Meeting Abstract
89.2 Thursday, Jan. 7 Under pressure: the biomechanical mechanism of rhythmic tracheal compression in carabid beetles SOCHA, J.J.*; COX, L.; LEE, W.K.; MEANS, M.; TOLLEY, J.; Virginia Tech; Virginia Tech; Argonne National Laboratory; Bucknell University; Virginia Tech jjsocha@vt.edu
Although diffusion is considered to be the dominant mechanism of respiration in insects, many species are known to exhibit active ventilation. Rhythmic tracheal compression (RTC) is one such form of ventilation, in which parts of the tracheal system collapse and reinflate multiple times per minute, with each compression resulting in movement of air out of the body. These compressions have been characterized using x-ray imaging; however, the morphological mechanism of RTC is unknown. From preliminary x-ray video data, we have identified a rhythmic dorsoventral abdominal contraction that co-occurs with tracheal collapse in the carabid beetles Platynus decentis and Pterostichus stygicus. In combination with the generally synchronous nature of tracheal compressions throughout the body, this suggests that RTC is caused by a global pressure change, whereby an increase in internal hemolymph pressure effects tracheal tube collapse. To explore this hypothesis, we take an integrative approach. Changes in hemolymph pressure were measured with fiber-optic probes inserted into the beetle’s thoracic hemocoel, while abdominal body movements and CO2 release patterns were recorded concurrently. To confirm that RTC co-occurs with rhythmic changes in pressure, we repeated these measurements under synchrotron x-ray imaging to directly visualize tube collapse in real time. Lastly, we dissected tracheae from the beetles and conducted in vitro pressure tests to determine thresholds of collapse in individual tracheal tubes. In general, tube collapse occurred at lower pressures than those observed in the living beetles. These data strongly support a global hemolymph pressure change mechanism of RTC in carabid beetles. Research supported by NSF 0938047, VT ICTAS, and the Jeffress Memorial Trust.
