Tracheal volume in the pupa on the saturniid moth Hyalophora cecropia determined with inert gases

SUMMARY Although general models of the processes involved in insect survival of freezing exist, there have been few studies directly investigating physiological processes during cooling, freezing and thawing, without which these models remain hypothetical. Here, we use open-flow respirometry to investigate the metabolism of the freeze-tolerant sub-Antarctic caterpillar Pringleophaga marioni Viette (Lepidoptera: Tineidae) during cooling,freezing and thawing and to compare animals exposed to non-lethal(–5.8°C) and lethal (–6.0°C, after which caterpillars are moribund for several days, and –18°C, after which caterpillars are completely unresponsive) freezing stress. We found a large decrease in metabolic rate (that is not associated with freezing) at–0.6±0.1°C and calculated a Q10 of 2.14×103 at this breakpoint. This breakpoint is coincident with the critical thermal minimum (CTmin) and is hypothesised to be a metabolic manifestation of the latter, possibly a failure of the Na+/K+-ATPase pump. This provides a plausible link between processes at the cellular level and observations of the action of the CTmin at tissue and whole-organism levels. Caterpillars froze at –4.6±0.1°C and had detectable metabolism when frozen. Post-thaw, metabolic rates were lower than pre-freezing measurements. Post-thaw metabolic rates did not differ between temperatures that did and did not kill the caterpillars, which suggests that mortality may be a result of a breakdown in processes at the organismal,rather than cellular, level of organisation.

Section: Resultssupporting

confidence: 54%

Metabolism of the sub-Antarctic caterpillar Pringleophaga marioni during cooling, freezing and thawing

Sinclair

Klok

Chown

2004

“…Tracheal volumes of insects have been estimated using water displacement (Wigglesworth, 1950), stereology (Schmitz and Perry, 1999) and inert gas-mass spectrometry (Bridges et al, 1980). The water displacement method is quick and inexpensive, but requires death of the animal, and may mis-measure V T due to water adherence to the cuticle and lack of fluid infiltration of the tracheoles.…”

Section: Introductionmentioning

confidence: 99%

“…The water displacement method is quick and inexpensive, but requires death of the animal, and may mis-measure V T due to water adherence to the cuticle and lack of fluid infiltration of the tracheoles. Bridges, Kestler and Scheid developed an inert gas wash-out and mass spectrometry technique to assess V T (Bridges et al, 1980). Their method provided the conceptual foundation for our approach, as it demonstrated the practical use of inert gases to measure V T .…”

Section: Introductionmentioning

confidence: 99%

Intraspecific variation in tracheal volume in the American locust,Schistocerca americana, measured by a new inert gas method

Lease

Wolf

Harrison

2006

SUMMARY The volume of a tracheal system influences breath-holding capacity and provides an index of an insect's investment in its respiratory system. Here,we describe a new, generally applicable method to measure tracheal volume that enables repeatable determinations on live animals. Animals are isolated in a closed chamber of a known volume and equilibrated with a helium:oxygen gas mixture. The chamber is then rapidly flushed with a nitrogen:oxygen gas mixture to eliminate the helium surrounding the animal, and sealed. After a period of time sufficient to allow equilibration of helium between tracheal system and chamber air, a gas sample is taken from the chamber, and tracheal volumes are calculated from the helium content of the sample, using a gas chromatograph. We show that relative investment in the tracheal system increases with age/size in the grasshopper; tracheal volume scales with mass to the power 1.3. This increased proportional investment in the tracheal system provides a mechanistic basis for the enhanced respiratory capacity of older grasshoppers. Tracheal volumes decrease strongly as grasshoppers grow within an instar stage, explaining reduced safety margins for oxygen delivery. Finally, tracheal volumes are smaller in gravid females than males, probably due to compression of air sacs by eggs.

“…The closed period, when all the spiracles are shut, prevents any gas exchange with the atmosphere (Bridges et al, 1980). Any closing saves water (the 'closing strategy'), as only CO 2 and O 2 are exchanged rapidly at the next opening; which is not the case for water vapour (the 'partial pressure Kestler, 2003).…”

Section: Introductionmentioning

confidence: 99%

The role of the mesothoracic spiracles in respiration in flighted and flightless dung beetles

Duncan

Byrne

2005

The relative role of the mesothoracic and abdominal spiracles in respiration was examined using flow-through respirometry in four dung beetle species from different habitats. Two species of flightless beetles, Scarabaeus (Pachysoma) gariepinus and Scarabaeus (Pachysoma) striatum, from the arid western region of southern Africa and a large flighted species, Pachylomerus femoralis, from a more mesic habitat were compared with Circellium bacchus, a flightless beetle from a low rainfall eastern area. All species showed a form of the discontinuous gas exchange pattern at rest. The mesic flighted species used a closed, flutter, open, cycle (CFO) while those species from more arid habitats used a closed, ventilation, cycle (CV) or a closed, burst cycle (CB). The relative importance of the mesothoracic spiracles in CO 2 emission varied between the species, even between those from the same genus and habitat. C. bacchus and P. femoralis represent extremes of CO 2 emission from the mesothoracic spiracles; from almost total to almost none, respectively. Overall, mesothoracic CO 2 emission and convection were more pronounced in the dry habitat species, supporting the hypothesis that both strategies aid in the reduction of water loss.