Discontinuous gas exchange and water loss in the keratin beetle Omorgus radula: further evidence against the water conservation hypothesis?

Discontinuous gas exchange cycles are demonstrated in Omorgus radula (Erich son) (Coleoptera, Trogidae) for the first time, thus extending evidence for such cycles to another family of beetles. The closed, flutter and open pha ses of the cycle were clearly distinguishable in this species, and the dura tion of these phases was 221 +/- 28, 1403 +/- 148 and 755 +/- 43 s (mean +/ - SE), respectively. No evidence for significant intraspecific mass scaling of VCO2 or any of the components of the cycle was found. Although the prol onged F-phase recorded here is unusual for many insects, it has previously been found in other scarabaeoid beetles, especially those from xeric enviro nments. It has been suggested that such modulation of the discontinuous gas exchange cycle may result in a reduced VCO2 and, consequently, reduced wat er loss. In O. radula VCO2 (15.25 +/- 1.49 mul/h) was considerably lower th an that predicted from its body mass (0.207 +/- 0.006 g). However, the smal l relative contribution of respiratory transpiration (6.5%) to total water loss indicated that reduced VCO2 has little to do with water economy. Rathe r, it may be a consequence of generally low activity levels of these beetle s. The low respiratory water loss, but distinct subterranean component in t he adult life of O. radula, lend some credence to the hypothesis suggesting that regular use of subterranean habitats might have been responsible for the evolution of discontinuous gas exchange cycles. However, non-adaptive h ypotheses can still not be discounted.