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Cockroaches breathe discontinuously to reduce respiratory water loss

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The reasons why many insects breathe discontinuously at rest are poorly understood and hotly debated. Three adaptive hypotheses attempt to explain the significance of these discontinuous gas exchange cycles (DGCs), whether it be to save water, to facilitate gas exchange in underground environments or to limit oxidative damage. Comparative studies favour the water saving hypothesis and mechanistic studies are equivocal but no study has examined the acclimation responses of adult insects chronically exposed to a range of respiratory environments. The present research is the first manipulative study of such chronic exposure to take a strong-inference approach to evaluating the competing hypotheses according to the explicit predictions stemming from them. Adult cockroaches (Nauphoeta cinerea) were chronically exposed to various treatments of different respiratory gas compositions (O(2), CO(2) and humidity) and the DGC responses were interpreted in light of the a priori predictions stemming from the competing hypotheses. Rates of mass loss during respirometry were also measured for animals acclimated to a range of humidity conditions. The results refute the hypotheses of oxidative damage and underground gas exchange, and provide evidence supporting the hypothesis that DGCs serve to reduce respiratory water loss: cockroaches exposed to low humidity conditions exchange respiratory gases for shorter durations during each DGC and showed lower rates of body mass loss during respirometry than cockroaches exposed to high humidity conditions.
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INTRODUCTION
Since Heller’s observation (Heller, 1930), the discontinuous gas
exchange cycles (DGCs) exhibited by many quiescent tracheated
arthropods have proven to be a source of intrigue and great debate.
Insect DGCs are distinguished from continuous and cyclic breathing
patterns by regular periods where respiratory gas exchange is
essentially prevented due to spiracular closure (Marais and Chown,
2003). Typically, DGCs comprise three phases: closed (C), flutter
(F) and open (O), and the patterns of respiratory gas exchange
occurring during these cycles has been extensively described in
lepidopteran pupae (e.g. Hetz and Bradley, 2005; Levy and
Schneiderman, 1966a; Levy and Schneiderman, 1966b; Terblanche
et al., 2008). During the C phase the spiracles are tightly occluded
and gas exchange with the atmosphere is essentially prevented.
Pressure within the tracheae declines as CO2is buffered within the
haemolymph and O2 is depleted due to respiration. Once the partial
pressure of oxygen (PO2) within the tracheal system has declined
to ~2–4 kPa, the F phase is initiated. During this phase the spiracles
open and close with high frequency, facilitating inward convective
movement of air, such that a low and stable PO2is maintained within
the tracheal system (Hetz and Bradley, 2005; Levy and
Schneiderman, 1966a). Outward movement of H2O and CO2is
minimised as a result of the inward convective movement of air,
and CO2continues to be buffered in the haemolymph (Wobschall
and Hetz, 2004). When the partial pressure of CO2(PCO2) within
the tracheal system reaches ~5–6 kPa, the spiracles open and
respiratory gases are exchanged with the atmosphere. CO2is
expelled in a burst and O2moves inwards until intratracheal PCO2
reaches ~3–4 kPa and the cycle is repeated (Levy and Schneiderman,
1966a).
DGCs are observed in a range of arthropod species (Klok et al.,
2002) and are present in at least five insect orders. Species exhibiting
DGCs inhabit xeric, mesic, subterranean and non-subterranean
environments, and are both winged and wingless. The presence of
DGCs in phylogenetically independent groups of insects (Blattodea,
Orthoptera, Coleoptera, Ledpidoptera and Hymenoptera) suggests
that the breathing pattern is adaptively significant, rather than exists
as an ancestral trait (Marais et al., 2005). Three main hypotheses
have emerged that attempt to explain the adaptive significance of
DGCs (Chown et al., 2006). The hygric hypothesis follows the
original suggestions of Buck, Keister and Specht (Buck et al., 1953)
that DGCs reduce transpiratory water loss. The chthonic hypothesis
(Lighton, 1998) postulates that DGCs are an adaptation to facilitate
efficient gas exchange under hypoxic and/or hypercapnic conditions,
often characteristic of underground environments. Lighton and
Berrigan (Lighton and Berrigan, 1995) originally proposed this
hypothesis in combination with the hygric hypothesis, such that
DGCs serve to facilitate gas exchange in challenging conditions
whilst also avoiding respiratory water loss. In recent literature,
however, the pure chthonic hypothesis, irrespective of water loss,
has become prominent (Chown et al., 2006). The final hypothesis
is the oxidative damage hypothesis (Bradley, 2000), which suggests
that DGCs function to limit oxidative damage to tissues. Because
the trachae are capable of rapidly delivering oxygen when required
(i.e. during flight), when at rest, near-ambient levels of oxygen at
the ends of the tracheoles may potentially be harmful to the insects’
tissues.
To date, research examining the adaptive function of DGCs has
not been well integrated. A mixture of mechanistic and comparative
studies fails to provide unequivocal support for any of the current
hypotheses. One possible approach for investigating the function
of DGCs involves analysing potential changes in the insects’ gas
exchange patterns in response to environmental variation. Many
organisms can respond to changes in the environment through
The Journal of Experimental Biology 212, 2773-2780
Published by The Company of Biologists 2009
doi:10.1242/jeb.031310
Cockroaches breathe discontinuously to reduce respiratory water loss
Natalie G. Schimpf*, Philip G. D. Matthews, Robbie S. Wilson and Craig R. White
School of Biological Sciences, Faculty of Biological and Chemical Sciences, University of Queensland, Brisbane 4000, Australia
*Author for correspondence (e-mail: n.schimpf@uq.edu.au)
Accepted 8 June 2009
SUMMARY
The reasons why many insects breathe discontinuously at rest are poorly understood and hotly debated. Three adaptive
hypotheses attempt to explain the significance of these discontinuous gas exchange cycles (DGCs), whether it be to save water,
to facilitate gas exchange in underground environments or to limit oxidative damage. Comparative studies favour the water saving
hypothesis and mechanistic studies are equivocal but no study has examined the acclimation responses of adult insects
chronically exposed to a range of respiratory environments. The present research is the first manipulative study of such chronic
exposure to take a strong-inference approach to evaluating the competing hypotheses according to the explicit predictions
stemming from them. Adult cockroaches (
Nauphoeta cinerea
) were chronically exposed to various treatments of different
respiratory gas compositions (O2, CO2and humidity) and the DGC responses were interpreted in light of the
a priori
predictions
stemming from the competing hypotheses. Rates of mass loss during respirometry were also measured for animals acclimated to
a range of humidity conditions. The results refute the hypotheses of oxidative damage and underground gas exchange, and
provide evidence supporting the hypothesis that DGCs serve to reduce respiratory water loss: cockroaches exposed to low
humidity conditions exchange respiratory gases for shorter durations during each DGC and showed lower rates of body mass
loss during respirometry than cockroaches exposed to high humidity conditions.
Key words: DGC, discontinuous gas exchange, hygric, chthonic, oxidative damage,
Nauphoeta cinerea
.
THE JOURNAL OF EXPERIMENTAL BIOLOGY
2774
morphological or physiological alterations that allow improved
function in the new conditions. This process of change in response
to environmental variation is known as phenotypic plasticity or
acclimation response (Fordyce, 2006). Until now, during
examination of DGCs, adult insects have only been subjected to
acute changes in respiratory gas conditions, as opposed to being
chronically exposed. It has therefore not yet been discovered
whether or not insects are capable of modifying their gas exchange
patterns in response to prolonged changes in respiratory
environments. The potential acclimation response of an insect to a
range of environmental conditions could be utilised to differentiate
among the three putative adaptive functions of DGCs, as each
hypothesis can be used to make distinct predictions regarding the
changes in DGC patterns in response to different respiratory
environments (Table1). The literature is largely devoid of prediction-
based approaches for understanding the function of DGCs, and such
a strong-inference approach would give more credibility to results
(Huey et al., 1999). The present research is the first manipulative
strong-inference study to address changes in the DGCs of adult
insects in response to chronic exposure to varying respiratory
environments. This research makes it possible to differentiate
among the competing hypotheses and provides insight into the
possible selective pressures that may have led to the evolution of
DGCs by evaluating the hypotheses according to the explicit
predictions stemming from them.
The present study aimed to test among the competing
hypotheses for the function of DGCs using the speckled cockroach
(Nauphoeta cinerea).Cockroaches were chronically exposed to
different concentrations of O2, CO2and water vapour [in practice
relative humidity (RH)] and DGC responses were examined in
light of the a priori predictions of the competing hypotheses
(Table 1). In the case of the hygric hypothesis, a positive
relationship between O phase duration and RH treatment is
predicted, as most respiratory water loss occurs during the O phase
(Chown et al., 2006). Thus, animals exposed to low levels of
ambient RH will have shorter O phases than animals acclimated
to high RH. In the case of the chthonic hypothesis, either a positive
relationship between CO2 treatment and the C and F phase
durations or a negative relationship between O2treatment and the
C and F phase durations is predicted, because the CO2and O2
partial pressure gradients required to facilitate efficient gas
exchange are generated during these phases. Thus, animals
acclimated to low O2, high CO2or both are predicted to have
relatively long C and F phases, such that large partial pressure
gradients are established to maintain adequate gas exchange under
hypoxic or hypercapnic conditions. Finally, in the case of the
oxidative damage hypothesis, a negative relationship between O
phase duration and O2treatment is predicted, because oxidative
damage would be greatest during the O phase. Thus, animals
exposed to high O2are predicted to have shorter O durations that
animals acclimated to low O2.
MATERIALS AND METHODS
Nauphoeta cinerea Olivier 1789 was a suitable study organism for
this research as, following preliminary investigations, it was shown
to exhibit a conspicuous DGC (Fig. 1). Final instar cockroaches were
obtained from The Herp Shop (Ardeer, Victoria, Australia) and
maintained as single-sex stock populations in 60 l plastic containers
at a constant temperature of 23±1.5°C and a 12 h:12 h L:D cycle.
Cockroaches were provided with an ad libitum diet of carrots and
dry cat food. The stock population was maintained at environmental
conditions: 21% O2, 0.03% (atmospheric) CO2and ambient RH
(~60–80%). Upon maturation, samples of male cockroaches from
the stock population were randomly selected and assigned to
acclimation treatments. Females were not used in this study to
eliminate changes in metabolism and gas exchange associated with
reproduction (Rossolimo, 1982), as female N. cinerea are
facultatively parthenogenetic (Corely et al., 2001).
In order to elucidate whether or not DGC patterns showed an
acclimation response, cockroaches were chronically exposed to a
number of different gas conditions. Exposure treatments lasted five
weeks, a period adequate to elicit acclimation responses in
cockroaches (Dehnel and Segal, 1956). For each of the gases [O2,
CO2and water vapour (RH)], a range of treatments from low to
high was used. Each treatment population (N~50) was housed in a
7 l polypropylene (Sistema, New Zealand) container under the same
temperature and L:D conditions as the stock population. The
treatment gases were set and delivered to the acclimation boxes at
a flow rate of ~200mlmin–1, measured with a mechanical flow meter
(Duff and McIntosh, Sydney, Australia). This ensured constant
turnover of the gas within the container and maintained a slight
positive pressure inside the container. Gas exited the container via
a minimum of 1 m of 8 mm outer diameter tubing.
To ascertain whether a change in DGC pattern occurred during
the exposure period, cockroach respiratory patterns were
characterised at 23±1°C upon completion of acclimation treatments.
As such, the rate of CO2 release of 12–16 randomly selected
cockroaches was measured using standard flow-through
respirometry (Withers, 2001). Two cockroaches were measured
simultaneously using each of the two sample cells of a Li-7000 (Li-
Cor, Nebraska, USA) CO2–H2O analyser. This precluded
simultaneous measurement of CO2and H2O but increased the
number of individuals that could be measured. Cockroaches were
placed individually in one of two 25 ml respirometry chambers to
which gas (see Table 2 and below for details) was delivered at a
constant flow rate of 200mlmin–1. Unless explicitly stated otherwise,
the incurrent gas was dry (Drierite, Sigma-Aldrich, Steinheim,
Germany) and CO2-free (Soda Lime, Fluka, Steinheim, Germany)
N. G. Schimpf and others
Table 1. Explicit predictions regarding the response of discontinuous gas exchange cycle phase durations following exposure to varying
respiratory environments
Treatments
Low High
Hypothesis Factor Phase response Factor Phase response
Hygric RH O duration decrease RH O duration increase
Chthonic CO2C and F duration decrease CO2C and F duration increase
O2C and F duration increase O2C and F duration decrease
Oxidative damage O2O duration increase O2O duration decrease
RH, relative humidity; O, open phase; C, closed phase; F, flutter phase.
THE JOURNAL OF EXPERIMENTAL BIOLOGY
2775Cockroaches DGC to save water
to maximise the accuracy of the analyser. The fractional CO2content
of the excurrent gas from each chamber was recorded to a computer
at a sampling frequency of 1 Hz.
All respirometry was performed during the inactive phase of the
circadian cycle (daytime), and food was withdrawn at least 24 h
prior to measurements. After being placed in the respirometry
chamber, cockroaches were allocated a one-hour ‘settling in’ period.
The gas exchange patterns of the animals were then measured under
the appropriate gases, which were presented sequentially in a random
order during a single respirometry session. The chamber was
darkened to encourage resting behaviour (and hence initiation of
DGCs). The mass of each cockroach was also recorded to 0.001 g
before and after respirometry measurements.
Oxygen exposure comprised four treatments: 5, 10, 21 and
40±1.1% O2, and carbon dioxide and relative humidity each
comprised three treatments (0.03, 3±0.03 and 6±0.3% CO2, and
25±0.1, 45±0.3 and 90±1.4% RH, respectively). Compressed mixes
of O2, CO2and N2obtained from and certified by a commercial
supplier (BOC gases, Brisbane, Australia) were used for the O2and
CO2acclimations. Desired levels of RH were produced by
equilibrating saturated air with water vapour at a range of
temperatures (2, 10 and 21°C for 25, 45 and 90% RH at 23°C) using
constant temperature cabinets, and were verified using a RH-300
Water Vapour Analyser (Sable Systems, Las Vegas, NV, USA).
Table 2 provides an overview of the nominal levels of acclimation
treatments (‘acclimation gas’ hereafter) and the gas conditions under
which DGCs were measured (‘measurement gas’ hereafter).
Following acclimation treatments, cockroaches were measured
under the conditions to which they were chronically exposed, as
well as under the conditions of the other treatments for a particular
gas where possible. Thus, animals acclimated to 5, 10, 21 or 40%
were measured at each of these O2concentrations in dry air, animals
acclimated to 0, 3 or 6% CO2were measured at 0% CO2in dry air
(measurement at higher levels of CO2was not possible because the
analyser saturated at 50 p.p.m. CO2), and animals acclimated to 25,
45 or 90% RH were measured at 25 and 45% RH (due to the risk
of condensation in the analyser at 90% RH).
The recorded data were used to characterise respiratory gas
exchange patterns in Microsoft Excel (Redmond, WA, USA), and
only individuals exhibiting DGCs were used for analysis. For each
DGC, total DGC (O+CF), O and CF phase durations were recorded
and metabolic rates were calculated according to Withers (Withers,
2001):
VCO2 =(VIFeCO2) / [1 + ({1/RE} – 1) FeCO2],
where VCO2=rate of CO2 production, VI=carbon dioxide
concentration, FeCO2=excurrent fraction of CO2 and RE=respiratory
exchange ratio, which was assumed to be 0.8. Rate of CO2
production was used as a proxy for metabolic rate.
C and F phases were combined due to the difficulty of
unambiguously differentiating the F phase in all individuals, and
because F phase may commence before CO2release is detected
using flow-through respirometry (Hadley and Quinlan, 1993;
Harrison et al., 1995; Wobschall and Hetz, 2004). Mixed model
analysis of variance (ANOVA) and analysis of covariance
(ANCOVA) were used to test for an effect of acclimation
treatment on total DGC, O and CF phase durations. The individual
identification number of cockroaches was included as a random
effect to account for the measurement of multiple cycles per
individual, and in the cases of O2and RH, to account for the
measurement of individuals in multiple gas conditions. In initial
analyses, the following variables were included: acclimation
treatment, time (am or pm), chamber, resting (settling in) gas,
measurement gas, measurement order, mass, metabolic rate and
identification number. In subsequent analyses, non-significant
variables were eliminated and any significant variables were
analysed for an interaction with acclimation treatment. Final
models always included acclimation treatment, measurement gas,
mass, metabolic rate and identification number regardless of their
significance. An interaction between acclimation treatment and
measurement gas was always tested for, and any other significant
covariates or interactions were also included. Data were tested
for normality using Shapiro–Wilk tests, and non-normal data were
transformed to improve normality (log10 or square root). In one
quarter of the cases, data did not reach normality. In these
circumstances the transformation that rendered the data closest
to normal distribution was accepted, as according to the Central
Limit Theorem, the distribution of means tends toward normality
0
10
20
30
40
00.2 0.4 0.6
Time (h)
[CO2] (p.p.m.)
Fig. 1. Measurement of carbon dioxide release over time from
Nauphoeta
cinerea
, demonstrating a conspicuous discontinuous gas exchange cycle.
Measurements were taken at a flow rate of 200 ml min–1.
Table 2. A summary of acclimation treatment conditions and nominal gas compositions in which discontinuous gas exchange patterns
were measured
TreatmentsLow acclimation Medium acclimation High acclimation DGC measurement conditions
Oxygen 5% O2
0% CO2
90% RH
10% O2
0% CO2
90% RH
21% O2
0% CO2
90% RH
40% O2
0% CO2
90% RH
5, 10, 21 and 40% O2
0% CO2
0% RH
Carbon dioxide 21% O2
0% CO2
90% RH
21% O2
3% CO2
90% RH
21% O2
6% CO2
90% RH
21% O2
0% CO2
0% RH
Relative humidity (RH) 21% O2
0% CO2
25% RH
21% O2
0% CO2
45% RH
21% O2
0% CO2
90% RH
21% O2
0% CO2
25 and 45% RH
THE JOURNAL OF EXPERIMENTAL BIOLOGY
2776
for large sample sizes despite a non-normal population distribution
(Quinn and Keough, 2002; Zar, 1974).
Additionally, to determine if RH acclimation had an effect on
water loss, rates of mass loss during respirometry were compared
for animals acclimated to 25, 45 and 90% RH using ANCOVA with
body mass as a covariate. All statistical tests were conducted using
JMP v.7.0.1 (SAS Institute Inc., Cary, NC, USA), and αwas set at
0.05 for all tests. For clarity, adjusted means are presented in figures,
and are shown ±s.e.m.
RESULTS
The effect of acclimation treatment on DGC duration is always
reported regardless of significance. There was never a significant
interaction between acclimation treatment and measurement gas
(P>0.05 in all cases). Other covariates and interactions are only
reported if their effects were significant, except in cases where a
significant covariate did not have a significant interaction with
acclimation treatment, in which case the non-significant interactions
are also reported. In addition, Table 3 provides a summary of the
mean initial mass and mean metabolic rates for each acclimation
treatment at the conclusion of the chronic exposure period.
Carbon dioxide
Mass had a significant effect on total DGC duration (ANOVA
F1,32=7.6, P=0.01) but there was no significant interaction between
mass and CO2acclimation treatment (ANOVA F2,26=0.84, P=0.44).
There was a significant effect of acclimation treatment on total DGC
duration (ANOVA F2,29=7.52, P=0.002), and 6% CO2exposure
resulted in significantly shorter DGC durations compared with 0%
and 3% (Tukey’s HSD) (Fig. 2).
There was a significant effect of mass and acclimation treatment
on O phase duration (ANOVA F1,29=4.58, P=0.04; F2,27=8.03,
P=0.002) but there was no significant interaction between mass and
treatment (ANOVA F2,24=0.56, P=0.58). O phase duration was
significantly shorter following 3% and 6% CO2treatments when
compared with 0% (Tukey’s HSD) (Fig. 2).
There was a significant effect of acclimation treatment on CF
phase duration (ANOVA F2,30=6.7, P=0.004). CF phase duration
was significantly shorter following exposure to 6% CO2 than
following exposure to 3%, and neither were significantly different
from 0% (Tukey’s HSD) (Fig. 2).
Relative humidity
Metabolic rate had a significant effect on total DGC duration
(ANOVA F1,138=6.8, P=0.01) but there was no significant interaction
between metabolic rate and RH acclimation treatments (ANOVA
F2,118=2.7, P=0.07). There was a significant effect of treatment
(ANOVA F2,24=6.1, P=0.007), with exposure to 90% RH resulting
in significantly longer total DGC duration compared with 25%
(Tukey’s HSD) (Fig. 3).
There was no effect of metabolic rate on O phase duration, so
metabolic rate was excluded from subsequent analyses of O phase.
There was a significant effect of acclimation treatment on O phase
duration (ANOVA F2,23=8.9, P=0.001). O phase duration was
significantly longer following exposure to 90% compared with 25%
RH (Tukey’s HSD) (Fig. 3).
Metabolic rate had a significant effect on CF phase duration
(ANOVA F1,101=13.0, P=0.0005) but there was no significant effect
of acclimation treatment (ANOVA F2,24=3.2, P=0.06, Tukey’s HSD)
(Fig. 3).
Mass loss was significantly affected by RH acclimation
(F2,23=24.0, P<0.0001) and correlated with body mass (F1,23=12.7,
P=0.002). Rate of mass loss was significantly reduced following
exposure to 25% RH compared with 45% and 90% RH (Tukey’s
HSD) (Fig. 4).
N. G. Schimpf and others
Table 3. A summary of mean initial mass and mean metabolic rate of cockroaches in each acclimation treatment
Acclimation treatment Metabolic rate (
V
CO2)
O2 (%)CO
2 (%) RH (%) Mass (g) ±s.e.m. (
N
) ±s.e.m. (
N
)
5 0 90 0.450±0.014 (8) 0.090±0.003 (8)
10 0 90 0.530±0.013 (11) 0.104±0.008 (11)
21 0 90 0.480±0.014 (16) 0.094±0.005 (16)
40 0 90 0.529±0.014 (9) 0.106±0.016 (9)
21 3 90 0.430±0.008 (11) 0.088±0.006 (11)
21 6 90 0.430±0.014 (10) 0.100±0.006 (10)
21 0 25 0.485±0.018 (10) 0.076±0.006 (10)
21 0 45 0.423±0.02 (6) 0.053±0.004 (6)
Measurements were taken at the conclusion of the chronic exposure treatments. RH, relative humidity.
0
2
4
6
8
10
12
DGC O CF
Phase
B
A
A
B
B
B
A
0% CO2
6% CO2
3% CO2
A
A,B
Duration (min)
Fig. 2. Adjusted least square means of total discontinuous gas exchange
cycles (DGC), open (O) and closed-flutter (CF) phase durations following
exposure to CO2treatments, shown +s.e.m. Exposure to 6% consistently
resulted in shorter phase durations than lower levels of CO2. Total sample
size:
N
=144 measurements from 36 individuals (0%:
N
=47 measurements
from 15 individuals; 3%:
N
=47 measurements from 11 individuals; 6%:
N
=50 measurements from 10 individuals). Columns within a phase that
share a letter (A or B) are not significantly different from each other
(Tukey’s HSD).
THE JOURNAL OF EXPERIMENTAL BIOLOGY
2777Cockroaches DGC to save water
Oxygen
Initial analyses revealed that O2 acclimation treatment, measurement
gas and measurement order had significant effects on total DGC
duration (ANOVA F3,66=4.2, P=0.008; F3,431=13.0, P<0.0001;
F3,424=4.6, P=0.004). There was also a significant interaction
between treatment and measurement order (ANOVA F9,420=3.3,
P=0.0007).
There was no effect of acclimation treatment on CF phase duration
(ANOVA F3,65=0.38, P=0.77) but there was a significant interaction
between acclimation treatment and measurement order (ANOVA
F9,420=2.1, P=0.03).
Acclimation treatment had a significant effect on O phase
duration (ANOVA F3,60=16.9, P=0.0001) but there was a
significant interaction between acclimation treatment and
metabolic rate, and between acclimation treatment and
measurement order (ANOVA F1,218=23.6, P<0.0001; F3,217=4.3,
P=0.006, respectively). Exploratory examination of these effects
suggested a difference in acclimation response between hypoxic
and hyperoxic conditions, and subsequent analyses were conducted
on hypoxic (5, 10 and 21% O2, measured at each of these levels)
and hyperoxic (21 and 40% O2, measured at each of these levels)
groups separately.
Hypoxic group
Acclimation treatment had a significant effect on total DGC duration
(ANOVA F2,49=5.4, P=0.007) and there was a significant interaction
between treatment and measurement order (ANOVA F6,247=2.6,
P=0.02). Only the 21% treatment measured in the first hour was
significantly different from that measured in the third hour (Tukey’s
HSD) (Fig. 5A).
Both acclimation treatment and measurement gas had a significant
effect on O phase duration (ANOVA F2,40=7.1, P=0.002;
F2,236=50.8, P<0.0001, respectively) and there was a significant
interaction between acclimation treatment and measurement order
(ANOVA F6,237=3.1, P=0.006). Only the 21% treatment measured
in the first hour was significantly different to the measurement in
the second hour (Tukey’s HSD) (Fig. 5B).
Measurement gas had a significant effect on CF phase duration
(ANOVA F2,252=27.4, P<0.0001) but there was no significant
effect of acclimation treatment (ANOVA F2,26=0.31, P=0.73)
(Fig. 5C).
Hyperoxic group
There was no significant effect of acclimation treatment on total
DGC duration (ANOVA F1,23=0.49, P=0.49), nor a significant effect
of any other variable.
Metabolic rate had a significant effect on O phase duration
(ANOVA F1,80=4.8, P=0.01) but there was no significant effect of
acclimation treatment (ANOVA F1,20=3.2, P=0.09).
Both resting gas and metabolic rate had a significant effect on
CF phase duration (ANOVA F3,15=3.8, P=0.03; F1,41=4.8, P=0.03).
Acclimation treatment had no significant effect on CF phase
duration (ANOVA F1,17=0.5, P=0.49).
Total sample size of N=137 measurements from 24 individuals
(21%: N=82 measurements from 15 individuals, 40%; N=55
measurements from 9 individuals).
DISCUSSION
The present research is the first of its kind to demonstrate that
adult insects alter their respiratory gas exchange patterns in
response to chronic exposure to varying environments.
Cockroaches showed a significant acclimation response to each
of the O2, CO2and RH treatments. These responses are
compared with the explicit predictions based on the three
A,B
A
B
A
A
A
A
A,B
B
DGC O CF
Phase
Duration (min)
0
2
4
6
8
10
12
14 25% RH
90% RH
45% RH
Fig. 3. Adjusted least square means of total discontinuous gas exchange
cycles (DGC), open (O) and closed-flutter (CF) phase durations following
exposure to relative humidity (RH) treatments, shown +s.e.m. Exposure to
90% RH resulted in longer DGC and O durations than exposure to lower
levels of RH. Total sample size:
N
=184 measurements from 27 individuals
(25%:
N
=72 measurements from 10 individuals; 45%:
N
=38 measurements
from 6 individuals; 90%:
N
=70 measurements from 10 individuals).
Columns within a phase that share a letter (A or B) are not significantly
different from each other (Tukey’s HSD).
0
2
4
6
8
10
12
25% 45% 90%
RH acclimation
Rate of mass loss (mg g–1 h–1)
A
B
B
Fig. 4. Mean rates of mass loss for the three relative humidity (RH)
treatments, shown +s.e.m. Exposure to 25% RH (
N
=10) resulted in a
decreased rate of mass loss compared with mass loss rates following
exposure to 45 and 90% RH (
N
=6 and 10, respectively). Columns that
share a letter (A or B) are not significantly different from each other
(Tukey’s HSD).
THE JOURNAL OF EXPERIMENTAL BIOLOGY
2778
adaptive hypotheses in order to elicit support for any number of
these hypotheses.
Chthonic hypothesis
CF phase duration was shortest following exposure to high levels
of CO2and longer when exposed to lower levels (Fig. 2). This
response runs counter to the predictions set out by the chthonic
hypothesis, which suggests that C and F phase duration will increase
in hypercapnia to facilitate adequate gas exchange via a steep
respiratory gas gradient. Similarly, there was no significant effect
of O2acclimation treatments on C and F phase duration. This further
refutes the chthonic hypothesis, which proposes an increase in the
C and F duration as O2levels decrease, again to facilitate adequate
gas exchange. Unfortunately, however, we were only able to
measure animals in conditions of 0% CO2, and so it remains
unknown how animals acclimated to high levels of CO2will
exchange respiratory gases in hypercapnia. The few species that
have been measured have been shown to cease DGCs in hypercapnia
(Harrison et al., 1995; Terblanche et al., 2008), and it would be
interesting to determine if this is also the case for cockroaches
acclimated to hypercapnia.
Oxidative damage hypothesis
The significant interaction between acclimation and measurement
order demonstrates that the effects of oxygen acclimation are
dependent on measurement order. Although Tukey’s HSD does not
identify any significant pair-wise differences between O2treatments
(Fig. 5A,B), there is an apparent positive relationship between
hypoxic O2treatments and the DGC and O phase durations. This
relationship is only apparent in the first one to two hours of
measurement (i.e. the second and third hours of total respirometry
session), after which it appears to be obscured. Nevertheless,
regardless of whether O phase duration increases with O2treatments
or remains unchanged, both responses are clearly inconsistent with
the predictions made by the oxidative damage hypothesis, which
states that the O phase should decrease in duration following
exposure to higher levels of oxygen in order to protect tissues from
oxidative damage. The lack of an acclimation response to hyperoxia
further suggests that DGCs are not required to limit oxidative
damage. Similarly, although intratracheal PO2is regulated at 4–5kPa
during the CF phase in atmospheres of up to 50 kPa O2in atlas
moths and silkworm pupae (Hetz and Bradley, 2005; Levy and
Schneiderman, 1966a), this regulation is not maintained at higher
PO2s (Levy and Schneiderman, 1966b).
Hygric hypothesis
The hygric hypothesis recently received support from work by
Marais et al. (Marais et al., 2005) and White et al. (White et al.,
2007) and the present research lends further credence to the original
explanation for the adaptive function of DGCs (Buck et al., 1953;
Buck and Keister, 1955; Burkett and Schneiderman, 1974a; Kestler,
1985; Levy and Schneiderman, 1966a; Lighton, 1990; Lighton et
al., 1993). Exposure to low levels of RH results in a reduction in
DGC duration, as well as a reduction in the duration of the O phase
whereas the duration of the CF phase was unaffected (Fig. 3). The
change in O duration is consistent with the explicit predictions that
stem from the hygric hypothesis (Table 1). O phase durations were
longest following acclimation to high levels of humidity where the
saturation deficit between the respiratory surfaces and that
atmosphere is likely to be small, and rates of water loss are likely
to be low. Following exposure to low humidity, O phase durations
were shorter, which presumably acted to reduce respiratory water
N. G. Schimpf and others
A
B
C
5% O2
21% O2
10% O2
0
2
4
6
8
10
12
14
16
O duration (min) DGC duration (min)
CF duration (min)
0
2
4
6
8
10
12
14
0
2
4
6
8
12 3
Measurement order
4
A,B
A,B
A,B
A,B
A,B
A
A,B
A,B
B
A,B
A,B
A,B
A,B
AA
A,B
A,B
B
A,B
A,B A,B
A,B
B
B
AA
A
A
A
A
A
AA
A
A
A
Fig. 5. Adjusted least square means of phase durations in the hypoxic
group of O2 treatments according to measurement order (hour), shown
+s.e.m. A positive relationship between acclimation and total discontinuous
gas exchange cycles (DGC) and open (O) phase durations is apparent but
only in the first two hours of measurement (A and B). There was no effect
of acclimation treatment on the closed-flutter (CF) phase duration (C). Total
sample size:
N
=275 measurements from 34 individuals (5%:
N
=69
measurements from 8 individuals; 10%:
N
=81 measurements from 11
individuals; 21%:
N
=125 measurements from 15 individuals). Columns that
share a letter (A or B) are not significantly different from each other
(Tukey’s HSD).
THE JOURNAL OF EXPERIMENTAL BIOLOGY
2779Cockroaches DGC to save water
loss. This finding is further supported by the fact that mean rates
of mass loss were 5–10-fold higher following acclimation to 45 and
90% RH treatments than when compared with 25% RH acclimation
(Fig. 4). It is acknowledged that mass loss alone is not a definitive
measure of respiratory water loss as it does not discriminate
between mass lost via defecation, cuticular or respiratory
transpiration. Further work examining only respiratory water loss
would provide an improved point of comparison.
Given that cockroaches show an acclimation response to altered
ambient humidity, it is surprising that measurement humidity did
not have a significant effect on phase durations. Cockroaches
therefore appear unable to detect acute changes in ambient
humidity. It is possible that the acute exposure is too short a time
for an observable response to occur but it is nevertheless clear that
cockroaches do not respond to RH immediately as they do to
changes in O2and CO2. Potentially, cockroaches chronically
exposed to low levels of humidity have lower levels of body
hydration than those chronically exposed to high levels of humidity.
Thus, the acclimation response to humidity may actually represent
a response to varying levels of hydration. Such a desiccated state
is likely to alter the haemolymph PCO2 and pH (Chown, 2002),
leading to a change in ventilation rate (Snyder et al., 1980).
However, while DGC frequency does increase following
acclimation to low RH, CF phase duration remains unchanged. If
desiccation-associated changes in haemolymph pH were
responsible for the acclimation response to RH, one might expect
to see a decrease in the CF phase duration as internal CO2would
reach the O phase trigger more quickly, because the volume, and
therefore presumably the CO2buffering capacity, of the
haemolymph is reduced. This however is not what is observed for
the CF phase duration. Alternatively, the level or concentration of
buffers could increase as a consequence of desiccation, and
therefore total buffer capacity would remain constant, in which case
CF duration would be expected to be independent of hydration
status. Clearly, chronic exposure to varying levels of ambient
humidity offers exciting opportunities to gain further insight into
the mechanistic basis of DGCs. At this stage, however, the
mechanism by which cockroaches sense and respond to altered
humidity remains unclear.
Conclusion
The present study has answered calls in the literature for a single-
species, strong-inference manipulative approach to examine the
evolutionary significance of DGCs (Chown, 2002; Chown et al.,
2006; Lighton, 2007; Lighton and Turner, 2008; Marais et al., 2005;
Quinlan and Gibbs, 2006; Terblanche et al., 2008). The present
research provides support for the hygric hypothesis and disputes
both the chthonic and oxidative damage hypotheses. This is in
contrast with a recent study by Terblanche et al., which provided
support for the oxidative damage hypothesis and limited support
for the hygric hypothesis (Terblanche et al., 2008). Terblanche et
al. exposed diapausing moth pupae Samia cynthia to a range of levels
of O2, CO2and humidity and interpreted the responses of the animals
in light of the explicit predictions of the competing hypotheses
(Terblanche et al., 2008). However, Terblanche et al. examined only
the effect of acute exposure on immature insects (Terblanche et al.,
2008). It is well documented that low O2and high CO2levels cause
insect spiracles to open (Beckel and Schneiderman, 1957; Burkett
and Schneiderman, 1967; Burkett and Schneiderman, 1974b), so it
is to be expected that DGCs will cease in hypoxia or hypercapnia.
Studies that only examine the DGC responses of insects to acutely
altered levels of respiratory gases are therefore of limited value when
distinguishing between the various hypotheses for the evolution of
DGCs.
Testing among the predictions that stem from the three adaptive
hypotheses explaining the evolution of DGCs demonstrates a clear
support for the hygric hypothesis. However, implicit in this
approach is the assumption that the best model is included in the
candidate set (Johnson and Omland, 2004; Quinn and Dunham,
1983). It remains to be seen whether future studies continue to find
support for water loss as the driving force for the evolution and
maintenance of discontinuous ventilation or whether new
hypotheses need to be considered. It has also been suggested that
several factors are likely to work together to influence the
expression of DGCs (Chown, 2002). It would be advantageous if
further research were to be conducted examining the effect on
DGCs of combinations of the gas conditions reported here. Such
an approach would aid in revealing possible interactive effects of
the gas variables that may not be detected when variables are
examined in isolation. Indeed in reality, insects encounter
microclimates of low O2and high CO2rather than the individually
manipulated gas variable of the present study (Anderson and Ultsch,
1987). Furthermore, the level of intratracheal O2influences the level
of CO2at which spiracles open, and vice versa (Burkett and
Schneiderman, 1967; Burkett and Schneiderman, 1974b), so it is
possible that a combination of hyperoxia and hypercapnia may elicit
acclimation responses different to those observed in the present
study. Such an approach could also reveal whether or not DGC
expression is prioritised according to the most costly variable in
the immediate respiratory environment. For example, for animals
experiencing water loss stress, DGCs may become important in
terms of the oxidative damage hypothesis. Wigglesworth
(Wigglesworth, 1935) documented the presence of fluid in the ends
of the tracheae under hyperoxic conditions and Kestler (Kestler,
1985) proposed that this fluid functioned to restrict tracheal
conductance and hence decrease potential damage resulting from
high levels of O2. If animals become dehydrated, they may be
unable to fill the tracheae with water, leaving them vulnerable to
oxidative damage. In such instances, O2levels may become an
important factor for the exhibition of DGCs.
The support garnered for the hygric hypothesis from the research
presented here suggests that reducing respiratory water loss was a
significant factor in the evolution of DGCs, at least in N. cinerea.
The hygric hypothesis is the first of the three adaptive hypotheses
to be supported by a variety of studies: two broad scale comparative
studies (Marais et al., 2005; White et al., 2007) that examined a
wide range of species from a diverse range of habitats, many
mechanistic studies dealing with acute exposures of respiratory gases
(e.g. Chown and Davis, 2003; Duncan et al., 2002a; Duncan et al.,
2002b; Duncan and Dickman, 2001; Lighton et al., 1993), and now
a mechanistic study that has examined the effect of chronic exposure
to various respiratory environments. A thorough understanding of
the evolution of physiological traits and their ecological implications
is aided by the strength of a number of complementary approaches
such as these (Huey and Kingsolver, 1993). Nevertheless, it is
important that further studies of acclimation to chronic exposure
are conducted on a variety of species, particularly from other orders
(such as Hymenoptera, Lepidoptera, Orthoptera and Coleoptera),
as it has been suggested that DGCs may have evolved for different
reasons in different species (Chown and Nicholson, 2004; Chown
et al., 2006). Such acclimation studies will reveal whether or not
other factors, such as O2or CO2, were important for the evolution
of DGCs in other species or whether in fact support is shown for a
single important evolutionary factor.
THE JOURNAL OF EXPERIMENTAL BIOLOGY
2780
Finally, it is important that future research addresses the intriguing
findings of the present study. Cockroaches responded to all
treatments by altering their respiratory gas exchange patterns but
the responses to CO2and O2are not congruent with the predictions
stemming from the chthonic and oxidative damage hypotheses. Both
the CO2and O2responses are opposite to what is predicted. Careful
consideration needs to be given as to why the DGCs are responding
to these factors in this manner, and exploratory analyses of these
new observations might lead to new theories for the evolution of
DGCs. It remains to be seen if such theories supplant Buck, Keister
and Specht’s (Keister and Specht, 1953) original hypothesis and the
results of the present study, which suggest that DGCs function to
reduce respiratory water loss.
LIST OF ABBREVIATIONS
C closed
DGC discontinuous gas exchange cycle
F flutter
O open
PCO2partial pressure of CO2
PO2partial pressure of O2
RH relative humidity
We thank two anonymous referees for their helpful comments on an earlier
version of this manuscript. This research was supported by the Australian
Research Council (project number DP0879605).
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N. G. Schimpf and others
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Water balance is strongly influenced by body surface area to volume ratio, such that differently sized individuals of the same species may differ in their capacity to tolerate dry conditions. The cockroach Nauphoeta cinerea is commonly used as a laboratory model in studies of water balance, but these studies have only considered adults, and so it remains unknown if previous studies of water balance in adults can be generalised to the whole life cycle. The present study determined the relationship between ontogeny and desiccation tolerance in N. cinerea using four different trials. Results generally confirm the initial expectation that juveniles would be less tolerant of desiccation. This finding indicates studies of water balance in N. cinerea adults cannot be generalised to the species as a whole, and demonstrates the importance of considering whole life cycles when determining a species’ minimum environmental and physiological requirements.
... Moisture-related factors might not only disrupt pit construction, but they may also affect the physiological status of the antlions. Generally, respiratory transpiration and metabolic rate are important processes related to water loss in insects (Chown 2002;Chown et al. 2011), such as in cockroach Nauphoeta cinerea (Olivier) (Schimpf et al. 2009) and mesic-and xeric-adapted Glossina species (Terblanche and Kleynhans 2009), where water loss in their body occur by means of respiration under low humidity conditions. Even though antlions usually show lower respiration or lower metabolic rates (Lucas 1985;Matsura and Murao 1994), it has been shown that mass loss, probably due to water loss, is affected by relative humidity (Rotkopf et al. 2012). ...
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Pit-building antlion larvae require not only dry and loose sand, but also other abiotic factors for beneficial pit site selection. Although wet soil is generally avoided by antlions, we assumed that antlion larvae of Baliga micans (McLachlan) (Neuroptera: Myrmeleontidae) prefer some degree of soil moisture because their relatively higher respiratory rate may cause water loss. We conducted behavioral experiments for pit construction in soils of different moisture content (0–29%) to quantitatively clarify soil moisture preference. Under the control containing only dry soil, some larvae died, no pits were frequently found, and larval weight decreased. The larvae constructed pits on the wet soil more frequently than on the dry soil. Particularly, the 2nd- and 3rd-instar larvae preferred the 9% soil and the 17% soil moisture, respectively. Therefore, the larvae showed soil moisture preference, owing to a probable physiological constraint. The soil moisture preference that secures the survival period is possibly a requisite trait for effective foraging.
... groups of insects, are resistant not only to low temperatures 20,21 but can also withstand hypoxia 22 , hypercapnia 23 , heat 24 , starvation 25 , xenobiotics 26 , or several weeks of food deprivation or ionizing radiation 27 . A number of representatives of this order show discontinuous respiration, which reduces the water loss, allowing them to survive when food and water are scarce 28,29 . Although most cockroach species are of tropical origin, some possess adaptations that allow them to survive in extreme environments, such as polar regions or deserts 20,21 . ...
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Low temperatures in nature occur together with desiccation conditions, causing changes in metabolic pathways and cellular dehydration, affecting hemolymph volume, water content and ion homeostasis. Although some research has been conducted on the effect of low temperature on Gromphadorhina coquereliana, showing that it can survive exposures to cold or even freezing, no one has studied the effect of cold on the hemolymph volume and the immune response of this cockroach. Here, we investigated the effect of low temperature (4 °C) on the abovementioned parameters, hemocyte morphology and total number. Cold stress affected hemocytes and the immune response, but not hemolymph volume. After stress, the number of circulating hemocytes decreased by 44.7%, but the ratio of apoptotic cells did not differ significantly between stressed and control individuals: 8.06% and 7.18%, respectively. The number of phagocyting hemocytes decreased by 16.66%, the hemocyte morphology drastically changed, and the F-actin cytoskeleton differed substantially in cold-stressed insects compared to control insects. Moreover, the surface area of the cells increased from 393.69 µm² in the control to 458.38 µm² in cold-treated animals. Together, our results show the links between cold stress and the cellular immune response, which probably results in the survival capability of this species.
... To do so, most arthropods benefit from different mechanisms to counterbalance water loss 8 . These mechanisms can be physiological, by modifying the water content of their faeces 9 or their respiration rate 10 , They can also be behavioural, such as hygrotaxis to acquire environmental moisture 11 through fog basking 12 or forming an aggregate to reduce individual water loss [13][14][15][16] mainly by reducing the individual surface area exposed to the air 17 . ...
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In collective decision-making, when confronted with different options, groups usually show a more marked preference for one of the options than do isolated individuals. This results from the amplification of individual preferences by social interactions within the group. We show, in an unusual counter-example, that when facing a binary choice between shelters with different relative humidities, isolated cockroaches of the species Periplaneta americana select the wettest shelter, while groups select the driest one. This inversion of selection results from a conflictual influence of humidity on the probabilities of entering and leaving each shelter. It is shown that the individual probability of entering the wettest shelter is higher than the group probability and is increased by previous entries and exits. The probability of leaving each shelter decreases in the population due to social interactions, but this decrease is less pronounced in the wettest shelter, suggesting weaker social interactions. A theoretical model is developed and highlights the existence of tipping points dependent on population size, beyond which an inversion of selection of a resting place is observed.
... The duration of the experiments did not allow observing significant variations in the basal oxygen levels as can be hypothesized from the results of other authors [31][32][33][34][35][36][37]. Prolonged monitoring will be carried out in future research. ...
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A new telemetric system for the electrochemical monitoring of dissolved oxygen is showed. The device, connected with two amperometric sensors, has been successfully applied to the wireless detection of the extracellular oxygen in the central complex of freely-walking Gromphadorhina portentosa. The unit was composed of a potentiostat, a two-channel sensor conditioning circuit, a microprocessor module, and a wireless serial transceiver. The amperometric signals were digitalized and sent to a notebook using a 2.4 GHz transceiver while a serial-to-USB converter was connected to a second transceiver for completing the communication bridge. The software, running on the laptop, allowed to save and graph the oxygen signals. The electronics showed excellent stability and the acquired data was linear in a range comprised between 0 and -165 nA, covering the entire range of oxygen concentrations. A series of experiments were performed to explore the dynamics of dissolved oxygen by exposing the animals to different gases (nitrogen, oxygen and carbon dioxide), to low temperature and anesthetic agents (chloroform and triethylamine). The resulting data are in agreement with previous O2 changes recorded in the brain of awake rats and mice. The proposed system, based on simple and inexpensive components, can constitute a new experimental model for the exploration of central complex neurochemistry and it can also work with oxidizing sensors and amperometric biosensors.
... Após medições com durações de até 10 minutos, em uma única sessão de respirometria por grupo, os espécimes foram retirados da câmara e, através de uma balança de precisão foi medida as massas corporais dos grupos (Schimpf et al. 2009). ...
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Article
Cold tolerance is considered an important factor determining geographic distribution of insects. We've previously shown that despite tropical origin, cockroach Gromphadorinha coquereliana is capable of surviving exposures to cold. However, freezing tolerance of this species had not yet been examined. Low temperature is known to alter membranes integrity in insects but whether chilling or freezing compromises DNA integrity remains a matter of speculation. In the present study, we subjected the G. coquereliana adults to freezing to determine their supercooling point (SCP) and evaluated whether the cockroaches were capable of surviving partial and complete freezing. Next, we conducted single cell gel electrophoresis assay (SCGE) to determine whether heat, cold and freezing altered haemocytes DNA integrity. The SCP of this species was high and around -4.76°C, which is within typical range of freezing-tolerant species. Most cockroaches survived one day after partial ice formation (20% mortality), but died progressively in the next few days after cold stress (70% mortality after 4 days). One day after complete freezing, most insects died (70% mortality), and after 4 days, 90% of them had succumbed. The SCGE assays showed substantial level of DNA damage in haemocytes. When cockroaches were heat-stressed, the level of DNA damage was similar to that observed in the freezing treatment; though all heat-stressed insects survived. The study shows that G. coquereliana can surprisingly be considered as moderately freezing-tolerant species, and for first time that extreme low temperature stress can affect DNA integrity, suggesting that this cockroach may possess an efficient DNA repair system.
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The Periodic Table of Life (PeTaL) is a system design tool and open source framework that uses artificial intelligence (AI) to aid in the systematic inquiry of nature for its application to human systems. This paper defines PeTaL’s architecture and workflow. Biomimicry, biophysics, biomimetics, bionics and numerous other terms refer to the use of biology and biological principles to inform practices in other disciplines. For the most part, the domain of inquiry in these fields has been confined to extant biological models with the proponents of biomimicry often citing the evolutionary success of extant organisms relative to extinct ones. An objective of this paper is to expand the domain of inquiry for human processes that seek to model those that are, were or could be found in nature with examples that relate to the field of aerospace and to spur development of tools that can work together to accelerate the use of artificial intelligence, topology optimization and conventional modeling in problem solving. Specifically, specialized fields such as paleomimesis, anthropomimesis and physioteleology are proposed in conjunction with artificial evolution. The overarching philosophy outlined here can be thought of as physiomimetics, a holistic and systematic way of learning from natural history. The backbone of PeTaL integrates an unstructured database with an ontological model consisting of function, morphology, environment, state of matter and ecosystem. Tools that support PeTaL include machine learning, natural language processing and computer vision. Applications of PeTaL include guiding human space exploration, understanding human and geological history, and discovering new or extinct life. Also discussed is the formation of V.I.N.E. (Virtual Interchange for Nature-inspired Exploration), a virtual collaborative aimed at generating data, research and applications centered on nature. Details of implementation will be presented in subsequent publications. Recommendations for future work are also presented.
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Flow-through respirometry systems that measure oxygen consumption (VO2), carbon dioxide production (VCO2) and evaporative water loss (EWL) require the accurate calibration of the flow meter and three separate analysers (O2, CO2 and H2O vapour). Correct measurement of VO2, VCO2 and EWL depends on the incurrent air flow (VI) and its condition (e.g. dry, CO2-free), and the excurrent air flow (VE) and its condition (e.g. dry, CO2-free), which can differ in different parts of the excurrent circuit. Usually either VI or VE is measured and the other is calculated from the gas composition. I describe here a procedure for precise calibration of CO2 and H2O analysers in a flow-through respirometry system by reference to a calibrated O2 analyser, using a small gas flame. Generic equations are derived for calculation of VO2, VO2 and EWL with a variety of configurations for a flow-through respirometry system. Procedures for selection of data from continuous records of VO2, VCO2 and EWL for calculation of minimal (basal or standard) values are briefly described. Finally, the importance of the correct order of data treatment prior to calculation is described.
Chapter
During the hundreds of million years available for genotypic, periodic, and short-term adaptations in insects the basic need for oxygen uptake and carbon dioxide release in highly changing and highly differing environments has led to a variety of structural and functional adaptations.
Book
1. Introduction 2. Estimation 3. Hypothesis testing 4. Graphical exploration of data 5. Correlation and regression 6. Multiple regression and correlation 7. Design and power analysis 8. Comparing groups or treatments - analysis of variance 9. Multifactor analysis of variance 10. Randomized blocks and simple repeated measures: unreplicated two-factor designs 11. Split plot and repeated measures designs: partly nested anovas 12. Analysis of covariance 13. Generalized linear models and logistic regression 14. Analyzing frequencies 15. Introduction to multivariate analyses 16. Multivariate analysis of variance and discriminant analysis 17. Principal components and correspondence analysis 18. Multidimensional scaling and cluster analysis 19. Presentation of results.
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1. Oxygen consumption has been studied in cultures of nymphal and adult cockroaches, Peniplaneta americana, that have been maintained at two experimental temperatures (10° and 16° C.) and the control temperature (26° C.) for a period of one to three weeks.2. It has been shown that the oxygen consumption of equal-weight nymphs when measured at 20° C. is higher in animals that have been maintained at the lower temperatures.3. Comparison of cold- (10° C.) and warm-adapted (26° C.) nymphs when measured at a series of temperatures (10° to 25° C.) demonstrates that cold-acclimated animals consume more oxygen per gram per hour than equal weight warm-adapted ones.4. Adult cockroaches show acclimation of their oxygen consumption to temperature. However, there isa differential response with respect to size; small adults acclimate to a greater degree than large ones. Further, all sizes of nymphs show a greater degree of acclimation than all sizes of adults.
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1. Forcing a few of the spiracles of the Agapema pupa to remain open abolishes the alternate retention and release ("burst") of CO2 and greatly augments water loss. The effects are reversed by sealing the inactivated spiracles.2. Pupae exposed to N2 after a normal CO2 burst has been produced release an additional volume of CO2 twice that of the original burst. The first cycle after such a "purge" is nearly twice as long as normal. These results further implicate the spiracles in CO2 retention and favor the idea that accumulation of CO2 triggers the burst.3. A statistical analysis of successive cycles within individual pupae indicates that burst volume tends to be constant, and comparison of individuals in a population shows significant inverse relations between metabolic rate and cycle length, and possibly between burst volume and cycle length. The significance of these findings is discussed in relation to the triggering of CO2 release and the rationale of the cycle.4. Mechanical disturbances may also tri...
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The respiratory physiology of four species of Australian desert-dwelling beetle was examined using a flow-through respirometry system over the temperature range of 20–40°C. The two species of tenebrionid beetles (Heleus waitei and Pterohelaeus sp.) did not exhibit the discontinuous gas exchange cycles (DGC), a mechanism to possibly reduce respiratory water loss rates, observed in other arid-dwelling beetles. There were small increases in metabolic rate with temperature resulting in a Q 10 of 1.84 for H. waitei and 1.99 for Pterohelaeus sp. Furthermore, H. waitei has no increase in metabolic rate over the temperature range 25–35°C (Q 10=1). The two species of carabid beetles (Cerotalis sp. and Carenum sp.) displayed the DGC respiratory pattern, having long flutter and burst periods. Both species also exhibited spiracular movement or muscular pumping in the burst period. Relatively low Q 10 values of 1.31 and 1.64 were measured for Cerotalis sp. and Carenum sp., respectively. Cerotalis sp. had no increase in metabolic rate over the temperature range 20–35°C (Q 10=1). In both species the temperature-associated increases in metabolic rate were modulated by increases in DGC frequency. All the four beetle species studied have fused elytra, a closed subelytral cavity and are nocturnally active, which should assist in reducing respiratory water loss rates, and occupy similar microhabitats. Thus we propose that the difference in respiratory patterns found between the tenebrionid and carabid beetles is related to their thorax morphology, food type and food availability.