LEHMANN, F. O.; Univ. of Ulm: The Control of Breathing at Elevated Locomotor Activity in flying Fruit Flies

The respiratory exchange system of many insects must maximize the flux of respiratory gases through the spiracles of the tracheal system while minimizing water loss. This trade-off between gas exchange and water loss becomes crucial when locomotor activity is increased during flight and metabolic needs may increase 10 to 15-fold over resting rates. Insects that keep their spiracles mostly closed during flight reduce water loss but limit the flux of oxygen and carbon dioxide in and out of the tracheal system and thus attenuate locomotor performance. Insects that keep their spiracles completely open allow maximum gas exchange but face desiccation stress more quickly. Experiments in which water vapor was used as a tracer gas to track changes in the conductance of the respiratory system indicated that flying fruit flies minimize potential water loss by matching the area of the open spiracles to their gas exchange required for metabolic needs. This behavior maintained approximately constant pressure for carbon dioxide of roughly 1.35 kPa and oxygen of 19.9 kPa within the tracheal system even though metabolic demands vary substantially during flight. Moreover, the modulation in mean cross-sectional area of the diffusive path reduces respirometric water loss by up to 23% compared to a strategy in which the spiracles are held wide open during flight. Although this finding may not explain the mechanism of how each spiracle contributes to overall tracheal conductance during flight, it has general implications for the ecology of flying insect because it demonstrates how small insects may cope with environmental challenges during increased locomotor performance.