SOCHA, J.J.*; FEZZAA, K.; LEE, W.K.; WATERS, J.S.; WESTNEAT, M.W.; Argonne National Laboratory; Argonne National Laboratory; Argonne National Laboratory; University of Chicago; University of Chicago: Tracheal compression patterns involved in gas exchange in the ground beetle, Platynus decentis

Insects use a variety of mechanisms to actively exchange respiratory gases. Tracheal compression is a recently described mechanism in which the major tracheal tubes dramatically inflate and deflate in periodic fashion in a variety of insects, including beetles, ants, and grasshoppers. Previous work has quantified compressions in the major tracheae of the head and prothorax of the ground beetle, Platynus decentis, finding substantial volume changes of up to 40%. Here we estimate total volume change due to tracheal compression throughout the entire body, including the legs. The internal structures of multiple beetles were visualized at 5X optical magnification using phase-enhanced synchrotron x-ray radiation (25 keV) recorded to 30 Hz video. Tracheal volume change was quantified by measuring change in tracheal width and length and calculating volume for an elliptical cylinder. In addition, we document previously undescribed patterns of compression. We found considerable variation in compression mechanics both within and among different tracheal tubes. Although tracheae appear to be compressed synchronously, the shape and direction of compression varies within local tracheal segments, and to a lesser extent, between beetles. Compression can occur in the lateral plane, dorsoventral plane, or in between, and can be bidirectional or unidirectional, in which one side of the tube is held stationary while the other side moves. In some places, unidirectional compressions take the shape of a prolate spheroid. Compression patterns suggest that tracheal compressions are caused by local muscular contractions, or by regional pressure changes in combination with differential tracheal material properties.