Osmotic and metabolic responses to dehydration and urea-loading in a dormant,terrestrially hibernating frog

Physiological responses to dehydration in amphibians are reasonably well documented, although little work has addressed this problem in hibernating animals. We investigated osmotic and metabolic responses to experimental manipulation of hydration state in the wood frog (Rana sylvatica), a terrestrial hibernator that encounters low environmental water potential during autumn and winter. In winter-conditioned frogs, plasma osmolality varied inversely with body water content (range 69–79%, fresh mass) primarily due to increases in sodium and chloride concentrations, as well as accumulation of glucose and urea. Decreased hydration was accompanied by a marked reduction in the resting rate of oxygen consumption, which was inversely correlated with plasma osmolality and urea concentration. In a separate experiment, resting rates of oxygen consumption in fully hydrated frogs receiving injections of saline or saline containing urea did not differ initially; however, upon dehydration, metabolic rates decreased sooner in the urea-loaded frogs than in control frogs. Our findings suggest an important role for urea, acting in concert with dehydration, in the metabolic regulation and energy conservation of hibernating R. sylvatica.     

The thermal environment of arboreal pools and its effects on the metabolism of the arboreal, oophagous tadpoles of a Taiwanese tree frog, Chirixalus eiffingeri (Anura: Rhacophoridae).

We have studied seasonal and diurnal fluctuations of water temperature in bamboo stumps and the effect of temperature on the energy metabolism of arboreal, oophagous tadpoles of Chirixalus eiffingeri. We collected tadpoles (Gosner stage 28-29) in February and August from Chitou, Taiwan and acclimated them to 12 and 22 degrees C. Using a closed system, we measured tadpole oxygen consumption (V.O(2)) at 12, 17 and 22 degrees C. The water temperature was lowest in February (11-13 degrees C), increased rapidly during March and April and was highest from May to August (20-24 degrees C). Diel fluctuations in the temperature of the pools of water in bamboo stumps mirrored fluctuations in air temperature. Tadpoles collected in February and August exhibited metabolic compensation in that tadpoles acclimated at 12 degrees C had significantly higher V.O(2) than those acclimated at 22 degrees C. There are at least two possible explanations for the presence of metabolic compensation in C. eiffingeri tadpoles. Firstly, the larval period of C. eiffingeri ranges from 40 to 78 days, a tadpole could experience relatively large fluctuations in body temperature (up to 10 degrees C) during the development. As a result, C. eiffingeri tadpoles most likely evolved metabolic compensation to maintain activity levels under different thermal environments. Secondly, because arboreal pools are small, thermally unstratified, aquatic microhabitats, tadpoles are unable to behaviorally select preferred temperatures. As a result, metabolic compensation allows tadpoles to regulate their physiological functions.     

The influence of circadian rhythms on pre- and post-prandial metabolism in the snake Lamprophis fuliginosus

Measuring standard metabolic rate (SMR) and specific dynamic action (SDA) has yielded insight into patterns of energy expenditure in snakes, but less emphasis has been placed on identifying metabolic variation and associated energy cost of circadian rhythms. To estimate SMR, SDA, and identify metabolic variation associated with circadian cycles in nocturnally active African house snakes (Lamprophis fuliginosus), we measured oxygen consumption rates (VO2) at frequent intervals before and during digestion of meals equaling 10%, 20% and 30% of their body mass. Circadian rhythms in metabolism were perceptible in the VO2 data during fasting and after the initial stages of digestion. We estimated SMR of L. fuliginosus (mean mass=16.7+/-0.3 g) to be 0.68+/-0.02 (+/-SEM) mL O2/h at 25 degrees C. Twenty-four hours after eating, VO2 peaked at 3.2-5.3 times SMR. During digestion of meals equaling 10-30% of their body mass, the volume of oxygen consumed ranged from 109 to 119 mL O2 for SMR, whereas extra oxygen consumed for digestion and assimilation ranged from 68 to 256 mL O2 (equivalent to 14.5-17.0% of ingested energy). The oxygen consumed due to the rise in metabolism during the active phase of the daily cycle ranged from 55 to 66 mL O2 during digestion. Peak VO2, digestive scope, and SDA increased with increasing meal size. Comparisons of our estimates to estimates derived from methods used in previous investigations resulted in wide variance of metabolic variables (up to 39%), likely due to the influence of circadian rhythms and activity on the selection of baseline metabolism. We suggest frequent VO2 measurements over multiple days, coupled with mathematical methods that reduce the influence of undesired sources of VO2 variation (e.g., activity, circadian cycles) are needed to reliably assess SMR and SDA in animals exhibiting strong circadian cycles.     

Second messenger and cAMP-dependent protein kinase responses to dehydration and anoxia stresses in frogs

The effects of whole body dehydration (up to 40% of total body water lost) or anoxia exposure (up to 2 days under N₂ gas) at 5 °C on tissue levels of adenosine 3′–5′ cyclic monophosphate (cAMP) and the percentage of cAMP-dependent protein kinase present as the free catalytic subunit (PKAc), as well as the levels of the protein kinase C (PKC) second messenger, inositol 1,4,5-trisphosphate (IP₃), were assessed in two anurans, the freeze-tolerant wood frog, Rana sylvatica, and the freeze-intolerant leopard frog, Rana pipiens. Dehydration of wood frogs resulted in a rapid elevation of liver cAMP and PKAc; cAMP was 3.4-fold greater than control values in animals that had lost 5% of total body water, whereas PKAc was elevated threefold in 20% dehydrated frogs. These results indicate protein kinase A mediation of the liver glycogenolysis and hyperglycemia that is induced by dehydration in this species. Skeletal muscle PKAc content also rose with dehydration but neither cAMP nor PKAc was affected by dehydration in leopard frog tissues. Anoxia exposure had different effects on signal transduction systems. PKAc was elevated after 1 h anoxia in R. sylvatica brain and was sustained over time but the enzyme was unaffected in other organs; by contrast, R. pipiens showed variable responses by PKAc to anoxia in three organs. Both species showed rapid (within 30 min) and large (3 to 7.8-fold) increases in IP₃ in liver of anoxic frogs that decreased slowly with continued anoxia. IP₃ also increased quickly in heart of anoxia-exposed wood frogs. This suggests that PKC may mediate various metabolic adjustments that promote hypoxia/anoxia resistance such as coordinating metabolic rate depression. A progressive rise in liver IP₃ during dehydration in wood frogs (reaching fourfold higher than controls in 40% dehydrated animals) may also mediate similar hypoxia resistance adaptations under this stress since anurans experience progressive hypoxia due to increased blood viscosity when water loss reaches high values. The patterns of second messenger and PKAc changes in wood frog liver during dehydration closely parallel the changes seen in these same parameters during natural freezing suggesting that the freeze tolerance of selected terrestrially hibernating anurans may have evolved out of various anuran mechanisms of dehydration resistance. Accepted: 2 January 1997     

Vertebrate freezing survival: Regulation of the multicatalytic proteinase complex and controls on protein degradation

The wood frog, Rana sylvatica, survives weeks of whole body freezing during winter hibernation, expressing numerous metabolic adaptations that deal not only with freezing but with its consequences including organ ischemia and cellular dehydration. The present study analyzes the 20s multicatalytic proteinase (MCP) complex from skeletal muscle to determine how protein degradation is managed in the ischemic frozen state. MCP was partially purified and assayed fluorometrically using three AMC-labeled substrates to compare multiple states: control (5 degrees C acclimated), 24 h frozen at -2.5 degrees C, 4 or 8 h thawed at 5 degrees C, 8 h anoxia, and 40% dehydration. MCP from frozen frogs showed significantly different K(m) and V(max) values compared with controls; e.g., K(m) Z-LLE-AMC increased by 45% during freezing and 52% under anoxia whereas V(max) decreased by 40%. After thawing, K(m) was restored and V(max) rose by 2.2-fold. Incubations promoting protein kinase or phosphatase action on MCP showed that phosphatase treatment strongly increased V(max) implicating reversible phosphorylation in MCP regulation during freeze-thaw. Western blotting showed a 36% decrease in MCP protein in muscle from frozen frogs. The 20s MCP preferentially degrades oxidatively-damaged proteins and evidence of impaired function during freezing came from a 1.4-fold increase in protein carbonyl content in muscle and liver during freezing. Ubiquitin and ubiquitin conjugate levels were unchanged in muscle but changed markedly in liver during freeze-thaw.     

Effects of maternal identity and incubation temperature on snapping turtle (Chelydra serpentina) metabolism

Individual variation in physiological traits may have important consequences for offspring survivorship and adult fitness. Variance in offspring phenotypes is due to interindividual differences in genotype, environment, and/or maternal effects. This study examined the contributions of incubation environment, maternal effects, and clutch identity to individual variation in metabolic rates in the common snapping turtle, Chelydra serpentina. We measured standard metabolic rate, as determined by oxygen consumption, for 246 individuals representing 24 clutches at 15 degrees and 25 degrees C, and we measured standard metabolic rates additionally for 34 individuals at 20 degrees and 30 degrees C. Standard metabolic rate for 34 snapping turtles measured at 15 degrees, 20 degrees, 25 degrees, and 30 degrees C increased with increasing temperature. Mean standard metabolic rate for 246 individuals was 0.247 microL O(2) min(-1) g(-1) at 15 degrees C and 0.919 microL O(2) min(-1) g(-1) at 25 degrees C. At 15 degrees C, mass at hatching, individual mass, and egg mass had no significant effects on metabolic rate, but at 25 degrees C, mass at hatching, individual mass, and egg mass did have significant effects on metabolic rate. Incubation temperature had no significant effect on metabolic rate at 15 degrees, but it did have a significant effect at 25 degrees C. Clutch identity had a significant effect on metabolic rate at both 15 degrees and 25 degrees C. Interindividual variation in standard metabolic rate due to incubation temperature, and especially clutch identity, could have large effects on energy budgets. Results suggest that there were both environmental and genetic effects on standard metabolic rate.     

Rates of oxygen consumption in four species of seabird at Palmer Station, Antarctic peninsula

1. We determined standard metabolic rates (SMR) of wild-caught adults of the Adelie penguin, southern giant fulmar, blue-eyed shag, and South Polar skua at Palmer Station, Antarctica, during January and February 1981. Oxygen consumption was measured volumetrically in a closed system at temperatures between 2 and 12 degrees C. 2. Mean SMR varied between 0.82 l O2/kg per hr for male fulmars and 1.30 l O2/kg per hr for unsexed adult skuas. Values were 174-198% of those predicted by the Lasiewski-Dawson equation for nonpasserines. 3. The SMR of the Adelie penguin was considerably higher than that reported in other studies and higher than most values for other species of penguins. 4. Our measurements of oxygen consumption agree with some estimates of metabolism based upon loss of mass by fasting birds during incubation.     

Effects of dehydration on organ metabolism in the frogPseudacris crucifer: hyperglycemic responses to dehydration mimic freezing-induced cryoprotectant production

The metabolic effects of evaporative water loss at 5 °C were assessed for both fall- and spring-collected spring peepersPsuedacris crucifer. Frogs readily endured the loss of 50% of total body water. During dehydration organ water content was defended with no change in water content in skeletal muscle, gut, and kidney of 50% dehydrated frogs and reduced water content in liver, brain and heart. Dehydration stimulated a rapid and massive increase in liver glucose production. In fall-collected frogs liver glucose rose by 120-fold to 2690±400 nmol · mg protein^-1 or 220 mol · g ww^-1 in 50% dehydrated frogs and glucose in other organs increased by 2.6- to 60-fold. Spring-collected frogs showed the same qualitative response to dehydration although absolute glucose levels were lower, rising maximally by 8.4-fold in liver. Glucose synthesis was supported by glycogenolysis in liver and changes in the levels of glycolytic intermediates in liver indicated that an inhibitory block at the phosphofructokinase locus during desiccation helped to divert hexose phosphates into the production of glucose. Liver energy status (ATP, total adenylates, energy charge) was maintained even after the loss of 35% of total body water but at 50% dehydration all parameters showed a sharp decline; for example, energy charge fell from about 0.85 to 0.42. Severe dehydration also led to an accumulation of lactate in four organs, probably hypoxia-induced the to impaired circulation. The hyperglycemic response ofP. crucifer to dehydration mimics the cryoprotectant synthesis response seen during freezing of this freeze-tolerant frog, suggesting that these share a common regultory mechanism and that the cryoprotectant response may have arisen out of pre-existing volume regulatory responses of amphibians. The hyperglycemic response to dehydration might also be utilized during winter hibernation to help retard body water loss by raising the osmolality of the body fluids in situations where hibernaculum conditions become dry.Abbreviations bin body mass - bw body water - CrP creatine phosphate - dw dry weight - F6P fructose-6-phosphate - FBP fructose-1,6-bisphosphate - G6P glucose-6-phosphate - PEP phosphoenolpyruvate - PFK phosphofructokinase - PYR pyruvate - ww wet weight     

Cooling rate influences cryoprotectant distribution and organ dehydration in freezing wood frogs.

Ice formation in the freeze-tolerant wood frog (Rana sylvatica) induces the production and distribution of the cryoprotectant, glucose. Concomitantly, organs undergo a beneficial dehydration which likely inhibits mechanical injury during freezing. Together, these physiological responses promote freezing survival when frogs are frozen under slow cooling regimes. Rapid cooling, however, is lethal. We tested the hypothesis that the injurious effects of rapid cooling stem from an inadequate distribution of glucose to tissues and an insufficient removal of water from tissues during freezing. Accordingly, we compared glucose and water contents of five organs (liver, heart, skeletal muscle, eye, brain) from wood frogs cooled slowly or rapidly during freezing to -2.5 degrees C. Glucose concentrations in organs from slowly cooled frogs were significantly elevated over unfrozen controls, but no significant increases occurred in rapidly cooled frogs. Organs from slowly cooled frogs contained significantly less water than did those from controls, whereas water contents from rapidly cooled frogs generally were unchanged. Rapid cooling therefore inhibited the production and distribution of cryoprotectant and organ dehydration during freezing. This inhibition may result from an accelerated, premature failure of the cardiovascular system.     

Metabolic depression and enhanced O(2) affinity of mitochondria in hypoxic hypometabolism

This study examined whether the steady-state hypometabolism seen in overwintering frogs (Rana temporaria) is reflected at the mitochondrial level either by a reduction in their resting (state 4) and active (state 3) respiration rates and/or by increases in O(2) affinity. We isolated mitochondria from the skeletal muscle of cold-submerged frogs at different stages during their hibernation in normoxic and hypoxic water. A modest metabolic depression at the whole animal level (normoxic submergence) was not associated with a reduction in mitochondrial state 4 and state 3 respiration rates. However, mitochondria isolated from frogs that were submerged for 1 mo manifested an increase in their O(2) affinity compared with controls and with animals submerged for 4 mo. Hypometabolism was more pronounced at the whole animal level during hypoxic submergence and was accompanied by 1) a reduction in mitochondrial state 4 and state 3 rates and 2) an increase in the O(2) affinity of mitochondria. These findings demonstrate that metabolic depression can be reflected at all levels of biological organization in hypoxia-tolerant animals.     

Dehydration increases the magnitude of selective brain cooling independently of core temperature in sheep

By cooling the hypothalamus during hyperthermia, selective brain cooling reduces the drive on evaporative heat loss effectors, in so doing saving body water. To investigate whether selective brain cooling was increased in dehydrated sheep, we measured brain and carotid arterial blood temperatures at 5-min intervals in nine female Dorper sheep (41 +/- 3 kg, means +/- SD). The animals, housed in a climatic chamber at 23 degrees C, were exposed for nine days to a cyclic protocol with daytime heat (40 degrees C for 6 h). Drinking water was removed on the 3rd day and returned 5 days later. After 4 days of water deprivation, sheep had lost 16 +/- 4% of body mass, and plasma osmolality had increased from 290 +/- 8 to 323 +/- 9 mmol/kg (P < 0.0001). Although carotid blood temperature increased during heat exposure to similar levels during euhydration and dehydration, selective brain cooling was significantly greater in dehydration (0.38 +/- 0.18 degrees C) than in euhydration (-0.05 +/- 0.14 degrees C, P = 0.0008). The threshold temperature for selective brain cooling was not significantly different during euhydration (39.27 degrees C) and dehydration (39.14 degrees C, P = 0.62). However, the mean slope of lines of regression of brain temperature on carotid blood temperature above the threshold was significantly lower in dehydrated animals (0.40 +/- 0.31) than in euhydrated animals (0.87 +/- 0.11, P = 0.003). Return of drinking water at 39 degrees C led to rapid cessation of selective brain cooling, and brain temperature exceeded carotid blood temperature throughout heat exposure on the following day. We conclude that for any given carotid blood temperature, dehydrated sheep exposed to heat exhibit selective brain cooling up to threefold greater than that when euhydrated.     

Role of osmolality and plasma volume during rehydration in humans

To determine how the sodium content of ingested fluids affects drinking and the restoration of the body fluid compartments after dehydration, we studied six subjects during 4 h of recovery from 90-110 min of a heat [36 degrees C, less than 30% relative humidity (rh)] and exercise (40% maximal aerobic power) exposure, which caused body weight to decrease by 2.3%. During the 1st h, subjects rested seated without any fluids in a thermoneutral environment (28 degrees C, less than 30% rh) to allow the body fluid compartments to stabilize. Over the next 3 h, subjects rehydrated ad libitum using tap water and capsules containing either placebo (H2O-R) or 0.45 g NaCl (Na-R) per 100 ml water. During the 3-h rehydration period, subjects restored 68% of the lost water during H2O-R, whereas they restored 82% during Na-R (P less than 0.05). Urine volume was greater in H2O-R than in Na-R; thus only 51% of the lost water was retained during H2O-R, whereas 71% was retained during Na-R (P less than 0.05). Plasma osmolality was elevated throughout the rehydration period in Na-R, whereas it returned to the control level by 30 min in H2O-R (P less than 0.05). Changes in free water clearance followed changes in plasma osmolality. The restoration of plasma volume during Na-R was 174% of that lost. During H2O-R it was 78%, which seemed to be sufficient to diminish volume-dependent dipsogenic stimulation.(ABSTRACT TRUNCATED AT 250 WORDS)     

不同补水方式对白星花金龟水分平衡的影响

为研究水分散失和水分补充对新疆新害虫白星花金龟Potosia brevitarsis Lewis的影响,在30℃恒温条件下,采用重量法测定白星花金龟脱水过程以及不同补水方式下(补蒸馏水;补盐水;补糖水)体内水分含量的变化,并与步甲、拟步甲的水分代谢进行比较。结果表明,白星花金龟的脱水与拟步甲科的网目拟地甲Opatrum subaratum Fald相似,在10h内脱水率均约为5%,而斑步甲Anisodactylus signatus 10h内脱水率约为20%。不同补水处理后,白星花金龟体内含水量迅速增加,随后继续脱水;脱水10d后,补蒸馏水、补盐水和补糖水处理的白星花金龟脱水率分别为28%,27%和21%,而未补水白星花金龟的脱水率为34%;未补水处理的甲虫脱水率和补蒸馏水和补盐水处理之间无显著性差异,而和补糖水处理之间存在显著性差异。未补水、补蒸馏水、补盐水和补糖水处理的LT50分别约为9,12,13和17d,补糖水能有效延长甲虫的存活时间。糖能有效地增加白星花金龟体内含水量,对维持其体内水分平衡起重要作用。     

Thermoregulation of weaned northern elephant seal (Mirounga angustirostris) pups in air and water

Fasting weaned northern elephant seal pups (Mirounga angustirostris) experience diverse environmental conditions on land and in water on a daily basis. Each environment undoubtedly induces distinct energetic costs that may vary for pups of differing body condition. To determine the energetic costs associated with different environmental conditions and whether costs vary between individuals, body mass, surface area, volume, body composition, resting metabolic rate, and core body temperature were determined for 17 weaned northern elephant seal pups from A?o Nuevo, California. Metabolic rate and body temperature were measured for pups resting in air (20.9 degrees +/-0.8 degrees C), cold water (3.8 degrees+/-0.4 degrees ;C), and warm water (14.5 degrees+/-0.2 degrees C). Resting metabolic rate increased with body mass (range: 62.0-108.0 kg) and was also correlated with lean mass and lipid mass. Metabolic rates ranged from 293.6 to 512.7 mL O(2) min(-1) and were lowest for pups resting in cold water. Thermal conductance, calculated from metabolic rate and core body temperature, ranged from 3.1 to 15.2 W degrees C(-1), with the highest values in air and the lowest values in cold water. Metabolic responses to the three environmental conditions did not differ with individual variation in body condition. For all elephant seal pups, a consequence of high lipid content is that thermoregulatory costs are greatest on land and lowest in cold water, a pattern that contrasts markedly with terrestrial mammals.     

Changes in body water and plasma constituents during bullfrog development: effects of temperature and hormones

The osmoregulatory responses to warmer temperatures and hormone treatment in cold-adapted (5 degrees C) Rana catesbeiana tadpoles and newly metamorphosed frogs were examined. Tadpoles transferred to 11 degrees C and 18 degrees C and left for 5 days lost 7% and 10% of their body weight. Plasma [Na+] was elevated 28% and 21%, respectively. Control (5 degrees C) animals maintained their body weight and plasma [Na+] constant. Daily treatment with either ovine prolactin (oPRL) or ovine growth hormone (oGH) prevented the weight loss and the increase in extracellular [Na+] that occurred when tadpoles were transferred to 18 degrees C. Neither propylthiouracil (PTU) nor arginine vasotocin (AVT) were effective in countering temperature-induced weight loss in tadpoles. Newly metamorphosed frogs transferred to 18 degrees C also lost weight; this was not prevented by daily treatment with saline, oPRL, oGH or PTU. However, in frogs treated daily with AVT, initial BW was regained by day 6. When warm-adapted (18 degrees C) tadpoles were treated daily for 18 days with saline, bPRL, bGH, thyroxine (T4), ergocornine, cortisol, or cortisol + T4, bPRL was most effective in retarding weight loss and maintaining body water content, whereas T4 + cortisol caused the greatest loss of weight and body water. By day 20, the correlations between weight loss and both body water content and hematocrit were highly significant. These data suggest that reported increases in plasma solute concentrations in larval amphibians may actually reflect decreases in extracellular fluid volume, rather than increased amounts of solutes, per se.     

普通朱雀标准代谢率的初步研究

以普通朱雀的耗氧量为指标 ,探讨了普通朱雀的能量代谢特征。普通朱雀的热中性区为 2 6.7～3 7.5℃ ,最低标准代谢率为 4 .2 1mlO2 g·h ,最低热传导为 0 .2 4mlO2 g·h·℃。环境温度 (Ta)在 5～ 2 5℃范围内 ,其代谢率与Ta呈负相关 ,回归方程为SMR =8.74 -0 .1 7Ta ,体温稍有降低。Ta超过 3 7.5℃ ,SMR升高。     

Metabolism during starvation/dehydration stress in two species of galagos

Two species of galagos (G. senegalensis moholi andG. garnettii) were subjected to dehydration and starvation stress in order to determine whether, as is common in other animals, these hypometabolic prosimians would lower their metabolic rate even further. Dehydration was confirmed by losses in body mass, a decrease in fecal water content and a rise in urine osmolality. At the height of dehydration, 20 to 25% reduction in body mass, 30 to 40% reduction in fecal water content and urine osmolality ranging from 1.8 to 3.5 Osmol kg⁻¹ H₂O, were recorded in some of the animals. Basal metabolic rate of 0.536 ml O₂ (g·h)⁻¹ inG. s. moholi and 0.302 ml O₂ (g·h)⁻¹ inG. garnettii were recorded, representing 50 to 42% reduction in metabolic rate, respectively, compared with mass specific values. In none of the tested animals did we observe significant reduction in basal metabolism during dehydration/starvation stress compared with the rates observed during the control period. Basal metabolism in the bushbabies seems to have reached the lowest level and no further adjustment is apparently possible as a strategy for energy saving during starvation and/or dehydration stress.     

Standard metabolic rate of the fire ant,Solenopsis invicta Buren: effects of temperature,mass, and caste

Standard metabolic rates of S. invicta workers, males, female alates, larvae and pupae were determined using closed-system respirometry. Vdot;(O(2)) (ml h(-1)) of all castes and life stages scaled with temperature and mass. Differences between castes and life stages are discussed in light of their different life histories and the different functions of these stages within the colony. Workers, female alates, male alates, larvae and pupae had mass-specific Vdot;(O(2)) (ml O(2) g wet weight(-1) h(-1), corrected to 25 degrees C) of 0.404+/-0.023, 0.316+/-0.010, 0.674+/-0.024, 0.291+/-0.020, and 0.227+/-0.015 (mean+/-SE), respectively. Measurement of CO(2) and O(2) made possible the examination of temperature and mass effects on respiratory quotient (RQ), as well as accurate transformation of O(2) consumption to metabolic rate (&mgr;W) for comparison with other ant species. Mass-specific metabolic rates of S. invicta females and workers compare favorably with data from 17 other ant species, but metabolic rates of males (177%) and pupae (42%) fall above and below predicted rates, respectively. Several equations relating temperature and mass to Vdot;(O(2)) are presented.     

Freeze tolerance in the gray treefrog: cryoprotectant mobilization and organ dehydration.

Freeze tolerance in the frog Rana sylvatica is supported by nonanticipatory mobilization of cryoprotectant (glucose) and redistribution of organ water. Other freeze-tolerant frogs may manifest these responses but differences exist. For example, the gray treefrog (Hyla versicolor) accumulates mostly glycerol as opposed to glucose. The current study reports additional novel features about cryoprotection in H. versicolor. Frogs were acclimated to low temperature for 12 weeks and frozen for 3 days at -2.4 degrees C. Some frogs were then thawed at 3 degrees C for 4 hr. Calorimetry revealed that frozen frogs had 53.9% +/- 11.1% of their body water in ice, and all frogs recovered following this procedure. Plasma glucose was low prior to the onset of freezing (1.1 +/- 0.9 micromol/ml) and it was 20x higher in postfreeze frogs. Constituting nearly 30% of plasma solute, glycerol was 117.2 +/- 13.6 micromol/ml prior to freezing and it remained equally high in postfreeze frogs. Liver water content was moderately lower in frozen frogs when compared to controls (62.9% +/- 3.7% vs. 68.6% +/- 1.7%), whereas postfreeze frogs excessively hydrated their livers (75.7% +/- 2.1%). Less-pronounced changes were seen in muscle water content. H. versicolor can mobilize its major cryoprotectant, glycerol, in response to extended cold acclimation, which is unique in comparison to other freeze-tolerant frogs, and it experiences only moderate organ dehydration during freezing. This species conforms with other freeze-tolerant frogs, however, by mobilizing glucose as a direct response to tissue freezing.