Physiological Zoology

Published by University of Chicago Press
Online ISSN: 0031-935X
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Article
Rainbow trout exposed to unbuffered water of pH 10.5 initially showed significant increases in blood pH, plasma cortisol and glucose, partial pressure of NH3 (PNH3), NH4+, and HCO3- values as well as loss of plasma Cl-, reduced partial pressure of CO2 (PCO2), and inhibition of total ammonia excretion rate. After the first day, fish resisted further change, and new levels were established (for blood pH and plasma PCO2 and PNH3 levels) or imbalances corrected, either partially (for total ammonia excretion) or completely (for plasma Cl-, HCO3-, cortisol, and glucose values). During the 7-d exposure, 80% of fish in unbuffered water survived, but in buffered water (0.75 mmol L(-1) glycine-buffered KOH at pH 10.5), survival was only 50% after 3 d, and ion regulatory failure was evident. Fish in buffered and unbuffered alkaline waters had similar total ammonia excretion rates, which suggests that glycine-buffered KOH was not sufficient to significantly reduce gill boundary layer acidification. After 7 d in unbuffered alkaline water, 30% of total ammonia excretion was linked with an amiloride-sensitive (0.1 mmol L(-1)) Na+ uptake mechanism. Treatment of alkaline-exposed trout with waterborne acetazolamide (1.5 mmol L(-1)) indicated that gill boundary layer H+ production, through hydration of CO2, had a role in excretion of total ammonia. Exposure to 4-acetamino-4'-isothiocyantostilbene-2,2'-disulphonic acid (SITS; 0.1 mmol L(-1)) following 24-h exposure to unbuffered alkaline water resulted in increased plasma HCO3- and lowered plasma Cl- concentrations, indicating the role of branchial Cl-/HCO3- exchange in regaining Cl- lost and eliminating the HCO3- accumulated during exposure to alkaline water.
 
Article
Plasma alkaline phosphatase and inorganic phosphorus levels were determined for 52 nestling Spanish imperial eagles from two wild populations and 22 captive adults and subadults (10 adults and 12 subadults). The exact age was known for all birds. Mean alkaline phosphatase and inorganic phosphorus were higher in chicks than in the captive adults and subadults. Sex differences were not observed, and nestlings from different populations showed similar values. No significant regression described the relationship between age and alkaline phosphatase or inorganic phosphorus throughout the nestling period. However, alkaline phosphatase and inorganic phosphorus decreased significantly throughout the subadult period, with age explaining 98.2% and 50.5% of the variation in alkaline phosphatase and inorganic phosphorus levels, respectively. Non-fully-ossified zones were measured in frontal bones of another 12 subadult eagles that died at known ages. Ossification increased throughout the subadult period and was significantly correlated with expected levels of alkaline phosphatase or inorganic phosphorus (i.e., values predicted from the regression equations derived from the first analysis). Minimum alkaline phosphatase levels and full ossification of the cranial roof coincided with puberty onset. We conclude that, in subadult Spanish imperial eagles, decreasing alkaline phosphatase and inorganic phosphorus values are related to the ossification of frontal bones, although a contribution of other unknown processes of late ossification cannot be excluded, and alkaline phosphatase (but not inorganic phosphorus) may be a useful parameter for age-predicting purposes.
 
Article
The feeding energetics of the Antarctic spiny plunderfish (Harpagifer antarcticus) were examined with respect to the effect of both ration size and animal size. Fish of different sizes were fed single meals at one of two ration levels (2.5% wet body mass and satiation) to determine the maximum aerobic scope that could be elicited by the specific dynamic action. The excretion rates of ammonia, urea, and fluorescamine-positive substances were also monitored. Neither fish size nor ration had any effect on the factorial aerobic scope of feeding, which suggests that cellular metabolic processes associated with feeding were satiated by relatively small meals. The factorial scope in ammonia excretion was affected by both ration and fish size, indicating that respiration and excretion respond to a meal independently. The duration of the specific dynamic action response (240-390 h) increased with fish size but not ration, whereas both the time to reach the peak oxygen consumption and the duration of the ammonia response increased with ration but not fish size. The percentage of the ingested energy that was expended following feeding (the specific dynamic action coefficient) was high at low rations (approximately 56%) but lower (roughly 10%) at satiation rations. This is because the absolute energetic cost of processing a meal was largely independent of meal size. The change in O:N ratios after feeding was very ration-dependent; at low rations, O:N ratios increased, whereas at satiation rations, the O:N ratios decreased.
 
Article
We examined oxygen consumption and total evaporative water loss of aardwolves (Proteles cristatus) at temperatures within and below their thermal neutral zone during both summer and winter. During summer (December), body masses of aardwolves averaged 8.1 +/- 0.7 kg (+/-1 standard deviation). Within their thermal neutral zone, oxygen consumption was 2,194 +/- 443 mL O2 h-1, or 1,058 kJ d-1. The relationship between oxygen consumption (VO2, mL O2 h-1) and ambient temperature (Ta, degree C) below the lower critical temperature was VO2 = 6,310-178 (Ta). During winter (August), aardwolves had an average mass of 7.8 +/- 0.7 kg and a basal metabolic rate of 1,844 +/- 224 mL O2 h-1, or 889 kJ d-1. Below the thermal neutral zone, VO2 = 4,308-116 (Ta). Basal metabolic rate and the slope of the line relating oxygen consumption to ambient temperature were both significantly higher in summer than in winter. Evaporative water loss increased with air temperature for both seasons but was higher in summer than winter. Wet thermal conductance was relatively constant below the thermal neutral zone, but was significantly higher in summer (0.022 +/- 0.001 mL O2 g-1 h-1 degree C-1) than in winter (0.015 +/- 0.001 mL O2 g-1 h-1 degree C-1).
 
Article
In an earlier study, we found that yellow-rumped warblers had in vitro active uptake rates of D-glucose that were only a few percent of the glucose absorption rate achieved at the whole-animal level. Here we used a pharmacokinetic technique to test whether a substantial amount of sugar can be absorbed passively. We used yellow-rumped warblers (Dendroica coronata), known for their seasonal frugivory, freely feeding on a synthetic mash formulated with naturally occurring concentrations of D-glucose. Birds absorbed 89.8% +/- 1.0% (SE) of the D-glucose in the mash. When fed the same mash with trace-labeled 3H L-glucose, the stereoisomer that does not interact with the intestinal Na(+)-glucose cotransporter, 3H appeared in plasma, an indication that this stereoisomer of glucose was absorbed. We used 3H levels in plasma and excreta in a pharmacokinetic model to calculate L-glucose extraction efficiency (i.e., the percent absorbed). Calculated mean extraction efficiency for the passively absorbed L-glucose averaged 91% +/- 23%. Our finding of considerable passive absorption reconciles the in vitro and in vivo results for D-glucose absorption and is in concert with results from five other avian species. The passive pathway appears to provide birds with an absorptive process that can respond quickly to changing luminal concentration and that is energetically inexpensive to maintain and modulate in real time but that may bear a cost. Less discriminate passive absorption might increase vulnerability to toxins and thus constrain foraging behavior and limit the breadth of the dietary niche.
 
Article
Terrestrial amphibians take up water by abducting the hind limbs and pressing a specialized portion of the ventral skin to a moist surface, using a characteristic behavior called the water absorption response. An assay of the water absorption response was used to quantify physiological factors associated with thirst and water uptake. Dramatic changes in the water absorption response resulted from subtle changes in hydration state and from altering the reserve water supply in the urinary bladder. The water absorption response could be induced by intraperitoneal and intracerebroventricular injection of angiotensin II, demonstrating that components of the renin-angiotensin system on both sides of the blood-brain barrier have a dipsogenic function in amphibians. These experiments also demonstrated that the water absorption response could be influenced by changes in barometric pressure. Toads avoided the water absorption response on hyperosmotic substrates, and behavioral experiments showed that the amphibian skin served a sensory function similar to that of the lingual epithelium of mammals. The water absorption response assay has enormous potential as a tool for the investigation of physiological processes and sensory capabilities of amphibians.
 
AE*s of different sugars in Cape sugarbirds, calculated by three methods 
Data used for calculation of AE*s of five 20% (w : w) sugar solutions fed to Cape sugarbirds 
Published AEs of three major nectar sugars in frugivorous and nectarivorous birds AE (%) 
Article
Nectarivore sugar preferences and nectar composition in the Cape Floristic Kingdom (southern Africa) differ from trends reported for analogous systems in America and Europe in that sugarbirds and sunbirds show no aversion to sucrose, which is the dominant nectar sugar in many of their food plants. To elucidate the physiological bases (if any) of nectarivore sugar preferences, we determined apparent sugar absorption efficiencies in a passerine endemic to this region, the Cape sugarbird Promerops cafer. Apparent absorption efficiencies for the three major nectar sugars, sucrose, glucose, and fructose, were extremely high (> 99%), as in other specialized avian nectarivores. Xylose, a pentose sugar recently reported in the nectar of some Proteaceae, was absorbed and/or metabolized inefficiently, with a mean of 47.1% of ingested sugar recovered in cloacal fluid. We did not measure the proportions of xylose that were absorbed and/or metabolized. We also compared three methods of estimating absorption efficiency: (1) measurements of total sugar in cloacal fluid with refractometry, without correction for differences between volumes of ingesta and excreta; (2) the same measurements combined with correction for volume differences; and (3) HPLC analyses quantifying individual sugars in cloacal fluid, with correction for volume differences. Refractometry has been frequently used in previous studies. For all sugars except xylose, method 1 yielded results similar to those obtained with method 2, but the convergence was artifactual, and we do not recommend use of this method. Apparent absorption efficiencies calculated with method 2 underestimated true absorption efficiency, because refractometry measures nonsugar solutes, but this error is biologically significant only when efficiencies are low.
 
Article
Metabolic consequences of osmotic stress were investigated in the toad Bufo viridis. Toads were acclimated either to terrestrial conditions in the absence of free water or to being partially immersed in 250 mmol L-1 NaCl, which was achieved by gradually increasing the salinity of the bath. This slow acclimation evoked little metabolic response, whereas the immediate osmotic challenge of water restriction resulted in a significant increase in the concentration of urea in the plasma and in liver glycogen. Urea accumulation, involving a transient increase in its rate of synthesis, allows the toads to lower their body water potential and thereby to absorb soil-bound water. The metabolic cost of this response is reduced by conserving the resulting by-product, glucose, as glycogen stored in the liver for future use.
 
Article
Channel catfish were collected on 11 different dates from October 1991 to July 1993 and acclimated in the laboratory to 7 degrees C, 15 degrees C, or 25 degrees C for 6 wk. Hepatosomatic index, mg protein mg-1 DNA, total liver DNA and protein, and the activities of liver glucose-6-phosphate dehydrogenase, 6-phosphogluconate dehydrogenase, lactate dehydrogenase, and malate dehydrogenase were measured to examine seasonal variation in the acclimation response. Liver and muscle cytochrome oxidase and lactate dehydrogenase activities were measured to compare tissue-specific responses. Hepatosomatic indexes of fall and winter channel catfish were highest at 7 degrees C, with values at 15 degrees C higher than at 25 degrees C, while spring and summer fish had the highest values at 15 degrees C, with values at 7 degrees C higher than those at 25 degrees C. Acclimation patterns for total liver protein and DNA, mg protein mg-1 DNA, and glycogen were generally higher in cold temperatures but varied seasonally in an unpredictable manner. Glucose-6-phosphate dehydrogenase, 6-phosphogluconate dehydrogenase, and malate dehydrogenase demonstrated positive acclimation in the fall and winter; fish collected in the spring and summer showed little or inverse acclimation. Liver lactate dehydrogenase activity showed little or no positive compensation at any time of the year. Cytochrome oxidase activity showed positive acclimation in muscle but not liver. All liver enzymes, even those that showed marginal acclimation on a protein basis, showed positive acclimation when activity was expressed on a whole-liver basis.
 
Mean monthly temperature near collection sites 
Article
Physiological acclimation that alters enzyme activity can compensate for the effect of temperature on function and may be achieved by altering enzyme concentration. This study uses phylogenetic analyses to investigate the evolutionary history of and to test several hypotheses about acclimation responses among all the glycolytic enzymes. These hypotheses are that (1) acclimation increases enzyme concentration at lower temperatures to compensate for reduced activity; (2) equilibrium enzymes tend to show acclimation responses; and (3) acclimation responses are more common in species whose populations experience either large temporal or geographical temperature variations. Using maximal activities as indices of enzyme concentration, the presence of acclimation responses in all the glycolytic enzymes in the heart ventricle was determined for five species in the teleost genus Fundulus. Three of these species are distributed along the steep thermal cline of the North American Atlantic coast, and thus these species experience both seasonal and geographical variation in temperature. The other two species are found in the Gulf of Mexico and experience seasonal variation similar to the Atlantic species but no geographical variation in temperature. Two Atlantic coast species, Fundulus heteroclitus and Fundulus majalis, have unique derived acclimation responses. No derived acclimation responses occur in the Gulf species. A conserved response in hexokinase was observed within one subgenus comprising both Atlantic and Gulf species. In F. heteroclitus, enolase responded to acclimation, and in F majalis, aldolase, triphosphate isomerase, and lactate dehydrogenase had acclimation responses. These enzymes are equilibrium enzymes, and the concentrations of all of them increase at lower temperatures, which would compensate for the effect of temperature on enzyme activity. The compensatory changes all occur in the Atlantic species and may be a mechanism for species to expand their ranges. These data suggest that physiological acclimation is evolutionarily labile.
 
Article
The atypical excitatory effect of acetylcholine on cardiac ventricular muscle was investigated in the horned shark, Heterodontus portusjacksoni. Electrically paced ventricular strips produced a massive 391.45% (+/-26.39%) increase in basal force of contraction in response to exogenously applied acetylcholine. The response was similar in nature to that produced by applied adrenaline, which caused a 382.52% (+/-72.47%) increase. The response to acetylcholine was blocked by the muscarinic cholinoceptor antagonist atropine and the competitive beta-adrenoceptor antagonist propranolol and was reduced by bretylium, an agent known to inhibit the release of catecholamines from adrenergic nerves. These findings strongly suggest that acetylcholine mediates a localised release of a catecholamine via muscarinic cholinoceptors in shark heart. A cholinergically controlled catecholamine store has been proposed (cholinergic-adreno complex), implying that elasmobranchs may be capable of finer control of cardiac output than has previously been suspected. This complex may represent a transitional adrenergic state between humoral and neuronal regulation. The spontaneously beating atrium showed no evidence of such an excitatory response to applied acetylcholine but produced an atropine-sensitive slowing, a response typical of other vertebrates.
 
Article
We examined the ionoregulatory capabilities of the blackskirt tetra (Gymnocorymbus ternetzi), which is native to ion-poor acidic waters of the Amazon River. Examination of Na+ uptake, which was only slightly sensitive to the uptake blocker amiloride, revealed several specializations for uptake in these waters. Kinetic analysis of Na+ uptake (at pH 6.5) revealed a high maximum rate of uptake and a low Michaelis-Menten constant, which allows the tetras to take up Na+ at high rates even at very low water levels. At pH 4.5, a pH where they experience sizable ion disturbances, they displayed several mechanisms to restore balance. Kinetic analysis at pH 4.5 revealed that the maximum uptake rate rose 67% while the Michaelis-Menten constant remained unchanged. Further tests showed that the upregulation of Na+ uptake occurred within 12 h in response to a doubling of Na+ efflux. Despite these specializations of the Na+ uptake mechanism, blackskirt tetras were not especially tolerant of low pH. Upon exposure to pH 4.0, they experienced a massive loss of Na+ due to a fourfold increase of Na+ efflux (relative to pH 5.0) and an 80% inhibition of uptake. Measurement of Na+ efflux in waters with different Ca2+ levels and in the presence of LaCl, a strong Ca2+ competitor, correlated the stimulation of Na+ efflux at low pH with a low branchial affinity for Ca2+. These tests indicate that blackskirt tetras possess abilities to resist the disruptive effects of moderately low pH but cannot survive in waters with a pH of 4.0 or less because of leaching of Ca2+ from branchial tight junctions, which stimulates ion losses.
 
Article
High-elevation populations of many grasshopper species produce small adults in response to shortened growing seasons and cooler ambient temperatures. Mass-specific metabolic rate tends to increase with elevation, and several authors have argued that this is an adaptation to accelerate development. In the present study, the relationship of thermoregulation and metabolism was investigated in adults of the acridid grasshopper Xanthippus corallipes from six populations along an elevation gradient. Thermoregulation was measured in the field, and several lines of evidence suggested that afternoon body temperatures were actively maintained within each population. Populations were found to maintain stable afternoon body temperatures that correlate negatively with elevation. Elevation had a strong negative effect on adult mass. Mass-specific metabolic rates at 35 degrees and 45 degrees C correlated positively with elevation. However, population differences in mass explained most of the variation in mass-specific metabolic rates, and when mass was used as a covariate, the effect of elevation disappeared. Mass-specific metabolic rates at afternoon field body temperatures were estimated and found not to differ among populations. Thus, differences in thermoregulation offset the effect of mass on mass-specific metabolic rate across populations, such that X. corallipes adults exhibited a common mass-specific metabolic rate in the wild, independent of large population differences in mass and ambient temperatures.
 
Article
The peak of the elevated oxygen consumption following feeding may be preabsorptive in some reptiles, possibly because of the up-regulation of gut function. The question of whether up-regulation has a substantial net cost and accounts for a large part of the cost of the specific dynamic action can be resolved by comparing the response to single and repeated meals. Oxygen consumption of the omnivorous tortoise Kinixys spekii was elevated for 3-4 d after a single meal, and the peak occurred while most food was still in the stomach. The cost of the specific dynamic action varied between diets, being 16%, 21%, and 30% of the energy absorbed from fungi, leaves, and millipedes, respectively, but was about 0.8 L O2 g-1 absorbed protein for all diets. The specific dynamic action doubled during continuous feeding on leaves and then accounted for 42% of the absorbed energy. The increase after repeated feeding shows that up-regulation of gut function can contribute little to the energy cost of the specific dynamic action in K. spekii; otherwise the cost would fall in subsequent meals.
 
Article
We have investigated the effects of chronic hypoxia on the acute adrenergic stress response of adult rainbow trout (Oncorhynchus mykiss). The goal of this study was to determine whether a prior 5-d exposure of fish to lowered environmental oxygen levels (60 or 80 Torr) would influence the nature of catecholamine secretion from chromaffin tissue in situ. Using a saline-perfused posterior cardinal vein preparation, it was demonstrated that the basal (unstimulated) secretion of noradrenaline and adrenaline was increased at 60-Torr hypoxia. In response to cholinergic (carbachol-elicited) stimulation, noradrenaline and adrenaline secretion were significantly affected by prior exposure to hypoxia. The construction of dose response curves revealed that noradrenaline secretion was enhanced at the lowest doses of carbachol (1 - 5 x 10(-7) mol kg(-1)) and that this was reflected by an approximate 10-fold reduction in the ED50 (the dose of carbachol eliciting half-maximal noradrenaline secretion). The effect of chronic hypoxia on in situ carbachol-evoked adrenaline secretion was similar but less pronounced. The results of this study suggest that during chronic moderate hypoxia, increased basal catecholamine secretion and enhanced responsiveness of chromaffin cells to cholinergic stimulation, as well aiding the ongoing stress, may assist the physiological adaptations to subsequent bouts of more severe acute stress.
 
Article
Yellow-rumped warblers (Dendroica coronata) are one of many avian species that change their diet seasonally. Using them, we tested the predictions that uptake of D-glucose and the amino acid L-leucine will increase as dietary levels of carbohydrate and protein, respectively, are increased and that mediated uptake capacity of the entire small intestine will match nutrient loads from daily food intake. Birds were fed three semisynthetic diets, formulated from fruit, insects, or seeds, for 7 d. Mediated D-glucose uptake in vitro was affected by diet, but contrary to our a priori prediction, fruit eaters eating the diet highest in carbohydrates had the lowest uptake rate. Na(+)-dependent L-leucine uptake at a low concentration (0.01 mmol L-1) was higher in insect and seed eaters, which is consistent with the prediction of adaptation to dietary protein, though dietary fat may also play a role. Mediated D-glucose uptake summed over small intestine length could explain only a small percentage of the estimated whole-animal absorption rate. We thus reject the predictions for carbohydrate but suggest an alternative interpretation of our results that is consistent with economical design.
 
Article
Historically, the discipline of comparative physiology and biochemistry has had two major goals: (1) elucidation of mechanisms and their adaptative significance, and (2) understanding of the evolution of mechanisms and adaptations. In general, the first goal has dominated the field. In a mechanistic/adaptational approach, the diversity of organisms is an experimental parameter in the investigation. Lineage-specific characteristics reveal both how physiological systems work and how different kinds of animals are adapted to different kinds of environments. We believe that this approach is far from outdated, in part because many animal groups have been investigated superficially if at all, and in part because the incorporation of fundamentally new technologies into our discipline permits us to address previously intractable questions about even intensively studied animal groups. In evolutionary physiology and biochemistry, the diversity of lineage-specific physiological systems and how they came to be is the subject of investigation. Early attempts to employ the evolutionary approach were not only few in number, they were unsatisfying in outcome because neither phylogenetic nor mechanistic/adaptational knowledge was adequate to serve as a firm foundation. We agree with earlier authors that new and more sophisticated applications of this approach, together with progress in understanding both animal phylogeny and mechanisms/adaptations, all promise to allow us at last to fulfill our second historic goal. In our view, an integration of the two approaches seems to present the most productive trajectory into the next century.
 
Article
The daily changes in body temperature experienced by Parabuthus villosus (Buthidae), a scorpion found on the gravel plains around Gobabeb, Namibia, and by Opisthophthalmus flavescens (Scorpionidae), a dune-dwelling species from the same area, were measured under similar field conditions. Thermocouples implanted under the segments of the mesosoma measured maximum temperatures as high as 43 degrees C in the shade. Air temperatures reached a maximum of 33 degrees C during the daytime and a minimum of 12 degrees C at night. Very low metabolic rates compared with those of other nonsedentary invertebrates were recorded in both species; oxygen consumption ranged from 8 microL g-1 h-1 at 16 degrees C to 115 microL g-1 h-1 at 40 degrees C. A pulsed Doppler system was used to measure heart rate in situ in free-moving scorpions. At night, heart rate declined to about 4 beats min-1 in resting undisturbed scorpions. During daylight excursions and while scorpions hunted for food, heart rates as high as 180 beats min-1 were observed. Heart rate was linearly correlated with temperature in P. villosus, with a slope of 2.37 (Q10 = 2.18), but in O. flavescens only a limited correlation was observed, with a slope of 1.18 (Q10 = 1.69). In O. flavescens, heart rate showed hysteresis as body temperature rose during daylight and then decreased during the late afternoon and evening; the reverse was observed in P. villosus. In both species, haemocyanin-oxygen affinity was independent of temperature, with a higher oxygen affinity and a larger pH sensitivity in O. flavescens. The Q10's of oxygen consumption and heart rate are quite different in O. flavescens but not as different in P. villosus. Although changes in the cardiovascular system, such as stroke volume, may also play a role in meeting increased oxygen demand, the features of the haemocyanin oxygen transport system, such as the absence of temperature sensitivity and a marked pH sensitivity, can also influence the maintenance of VO2 under temperature stress. The differences in the normal thermal habitats of the two species may be used to explain the distinctions between the evolved physiological responses to temperature increase shown by the two species.
 
Article
Hyper- and hypothyroidism were induced by subcutaneous injection of thyroxine and by oral administration of methimazol in Brandt's voles. The effects of the two treatments on metabolic thermogenesis at 25 degrees C and 4 degrees C were investigated. The level of resting metabolic rate was closely related to thyroid status: high in the hyperthyroid case and low in the hypothyroid case. However, no increase in resting metabolic rate occurred in either case during further cold acclimation. Hyperthyroidism resulted in an increased nonshivering thermogenesis, which was much enhanced by lower temperature, but hypothyroidism led to a suppressed nonshivering thermogenesis in the cold. The state-4 and state-3 respirations and the activities of cytochrome-c oxidase of liver mitochondria were elevated in hyperthyroid animals but attenuated in hypothyroid ones. However, these levels were scarcely changed after further cold acclimation. Both hyperthyroidism and cold acclimation induced the recruitment of brown adipose tissue, but brown adipose tissue was different biochemically in the two cases: in hyperthyroidism, the total protein was reduced, while fat content increased; in cold acclimation, the total and mitochondrial proteins were increased. However, in hypothyroid voles, the normal adaptive changes in brown adipose tissue were impaired in further cold acclimation. The activity of cytochromec oxidase in brown adipose tissue was increased by hyperthyroidism and enhanced in further cold. In contrast, its activity was inhibited in hypothyroid animals, though activated to some extent in cold. These results demonstrate that normal thyroid function is essential for the cold-induced increase of resting metabolic rate and nonshivering thermogenesis and that there is a synergism between thyroid hormone and cold acclimation in the regulation of nonshivering thermogenesis in Brandt's vole. In addition, the blunted response of brown adipocytes to the cold may be the cytological mechanism for the suppressed nonshivering thermogenesis found with hypothyroidism.
 
Article
Adélie penguins are very abundant in Antarctica and constitute a large biomass of predatory consumers in the Antarctic ecosystem. Adélies eat almost exclusively krill (Euphausia spp.), and to determine krill requirements by Adélies, information on energetics is needed, including energy intake of the chicks. I measured energy use and growth in Adélie penguin chicks, using both field and laboratory techniques. Field metabolic rate was quite variable, but mass-specific rates were not correlated with body mass. Growth followed the logistic equation: the growth constant was 0.143 d-1, and the asymptote for growth to fledging was 3,200 g. Different body organs had similar energy densities (in kilojoules per gram of dry mass), and total body energy density did not vary with chick mass. However, proportional mass of the skin increased rapidly as chicks grew, making the skin an important energy store in larger chicks. Metabolic efficiency measured in the laboratory averaged 69% and did not vary with chick mass. Total energy ingested over the 50-d development period was 162 MJ, which corresponds to approximately 33.6 kg of fresh krill. Previous studies of Adélie energetics have focused on adult energy balance and have calculated chick energy requirements indirectly on the basis of adults' stomach loads of krill and frequency of feeding chicks. Values from previous studies do not agree with those from the present study. The method used in the present study is more informative and accurate for measuring energy use by chicks, since measurements are made directly from chicks.
 
Article
Despite the apparent importance of solar radiation as a source of heat for free-living animals, there exists no substantial body of empirical data describing physiological responses to solar radiation under the range of convective conditions likely to occur in nature. We therefore quantified effects of simulated solar radiation and wind on metabolic heat production in the rock squirrel, Spermophilus variegatus. This diurnal mammal inhabits the Sonoran Desert and seasonally replaces its pelage in a fashion in which it retains constant external appearance but incorporates optical and structural changes that are thought to significantly alter heat-transfer properties of the coat. At a given wind speed, the presence of 950 W m-2 of simulated solar radiation reduces metabolic heat production by 15% (at a wind speed of 4 m s-1) to 37% (at a wind speed of 0.25 m s-1). Independent of effects of irradiance, metabolic heat production significantly increases with wind speed such that as wind speed is increased from 0.25 m s-1 to 4.0 m s-1, metabolic heat production is elevated by 66% (sunlight absent) or 88% (sunlight present). Previous analyses demonstrated that when exposed to identical radiative and convective environments rock squirrels with summer pelages accrue solar heat loads 33%-71% lower than those experienced by animals with winter coats. This reduction of solar heat gain during the extremely hot Sonoran Desert summer apparently constitutes a previously unappreciated mode of thermal adaptation by seasonal adjustment of radiative heat gain without changes in the animal's appearance.
 
Article
We examined the adrenal response to handling stress of birds in different body conditions. In order to affect the birds' body condition, young (73-d old) female American kestrels (Falco sparverius) were maintained for 6 wk on one of three diets: a control diet (fed ad lib.) and two calorically restricted diets. To invoke a stress response, we removed birds from their cages and took repeated blood samples over the course of an hour. All birds responded to handling stress with an increase in plasma corticosterone, but control birds (in good body condition) showed a more rapid increase to maximum corticosterone levels, followed by a decrease. Both groups of food-restricted birds had a slower rate of increase to maximum corticosterone levels and then maintained high corticosterone levels through 60 min. These results suggest that birds in good physical condition respond more quickly to stressors and adapt physiologically to stressful situations more rapidly than do birds in poor physical condition. This difference may reflect the ability of birds in good condition to mobilize fat for energy, while birds in poor condition must mobilize protein (i.e., muscle).
 
Walking speed (cm/s) of three lines of Drosophila melanogaster that have been evolving at 16.5, 25, or 29C. Data for 
Orthogonal polynomial analyses of the effects (linear and quadratic) of line temperature on performance traits 
Orthogonal polynomial analysis of effects of selection temperature and sex on knock-down temperature of adults 
Orthogonal polynomial analysis of effects of selection temperature and sex on heat tolerance of adults and eggs 
Orthogonal polynomial analysis of effects of selection temperature and sex on cold tolerance of adults and eggs 
Article
We compared aspects of the thermal sensitivity of replicated lines of Drosophila melanogaster that had been evolving by laboratory natural selection at three selection temperatures: 16.5 degrees C (10+ yr), 25 degrees C (9+ yr), or 29 degrees C (4+ yr). The 16.5 degrees C and 25 degrees C lines are known to have diverged in fitness at 16.5 degrees C versus 25 degrees C and also in heat tolerance. We designed new experiments to explore further possible shifts in thermal sensitivity of these lines. The optimal temperature for walking speed of adults was positively related to selection temperature, but differences among lines in thermal sensitivity of walking speed were small. Performance breath was inversely related to selection temperature. Tolerance of adults to an acute heat shock was also positively related to selection temperature, but tolerance to a cold shock was not. Thus, fitness at moderately high temperatures is genetically coupled with tolerance of extreme high (but not of low) temperature. Knock-down temperature and walking speed at high temperature, however, were independent of selection temperature. In contrast to adults, eggs from different lines had similar heat and cold tolerance. Thus, long-term natural selection has led to divergence in thermal sensitivity of some (but not of all) traits and may have had more of an impact on adults than on eggs. Attempts to predict evolutionary states in nature are, however, complicated because of the observed genetic correlations and the simple selection scheme.
 
Relationship between center toe temperature and midback temperature in gentoo penguins. Open squares show values for chicks, and filled squares show values for adults. 
Calculated overall heat loss from adult and chick gentoo penguins via radiation as a function of ground temperature. The presented data were derived by incorporating the mathematical expression for the relationship between body surface temperature at specific localities and ground temperature together with values for the particular surface area measured in the Stefan-Boltzmann equation (see text). All relevant radiation values were then summed. Calculated heat losses via the feet, flippers, and the rest of the body are shown for comparison with the whole bird. 
Article
Adult penguins and their chicks differ considerably in their apparent body insulation. The chicks are covered in down, whereas the adults have the short, hard body feathers characteristic of the family, so mechanisms of heat loss may vary considerably between the two groups. We examined radiative heat loss by measuring body surface temperatures of gentoo penguins (Pygoscelis papua) in Antarctica. At the time the birds were considered to be in their thermoneutral zone, and there was little or no wind. Measurements of infrared emission were made on breeding adults and in large downy, and thermally independent, chicks in relation to environmental temperature. All 28 external body surface sites measured were positively correlated with ambient temperature, although there was considerable intersite variability in the relationship between site temperature and ambient temperature. Foot temperature increased most rapidly per degree ambient temperature increase, followed by the flippers, followed by the trunk. This pattern was particularly pronounced in the chicks, indicating that the exceptional heat-loss capacities of the feet may counteract for the reduced capacity of the flippers. Net heat transfer by radiation was examined using Stefan-Boltzmann's law and preliminary data on the surface area of a gentoo penguin body. This showed that between ground temperatures of 5 degrees and 15 degrees C overall heat transfer remains essentially constant, although radiative heat loss from the trunk decreases, this being counteracted by increasing heat transfer from the flippers and feet. Over the same temperature range the specific radiation heat transfer of the feet increased approximately 100 times faster per degree ambient temperature increase than did that of the flippers. This and the bimodality in foot temperature found in the study birds even under constant ambient temperatures indicate that within the thermoneutral zone heat loss by radiation in gentoo penguins is primarily executed using the feet, through which the blood circulates in pulses.
 
Article
Oxygen stores available for aerobic diving were studied in the freshwater turtle (Mauremys caspica leprosa) at three constant body temperatures (15°, 25°, and 35°C) and during the thermal transient (30°-15°C) induced by immersion in cold water. The term 'aerobic dive limit' has been defined as the maximal duration of the dive before lactate increases. This increase occurs when a critical PO2 value is reached, and it is well characterized at lung level by a sharp increase in the lung apnoeic respiratory quotient. Kinetic analysis of lung gas composition during forced dives at fixed body temperature shows that critical PO2 values rise with temperature and that the postventilatory PO2 at the beginning of a dive decreases, so that the two temperature-dependent factors lead to a significant decrease with temperature in the lung O2 stores available for aerobic diving. During dives with transient body cooling, a natural condition in M. caspica leprosa, temperature equilibration occurs fast enough to expand aerobic scope by bearing the critical PO2 to the same value obtained at a fixed temperature of 15°C. These dives are characterized by reversed CO2 transport (from lung to tissues) and therefore by negative values of the lung respiratory quotient; a decrease in temperature increases CO2 capacitance of tissues, resulting in a fall in PCO2 at constant CO2 content. Because this does not occur in the gas phase, PCO2 difference can lead to diffusion in the direction opposite from normal. This pattern may favour lung-to-tissue O2 transfer, through the Bohr effect. Therefore, the aerobic dive limit is reduced at high temperature not only through a metabolic rate effect but also through a marked decrease in the available O2 stores; fast body cooling (30°-15°C) associated with immersion in cold water extends the O2 stores available for aerobic diving to a level similar to that of immersions at constant body temperatures that are in equilibrium with water temperature.
 
Article
Food consumption was measured in six female and seven male hand-raised marsh harrier (Circus aeruginosus) nestlings. Females consumed on average 4,321 g and males consumed 3,571 g of food during the nestling stage from 0 to 36 d. Total consumption until 56 d was 6,960 g and 5,822 g for females and males, respectively. On the basis of Fisher's sex ratio theory, this food intake ratio of 0.46 (intake male/[intake male + female]) would explain the observed male-biased fledging sex ratio of 55% males in marsh harrier broods. Growth, gross energy intake, and metabolizable energy intake were measured, along with metabolism of the nestlings, enabling us to determine energy allocation. The assimilation quotient (Q = 0.72) did not differ systematically between the sexes. Differences in metabolic rates between males and females at 15 and 30 d of age were fully attributable to the difference in body mass. Sexual size dimorphism in marsh harriers (female body mass around 60 d of age is 1.28 times greater than male mass) did not fully explain the difference in food intake between male and female nestlings: an analysis of energy requirements for growth and body mass in 16 avian species shows that energy intake was less than proportional to the average body mass at release. The data presented in this study are in agreement with Fisher's theory of inverse proportionality between the sex-specific ratios of energy requirements for growth and of offspring numbers in the marsh harrier population.
 
Article
Basal metabolic rate in the field vole (Microtus agrestis) was studied in relation to body composition and daily energy expenditure in the field. Daily energy expenditure was measured by means of doubly labelled water (D2 18O). In the same individuals, basal metabolic rate was subsequently derived from O2 consumption in an open-circuit system in the laboratory. Body composition was obtained by dissecting the animals and determining fresh, dry, and lean dry mass of different organs. Daily energy expenditure for free-living field voles ranged from 1.8 to 4.5 times basal metabolic rate, with an average of 2.9 times basal metabolic rate. Variation in both daily energy expenditure and basal metabolic rate was best explained by body mass. Gender or reproductive activity did not have significant additive effects. Daily energy expenditure and basal metabolic rate showed significant positive relationships to body mass with similar mass exponents of 0.493 and 0.526, respectively. Overall, there was a significant correlation between daily energy expenditure and basal metabolic rate, but the mass-independent residuals (deviations from the allometrically predicted values) did not correlate. Carcass analysis revealed that a number of organs were slightly better predictors for daily energy expenditure and basal metabolic rate than was fresh body mass. Mass-independent residuals of lean dry heart mass and basal metabolic rate were positively correlated, which is in agreement with the idea that basal metabolic rate reflects the size of metabolically active organs. The study does not provide support for an intraindividual association of basal metabolic rate with daily energy expenditure in the field.
 
Top-cited authors
Kenneth Nagy
  • University of California, Los Angeles
Gary Packard
  • Colorado State University
Fritz Geiser
  • University of New England (Australia)
Gerald L Kooyman
  • University of California, San Diego
Theodore Garland
  • University of California, Riverside