Ontogenetic effects on aerobic and anaerobic metabolism during jumping in the American locust, Schistocerca americana
Section of Organismal, Integrative, and Systems Biology, School of Life Sciences, Arizona State University, PO Box 874601, Tempe, AZ 85287-4501, USA
* Author for correspondence at present address: Division of Physiology, Department of Medicine, School of Medicine, University of California, San Diego, 9500 Gilman Drive, 0623A, La Jolla, CA 92093-0623, USA (e-mail: skirkton{at}ucsd.edu)
Accepted 14 June 2005
![]() |
Summary |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
Key words: development, endurance, power output, lactate, oxygen consumption, grasshopper, Schistocerca americana
![]() |
Introduction |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
Among invertebrates, developmental effects on locomotory performance have
been best studied in jumping grasshoppers. During ontogeny, the power output
during single, maximal jumps increased sixfold in Schistocerca
gregaria grasshoppers (Gabriel,
1985a; Queathem,
1991
; Katz and Gosline,
1993
). This increase in single jump power output was first
attributed to a greater proportion of jumping muscle mass and improved energy
storage in the exoskeleton of the femur (Gabriel,
1985a
,b
).
However, a second study showed that adults have stiffer cuticular springs but
may have the same proportion of muscle as juveniles, leaving the mechanism of
increased power output of maximal jumps during development unresolved
(Katz and Gosline, 1993
). No
studies to date have examined the effect of ontogeny on sustained locomotory
performance in grasshoppers or other insects.
Ontogenic effects on aerobic and anaerobic metabolism of active insects are
also not known. Adult grasshoppers produce lactate at relatively high rates
during jumping (Zebe and McShan,
1957; Gade, 1984
;
Harrison et al., 1991
). If
juveniles do not produce lactate during jumping, this could at least partially
explain the increase in single-jump power output in grasshoppers, and such a
pattern would be consistent with the suggestion that larger insects experience
more problems with oxygen delivery (Graham
et al., 1995
). Resting mass-specific metabolic rates fall with age
in grasshoppers, but the safety margin for oxygen delivery increases,
suggesting an improved oxygen delivery system in larger/older grasshoppers
(Greenlee and Harrison, 2004
).
Morphological measures indicate that mitochondrial content and tracheal oxygen
delivery capacities within the jumping leg of grasshoppers increase strongly
with age (Hartung et al.,
2004
). Thus, the data to date suggest that larger/older
grasshoppers do not experience increased problems with oxygen delivery that
might reduce locomotory performance. In the present study, we used a wide
range of developmental stages (2nd, 4th, 6th instars and adults), representing
a 30-fold increase in body mass, to determine how ontogeny affected power
output, endurance, lactate concentrations, oxygen consumption and carbon
dioxide production during repeated jumping in S. americana.
If older/larger grasshoppers experience more problems with oxygen delivery
due to longer tracheae, as suggested by Graham et al.
(1995), then their locomotion
may be more oxygen sensitive than juveniles. For example, if older/larger
grasshoppers experience oxygen limitations during jumping, we would predict
that their jump performance would be stimulated by hyperoxia, and strongly
inhibited by hypoxia; if smaller/younger grasshoppers have excessive oxygen
delivery capacities, their locomotory performance should be relatively oxygen
insensitive. As noted above, evidence from resting grasshoppers suggests that
older S. americana grasshoppers have improved oxygen delivery
relative to younger animals, probably due to improved convective ventilation
(Greenlee and Harrison, 2004
).
However, metabolic rates and critical oxygen partial pressure
(PO2) values for insects during flight are much
higher than measured for insects at rest
(Chadwick and Gilmour, 1940
;
Davis and Fraenkel, 1940
;
Joos et al., 1997
;
Harrison and Lighton, 1998
;
Greenlee and Harrison, 2004
).
If body size imposes limits on tracheal oxygen delivery, these are most likely
to be evident during locomotion, when gas exchange requirements are high.
![]() |
Materials and methods |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
Morphological changes during development
We measured body mass and femur mass (±0.1 mg) using a Mettler
Analytical AE 240 Dual Range Balance (Hightstown, NJ, USA). Femur length was
measured to the nearest 0.01 mm with a Mitutoyo Digimatic CD-6 digital
micrometer (Kawasaki, Japan). We then sliced the femur longitudinally in half
and placed it into 0.35 mol l1 NaOH for approximately 24 h
for tissue digestion (Marden,
1988). After the tissue was removed, the femoral exoskeleton was
washed in distilled water, blotted dry and re-weighed. The femoral
exoskeletons of 6th instars and adults were weighed on the analytical balance
and those of the 2nd and 4th instars were weighed on a Cahn C-33 microbalance
(±0.01 mg; Cerritos, CA, USA). Wet tissue mass was calculated as the
difference between the exoskeleton mass and wet femur mass. We calculated the
extensor tibia muscle mass to be 66% of the measured wet tissue mass
(Hartung et al., 2004
).
Measurements of jumping performance
Grasshoppers were removed from the colony on the day of the experiment and
kept in a group with food at 35°C. Approximately 1 h before a jumping
trial, we weighed the individual to be jumped and removed the distal third of
the adult wings to prevent flight. Grasshoppers were encouraged to jump by
physical prodding for up to 5 min or until fatigued, defined as a 30-s pause
between subsequent jumps with continued prodding. The method of physical
stimulation was varied throughout the trial to motivate the grasshopper.
Grasshoppers were jumped on a cotton bed-sheet (310x80 cm) that was
divided into a 10 cm (adult) or 5 cm (juvenile) numbered grid system within a
35°C temperature controlled room. As grasshoppers jumped between squares
during the trial, the grid number was called out and recorded onto an
audiotape. Distances were measured from the center of each square.
Jump frequency, total distance jumped, and mean distance per jump were
measured during each minute of the trial. The jump energy (E) was
calculated from:
![]() | (1) |
![]() | (2) |
Lactate concentration during jumping
Grasshoppers similar in age to the ones used in the jumping performance
experiment were jumped in a 100 liter Plexiglas gloved box at 35°C for 0,
15, 30, 60, 120, 300 or 600 s (N=810 at each time). After
jumping, animals were frozen in liquid nitrogen and stored at 20°C.
Later, the body mass, femur mass, femur length and lactate concentrations were
measured.
Frozen femurs were diluted 9x with chilled 0.6 mol l1 perchloric acid and pulverized with a ground-glass-tissue homogenizer immersed in ice-water. After centrifugation (Beckman Microfuge E, Palo Alto, CA, USA) for 5 min at 15 850 g, the supernatant was removed and diluted 9x with a 25 mmol l1 2-amino-2-methyl-1-propanol buffer. Lactate was measured in the supernatant using a fluorometric assay (Passonneau and Lowry, 1993) with a Standard Curve Filter Fluorometer (Optical Technology Devices Inc., Elmsford, NY, USA). Each sample was run six times [three with lactate dehydrogenase (LDH) and three without LDH to account for background noise].
O2 consumption and CO2 production during jumping and recovery
Gas exchange for jumping S. americana was measured using Plexiglas
chambers for all ages except the 2nd instars, which were jumped in a portion
of a 60 cm3 syringe. Each age group (N=7 per group) was
tested using a different-sized chamber and flow rates so that the 95%
equilibrium time was approximately 45 s in each case
(Lasiewski et al., 1966): 2nd
instars, 10 ml chamber, 35.0 ml min1 flow rate; 4th instars,
39.5 ml chamber, 138.4 ml min1; 6th instars, 116.4 ml
chamber, 377.8 ml min1; adults, 246.3 ml chamber, 563.1 ml
min1. Each jumping chamber was air tight except for
incurrent and excurrent air-flow ports. The smooth bottom surface of the
chamber was covered with coarse sand paper to facilitate jumping. Grasshoppers
were encouraged to jump using the end of a small paint brush attached to a
wire that was inserted through a rubber septum.
To reduce fluctuations in the background oxygen level, dry, CO2-free air (Balston purge-gas generator; Havervill, MA, USA) was generated and stored in a gas cylinder, which was warmed with heating pads to improve mixing. The purge gas generator was then disconnected, and air flow from the cylinder to the respirometry system was controlled by a Brooks 5878 mass flow controller and three 5850i Brooks mass flow meters (Brooks Instruments, Hatfield, PA, USA). One meter controlled air flow to the respirometry chamber and the grasshopper, the second meter was used to flush the respirometry chamber between trials, and the third meter controlled a line that flowed to the reference channel of the gas analyzers (Fig. 1). Using three-way valves, we could switch between recording either the baseline O2 and CO2 levels (while the animal chamber was being flushed) or the grasshopper's gas exchange.
|
After recording a starting baseline CO2 and O2 level for 5 min, the three-way valves were switched to record the animal's resting CO2 production and O2 consumption for 10 min. Next, the jumping metabolic rate was measured for 5 min by turning on a light in the incubator and stimulating the grasshopper to jump with the brush. After 5 min, the light was turned off and the grasshopper's whole-body CO2 production and O2 consumption during recovery were measured for approximately 10 min before switching back to the bypass and recording baseline values for the last 5 min of the trial. In control tests, there was no evidence of leaks when switching between the different experimental streams nor when manipulating the brush in the chamber. The signal-to-noise resolution of the respirometry system ranged from 12 (resting 2nd instars) to 95 (jumping adults) for O2, and from 337 (resting 2nd instars) to 1554 (jumping adults) for CO2. Immediately following the trial, the animal was weighed on the analytical balance (±0.1 mg).
To quantify how the aerobic ATP production of the jumping muscles may
change during ontogeny, we calculated the locomotory rate of oxygen uptake
(O2) of the
jumping muscle by comparing the
O2 values for
animals stimulated to locomote before and after autotomizing their jumping
legs. Each grasshopper was encouraged to autotomatize its hind femurs by
gently rubbing the femoral joints with warmed scissors. Autotomy caused
minimal damage to the animal because there are no direct muscles in the
autotomical plane, and after the leg is detached a membrane closes the wound,
minimizing haemolymph bleeding (Arbas and
Weidner, 1991
). Also, the thoracic muscles responsible for moving
the femur do not show denervation for at least 3 days
(Personius and Arbas, 1998
) or
muscular atrophy for 7 days after the autotomy
(Arbas and Weidner, 1991
). The
hindleg-less grasshopper was returned to a 35°C container with food and
water. The metathoracic hind femurs were weighed on an analytical balance, and
extensor tibia muscle mass was calculated as previously described.
O2 consumption and CO2 emission were re-measured exactly
as described above for juveniles on the following day and for adults after 2
days.
Injections of room air were used for each chamber and flow rate to correct
for lag time from the chamber to the analyzers (approximately 1 min) and
between analyzers. The rates of whole-body O2 consumption and
CO2 emission
(O2,wb and
CO2,wb,
respectively; µmol g1 h1) were
calculated similarly to Greenlee and Harrison
(2004
) and converted from ml
g1 min1 to µmol g1
h1. There were no statistically significant differences in
jump frequencies between the grasshoppers forced to jump in the respiratory
chamber and those jumped in the temperature-controlled room, so these values
are not reported.
Oxygen sensitivity during jumping
Oxygen sensitivity during jumping was measured in a 100 liter Plexiglas
gloved box at 35°C. The gloved box was perfused at 6 l
min1 with artificial oxygen atmospheres (5 kPa, 12 kPa, 21
kPa or 45 kPa balance nitrogen) created by mixing oxygen and nitrogen
supplied from compressed tanks via needle valves with mixtures
confirmed using an S-3A/I AEI Technologies Oxygen Analyzer (Pittsburgh, PA,
USA). Within the gloved box, a fan promoted air circulation, a thermocouple
recorded air temperature, and the bottom was covered with a soft paper to
provide traction for the jumping grasshoppers.
O2 did not vary
from the reported mix in the empty gloved box.
Individual grasshoppers were placed in the adjoining airlock for 30 s to equilibrate to the oxygen tension before being released into the chamber. Grasshoppers were forced to jump for up to 10 min or until fatigued (defined as when 30 s passed between jumps). Each animal was tested in a single oxygen atmosphere (N=58 per oxygen tension).
Statistical analysis
The effects of age and time during the trial on jump performance data were
analyzed using repeated-measures analysis of variance (ANOVA) with Systat 10.2
(Systat Software Inc., Richmond, CA, USA). We utilized ANOVA with
Bonferroni-corrected post-hoc comparisons to compare the lactate
concentrations among different aged grasshoppers at specific minutes during
the trial (Sokal and Rohlf,
1995). The
O2,
CO2 and oxygen
sensitivity data were analyzed using ANOVA with Bonferroni-corrected
post-hoc comparisons. In all cases, our level of significance was
0.05. Unless otherwise noted, all reported values are the means ±
standard errors.
![]() |
Results |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
|
|
|
|
O2 consumption and CO2 production during rest, jumping and recovery
During jumping, maximal (30 s period)
O2,wb and
CO2,wb increased
significantly with age (O2: Fig.
5A; ANOVA, F3,24=38.2, P<0.001;
CO2: Fig. 5B; ANOVA,
F3,24=33.1, P<0.001).
O2,wb and
CO2,wb of
jumping adults were double that of the 2nd instars
(Fig. 5). The scope in
O2,wb (jumping
relative to resting values) increased with age (2nd instars, 2.0; 4th instars,
2.4; 6th instars, 3.4; adults, 4.2). After 2 min of recovering, there was no
effect of age on
O2,wb
(Fig. 6A), but
CO2,wb was
inversely related to age (Fig.
6B; ANOVA, F3,24=13.8, P<0.001).
Similarly, during jumping, age had a significant effect on the amount of
O2 consumed by the jumping muscle
(Fig. 7A; ANOVA,
F3,24=6.6, P<0.01) and CO2 produced
(Fig. 7B; ANOVA,
F3,24=4.6, P<0.05), with both increasing with
ontogeny.
|
|
|
|
Oxygen sensitivity during jumping
Within an age group, hypoxia affected first-minute jump rates. Extreme
hypoxia (5 kPa O2) significantly reduced first-minute jump rate for
grasshoppers of all ages, while moderate hypoxia (12 kPa O2)
significantly reduced first-minute jump rate only in the 2nd instars
(Fig. 9; ANOVA,
F3,20=4.8, P<0.05) and adults
(Fig. 9; ANOVA,
F3,30=28.6, P<0.001). When compared with
normoxia (21 kPa), there was no effect of hyperoxia (45 kPa) on first-minute
jump rate for 2nd and 4th instar grasshoppers of any age; however, hyperoxia
increased the first-minute jump rate in 6th instars
(Fig. 9; ANOVA,
F3,21=20.3, P<0.001) and adults
(Fig. 9; ANOVA,
F3,30=28.6, P<0.001).
|
|
![]() |
Discussion |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
Similar to other developmental studies of locomotory
O2
(Full, 1987
;
Chappell and Bachman, 1995
;
Chappell et al., 1999
), the
factorial aerobic scope increased with ontogeny. The whole-body aerobic scope
increased from 2.1 in 2nd instars up to 4.2 in adults. Compared with other
types of insect locomotion, the aerobic scope calculated during jumping is low
(running ectothermic insects, 8; running endothermic insects, 26; flying
insects, 129; Full, 1997
).
While the aerobic scopes are low, the amount of oxygen consumed during jumping
in S. americana adults (7.2 ml g1
h1) was greater than the mean oxygen consumption of running
insects (2.44.5 ml g1 h1;
Harrison and Roberts, 2000
),
suggesting that the relatively low scopes are due to elevated resting rates in
this study. Our measured values for resting
O2 were
approximately double those reported by Greenlee and Harrison
(2004
), perhaps because the
animals could be much more active in the larger chamber we used (we did not
monitor activity during the prejump, resting
O2
measurements). If the resting
O2 from Greenlee
and Harrison (2004
) is used,
aerobic scopes increase to approximately 10 in adults, a value well within the
range for an ectothermic running insect.
The high oxygen consumption of jumping S. americana compared with
insect runners is consistent with the high mitochondrial contents of the
muscle (Hartung et al., 2004).
The only other reported
O2max for
grasshopper jumping (Melanoplus bivittatus; 1.3 ml
g1 h1, 58 µmol g1
h1; Harrison et al.,
1991
) was
5-fold lower than measured in this study. M.
bivittatus may not have such a well-developed respiratory system as
S. americana since peak gas exchange rates occurred after, rather
than during, jumping in M. bivittatus, and oxygen consumption rates
returned to resting rates much more slowly
(Harrison et al., 1991
).
Strong support for the validity of this surprising interspecific difference is
provided by the observation that traveling speeds during jumping are 4-fold
higher in S. americana than in M. bivittatus
(Harrison et al., 1991
).
What explains the reduced endurance of older grasshoppers?
Unlike the situation for most vertebrates, older animals had reduced
endurance in S. americana grasshoppers (Figs
2,
3). These trade-offs in
performance variables may relate to life history. While juvenile grasshoppers
utilize jumping as their primary mechanism for escape from predators and
migration (Ellis, 1951), the
powerful single jumps of adults are thought to be necessary to achieve the
take-off velocity required for flight
(Katz and Gosline, 1993
).
The stimulation method used during this study seems unlikely to be the
cause of the decreased endurance with development. Based on data from running
vertebrates (Heglund et al., 1974) and invertebrates (reviewed in
Full, 1997), one might expect
the jump frequency of grasshoppers to scale with body mass raised to the
0.14 to 0.25. Within the first minute of our experiment, when
grasshoppers needed no prodding, the scaling of jump frequency with body mass
was 0.06, suggesting that larger grasshoppers jumped more than expected
based on vertebrate data. During the second minute of repeated jumping, the
scaling coefficient was 0.12. However, by the third minute, the scaling
coefficient (0.21) was similar to values reported for running animals.
This suggests that the increased jump frequency of older grasshoppers in the
first minute was due to increased reliance on aerobic metabolism in larger
animals, rather than the method of stimulation. After two minutes of repeated
jumping, when aerobic ATP production dominates, the scaling of jump
performance matches running animals.
The reduced endurance of older grasshoppers is correlated with the
increased utilization of anaerobic metabolism during the initial minutes when
jump frequencies and power outputs are very high compared with younger animals
(Fig. 4). During the first two
minutes of jumping, the contribution of anaerobic ATP production ranged from
0% in 2nd instars to approximately 40% for older animals
(Table 2). The constant lactate
levels in the muscle after two minutes of jumping, and lack of appearance of
lactate in the haemolymph, indicate that net lactate production is negligible
after the first few minutes and suggest that prolonged hopping is completely
supported by aerobic metabolism. A predominant reliance on aerobic ATP
production during repeated jumping has also been shown in adults of the
two-striped grasshopper (Harrison et al.,
1991).
|
Potentially, the increased usage of anaerobic metabolism due to inadequate
oxygen delivery during the first minutes of jumping may cause the reduced
endurance with age. The stimulation of first-minute jump rate in older animals
by hyperoxia (Fig. 9) and the
increased lactate concentration in older animals suggest that the Pasteur
effect is stimulating lactate production. Lactic acid has long been considered
to be an agent of muscle fatigue, primarily due to effects on muscle pH
(Juel, 1996). Leg
CO2 also rises
dramatically during jumping of adult grasshoppers
(Krogh, 1913
;
Krolikowski and Harrison,
1996
), which will further reduce muscle pH, potentially causing
fatigue. However, the lack of an effect of hyperoxia on endurance argues
against this hypothesis. If lactate production is caused by low muscle
O2, then
hyperoxia should have reduced lactate production and increased endurance in
older animals. More recent studies have suggested that muscle fatigue during
burst locomotion may be due to accumulation of inorganic phosphates (reviewed
in Westerblad et al., 2002
).
Adult Locusta migratoria use arginine phosphate to power the initial
seconds of jumping (Hitzemann,
1979
; Schneider et al.,
1989
). Potentially, the use of arginine phosphate increases with
age, and increased accumulation of inorganic phosphate explains the reduced
endurance with age.
One of the mysteries of fatigue in jumping grasshoppers is the apparent
temporal dissociation between the metabolic events thought to affect fatigue
and the organism-level changes in performance. Arginine phosphate utilization
is completed within the first five jumps (<15 s) in adult grasshoppers
(Hitzemann, 1979;
Schneider et al., 1989
), and
lactate concentrations are similar after two minutes
(Fig. 4), but power output
falls steadily over many minutes (Fig.
3). These data suggest that other processes (e.g. muscle glycogen
depletion, neurotransmitter depletion, changes in hormone levels, behavioral
habituation) may contribute to long-term fatigue in grasshoppers.
Safety margins for oxygen delivery decrease with age
Although older S. americana have increased aerobic capacities and
tracheal oxygen delivery capacities
(Hartung et al., 2004), it
does appear that there is an increasing tendency for oxygen limitation of jump
performance with age. Hyperoxia improved the jump rate in the first minute
(Fig. 9) only for larger/older
grasshoppers, suggesting that oxygen delivery is inadequate during the first
minute only in adults and 6th instars. In many tissues, inadequate oxygen
concentrations can cause lactate production (Pasteur effect), and so one
hypothesis is that inadequate oxygen delivery during the first minutes of
jumping causes the increased lactate levels in older grasshoppers. Therefore,
the usually high jump rates of 6th instar grasshoppers at 12 kPa and their
rapid fatigue may be due to increased lactate production. The effect of
lactate increasing initial jump frequency is supported by the finding that
anaerobic and aerobic metabolism correlate with different scaling coefficients
during repeated jumping. Measurements of the effect of hyperoxia on lactate
production rates during jumping would test this hypothesis. Also, the
increased sensitivity of endurance to hypoxia in 6th instars and adults is
consistent with a reduced safety margin for oxygen delivery during ontogeny
for jumping grasshoppers.
Changes in muscle metabolic potential explain the increase in power output with age
Previous research has suggested that the increased power output during
jumping of older grasshoppers was attributed to increased muscle mass:body
mass ratio (Gabriel, 1985a).
However, our more extensive data set clearly showed that muscle mass developed
isometrically with changes in body mass in S. americana
(Table 1). In addition, when
all developmental stages are included from Gabriel's study on S.
gregaria (Gabriel,
1985a
), the proportion of extensor tibia muscle to body mass
appears nearly isometric (1st instars 6.1%, 2nd instars 4.7%, 3rd instars
5.0%, 4th instars 4.3%, 5th instars 5.5%, adults 6.3%; N=5 for each
age). Thus, it seems likely that isometric development of jumping muscle mass
occurs throughout Schistocerca, as in the related African migratory
locust (L. migratoria migratoriodes;
Duarte, 1938
).
Originally, the increased femoral exoskeleton thickness was thought to
explain the greater power output in older grasshoppers by improving cuticular
energy storage (Gabriel,
1985b). However, it was later reasoned that thicker femoral walls
would make it more difficult for grasshoppers with similar proportions of
muscle to bend the cuticle to store energy, so a stiffer spring could not, on
its own, explain improved jump performance
(Katz and Gosline, 1992
).
These estimates of energy storage assumed constant muscle properties across
instars (Gabriel,
1985a
,b
;
Katz and Gosline, 1993
).
However, adult leg muscles have double the mitochondrial content and a 12-fold
greater tracheal diffusing capacity than second instars
(Hartung et al., 2004
). Our
data showed that the oxygen consumption rate of the jumping muscle increased
6-fold during development (during the first 2 min;
Table 2). In addition, the
muscles of older grasshoppers produced ATP anaerobically at much higher rates
(Fig. 4;
Table 2). The 10-fold increase
in total leg-muscle specific ATP production rates exceeds the greater than
2-fold increase in body-mass specific power output, perhaps because of
complexities in the mechanism of power production from a near-isometrically
contracting muscle and a spring system
(Bennet-Clark, 1975
).
Nonetheless, it is now clear that increases in the capacity of the jumping
muscle to produce ATP (Table 2)
allow older/larger grasshoppers to utilize their stiffer leg springs to
produce greater power.
![]() |
Acknowledgments |
---|
![]() |
References |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
Arbas, E. A. and Weidner, M. H. (1991). Transneuronal induction of muscle atrophy in grasshoppers. J. Neurobiol. 22,536 -546.[CrossRef][Medline]
Bennet-Clark, H. C. (1975). The energetics of the jump of the locust Schistocerca gregaria. J. Exp. Biol. 63,53 -83.[Abstract]
Chadwick, L. E. and Gilmour, D. (1940). Respiration during flight in Drosophilia repleta Wollaston: oxygen consumption considered in relation to the wing-rate. Physiol. Zool. 13,398 -410.
Chappell, M. A. and Bachman, G. C. (1995). Aerobic performance in Beldings ground squirrels (Spermophilus beldingi): variance, ontogeny, and the aerobic capacity model of endothermy. Physiol. Zool. 68,421 -442.
Chappell, M. A., Bech, C. and Buttemer, W. A.
(1999). The relationship of central and peripheral organ masses
to aerobic performance variation in house sparrows. J. Exp.
Biol. 202,2269
-2279.
Davis, R. A. and Fraenkel, G. (1940). The oxygen consumption of flies during flight. J. Exp. Biol. 17,402 -407.
Doré, E., Bedu, M., Franca, N. M., Diallo, O., Duche, P. and Van Praagh, E. (2000). Testing peak cycling performance: effects of braking force during growth. Med. Sci. Sports Exerc. 32,493 -498.[CrossRef][Medline]
Duarte, A. J. (1938). Problems of growth of the African migratory locust. Bull. Entomol. Res. 29,425 -456.
Ellis, P. E. (1951). The marching behaviour of hoppers of the African migratory locust, Locusta migratoria migratorioides (R. & F.), in the laboratory. Anti-Locust Bulletin 7,1 -48.
Full, R. J. (1987). Locomotion energetics of the ghost crab. I. Metabolic cost and endurance. J. Exp. Biol. 130,137 -153.
Full, R. J. (1997). Invertebrate locomotor systems. In Handbook of Physiology Section 13: Comparative Physiology, vol. II (ed. W. H. Dantzler), pp. 853-930. New York: Oxford University Press.
Gabriel, J. M. (1985a). The development of the locust jumping mechanism. I. Allometric growth and its effects on jumping performance. J. Exp. Biol. 118,313 -326.
Gabriel, J. M. (1985b). The development of the locust jumping mechanism. II. Energy storage and muscle mechanics. J. Exp. Biol. 118,327 -340.
Gade, G. (1984). Anaerobic energy metabolism. In Environmental Physiology and Biochemistry of Insects (ed. K. H. Hoffmann), pp.119 -136. Berlin: Springer-Verlag.
Garland, T. (1984). Physiological correlates of locomotory performance in a lizard: an allometric approach. Am. J. Physiol. 247,R806 -R815.[Medline]
Garland, T. and Else, P. L. (1987). Seasonal, sexual, and individual variation in endurance and activity metabolism in lizards. Am. J. Physiol. 252,R439 -R449.[Medline]
Graham, J., Dudley, R., Aguilar, N. and Gans, C. (1995). Implications of the late Palaeozoic oxygen pulse for physiology and evolution. Nature 375,117 -120.[CrossRef]
Greenlee, K. J. and Harrison, J. F. (2004).
Development of respiratory function in the American locust Schistocerca
americana I. Across-instar effects. J. Exp. Biol.
207,497
-508.
Harrison, J. F. and Kennedy, M. J. (1994). In vivo studies of the acid-base physiology of grasshoppers: the effect of feeding state on acid-base and nitrogen excretion. Physiol. Zool. 67,120 -141.
Harrison, J. F. and Lighton, J. R. B. (1998).
Oxygen sensitive flight metabolism in the dragonfly Erythemis
simplicicollis. J. Exp. Biol.
201,1739
-1744.
Harrison, J. F. and Roberts, S. P. (2000). Flight respiration and energetics. Annu. Rev. Physiol. 62,179 -205.[CrossRef][Medline]
Harrison, J. F., Phillips, J. E. and Gleeson, T. T. (1991). Activity physiology of the two-striped grasshopper, Melanoplus bivittatus: gas exchange, hemolymph acid base status, lactate production, and the effect of temperature. Physiol. Zool. 64,451 -472.
Hartung, D. K., Kirkton, S. D. and Harrison, J. F. (2004). Ontogeny of tracheal system structure: a light and electron-microscopy study of the metathoracic femur of the American locust, Schistocerca americana. J. Morphol. 262,800 -812.[CrossRef][Medline]
Heglund, N. C. and Taylor, C. R. (1974). Scaling stride frequency and gait to animal size: mice to horses. Science 186,1112 -1113.[Medline]
Hitzemann, K. (1979). Untersuchungen über den Energiestoffwechsel in der Sprungmuskulatur von Locusta migratoria (L.). Thesis, Zoologisches Institut Universitat Munster.
Hochachka, P. W. and Somero, G. N. (1984). Biochemical Adaptation. Princeton: Princeton University Press.
Joos, B., Lighton, J. R. B., Harrison, J. F., Suarez, R. K. and Roberts, S. P. (1997). Effects of ambient oxygen tension on flight performance, metabolism, and water loss of the honeybee. Physiol. Zool. 70,167 -174.[Medline]
Juel, C. (1996). Lactate/proton co-transport in skeletal muscle: regulation and importance for pH homeostasis. Acta Physiol. Scand. 156,369 -374.[CrossRef][Medline]
Katz, S. L. and Gosline, J. M. (1992). Ontogenetic scaling and mechanical behaviour of the tibiae of the African desert locust. J. Exp. Biol. 168,125 -150.
Katz, S. L. and Gosline, J. M. (1993).
Ontogenetic scaling of jump performance in the African desert locust
(Schistocerca gregaria). J. Exp. Biol.
177,81
-111.
Krogh, A. (1913). On the composition of the air in the tracheal system of some insects. Skank. Arch. Physiol. 29,29 -36.
Krolikowski, K. and Harrison, J. F. (1996).
Haemolymph acid-base status, tracheal gas levels and the control of
post-exercise ventilation rate in grasshoppers. J. Exp.
Biol. 199,391
-399.
Lasiewski, R. C., Acosta, A. L. and Bernstein, M. L. (1966). Evaporative water loss in birds. I. Characteristics of open flow method of determination and their relation to estimates of thermoregulatory ability. Comp. Biochem. Physio. 19,445 -447.[CrossRef]
Marden, J. H. (1988). Bodybuilding dragonflies: costs and benefits of maximizing flight muscle. Physiol. Zool. 62,505 -521.
Personius, K. E. and Arbas, E. A. (1998). Muscle degeneration following remote nerve injury. J. Neurobiol. 36,497 -508.[CrossRef][Medline]
Pough, F. H. (1977). Ontogenetic change in blood-oxygen capacity and maximum activity in garter snakes (Thamnophis sirtalis). J. Comp. Physiol. 116,337 -345.[CrossRef]
Pough, F. H. (1978). Ontogenetic changes in endurance in water snakes (Natrix sipedon): physiological correlates and ecological consequences. Copeia 1978,69 -75.
Pough, F. H. and Kamel, S. (1984). Post-metamorphic change in activity metabolism of anurans in relation to life-history. Oecologia 65,138 -144.[CrossRef]
Queathem, E. (1991). The ontogeny of grasshopper jumping performance. J. Insect Physiol. 37,129 -138.[CrossRef]
Queathem, E. J. and Full, R. J. (1995). Variation in jump force production within an instar of the grasshopper Schistocerca americana. J. Zool. 235,605 -620.
Schneider, A., Wiesner, R. J. and Grieshaber, M. K. (1989). On the role of arginine kinase in insect flight muscle. Insect Biochem. 19,471 -480.[CrossRef]
Sokal, R. R. and Rohlf, F. J. (1995). Biometry. New York: W. H. Freeman and Company.
Somero, G. N. and Childress, J. J. (1980). A violation of the metabolism-size scaling paradigm activities of glycolytic-enzymes in muscle increase in larger-size fish. Physiol. Zool. 53,322 -337.
Taylor, D. J., Kemp, G. J., Thompson, C. H. and Radda, G. K. (1997). Ageing: effects on oxidative function of skeletal muscle in vivo. Mol. Cell. Biochem. 174,321 -324.[CrossRef][Medline]
Wakeling, J. M., Kemp, K. M. and Johnston, I. A.
(1999). The biomechanics of fast-starts during ontogeny in the
common carp Cyprinus carpio. J. Exp. Biol.
202,3057
-3067.
Westerblad, H., Allen, D. G. and Lannergren, J. (2002). Muscle fatigue: Lactic acid or inorganic phosphate the major cause? News Physiol. Sci. 17, 17-21.[Medline]
Zebe, E. C. and McShan, W. H. (1957). Lactic
and a-glycerophosphate dehydrogenases in insects. J. Gen.
Physiol. 40,779
-790.