Jumping Muscle Research Articles

Gravid grasshoppers produce more energy but jump shorter distances

The negative effects of gravidity on locomotion have been well documented in terrestrial vertebrates but are relatively unknown in insects. During gravidity, the egg mass of Schistocerca americana grasshoppers can be up to 40% of their body mass. However, jumping muscle mass remains relatively unchanged during gravidity. Using female grasshoppers that ranged in body size from 1.6 g to 3.3 g (n=25), we investigated how gravidity affects maximal jump performance. Each grasshopper’s maximal jump was captured using eight Qualisys infrared high-speed cameras filming at 1121 fps. Biomechanical data were generated using Qualisys Track Manager and the effects of body size/gravity were analyzed using regression in JMP. Larger grasshoppers have significantly more eggs, a larger egg mass, and a greater portion of their body dedicated to eggs (egg mass: y=0.52x-0.82; r 2 =0.76; p<0.0001). We found that the take off angle, take off acceleration, force, and time spent in the air during a jump was similar regardless of body size or gravidity. However, larger, more gravid grasshoppers had significantly lower take off velocities (y=-0.40x+4.36; r 2 =0.22; p<0.02) and did not jump as far (y=-0.18x+1.44; r 2 =0.18; p<0.05). When we compared the actual jump distance to the predicted jump range, we found that more gravid grasshoppers were significantly closer to the expected range than smaller, less gravid grasshoppers (y=6.23x+77.31; r 2 =0.16; p<0.05). In addition, more gravid grasshoppers produced significantly more energy during a jump than less gravid animals (y=2.94x+5.77; r 2 =0.19; p<0.05). The increased jump energy of more gravid grasshoppers may be due to an increased reliance on anaerobic ATP production. This supports previous work that gravid grasshoppers have more problems with oxygen delivery. For example, gravidity reduces the total tracheal respiratory volume by 10%, reduces tidal volumes, and increases respiratory rates. Future work will measure phospho-arginine and lactate to determine, if due to oxygen delivery problems, gravid grasshoppers rely more on anaerobic ATP to produce powerful escape jumps. This research was supported by the National Science Foundation (Award 1827495 to SDK) and Union College Biology Department. This is the full abstract presented at the American Physiology Summit 2023 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

Hypoxia Decreases Jump Rate and Increases Lactate Production in Late‐Stage Grasshoppers

Insects are the most evolutionarily successful animals in part due to their air‐filled tracheal respiratory system. The tracheal system is an intricate network of tubes that exchange gases between the atmosphere and tissues. Some insects, including grasshoppers, also have air sacs that enhance convective airflow. During intermolt periods, the American locust (Schistocerca americana) doubles their body mass, which may compress the tracheae. In a recent study, late‐stage grasshoppers had reduced air sac ventilation frequency, decreased convective capabilities, and less of their body dedicated to their respiratory system. We hypothesized that these developmental changes may reduce both oxygen delivery and jump performance. We forced early‐stage (day 2) and late‐stage (day 8) 6th instar grasshoppers to jump in artificial oxygen atmospheres (5%, 10%, 21%, 40% oxygen: balance nitrogen) in a 100 L gloved box. After jumping, grasshoppers were immediately frozen in liquid nitrogen for a fluorometric lactate assay. We predicted that if oxygen delivery is compromised during development, then late‐stage grasshopper jump rate and lactate production would correlate with oxygen level.Within the first one to two minutes of jumping, there were no significant differences in jump rate between early‐ and late‐stage grasshoppers at any oxygen level. This result was not surprising since previous work has shown that the first two minutes of jumping is fueled primarily by anaerobic ATP production. At moderate hypoxia (10% O2) and normoxia (21% O2), there were no differences in jump rate between early‐ and late‐stage grasshoppers. In extreme hypoxia (5% O2), there was no difference in jump performance for the first two minutes, but late‐stage grasshoppers had a 1.6‐fold lower average jump rate in minutes three through five. In hyperoxia (40% O2), jump performance was similar during the first minute, and late‐instar grasshoppers jump rates increased on average by 1.4‐fold in minutes two through five.Late‐instar grasshopper muscles produced significantly greater lactate regardless of oxygen level. Within each group, oxygen level did not significantly affect jumping muscle lactate production. However, late‐stage grasshoppers produced 26.3% significantly more lactate in 5% oxygen than 40% oxygen (post‐hoc Student’s t; p<0.04). Future research will examine how age and oxygen level impact HIF‐1 expression in grasshoppers. Since late‐stage grasshoppers have lower jump rates and increased lactate production, we predict they will also have elevated HIF‐1 protein levels.

Gravidity Impacts Respiratory Function, Tracheal Volume, and Jump Performance in Grasshoppers

The negative effects of gravidity on respiration and locomotion have been well documented in terrestrial vertebrates but is relatively unknown in insects. During gravidity, the egg mass of Schistocerca americanagrasshoppers can be up to 40% of their body mass. We investigated whether this increase in egg mass impacted oxygen delivery, jump performance, and anaerobic metabolism. Using micro‐dissections and live video analysis, we examined the tracheal system of thirty‐six female grasshoppers across a range of body masses. We found that larger grasshoppers had significantly more eggs, a larger egg mass, and a greater portion of their body dedicated to eggs. In addition, abdominal compressibility (tidal volume) significantly decreased with gravidity. However, there was a significant positive correlation between gravidity and abdominal compression rate, suggesting that gravid grasshoppers make up for smaller tidal volumes by increasing respiratory rate. Furthermore, abdominal compression rates correlated with the inflation of proximal and distal femoral air sacs suggesting a direct impact on oxygen delivery to the jumping muscle. Using microCT analysis, the percent of tracheal volume in the grasshoppers significantly decreased with gravidity (23.6% in nongravid to 13.8% in gravid). During five‐minutes of repeated jumping, gravid grasshoppers had a significantly 30% lower jump rate. However, the average distance per jump did not vary with gravidity. There was no significant effect of gravidity on muscle lactate measured after five minutes of jumping. However, muscle lactate was positively correlated with total distance jumped during the five minutes, which was significantly higher in nongravid grasshoppers. In conclusion, gravidity lowered tracheal volumes, altered ventilatory mechanisms, and reduced jump performance.

Jumping in lantern bugs (Hemiptera, Fulgoridae).

ABSTRACTLantern bugs are amongst the largest of the jumping hemipteran bugs, with body lengths reaching 44 mm and masses reaching 0.7 g. They are up to 600 times heavier than smaller hemipterans that jump powerfully using catapult mechanisms to store energy. Does a similar mechanism also propel jumping in these much larger insects? The jumping performance of two species of lantern bugs (Hemiptera, Auchenorrhyncha, family Fulgoridae) from India and Malaysia was therefore analysed from high-speed videos. The kinematics showed that jumps were propelled by rapid and synchronous movements of both hind legs, with their trochantera moving first. The hind legs were 20–40% longer than the front legs, which was attributable to longer tibiae. It took 5–6 ms to accelerate to take-off velocities reaching 4.65 m s−1 in the best jumps by female Kalidasa lanata. During these jumps, adults experienced an acceleration of 77 g, required an energy expenditure of 4800 μJ and a power output of 900 mW, and exerted a force of 400 mN. The required power output of the thoracic jumping muscles was 21,000 W kg−1, 40 times greater than the maximum active contractile limit of muscle. Such a jumping performance therefore required a power amplification mechanism with energy storage in advance of the movement, as in their smaller relatives. These large lantern bugs are near isometrically scaled-up versions of their smaller relatives, still achieve comparable, if not higher, take-off velocities, and outperform other large jumping insects such as grasshoppers.

Chronic electrical stimulation reduces reliance on anaerobic metabolism in locust jumping muscle

Chronic electrical stimulation (CES) is a well-documented method for changing mammalian muscle from more fast-twitch to slow-twitch metabolic and contractile profiles. Although both mammalian and insect muscles have many similar anatomical and physiological properties, it is unknown if CES produces similar muscle plasticity changes in insects. To test this idea, we separated Schistocerca americana grasshoppers into two groups (n = 37 to 47): one that was subjected to CES for 180 min each day for five consecutive days and one group that was not. Each group was then electrically stimulated for a single time period (0, 5, 30, 60, or 180 min) before measuring jumping muscle lactate, a characteristic of fast-twitch type fibers. At each time point, CES led to a significantly reduced jumping muscle lactate concentration. Based on similar short-term CES mammalian studies, the reduction in lactate production was most likely due to a reduced reliance on anaerobic metabolism. Thus, longer stimulation periods should result in greater aerobic enzymatic activities, altered myosin ATPase, and shift fiber types. This is the first study to use electrical stimulation to explore insect muscle plasticity and our results show that grasshopper jumping muscle responds similarly to mammalian muscle.

Interspecific effects of body size on grasshopper jumping performance

The scaling of jump performance has been relatively well studied in vertebrates; however, less is known about how interspecific body size differences affect insect jumping. In this study, we compare the morphology, jump performance, lactate production, and relative cost of drag in sixteen species of grasshoppers using both standard regression and phylogenetic generalized least squares analyses. In contrast to the situation observed across species in vertebrates, and during ontogeny in Schistocerca americana grasshoppers, small grasshopper species had similar jump distances as larger species, despite losing more energy to drag. This surprising result could be at least partially explained by the fact that smaller grasshopper species had relatively more jumping muscle mass, relatively longer femurs, and produced more lactate during repeated jumping. These data suggest that selection has acted strongly to improve jump performance in smaller grasshoppers via a variety of morphological and biochemical adaptations.

Effect of Electrical Stimulation on Grasshopper Jumping Muscle

Skeletal muscles can undergo biochemical and physiological changes due to exercise training. For example, aerobic exercise training may lead to an increased mitochondria volume, a higher proportion of slow twitch myosin ATPase, and a reduced rate of lactic acid production. Similar changes in mammalian muscle have also been demonstrated using electrical stimulation. However, it is unclear if invertebrate muscle also responds to training or electrical stimulation. We examine whether Schistocerca americana grasshopper jumping muscles are affected by electrical stimulation. Grasshopper jumping muscle is one of the few invertebrate muscles to produce lactic acid during locomotion. Electrical probe leads are placed near the coxa on the ventral side of the animal. The muscle was stimulated with a single pulse width of 2 ms at 0.075 V and repeated at a frequency of 100 Hz. We electrically stimulate the entire jumping muscle, including both the flexor and the extensor, to elicit continuous muscle contractions in a single metathoracic leg. To invoke a training response, a grasshopper is stimulated for 5 hours daily for 5 consecutive days. The lactate production rate of trained and untrained grasshopper muscle will then be fluorometrically measured after 5 min, 30 min, 60 min, 180 min, or 300 min of electrical stimulation. We predict that repeated stimulation would alter the rate of lactic acid production. Since grasshopper jumping muscle is similar to human muscle, this research may provide insight into fundamental questions about muscle plasticity.Support or Funding InformationUnion College Undergraduate Research Committee

Take-off speed in jumping mantises depends on body size and a power-limited mechanism.

ABSTRACTMany insects such as fleas, froghoppers and grasshoppers use a catapult mechanism to jump, and a direct consequence of this is that their take-off velocities are independent of their mass. In contrast, insects such as mantises, caddis flies and bush crickets propel their jumps by direct muscle contractions. What constrains the jumping performance of insects that use this second mechanism? To answer this question, the jumping performance of the mantis Stagmomantis theophila was measured through all its developmental stages, from 5 mg first instar nymphs to 1200 mg adults. Older and heavier mantises have longer hind and middle legs and higher take-off velocities than younger and lighter mantises. The length of the propulsive hind and middle legs scaled approximately isometrically with body mass (exponent=0.29 and 0.32, respectively). The front legs, which do not contribute to propulsion, scaled with an exponent of 0.37. Take-off velocity increased with increasing body mass (exponent=0.12). Time to accelerate increased and maximum acceleration decreased, but the measured power that a given mass of jumping muscle produced remained constant throughout all stages. Mathematical models were used to distinguish between three possible limitations to the scaling relationships: first, an energy-limited model (which explains catapult jumpers); second, a power-limited model; and third, an acceleration-limited model. Only the model limited by muscle power explained the experimental data. Therefore, the two biomechanical mechanisms impose different limitations on jumping: those involving direct muscle contractions (mantises) are constrained by muscle power, whereas those involving catapult mechanisms are constrained by muscle energy.

Changes in Grasshopper Jumping Muscle During Intermolt Development

During the sixth instar, the American locust (Schistocerca americana) doubles in mass, but its body size remains relatively constant throughout the instar due to its rigid exoskeleton. Previous work has shown that tracheal air sac size is reduced at the end of the intermolt period. For late stage grasshoppers, this change in the tracheal function correlates with reduced jump performance and their inability to maintain resting metabolic rates in hypoxia. We hypothesized that if late stage grasshoppers had a potential reduction in oxygen delivery, their jumping muscle would rely more on anaerobic metabolism. Early sixth instar (day 2) and late sixth instar (day 8) female grasshoppers were randomly assigned into five jumping groups (0, 30, 60, 120, or 300 seconds; n=10). During repeated jumping, the number of jumps was recorded for each animal. Immediately after jumping, grasshoppers were frozen in liquid nitrogen. A fluorometric assay was developed to measure lactate in the jumping muscle. After 30 seconds of jumping, femoral muscle lactate levels increased 12‐fold in the day 2 animals and 23‐fold in the day 8 animals. Regardless of time spent jumping, day 8 grasshopper jumping muscle had 20‐25% more lactate than day 2 jumping muscles. We also measured lactate dehydrogenase (LDH) and citrate synthase (CS) activity levels in separate day 2 and day 8 sixth instar female grasshoppers (n=12). While jumping muscle CS activity did not vary during the instar, day 8 grasshoppers had a 28% increase in jumping muscle LDH activity. Therefore, we conclude that decreases in the tracheal volume during the intermolt period correlate with an increased reliance on anaerobic metabolism in the jumping muscle, which leads to greater lactate production and higher rates of fatigue during repeated jumping.

Post‐exercise fate of lactate in the American locust (1101.2)

The fate of lactate after exercise varies between animal groups. Mammals oxidize lactic acid in their muscles, fish oxidize lactic acid in their liver, and reptiles use both their muscles and liver to oxidize post‐exercise lactate. Grasshoppers are unique among insects in that they produce lactic acid during repeated jumping. However, it is unclear where the lactate is oxidized. Using the American locust (Schistocerca americana), we measured lactate levels in the jumping muscle at different time points after jumping. Lactate levels were measured using a fluorometric plate assay. Immediately after three minutes of jumping, muscle lactate levels were approximately 23 mmol kg‐1. After fifteen minutes of rest, lactate levels decreased by 40% in the jumping muscle. After one hour of rest, muscle lactate levels had decreased by 70% of their post‐exercise level. After approximately three hours of rest, muscle lactate was similar to pre‐jumping levels. We have previously demonstrated that lactate production correlates with jumping fatigue rate in S. americana grasshoppers. Current work is examining whether hemolymph or fat body lactate levels vary after jumping. A decrease in muscle lactate levels during recovery, combined with a rise in hemolymph and fat body lactate levels would suggest a non‐muscle model for lactate oxidation in grasshoppers.Grant Funding Source: Supported by Union College Undergraduate Research Grants

Jumping mechanisms in flatid planthoppers (Hemiptera, Flatidae)

The jumping performance of three species of hemipterans from Australia and Europe belonging to the family Flatidae was analysed from images captured at a rate of 5000 s(-1). The shape of a flatid was dominated by large triangular or wedge-shaped front wings, which, when folded, covered and extended above and behind the body to give a laterally compressed and possibly streamlined appearance. The body lengths of the three species of adults ranged from 7 to 9 mm and their mass from 8 to 19 mg. The propulsive hind legs were 30% longer than the front legs but only 36-54% of the body length. Jumps with the fastest take-off velocities of 2.8-3.2 m s(-1) had acceleration times of 1.4-1.8 ms. During such jumps, adults experienced an acceleration of 174-200 G: . These jumps required an energy expenditure of 76-225 μJ, a power output of 13-60 mW and exerted a force of 9-37 mN. The required power output per mass of jumping muscle in adults ranged from 24,000 to 27,000 W kg(-1) muscle, 100 times greater than the maximum active contractile limit of normal muscle. The free-living nymphs were also proficient jumpers, reaching take-off velocities of 2.2 m s(-1). To achieve such a jumping performance requires a power amplification mechanism. The energy store for such a mechanism was identified as the internal skeleton linking a hind coxa to the articulation of a hind wing. These pleural arches fluoresced bright blue when illuminated with UV light, indicating the presence of the elastic protein resilin. The energy generated by the prolonged contractions of the trochanteral depressor muscles was stored in distortions of these structures, and the rapid elastic recoil of these muscles powered the synchronous propulsive movements of the hind legs.

Investigating jumping of various Caelifera grasshopper species over an altitudinal gradient in New York

In many animals, aerobic activity declines with increasing altitude. We examined whether repeated jumping in grasshoppers showed similar trends. Grasshoppers were collected from six locations in New York state that were classified as high‐elevation (1450 m, N= 9), middle‐elevation (960–1000 m, N=16) and low‐elevation (90–150 m, N=18) Grasshoppers were forced to jump repeatedly for ten minutes in a 30 °C temperature room. After jumping, muscle mass, body mass and femur length were measured. Across all elevations, there were no significant differences in jump frequency or jump distance. However, we noted a similar herbaceous habitat at each location suggesting the similar habitats may result in similar jump performances. Although we were not able to collect the same species at every altitude, certain interesting life‐history trends were apparent. The smallest grasshoppers (Chorthippus curtipennis) had the greatest ratio of jumping muscle mass to body mass, produced the longest jumps per body size, but also fatigued fastest. Smaller grasshoppers have higher predation rates; therefore, C. curtipennis’ higher proportional muscle mass may allow it to produce farther escape jumps at the cost of higher fatigue rates. These findings suggest that across our altitudinal gradient, life‐history differences between species rather than altitude may be more important in explaining jump performance differences. Funding was provided through Union College Summer Research Grants.

Micro‐CT measured tracheal changes in the metathoracic femur of developing American locusts

In support of the hypothesis that larger insects have more oxygen delivery problems, older/larger grasshoppers have more abdominal respiratory structures. However, it is unclear if they also have more femoral respiratory structures because the anaerobic capacity of the jumping muscle increases during development. Disarticulated adult and juvenile femurs were dried overnight and placed individually in the scanning chamber of a SkyScan 1074 micro‐computed tomography unit. Images were reconstructed into transverse cross sections using computer software. Transverse sections at “stations” 20% (closest to the thorax), 40% and 60% (closest to the knee) of the length along each femur were analyzed. Near the thorax, the adult femur has three dorsal tracheae, a pair of ventral tracheae and a medial trachea. The adult dorsosagittal and dorsomedial tracheae merge at the 30% station; the ventral tracheae merge and the medial trachea vanishes at the 50% station. Near the thorax, the juvenile femur includes a single central trachea. We found tracheae void fractions to increase about 50% along the adult femur and to decrease about 50% along the juvenile femur. Void fractions were similar between adult and juvenile at the 40% station. These results suggest that older/larger grasshoppers have proportionally more respiratory structures in the distal portion of the jumping leg. Supported in part by NSF DUE 0511287 (AJR).

Effect of gravidity on jump performance and muscle physiology in the American locust

The effect of gravidity (or load) on jumping is not well documented. Lizards produced shorter jumps when a load equal to 30% of body mass was attached. However in Schistocerca americana grasshoppers, 20% heavier gravid females have the same jump distance as non‐gravid females. We tested the hypothesis that grasshoppers increase their jumping muscle contraction duration when gravid (or loaded). We examined the effect of added mass on jump performance by attaching weights (20% or 40% of body mass) to gravid females, non‐gravid females, and males. We used high‐speed video analysis to compare jump performance and electromyography to measure jumping muscle contraction times. Results indicate that muscle contraction duration increased 20% from non‐gravid to gravid females. When an additional weight equal to 20% of body mass was attached, muscle contraction duration increased by over 30% for all grasshoppers. Further loading (40% of body mass) caused muscle contraction duration to increase 130% from un‐loaded controls in both males and gravid females, but it increased over 200% in nongravid females. These results suggest muscle contraction duration is proportional to load. Increasing muscle contraction time would allow grasshoppers to store more energy in their catapult mechanism prior to jumping, thereby allowing gravid females to have the same jump distance as non‐gravid females.

Jumping mechanisms in dictyopharid planthoppers (Hemiptera, Dicytyopharidae)

The jumping performance of four species of hemipterans belonging to the family Dictyopharidae, from Europe, South Africa and Australia, were analysed from high-speed images. The body shape in all was characterised by an elongated and tapering head that gave a streamlined appearance. The body size ranged from 6 to 9 mm in length and from 6 to 23 mg in mass. The hind legs were 80-90% of body length and 30-50% longer than the front legs, except in one species in which the front legs were particularly large so that all legs were of similar length. Jumping was propelled by rapid and simultaneous depression of the trochantera of both hind legs, powered by large muscles in the thorax, and was accompanied by extension of the tibiae. In the best jumps, defined as those with the fastest take-off velocity, Engela minuta accelerated in 1.2 ms to a take-off velocity of 5.8 m s(-1), which is the fastest achieved by any insect described to date. During such a jump, E. minuta experienced an acceleration of 4830 m s(-2) or 490 g, while other species in the same family experienced 225-375 g. The best jumps in all species required an energy expenditure of 76-225 μJ, a power output of 12-80 mW and exerted a force of 12-29 mN. The required power output per mass of jumping muscle ranged from 28,000 to 140,200 W kg(-1) muscle and thus greatly exceeded the maximum active contractile limit of normal muscle. To achieve such a jumping performance, these insects must be using a power amplification mechanism in a catapult-like action. It is suggested that their streamlined body shape improves jumping performance by reducing drag, which, for a small insect, can substantially affect forward momentum.

Jumping mechanisms in gum treehopper insects (Hemiptera, Eurymelinae)

Jumping in a species of Australian gum treehopper was analysed from high-speed images. Pauroeurymela amplicincta adults and nymphs lived together in groups that were tended by ants, but only adults jumped. The winged adults with a body mass of 23 mg and a body length of 7 mm had some morphological characteristics intermediate between those of their close relatives the leafhoppers (Cicadellidae) and the treehoppers (Membracidae). They, like leafhoppers, lacked the prominent prothoracic helmets of membracid treehoppers, and their large hind coxae were linked by press studs (poppers), that are present in leafhoppers but not treehoppers. The hindlegs were only 30-40% longer than the other legs and 67% of body length. They are thus of similar proportion to the hindlegs of treehoppers but much shorter than those of most leafhoppers. Jumping was propelled by the hindlegs, which moved in the same plane as each other beneath and almost parallel to the longitudinal axis of the body. A jump was preceded by full levation of the coxo-trochanteral joints of the hindlegs. In its best jumps, the rapid depression of these joints then accelerated the insect in 1.4 ms to a take-off velocity of 3.8 m s(-1) so that it experienced a force of almost 280 g. In 22% of jumps, the wings opened before take-off but did not flap until the gum treehopper was airborne, when the body rotated little in any plane. The energy expended was 170 μJ, the power output was 122 mW and the force exerted was 64 mN. Such jumps are predicted to propel the insect forwards 1450 mm (200 times body length) and to a height of 430 mm if there is no effect of wind resistance. The power output per mass of jumping muscle far exceeded the maximum active contractile limit of muscle and indicates that a catapult-like action must be used. This eurymelid therefore out-performs both leafhoppers and treehoppers in i ts faster acceleration and in its higher take-off velocity.

Using synchrotron X‐ray imaging to visualize tracheal changes during development in American locusts

During their eight‐week development, Schistocerca americana grasshoppers hatch as 15 mg 1st instars and grow into nearly 3 g adults. It has been suggested that larger insects may have more problems with O2 delivery. In support of this idea, S. americana CO2 emission rates only scale with body mass0.76 during development, and larger, older grasshoppers fatigue more rapidly during repeated jumping. Furthermore, the jumping muscle of larger, older grasshoppers relies more on anaerobic metabolism. To test the hypothesis, that larger, older grasshoppers have decreased O2 delivery, we used synchrotron X‐ray imaging to visualize tracheal air sac compressions in the abdomen, proximal femur, and distal femur of developing S. americana in 21% and 5% O2. For all ages, hypoxia significantly increased air sac ventilation rates throughout the body. There was no effect of body size across development on ventilation rates of abdominal or distal femoral air sacs in either 21% or 5% O2. However, larger, older grasshoppers had ventilation rates in the proximal femoral air sacs that were 70% lower in both 21% and 5% O2 than those of smaller, younger animals. The reduced ventilation rate of femoral air sacs in larger grasshoppers provides a respiratory mechanism that explains their greater reliance on anaerobic metabolism and also supports the hypothesis that they have more problems with O2 delivery. (Support provided by NSF, NIH, US DOE).

Each to their own: skeletal muscles of different function use different biochemical strategies during aestivation at high temperature

Preservation of muscle morphology depends on a continuing regulatory balance between molecules that protect and molecules that damage muscle structural integrity. Excessive disruption of the biochemical balance that favours reactive oxygen species (ROS) in disused muscles may lead to oxidative stress, which in turn is associated with increased atrophic or apoptotic signalling and/or oxidative damage to the muscle and thus muscle disuse atrophy. Increases in the rate of oxygen consumption likely increase the overall generation of ROS in vivo. Temperature-induced increases in oxygen consumption rate occur in some muscles of ectotherms undergoing prolonged muscular disuse during aestivation. In the green-striped burrowing frog, Cyclorana alboguttata, both large jumping and small non-jumping muscles undergo atrophy seemingly commensurate with their rate of oxygen consumption during aestivation. However, because the extent of atrophy in these muscles is not enhanced at higher temperatures, despite a temperature-sensitive rate of oxygen consumption in the jumping muscle, we proposed that muscles are protected by biochemical means that, when mobilised at higher temperatures, inhibit atrophy. We proposed that the biochemical response to temperature would be muscle-specific. We examined the effect of temperature on the antioxidant and heat shock protein systems and determined the extent of oxidative damage to lipids and proteins in two functionally different skeletal muscles, the gastrocnemius (jumping muscle) and the iliofibularis (non-jumping muscle), by aestivating frogs at 24 and 30°C for 6 months. We assayed small molecule antioxidant capacity, mitochondrial and cytosolic superoxide dismutase activities and Hsp70 concentrations to show that protective mechanisms in disused muscles are differentially regulated with respect to both temperature and aestivation. High aestivation temperature results in an antioxidant response in the metabolically temperature-sensitive jumping muscle. We assayed lipid peroxidation and protein oxidation to show that oxidative damage is apparent during aestivation and its pattern is muscle-specific, but unaffected by temperature. Consideration is given to how the complex responses of muscle biochemistry inform the different strategies muscles may use in regulating their oxidative environment during extended disuse and disuse at high temperature.

Antibody Labelling of Resilin in Energy Stores for Jumping in Plant Sucking Insects

The rubbery protein resilin appears to form an integral part of the energy storage structures that enable many insects to jump by using a catapult mechanism. In plant sucking bugs that jump (Hemiptera, Auchenorrhyncha), the energy generated by the slow contractions of huge thoracic jumping muscles is stored by bending composite bow-shaped parts of the internal thoracic skeleton. Sudden recoil of these bows powers the rapid and simultaneous movements of both hind legs that in turn propel a jump. Until now, identification of resilin at these storage sites has depended exclusively upon characteristics that may not be specific: its fluorescence when illuminated with specific wavelengths of ultraviolet (UV) light and extinction of that fluorescence at low pH. To consolidate identification we have labelled the cuticular structures involved with an antibody raised against a product of the Drosophila CG15920 gene. This encodes pro-resilin, the first exon of which was expressed in E. coli and used to raise the antibody. We show that in frozen sections from two species, the antibody labels precisely those parts of the metathoracic energy stores that fluoresce under UV illumination. The presence of resilin in these insects is thus now further supported by a molecular criterion that is immunohistochemically specific.

Intermolt development reduces oxygen delivery capacity and jumping performance in the American locust (Schistocerca americana)

Among animals, insects have the highest mass-specific metabolic rates; yet, during intermolt development the tracheal respiratory system cannot meet the increased oxygen demand of older stage insects. Using locomotory performance indices, whole body respirometry, and X-ray imaging to visualize the respiratory system, we tested the hypothesis that due to the rigid exoskeleton, an increase in body mass during the intermolt period compresses the air-filled tracheal system, thereby, reducing oxygen delivery capacity in late stage insects. Specifically, we measured air sac ventilation frequency, size, and compressibility in both the abdomen and femur of early, middle, and late stage sixth instar Schistocerca americana grasshoppers. Our results show that late stage grasshoppers have a reduced air sac ventilation frequency in the femur and decreased convective capacities in the abdomen and femur. We also used X-ray images of the abdomen and femur to calculate the total proportion of tissue dedicated to respiratory structure during the intermolt period. We found that late stage grasshoppers had a lower proportion of their body dedicated to respiratory structures, especially air sacs, which convectively ventilate the tracheal system. These intermolt changes make oxygen delivery more challenging to the tissues, especially critical ones such as the jumping muscle. Indeed, late stage grasshoppers showed reduced jump frequencies compared to early stage grasshoppers, as well as decreased mass-specific CO(2) emission rates at 3 kPa PO(2). Our findings provide a mechanism to explain how body mass changes during the intermolt period reduce oxygen delivery capacity and alter an insect's life history.