P1.227 Wednesday, Jan. 4 Does tracheal compression in carabid beetles function as a unidirectional pump? HOCHGRAF, JS*; SOCHA, JJ; Virginia Tech; Virginia Tech email@example.com
Insects breathe using an extensive system of tracheal tubes that ramify throughout the body. Rhythmic tracheal compression, the periodic collapse and reinflation of parts of the tracheal system, has been identified in multiple taxa, but little is known about the precise dynamics of tube collapse. It has been hypothesized that tracheal collapse occurs synchronously throughout the body, but it is possible that tube collapse proceeds unidirectionally along the length of a tube, functioning as a pump to transport air and augmenting gas exchange. This study aims to characterize patterns of tracheal compression in one species of carabid beetle, Platynus decentis, to test the hypothesis of directional compression. The internal tracheae of living beetles were visualized using synchrotron x-ray imaging at the Advanced Photon Source, Argonne National Laboratory. We identified that tracheal tube collapse was characterized by the formation of discrete, buckled regions in the tube wall, which gave the appearance of dimpling. Dimple formation in the main dorsal tracheal trunks of the prothorax occurred as two semi-circular fronts spreading symmetrically along the longitudinal tube axis. In the transverse axis, the main ventral trunks collapsed in the medial to lateral direction, whereas the dorsal trunks collapsed dorsoventrally. Along the length of a tracheal tube, dimples formed synchronously, not sequentially. Synchronous longitudinal compression and consistent dimple formation kinematics within an animal suggest that Platynus decentis employs a stereotyped mechanism to produce cycles of tracheal collapse and reinflation, but such compression does not function as a unidirectional pump. Further data on spiracle opening and closing patterns are needed to determine actual airflow patterns within the body.