GREENLEE, K.J.; HARRISON, J.F.; HENRY, J.R.*; WESTNEAT, M.; KIRKTON, S.D.; LEE, W.-K.; Baylor College of Medicine, Houston; Arizona State University, Tempe; Arizona State University, Tempe; Field Museum of Natural History; University of California, San Diego; Argonne National Laboratory; ; : An analysis of grasshopper tracheal morphology across instars using synchrotron x-ray imaging

As the mass of an American locust (Schistocerca americana) increases 140-fold during ontogeny, the critical partial pressure of oxygen for grasshoppers at rest drops substantially and maximal mass-specific tracheal conductance increases 4-fold. The increase in mass-specific tracheal conductance with age appears to be due to increased ventilatory response and a greater percent change in abdominal height. We used x-ray synchrotron imaging to test for morphological mechanisms which may explain the increase in tracheal conductance and tidal volumes. We analyzed 50% of each animal across all segments in each instar using point-counting methods to estimate the cross-sectional area of an animal�s body, tracheae, and air sacs. Both the fractional content of major tracheae and air sacs increase with age. Adult grasshoppers have 3 times the percent imaged area of tracheae and air sacs relative to first instars, who have very few air sacs. This finding illustrates how morphological changes during development can improve tracheal conductance. This research was supported by NSF grant IBN-9985857 to JFH.