and heart rate did not vary with body position. The mechanisms by which insects resist gravity effects on hemolymph distribution remain unclear, but the occurrence of differential air sac behaviors in adjacent segments suggest that flexible functional valves exist between body compartments. This research was funded by NSF 0938047.
