03096nas a2200229   4500008004100000245010200041210006900143260000800212300001400220490000800234520233100242653002702573653001602600653001702616653001902633653001202652653001502664653001502679100002202694700002502716856012502741       2003                        eng d00aDiscontinuous gas exchange and the significance of respiratory water loss in scarabaeinae beetles0 aDiscontinuous gas exchange and the significance of respiratory w  cJul  a3547-35560 v2063 aRespiratory water loss in insects is a controversial topic. Whilst earlier studies considered respiratory transpiration a significant component of overall water loss, to the extent that it was thought to be responsible not only for the evolution of discontinuous gas exchange cycles (DGCs) but also for variation in DGC patterns, later work repeatedly questioned its importance. In particular, investigations of the proportional contribution of respiratory transpiration to total water loss in species showing DGCs suggested that respiratory transpiration was unlikely to be important in these species. In turn, these studies have been criticized on analytical grounds. In this study we investigated variation in cuticular and respiratory water loss rates in five Scarabaeus dung beetle species, all of which show discontinuous gas exchange cycles, to ascertain the significance of respiratory water loss using modern analytical techniques. In particular, we determined whether there is variation in water loss rates amongst these beetles, whether both respiratory and cuticular water loss rates contribute significantly to variation in the former, and whether metabolic rate variation and variation in the duration of the DGC periods contribute significantly to variation in respiratory water loss rate. Total water loss rate varied such that species from arid areas had the lowest rates of water loss, and both cuticular and spiracular transpiration contributed significantly to variation in overall water loss rate. Moreover, variation in metabolic rate and in the duration of the DGC periods contributed significantly to variation in respiratory water loss rate. By contrast, examination of proportional water loss revealed little other than that it varies between 6.5% and 21%, depending on the species and the temperature at which it was examined. Cuticular water loss scaled as mass0.721, but did not differ from that expected from geometric considerations alone. By contrast, respiratory water loss scaled as mass0.531, suggesting that gas exchange takes place by diffusion and convection. Our results provide direct evidence that respiratory water loss forms a significant component of water balance, and that changes in both metabolic rate and DGC characteristics contribute to modulation of respiratory water loss. 10adesiccation resistance10adung beetle10agas exchange10ametabolic rate10ascaling10aScarabaeus10awater loss1 aChown, Steven, L.1 aDavis, Adrian, L. V.  uhttps://scarabnet.myspecies.info/discontinuous-gas-exchange-and-significance-respiratory-water-loss-scarabaeinae-beetles