Meeting Abstract
All insects use pressure gradients produced by metabolism to move gas diffusively through an internal tracheal system. Some species augment this gas exchange using tracheal compression, a volume displacement of the tracheal tubes that generates bulk flow of air. At least three distinct behaviors are thought to affect such flow: abdominal pumping, collapse of internal tracheal tubes, and active opening and closing of spiracles. The specific coordination of these events should influence internal and external airflow patterns, and therefore may vary with changing metabolic requirements, including oxygen availability in the air. Due to its large size and viewable spiracles, the Madagascar hissing cockroach (G. portentosa) is a useful model for studying the coordination of respiratory behaviors. We used these roaches to study how the animal modifies its respiratory behavior to compensate for a reduced availability of oxygen. N adult specimens, both males and females, were exposed to 15%, 10%, 5%, and 0% oxygen. The Advanced Photon Source at Argonne National Lab was used to capture x-ray video of internal abdominal structures, while the abdomen and abdominal spiracles were recorded using separate visible-light video cameras. As oxygen concentration decreased, abdominal pumping frequency increased, along with tracheal collapse. Furthermore, spiracles opened more rapidly, spent more time open during each abdominal pump event, and fluttered less between events. At sub-critical oxygen concentrations (<5%), pumping ceased entirely and the spiracles remained fully open. By understanding how the hissing cockroach modulates its respiratory behavior in response to changing flow requirements, we have improved our knowledge of the network characteristics of actively-ventilating insects. Supported by NSF 0938047.
