How Locusts Breathe

During discontinuous gas exchange cycles in insects, spiracular opening follows a typical prolonged period of spiracle closure. Gas exchange with the environment occurs mostly during the period of full spiracular opening. In this study we tested the hypothesis that recently reported ventilatory movements during the spiracle closure period serve to mix the tracheal system gaseous contents, and support diffusive exchanges with the tissues. Using heliox (21% O 2 , 79% He), we found that by increasing oxygen diffusivity in the gas phase, ventilatory movements of Schistocerca gregaria were significantly delayed compared with normoxic conditions. Exposure to hyperoxic conditions (40% O 2 , 60% N 2 ) resulted in a similar delay in forced ventilation. Together, these results indicate that limits to oxygen diffusion to the tissues during spiracle closure trigger ventilatory movements, which in turn support tissue demands. These findings contribute to our understanding of the mechanistic basis of respiratory gas exchange between insect tissues and the environment.

Section: Short Communicationmentioning

confidence: 94%

Section: Introductionmentioning

confidence: 99%

Oxygen diffusion limitation triggers ventilatory movements during spiracle closure when insects breathe discontinuously

Huang

Sender

Gefen

2014

“…The system consists of air-filled tubes that open to the air through spiracles on the surface of the thorax and abdomen, branch throughout the body, and eventually reach the cells with blindended tracheoles. Oxygen (O 2 ) and carbon dioxide (CO 2 ) move through the smaller tubes largely by diffusion down gradients in partial pressure (P O2 , P CO2 ), although the outer tracheae are connected and can be ventilated by movements of the body (Harrison et al, 2013). Many aquatic insects still use the gas-filled tracheal system, but interface it with snorkels, tracheal gills or air bubbles on their bodies that act not only as an O 2 store, but also as a 'physical gill' capable of exchanging O 2 and CO 2 with the water (Seymour and Matthews, 2013).…”

Section: Introductionmentioning

confidence: 99%

Respiratory function of the plastron in the aquatic bug,Aphelocheirus aestivalis(Hemiptera, Aphelocheiridae)

Seymour

Jones

Hetz

2015

The river bug Aphelocheirus aestivalis is a 40 mg aquatic insect that, as an adult, relies totally on an incompressible physical gill to exchange respiratory gases with the water. The gill (called a 'plastron') consists of a stationary layer of air held in place on the body surface by millions of tiny hairs that support a permanent air-water interface, so that the insect never has to renew the gas at the water's surface. The volume of air in the plastron is extremely small (0.14 mm 3 ), under slightly negative pressure and connected to the gas-filled tracheal system through spiracles on the cuticle. Here, we measure P O2 of the water and within the plastron gas with O 2 -sensing fibre optics to understand the effectiveness and limitations of the gas exchanger. The difference in P O2 is highest in stagnant water and decreases with increasing convection over the surface. Respiration of bugs in water-filled vials varies between 33 and 296 pmol O 2 s −1 , depending on swimming activity. The effective thickness of the boundary layer around the plastron was calculated from respiration rate, P O2 difference and plastron surface area, according to the Fick diffusion equation and verified by direct measurements with the fibreoptic probes. In stagnant water, the boundary layer is approximately 500 μm thick, which nevertheless can satisfy the demands of resting bugs, even if the P O2 of the free water decreases to half that of air saturation. Active bugs require thinner boundary layers (∼100 μm), which are achieved by living in moving water or by swimming.

“…The F-phase includes the rapid opening and closing of the spiracles to regulate intratracheal O 2 levels with some limited CO 2 release (Levy and Schneiderman, 1966;Lighton, 1994;Hetz and Bradley, 2005). Spiracles remain open during the O-phase, with gases being exchanged rapidly with the atmosphere by diffusion and convection (Lighton, 1988;Duncan et al, 2010;Harrison et al, 2013). During the C-and F-phase of the DGE cycle, the CO 2 that accumulates in the insect is buffered in the haemolymph.…”

Section: Introductionmentioning

confidence: 99%

A hierarchy of factors influence discontinuous gas exchange in the grasshopper Paracinema tricolor (Orthoptera: Acrididae)

Groenewald

Chown

Terblanche

2014

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% O 2 , 40% O 2 ) gas conditions, or dehydrated or hydrated, whereafter their CO 2 release was measured under a range of O 2 and relative humidity (RH) conditions (5%, 21%, 40% O 2 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% O 2 treatment conditions (5% O 2 , 44.1±29.3 min; 40% O 2 , 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, CO 2 excretion and pH modulation, oxidative damage protection and water savings.