Gas exchange patterns and water loss rates in the Table Mountain Cockroach (Aptera fusca) (original) (raw)

Gas exchange and water loss in A. fusca 2 SUMMARY 16 The importance of metabolic rate and/or spiracle modulation for saving respiratory 17 water is contentious. One major explanation for gas exchange pattern variation in 18 terrestrial insects is to effect a respiratory water loss (RWL) saving. To test this, we 19 measured V . CO 2 and V . H 2 O in a previously unstudied, mesic cockroach, Aptera fusca, 20 and compared gas exchange and water loss parameters among the major gas 21 exchange patterns (continuous, cyclic, discontinuous gas exchange (DGE)) at a range 22 of temperatures. Mean V . CO 2 , V . H 2 O, and V . H 2 O per unit V . CO 2 did not differ among the 23 gas exchange patterns at all temperatures (p>0.09). There was no significant 24 association between temperature and gas exchange pattern type (p=0.63). Percentage 25 of RWL (relative to total water loss) was typically low (9.79±1.84%) and did not differ 26 significantly among gas exchange patterns at 15°C (p=0.26). The method of estimation 27 had a large impact on the %RWL and of three techniques investigated (traditional, 28 regression, hyperoxic switch), the traditional method generally performed best. In 29 many respects, A. fusca has typical gas exchange for what might be expected from 30 other insects studied to date (e.g. V . CO 2 , V . H 2 O, RWL and CWL). However, we found 31 for A. fusca that V . H 2 O expressed as a function of metabolic rate was significantly 32 higher than the expected consensus relationship for insects, suggesting it is under 33 considerable pressure to save water. Despite this, we found no consistent evidence 34 supporting the conclusion that transitions in pattern type yield reductions in RWL in 35 this mesic cockroach. 36 37 Key words: water conservation, hyperoxic switch method, regression method, metabolic 38 rates, metabolic efficiency. 39 40 The Journal of Experimental Biology -ACCEPTED AUTHOR MANUSCRIPT Gas exchange and water loss in A. fusca 61 associated CO 2 emission patterns: the open (O) spiracle phase, when gas exchange takes place 62 freely through diffusion (although sometimes aided by active convection (e.g. Loveridge, 63 1968; Miller, 1973; Groenewald et al., 2012)); the closed (C) spiracle phase, when there is no 64 exchange of gas between the insect's tracheae and the outside environment; and the flutter (F) 65 phase, when spiracles open and close rapidly and some exchange of gases occurs (e.g.