GIBBS, A.G.*; MARRON, M.T.; KAIN, K.J.; ALTHOFF, L.: Mechanisms of water conservation in desert Drosophila.

Cactophilic fruitflies from the Sonoran Desert lose water much less rapidly than mesic species. Water is lost by three routes: excretion, cuticular transpiration, and respiration through the spiracles. Excretory losses comprised ~1% of total water loss and did not differ between desert and mesic species. Flies defecated once every 5 hours, with a mean water content of <0.5 nL/turd. Inter-specific differences in cuticular hydrocarbons (the main barrier to transpiration) were not correlated with rates of water loss, and hydrocarbon composition primarily reflected phylogeny. By elimination, desert Drosophila appear to have reduced respiratory water loss. In accordance with this conclusion, desert species were less active and had lower metabolic rates, thereby reducing the need to open the spiracles for gas exchange. A cyclic pattern of carbon dioxide release similar to discontinuous ventilation (DV) was observed in desert species only. Unlike classical DV, however, flies exhibited this pattern only while active, and cyclic ventilation had no detectable effect on water loss. Supported by NSF award IBN-0110626.