Meeting Abstract
Recent geochemical models suggest that oxygen has varied from 12% to 31% over the last 500 million years. These changes in atmospheric oxygen would have had multiple effects on the physiology and evolution of organisms living at that time. We have hypothesized that the unique tracheal respiratory system of insects may have made them uniquely susceptible to changes in atmospheric oxygen. Previously, we have shown that as some insects increase in body size, their tracheal system increases at a faster rate and may eventually limit the maximum body size of insect species. We have also shown that rearing oxygen is inversely correlated with tracheal diameters in several groups of insects. However, a limit of these studies has been a focus on only the larger tracheae that drive the bulk flow through the system. Here we use confocal imaging to look at the effect of rearing oxygen on the smallest component of the respiratory system – the blind ended tracheoles. We reared Drosophila melanogaster under three different oxygen concentrations (12%, 21%, and 31%) that match the variation seen over geologic time. We imaged the tracheal and tracheolar network taking advantage of their auto-fluorescent properties and used these images to reconstruct high resolution 3D models of the respiratory system. We then measured tracheal and tracheolar diameters and characterized the network branching properties of the flight muscle in D. melanogaster reared under the three oxygen levels. We have identified effects of rearing oxygen on the density of tracheoles, tracheolar diameters, and branching patterns. All of these have major impacts on oxygen delivery and may be a major driver in the modulation of insect body size by atmospheric oxygen.
