KAISER, A.*; KLOK, C.J.; SOCHA, J.; LEE, W.K.; FEZZAA, K.; QUINLAN, M.C.; HARRISON, J.F.; Midwestern University, Glendale, AZ; Arizona State University, Tempe, AZ; Argonne National Laboratory, Argonne, IL; Argonne National Laboratory, Argonne, IL; Argonne National Laboratory, Argonne, IL; Midwestern University, Glendale, AZ; Arizona State University, Tempe, AZ: Structure, function, and allometry of the tracheal system of Darkling Beetles (Tenebrionidae)
The air-filled tracheal system of insects utilizes the advantages of the high solubility of oxygen in air and the low energetic costs of gaseous transport to support very high rates of oxygen uptake. However, does use of this system limit insect size? In this study we compare tracheal structure and function of four species of adult Darkling Beetles (Tenebrionidae) over a range of body mass from 1.6 mg (Tribolium castaneum) to 1700 mg (Eleodes obscura). We analysed tracheal structures and dimensions using phase-contrast x-ray synchrotron imaging at Argonne National Laboratory. The general layout of the tracheal system was very similar in all four species. All but the prothoracic pair of spiracles open into the subelytral cavity. Structure and function of spiracular valves are similar in all species. The tracheal manifolds are connected by tracheal trunks. Air sacks are absent. Swaying of the tracheal system, caused by abdominal movements, and tracheal compressions were observed in all species, but occurred more frequently in larger beetles. Both mechanisms are likely to induce convective gas transport. The tracheal system takes up a bigger proportional area in larger beetles, thus exhibiting a greater investment in respiratory structures. Mass-specific metabolic rates decrease with size, so tracheal investment relative to mass-specific oxygen demand increases dramatically. Hyperdevelopment of the tracheal system in larger insects may allow compensation for distance effects on diffusion, but may eventually result in limitation on insect size. NSF 0419704 (J.F.H), NSF IBN�0344963 (M.C.Q.)
