Meeting Abstract

P1-284  Thursday, Jan. 4 15:30 – 17:30  Gravity Effects on Hemolymph and Air Distribution in the Grasshopper, Schistocerca americana HARRISON, J.F.*; KASSI, A.; ADJERID, K.; AVILES, J.; KLOK, C.J.; VANDENBROOKS, J.M.; DUELL, M.E.; CAMPBELL, J.E.; ALANIS, E.; ABDO, C.; PENDAR, H.; SOCHA, J.J.; Arizona State University; Arizona State University; Virginia Tech; Virginia Tech; Arizona State University; Arizona State University; Arizona State University; Arizona State University; Arizona State University; Arizona State University; Virginia Tech; Virginia Tech j.harrison@asu.edu http://jharrison.faculty.asu.edu

The cardiovascular physiology of vertebrates is strongly affected by gravity, but possible effects of gravity on the open circulatory systems of invertebrates have been unstudied, possibly because it has been assumed that these would be negligible at small body sizes. We studied the effect of body orientation on the distribution of air and hemolymph in adult and juvenile grasshoppers, Schistocerca americana, using synchrotron x-ray imaging and radio-tracers. Regardless of age or size, changes in body orientation caused substantial gravity-driven blood flow and compression of lower air sacs and expansion of higher air sacs. Gravitational effects were greater when grasshoppers were anaesthetized by N₂, demonstrating that effects of gravity are actively resisted. Heart rates were higher in head-up vs. head-down animals, consistent with a compensatory baroreceptor response since grasshoppers hearts generally pump toward the head. Pressure differences between thorax and abdomen provided direct evidence for a functional valve that likely acts to restrict gravity-effects on hemolymph. These results suggest that, as for vertebrates, body orientation and gravity have strong effects on blood flow and physiology in terrestrial invertebrates. Supported by NSF IOS 1558052 and NSF EFRI BSBA 0938047.