title: A hierarchy of factors influence discontinuous gas exchange in the grasshopper Paracinema tricolor (Orthoptera: Acrididae).
abstract: The evolutionary origin and maintenance of discontinuous gas exchange (DGE) in tracheate arthropods are poorly understood and highly controversial. We investigated prioritization of abiotic factors in the gas exchange control cascade by examining oxygen, water and haemolymph pH regulation in the grasshopper Paracinema tricolor. Using a full-factorial design, grasshoppers were acclimated to hypoxic or hyperoxic (5% O2, 40% O2) gas conditions, or dehydrated or hydrated, whereafter their CO2 release was measured under a range of O2 and relative humidity (RH) conditions (5%, 21%, 40% O2 and 5%, 60%, 90% RH). DGE was significantly less common in grasshoppers acclimated to dehydrating conditions compared with the other acclimations (hypoxia, 98%; hyperoxia, 100%; hydrated, 100%; dehydrated, 67%). Acclimation to dehydrating conditions resulted in a significant decrease in haemolymph pH from 7.0±0.3 to 6.6±0.1 (mean ± s.d., P=0.018) and also significantly increased the open (O)-phase duration under 5% O2 treatment conditions (5% O2, 44.1±29.3 min; 40% O2, 15.8±8.0 min; 5% RH, 17.8±1.3 min; 60% RH, 24.0±9.7 min; 90% RH, 20.6±8.9 min). The observed acidosis could potentially explain the extension of the O-phase under low RH conditions, when it would perhaps seem more useful to reduce the O-phase to lower respiratory water loss. The results confirm that DGE occurrence and modulation are affected by multiple abiotic factors. A hierarchical framework for abiotic factors influencing DGE is proposed in which the following stressors are prioritized in decreasing order of importance: oxygen supply, CO2 excretion and pH modulation, oxidative damage protection and water savings.
authors: Department of Conservation Ecology and Entomology, Centre for Invasion Biology, Faculty of AgriSciences, Stellenbosch University, Private Bag X1, Matieland 7602, Stellenbosch, South Africa berg@sun.ac.za.
authors: Berlizé
authors: B
authors: Groenewald
authors: School of Biological Sciences, Monash University, Melbourne, VIC 3800, Australia.
authors: Steven L
authors: SL
authors: Chown
authors: Department of Conservation Ecology and Entomology, Centre for Invasion Biology, Faculty of AgriSciences, Stellenbosch University, Private Bag X1, Matieland 7602, Stellenbosch, South Africa.
authors: John S
authors: JS
authors: Terblanche
mesh_terms: D000064:Acclimatization; D000818:Animals; D002245:Carbon Dioxide / Q000737:chemistry / Q000378:metabolism*; D003681:Dehydration; D005740:Gases / Q000737:chemistry / Q000378:metabolism; D006110:Grasshoppers / Q000378:metabolism*; D006458:Hemolymph / Q000737:chemistry*; D006813:Humidity; D006863:Hydrogen-Ion Concentration; D010100:Oxygen / Q000737:chemistry / Q000378:metabolism*; D010101:Oxygen Consumption; D012119:Respiration; D014867:Water / Q000378:metabolism
chemical_list: D005740:Gases; D014867:Water; D002245:Carbon Dioxide; D010100:Oxygen
keywords: Discontinuous gas exchange; Oxidative damage; Prioritization; Water regulation; pH regulation