Effects of rearing oxygen level on the structure of the adult tracheal system in Drosophila melanogaster. Jon F Harrison, James Waters, Stephanie Heinrich, Taylor Biddulph, Sandra Kovacevic. School of Life Sciences, Arizona State University, Tempe, AZ.

   Insect tracheal systems are known to respond in a compensatory manner to rearing oxygen level, but the functional extent of compensation remains unclear, as does whether compensation extends from the larval to the adult stage. In this study, we investigated the structure, and phenotypic plasticity of the tracheal system of Drosophila melanogaster . Flies were reared from egg through adulthood in 10, 21 or 40% oxygen atmospheres, and their tracheal system assessed on the fourth day of adulthood. The tracheal system of the whole body was assessed with a 3D tomographic technique using synchrotron x-rays at Argonne National Laboratory. In addition, tracheoles in the flight muscle were imaged using confocal microscopy. We did not detect changes in the branching structure or number of branches in the major, large-diameter tracheae of the thorax. However, there was strong compensatory variation in the number and density of tracheoles in the flight muscle. In addition, we were surprised to find that the diameter of the terminal tracheoles decreased for flies reared in hypoxia. These results contrast to observations in the tracheal trunks of larvae, which can show increases in diameter in hypoxic-reared animals. Perhaps the decreased diameters of tracheoles benefit oxygen diffusion into muscle by increasing surface/volume ratios of these tubes. This research was supported by NSF 0938047to JFH.