Ventilation in Cataglyphis bicolor: Regulation of carbon dioxide release from the thoracic and abdominal spiracles

SUMMARY The role of the subelytral cavity in flightless beetle species as an adaptation to water saving in arid habitats is still in dispute. We found that relatively little CO2 was released from the subelytral cavity of a large apterous beetle Circellium bacchus during simultaneous measurements of CO2 emission from the anterior mesothoracic spiracles and posterior body, which included the subelytral spiracles. However, when we sampled air directly from inside the subelytral cavity, we discovered that this pattern was reversed. A discontinuous gas exchange cycle(DGC) was recorded from the posterior body half, revealing a flutter phase that had been absent from the anterior mesothoracic DGC. The anterior mesothoracic and posterior subelytral spiracles act in synchrony to maintain high CO2 and water vapour levels inside the subelytral cavity. In addition, the O2 concentration of the air within the subelytral cavity is lower than the air around the elytral case, irrespective of the time of sampling. These findings lead us to conclude that the subelytral spiracles work in a coordinated fashion with the anterior spiracles to create a DGC,which allows us to extend the hypothesis of the function of the subelytral cavity as a respiratory water-saving device.

Section: Spiracular Coordinationmentioning

confidence: 60%

Section: Role Of Subelytral Cavity In Water Conservationmentioning

confidence: 77%

The role of the subelytral spiracles in respiration in the flightless dung beetle Circellium bacchus

Byrne

Duncan

2003

“…Previous studies have used decapitation, decerebration and anaesthetisation to elicit DGCs in cockroaches (Edwards and Miller, 1986;Matthews and White, 2011b), ants (Duncan and Newton, 2000;Lighton, 1992;Lighton et al, 1993;Quinlan and Lighton, 1999) and moth pupae (Ito, 1954;Levy and Schneiderman, 1966). While it has been acknowledged that decerebration may alter the interactions between respiratory pattern generators, and so alter the behaviour of the DGCs produced by decapitated individuals (Quinlan and Lighton, 1999), the primary cause underlying the emergence of DGCs in decerebrated insects was believed to be their quiescence and low MR, a state that is not significantly different to that exhibited by resting individuals spontaneously displaying DGCs (Lighton et al, 1993;Lighton and Garrigan, 1995;Quinlan and Lighton, 1999).…”

Section: Discussionmentioning

confidence: 99%

“…While it has been acknowledged that decerebration may alter the interactions between respiratory pattern generators, and so alter the behaviour of the DGCs produced by decapitated individuals (Quinlan and Lighton, 1999), the primary cause underlying the emergence of DGCs in decerebrated insects was believed to be their quiescence and low MR, a state that is not significantly different to that exhibited by resting individuals spontaneously displaying DGCs (Lighton et al, 1993;Lighton and Garrigan, 1995;Quinlan and Lighton, 1999). By reversibly inactivating the insect's brains, we have demonstrated that DGCs can emerge due to a decrease in the activity of the insect's nervous system.…”

Section: Discussionmentioning

confidence: 99%

Reversible brain inactivation induces discontinuous gas exchange in cockroaches

Matthews

White

2013

SUMMARYMany insects at rest breathe discontinuously, alternating between brief bouts of gas exchange and extended periods of breathholding. The association between discontinuous gas exchange cycles (DGCs) and inactivity has long been recognised, leading to speculation that DGCs lie at one end of a continuum of gas exchange patterns, from continuous to discontinuous, linked to metabolic rate (MR). However, the neural hypothesis posits that it is the downregulation of brain activity and a change in the neural control of gas exchange, rather than low MR per se, which is responsible for the emergence of DGCs during inactivity. To test this, Nauphoeta cinerea cockroaches had their brains inactivated by applying a Peltier-chilled cold probe to the head. Once brain temperature fell to 8°C, cockroaches switched from a continuous to a discontinuous breathing pattern. Re-warming the brain abolished the DGC and re-established a continuous breathing pattern. Chilling the brain did not significantly reduce the cockroachesʼ MR and there was no association between the gas exchange pattern displayed by the insect and its MR. This demonstrates that DGCs can arise due to a decrease in brain activity and a change in the underlying regulation of gas exchange, and are not necessarily a simple consequence of low respiratory demand.

“…Moreover, it has also been argued that there is adaptive variation in the durations of the C-, F-, and O-periods to further reduce water loss. That is, a reduced O-period, and prolonged C-and F-periods are likely to further restrict respiratory water loss (Lighton, 1990;Lighton et al, 1993b;Davis et al, 1999;Bosch et al, 2000;Duncan et al, 2002a;Duncan, 2003). Whilst several other hypotheses for the evolution and maintenance of DGCs have been proposed (Lighton and Berrigan, 1995;Lighton, 1998;Bradley, 2000), these are also largely adaptive in nature (though for an exception, see Chown and Holter, 2000).…”

mentioning

confidence: 99%

Repeatability of standard metabolic rate and gas exchange characteristics in a highly variable cockroach,Perisphaeriasp.

Marais

Chown

2003

SUMMARYFor natural selection to take place several conditions must be met,including consistent variation among individuals. Although this assumption is increasingly being explored in vertebrates, it has rarely been investigated for insect physiological traits, although variation in these traits is usually assumed to be adaptive. We investigated repeatability (r) of metabolic rate and gas exchange characteristics in a highly variable Perisphaeriacockroach species. Although this species shows four distinct gas exchange patterns at rest, metabolic rate (r=0.51) and the bulk of the gas exchange characteristics (r=0.08–0.91, median=0.42) showed high and significant repeatabilities. Repeatabilities were generally lower in those cases where the effects of body size were removed prior to estimation of r. However, we argue that because selection is likely to act on the trait of an animal of a given size, rather than on the residual variation of that trait once size has been accounted for, size correction is inappropriate. Our results provide support for consistency of variation among individuals, which is one of the prerequisites of natural selection that is infrequently tested in insects.