A New Hypothesis for Cardio-respiratory Mechanics in Insects

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The immense ecological success of insects makes them extremely important agricultural pests, disease vectors, and food web components. Despite the importance of insects, only a minimal understanding of many aspects of their basic physiology still exists. Blood and air flow are critical for the transport of nutrients, hormones, and gases within an insect's body, but a comprehensive understanding of the biomechanical processes that drive fluid flow is lacking. This project tests a new hypothesis that some insects use an abdominal pump linked functionally to a "gut piston" to generate the principal forces driving air and blood flow. This research is motivated by three questions: 1) How does the abdominal pump help to create airflow and mixing in the insect gas exchange and transport system? 2) How are pressure differences created within the main body cavity? 3) How important is the abdominal pump for circulation? A variety of experimental and computational methods will be used to test for linkages between these systems. This research will clarify how insects pump fluids, and contribute to a broader understanding of mechanically coupled systems, with potential applications in vertebrate (including human) physiology and mechanical engineering. Mechanically-coupled physiological systems have been relatively well-studied in vertebrates, but rarely at the small sizes of insects. This research will provide, therefore, new insights into the physical basis of flow production in the most diverse group of animals on the planet. This project also includes initiatives to involve individuals from diverse backgrounds in research, and to share this research with the local and broader public. This effort includes a new program that will bring Chicago Public School students to Argonne National Laboratory to experience how synchrotron X-rays are used to image insects.This project proposes that the tenebrionid beetle Zophobas morio, and perhaps many insect species, utilizes a linked abdominal pump and "gut piston" to drive the majority of air and blood flow. A new hypothesis posits that 1) the abdominal pump raises hemolymph pressure and displaces a large amount of body volume, inducing airflows and hemolymph flows, and 2) a synchronous "gut piston" pressurizes the thoracic and head compartments, compressing tracheae within them, and thereby further augments pressures that drive air and blood flow within these regions. To test these hypotheses, a combination of newly developed and established techniques to measure abdominal pump volume, cardiac output, hemolymph pressures, hemolymph mixing, and tracheal airflow will be used. Specifically, this project will determine the following: how hemolymph pressures induce compression and airflow in the tracheal system; how differential pressures are created within the coelom and dorsal vessel; and how these components integrate to produce blood flows in the body. To test for linkages between abdominal pumping, hemolymph pressures, gut piston function, hemolymph mixing, and tracheal collapse, correlational approaches will be combined with experimental procedures to directly test the effects of changes in heart and abdominal pump function on airflow and blood circulation. An adaptive and parallelized immersed boundary method will also be used to solve for the flows and mixing patterns generated by the deformations of elastic and/or poroelastic models of the heart, tracheal tubes, and abdomen. Experimental measurements from the beetle will be used to validate the model, and the model will be used to address hypotheses that are difficult to probe experimentally.