Meeting Abstract

P1.158  Sunday, Jan. 4  Synchrotron x-ray imaging reveals tracheal system response to hypoxia in the tobacco hornworm, Manduca sexta EUBANKS, H.B.; ISAAK, S.; KIRKTON, S.D.; LEE, W.K.; GREENLEE, K.J.*; Mississippi Valley State University; North Dakota State University; Union College; Argonne National Laboratory; North Dakota State University kendra.greenlee@ndsu.edu

Some insects are able to tolerate very low levels of oxygen by increasing tidal volume and breathing frequency. Tobacco hornworm caterpillars also tolerate extreme hypoxia. However, the mechanism of ventilation is unknown in caterpillars, because they do not show abdominal pumping and lack air sacs. Preliminary data showed that caterpillars in 3-5% oxygen exhibit rhythmic body contractions. To test the hypothesis that these movements are related to breathing, we used synchrotron x-ray imaging in conjuction with high-speed respirometry to document tracheal system compression as it correlates with body movements and gas exchange in these caterpillars. We found that caterpillars do not show tracheal system compressions in normal air and carbon dioxide emission is not correlated with any particular body movement. However, in hypoxia, tracheae rhythmically compress, and the tracheal compressions are highly correlated with external body movements and carbon dioxide emission peaks. To further test the hypothesis that these external movements are driving gas exchange and not just an artifact of x-ray exposure, we performed a similar experiment in the lab using high-speed respirometry in conjunction with videography. We again found a high correlation between body compressions and carbon dioxide emission peaks. These data support the hypothesis that caterpillars use ventilatory movements to breathe in low oxygen. While caterpillars are not likely to experience hypoxia in nature, caterpillars may experience low internal oxygen during exercise, at high altitude or near the end of an instar when gas exchange is more difficult.