9 research outputs found
Control of discontinuous gas exchange in Samia cynthia: effects of atmospheric oxygen, carbon dioxide and moisture
The evolution of discontinuous gas exchange (DGE) in insects is highly controversial. Adaptive hypotheses which have obtained
experimental support include a water savings mechanism for living in dry environments (hygric hypothesis), a reduction in oxidative damage due to a high-performance oxygen delivery system (oxidative damage hypothesis), and the need for steep
intratracheal partial pressure gradients to exchange gases under the hypercapnic and/or hypoxic conditions potentially encountered in subterranean environments (chthonic hypothesis). However, few experimental studies have simultaneously assessed multiple competing hypotheses within a strong inference framework. Here, we present such a study at the species level for a diapausing moth pupa, Samia cynthia. Switching gas conditions from controlled normoxic, normocapnic and intermediate
humidity to either high or low oxygen, high or low moisture, elevated carbon dioxide, or some combination of these, revealed that
DGE was abandoned under all conditions except high oxygen, and high or low gas moisture levels. Thus, support is found for the oxidative damage hypothesis when scored as maintenance of DGE. Modulation of DGE under either dry or hyperoxic conditions
suggested strong support for the oxidative damage hypothesis and some limited support for the hygric hypothesis. Therefore,
this study demonstrates that the DGE can be maintained and modulated in response to several environmental variables. Further
investigation is required using a strong-inference, experimental approach across a range of species from different habitats to
determine how widespread the support for the oxidative damage hypothesis might be.Centre of Excellence for Invasion Biolog
Respiratory dynamics of discontinuous gas exchange in the tracheal system of the desert locust, Schistocerca gregaria
CITATION: Groenewald, B., et al. 2012. Respiratory dynamics of discontinuous gas exchange in the tracheal system of the desert locust, Schistocerca gregaria. Journal of Experimental Biology, 215(13):2301-2307. doi:10.1242/jeb.070995The original publication is available at https://journals.biologists.com/jebGas exchange dynamics in insects is of fundamental importance to understanding evolved variation in breathing patterns, such
as discontinuous gas exchange cycles (DGCs). Most insects do not rely solely on diffusion for the exchange of respiratory gases
but may also make use of respiratory movements (active ventilation) to supplement gas exchange at rest. However, their temporal
dynamics have not been widely investigated. Here, intratracheal pressure, CO2 and body movements of the desert locust
Schistocerca gregaria were measured simultaneously during the DGC and revealed several important aspects of gas exchange
dynamics. First, S. gregaria employs two different ventilatory strategies, one involving dorso-ventral contractions and the other
longitudinal telescoping movements. Second, although a true spiracular closed (C)-phase of the DGC could be identified by
means of subatmospheric intratracheal pressure recordings, some CO2 continued to be released. Third, strong pumping actions
do not necessarily lead to CO2 release and could be used to ensure mixing of gases in the closed tracheal system, or enhance
water vapour reabsorption into the haemolymph from fluid-filled tracheole tips by increasing the hydrostatic pressure or forcing
fluid into the haemocoel. Finally, this work showed that the C-phase of the DGC can occur at any pressure. These results provide
further insights into the mechanistic basis of insect gas exchange.National Research Foundationhttps://journals.biologists.com/jeb/article/215/13/2301/10912/Respiratory-dynamics-of-discontinuous-gas-exchangePublisher's versio
Reactive oxygen species production and discontinuous gas exchange in insects
While biochemical mechanisms are typically used by animals to reduce oxidative damage, insects are
suspected to employ a higher organizational level, discontinuous gas exchange mechanism to do so.
Using a combination of real-time, flow-through respirometry and live-cell fluorescence microscopy, we
show that spiracular control associated with the discontinuous gas exchange cycle (DGC) in Samia cynthia
pupae is related to reactive oxygen species (ROS). Hyperoxia fails to increase mean ROS production,
although minima are elevated above normoxic levels. Furthermore, a negative relationship between mean
_V
CO2 and mean ROS production indicates that higher ROS production is generally associated with lower
_V
CO2 . Our results, therefore, suggest a possible signalling role for ROS in DGC, rather than supporting
the idea that DGC acts to reduce oxidative damage by regulating ROS production
Control of discontinuous gas exchange in Samia cynthia: Effects of atmospheric oxygen, carbon dioxide and moisture
The evolution of discontinuous gas exchange (DGE) in insects is highly controversial. Adaptive hypotheses which have obtained experimental support include a water savings mechanism for living in dry environments (hygric hypothesis), a reduction in oxidative damage due to a high-performance oxygen delivery system (oxidative damage hypothesis), and the need for steep intratracheal partial pressure gradients to exchange gases under the hypercapnic and/or hypoxic conditions potentially encountered in subterranean environments (chthonic hypothesis). However, few experimental studies have simultaneously assessed multiple competing hypotheses within a strong inference framework. Here, we present such a study at the species level for a diapausing moth pupa, Samia cynthia. Switching gas conditions from controlled normoxic, normocapnic and intermediate humidity to either high or low oxygen, high or low moisture, elevated carbon dioxide, or some combination of these, revealed that DGE was abandoned under all conditions except high oxygen, and high or low gas moisture levels. Thus, support is found for the oxidative damage hypothesis when scored as maintenance of DGE. Modulation of DGE under either dry or hyperoxic conditions suggested strong support for the oxidative damage hypothesis and some limited support for the hygric hypothesis. Therefore, this study demonstrates that the DGE can be maintained and modulated in response to several environmental variables. Further investigation is required using a strong-inference, experimental approach across a range of species from different habitats to determine how widespread the support for the oxidative damage hypothesis might be.Articl
Reactive oxygen species production and discontinuous gas exchange in insects
While biochemical mechanisms are typically used by animals to reduce oxidative damage, insects are suspected to employ a higher organizational level, discontinuous gas exchange mechanism to do so. Using a combination of real-time, flow-through respirometry and live-cell fluorescence microscopy, we show that spiracular control associated with the discontinuous gas exchange cycle (DGC) in Samia cynthia pupae is related to reactive oxygen species (ROS). Hyperoxia fails to increase mean ROS production, although minima are elevated above normoxic levels. Furthermore, a negative relationship between mean VCO2 and mean ROS production indicates that higher ROS production is generally associated with lower VCO2. Our results, therefore, suggest a possible signalling role for ROS in DGC, rather than supporting the idea that DGC acts to reduce oxidative damage by regulating ROS production. © 2011 The Royal Society