Showing papers in "Physiological and Biochemical Zoology in 1999"
TL;DR: Sizes of “exercise organs” such as pectoral muscle and heart were best correlated with body mass, whereas sizes of organs used during foraging and nutrient extraction (intestine, liver) werebest correlated with rate of mass gain.
Abstract: The adaptive value of size changes in different organ and muscle groups was studied in red knots (Calidris canutus islandica) in relation to their migration. Birds were sampled on five occasions: at arrival in Iceland in May 1994, two times during subsequent refueling, at departure toward, and on return from, the high arctic breeding grounds. During their 24-d stopover in May, body mass increased from 144.3 to 214.5 g. Mass gains were lowest over the first week (0.85 g/d, only fat-free tissue deposited). Over the subsequent 10 d, average mass increased by 5.0 g/d (fat contributing 78%), and over the last week before takeoff, it increased by 2.0 g/d (fat contributing over 100% because of loss of lean components). There were no sex differences in body and fat mass gains. Over the first interval, lean masses of heart, stomach, and liver increased. During the middle 10 d, sizes of leg muscle, intestine, liver, and kidneys increased. Stomach mass decreased over the same interval. In the last interval before takeoff, the stomach atrophied further and the intestine, leg muscles, and liver became smaller too, but pectoral muscles and heart increased in size. Sizes of "exercise organs" such as pectoral muscle and heart were best correlated with body mass, whereas sizes of organs used during foraging (leg muscles) and nutrient extraction (intestine, liver) were best correlated with rate of mass gain. Kidneys changed little before takeoff, which suggests that they are needed as much during flight as during refueling.
305 citations
TL;DR: The results suggest that the structure of the feeding hierarchy may not be determined solely by competitive ability but may also be greatly influenced by differences in the feeding behaviour of unstressed fish versus stressed fish caused by cortisol elevation in the latter.
Abstract: Plasma cortisol elevation, a common consequence of stress, occurs in salmonids of subordinate rank; these fish acquire a smaller share of available food and grow more slowly. This study examined the role of cortisol itself in these phenomena. Cortisol implants, with parallel sham and control treatments, were used to create a chronic threefold elevation in plasma cortisol levels in juvenile rainbow trout, and the individual feeding patterns of the fish were evaluated using X‐ray radiography. The three treatment groups were (1) held alone and fed to satiation, thereby providing a measure of voluntary appetite, or mixed together in equal proportions and fed to either (2) satiation or (3) half‐satiation, thereby allowing assessment of the additional effects of competitive interaction and food limitation. Chronic plasma cortisol elevation had significant negative effects on individual appetite, growth rate, condition factor, and food conversion efficiency, independent of whether the fish were held und...
265 citations
TL;DR: For example, this paper examined variation in and patterns of milk composition and production, maternal energy output, and pup growth and energy deposition over the entire lactation period in 18 grey seal mother-pup pairs using hydrogen isotope (3H2O and D2O) dilution.
Abstract: Phocid seals are one of the few groups of mammals capable of sustaining the energetic demands of lactation entirely through body nutrient stores while fasting. Lactation performance of the female in turn influences the rate and pattern of pup growth. We examined variation in and patterns of milk composition and production, maternal energy output, and pup growth and energy deposition over the entire lactation period in 18 grey seal mother-pup pairs using hydrogen isotope (3H2O and D2O) dilution. Milk composition was independent of maternal mass and nutrient stores, indicating dependence on other physiological and genetic factors. Heavier females lactated longer (r2=0.653, P<0.001), had higher total milk outputs (r2=0.652, P<0.001), and produced larger pups at weaning (r2=0.417, P=0.005). While fatter females lactated for longer periods of time (r2=0.595, P<0.001), females with a larger lean body mass at parturition produced more milk (r2=0.579, P<0.001). Total milk energy output was the strongest predictor of pup weaning mass, which, along with the pup's efficiency of energy storage, accounted for 91% of the variation in weaning mass. Nevertheless, there was sufficient plasticity in milk composition and energy output that some smaller females produced relatively large pups. Few females appeared to deplete body nutrients to the point where it might limit the duration of lactation.
151 citations
TL;DR: The combined result of this approach suggests that birds increase their dry heat transfer even when Ta is above, and the current model of heat balance in birds at high ambient temperatures is considered.
Abstract: A number of authors have suggested that hyperthermia, the elevation of body temperature (Tb) 2°–4°C above normal, contributes to a reduction in total evaporative water loss (TEWL) in birds. Information about the role of hyperthermia in the water economy of birds is scattered throughout the literature. We purposed to collate the available information on this subject, to reevaluate the benefits and costs of this process, and to assess its net effect on the water economy of birds, especially species living in deserts. In this review, we first consider the current model of heat balance in birds at high ambient temperatures (Ta), and show that, in most studies performed at a high Ta, birds were increasing their Tb, a violation of the assumption of steady state conditions. Next, we incorporate the rate of heat gain into calculations of the dry heat transfer coefficient (h), below and above temperature equality ( \documentclass{aastex} \usepackage{amsbsy} \usepackage{amsfonts} \usepackage{amssymb} \usep...
139 citations
TL;DR: The doubly labeled water (DLW) method was validated against respiration gas analysis in growing precocial chicks of the black‐tailed godwit and the northern lapwing and it was found that there was no relationship between the relative growth rate of the chick and the relative error of the DLW method.
Abstract: The doubly labeled water (DLW) method was validated against respiration gas analysis in growing precocial chicks of the black‐tailed godwit (Limosa limosa) and the northern lapwing (Vanellus vanellus). To calculate the rate of CO2 production from DLW measurements, Lifson and McClintock's equations (6) and (35) were employed, as well as Speakman's equation (7.17) (all single‐pool models). The average errors obtained with the first two equations (+7.2% and −11.6%, respectively) differed significantly from zero but not the error obtained with Speakman's equation (average: −2.9%). The latter error could be reduced by taking a fractional evaporative water loss of 0.13, instead of the value of 0.25 recommended by Speakman. Application of different two‐pool models resulted in relative errors of the DLW method of −15.9% or more. After employing the single‐pool model with a fractional evaporative water loss value of 0.13, it was found that there was no relationship between the relative growth rate of the ...
117 citations
TL;DR: The roles of ultimate and proximate factors in regulating basal and summit metabolic rates of passerine birds during winter have received little study, and the extent to which winter temperatures affect these variables is unknown.
Abstract: The roles of ultimate and proximate factors in regulating basal and summit metabolic rates of passerine birds during winter have received little study, and the extent to which winter temperatures affect these variables is unknown. To address this question, we measured basal and summit (maximum cold‐induced) metabolic rates in black‐capped chickadees (Poecile atricapillus), dark‐eyed juncos (Junco hyemalis), and American tree sparrows (Spizella arborea) during winters from 1991/1992 to 1997 in southeastern South Dakota. Both temperature and these metabolic rates varied within and among winters. Least‐squares regression revealed significant negative relationships for normalized basal and summit metabolism against mean winter temperature for all species pooled ( \documentclass{aastex} \usepackage{amsbsy} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{bm} \usepackage{mathrsfs} \usepackage{pifont} \usepackage{stmaryrd} \usepackage{textcomp} \usepackage{portland,xspace} \usepackage{amsmath,amsx...
116 citations
TL;DR: Total protein, β‐hydroxybutyrate, triiodothyronine, thyroxine, and lymphocyte and heterophil percentages may be the most reliable indicators of the nutritional status and the condition of free‐living herring gulls.
Abstract: Populations of scavenging seabird species in the North Sea may fluctuate with an artificial food source: the availability of fishery waste. To document this impact, it is necessary to assess the birds' nutritional status during periods with decreased fishing activity. Reference data for this purpose was collected from 22 herring gulls investigated during laboratory fasting. After 6 d of food deprivation and body mass losses exceeding 15%, the first birds entered starvation phase 3. Comparatively, this is a rather weak fasting capacity. Plasma levels of total protein and thyroid hormones decreased and β‐hydroxybutyrate increased with fasting duration. The leucocyte proportions were shifted from lymphocytes to heterophils. After 3 d of refeeding, most of the fasting changes were reversed. Plasma enzyme activities increased and hematocrit, hemoglobin, and erythrocyte numbers decreased in both fasting and control birds, most likely as a result of experimental stress and repeated blood sampling. Gluco...
116 citations
TL;DR: The results suggest that, in small mammals, a substantial evolutionary increase in daily movement distances can be achieved by increasing running speed, without remarkable increases in total energy expenditure.
Abstract: Laboratory house mice (Mus domesticus) that had experienced 10 generations of artificial selection for high levels of voluntary wheel running ran about 70% more total revolutions per day than did mice from random‐bred control lines. The difference resulted primarily from increased average velocities rather than from increased time spent running. Within all eight lines (four selected, four control), females ran more than males. Average daily running distances ranged from 4.4 km in control males to 11.6 km in selected females. Whole‐animal food consumption was statistically indistinguishable in the selected and control lines. However, mice from selected lines averaged approximately 10% smaller in body mass, and mass‐adjusted food consumption was 4% higher in selected lines than in controls. The incremental cost of locomotion (grams food/revolution), computed as the partial regression slope of food consumption on revolutions run per day, did not differ between selected and control mice. On a 24‐h ba...
115 citations
TL;DR: A number of authors have addressed the issue of partwhole correlation within the context of scaling and the analysis of ratios, but descriptions of the effects of part-wholes correlation in ANCOVA, multiple regression, and residual analysis, however, have been only anecdotal.
Abstract: Many physiological and life-history traits scale with body mass, and this mass dependence must often be taken into account when comparing group means or when analyzing correlations between traits. Residual analysis (Bennett 1987), multiple regression (Hayes and Shonkwiler 1996), and analysis of covariance (ANCOVA, Atchley et al. 1976; Packard and Boardman 1987) have been proposed as robust techniques to reduce or eliminate mass dependence, since the use of ratios (i.e., the trait value divided by body mass) is problematic (Packard and Boardman 1987). The first of these three methods all involve regression, so problems may arise when the physiological trait of interest is the mass of an organ or tissue and the covariate is body mass. In a regression between organ mass and body mass, both variables include the mass of the organ. This tends to create a positive relationship between the two variables, even when no correlation between organ mass and the rest of body mass (i.e., body mass minus organ mass) exists. Sokal and Rohlf (1995) referred to the correlation between a part (e.g., organ mass) and the whole (e.g., body mass) as “part-whole correlation.” A number of authors have addressed the issue of partwhole correlation within the context of scaling (e.g., Prothero 1986; LaBarbera 1989) and the analysis of ratios (e.g., Atchley et al. 1976; Jackson and Somers 1991 and references therein). Descriptions of the effects of part-whole correlation in ANCOVA, multiple regression, and residual analysis, however, have been only anecdotal. For instance, Tracy and Sugar (1989) and Burness et al. (1998) described examples where removal of partwhole correlation changed the results of ANCOVA and residual analysis, respectively. A more in-depth study of the effects of part-whole correlation on regression-type analyses (e.g., multiple regression, residual analysis, and ANCOVA) is lacking, and as a result, this potential problem is often ignored. For instance,
101 citations
TL;DR: This work explored the use of ultrasonographic imaging, a relatively simple noninvasive technique, to measure size of pectoral muscles and stomach in two small shorebird species (red knots Calidris canutus and golden plovers Pluvialis apricaria).
Abstract: Organs, even of fully grown adult birds, mammals, and reptiles, may show substantial size changes in relation to specific performances. These changes are difficult to study, because measurements usually can only be obtained following the death of the animal. We explored the use of ultrasonographic imaging, a relatively simple noninvasive technique, to measure size of pectoral muscles and stomach in two small shorebird species (red knots Calidris canutus and golden plovers Pluvialis apricaria). Accuracy of ultrasound measurements in estimating organ mass in red knots was reasonably high. Depending on the equipment used, the error of individual measurements was 20%–25% for the pectoral muscles and 26%–44% for the stomach. In plovers the technique was less accurate, probably because of the low variability of the organs involved. Ultrasound scanning is particularly suited to measure rapidly changing organ sizes over short time intervals. We demonstrate this with an example in which changes in individ...
91 citations
TL;DR: Divalent anion secretion events of the gut have been defined relative to potential roles they may have in hyporegulation of the blood and in hepatopancreatic detoxification events involving complexation with cationic metals.
Abstract: Epithelial cells of the gut, antennal glands, integument, and gills of crustaceans regulate the movements of ions into and across these structures and thereby influence the concentrations of ions in the hemolymph. Specific transport proteins serving cations and anions are found on apical and basolateral cell membranes of epithelia in these tissues. In recent years, a considerable research effort has been directed at elucidating their physiological and molecular properties and relating these characteristics to the overall biology of the organisms. Efforts to describe ion transport in crustaceans have focused on the membrane transfer properties of Na+/H+ exchange, calcium uptake as it relates to the molt cycle, heavy metal sequestration and detoxification, and anion movements into and across epithelial cells. In addition to defining the properties and mechanisms of cation movements across specific cell borders, work over the past 5 yr has also centered on defining the molecular nature of certain tr...
TL;DR: The results suggest that M. condylurus is well suited to tolerate high Ta, and this may enable it to exploit thermally challenging roost sites and to colonise habitats and exploit food sources where less stressful roosts are limiting.
Abstract: The Angolan free‐tailed bat (Mops condylurus) uses roosts that often exceed 40°C, an ambient temperature (Ta) that is lethal to many microchiropterans. We measured the physiological responses of this species at Ta's from 15° to 45°C. Torpor was commonly employed during the day at the lower Ta, but the bats generally remained euthermic at night, with a mean body temperature (Tb) of 35.2°C. Metabolic rate reflected the pattern of Tb, increasing with falling Ta at night but decreasing during the day. Metabolic rate and evaporative losses were lower in torpid than in euthermic bats. Body temperature increased at each Ta >35°C and was 43°C at Ta of 45°C. At Ta of 40°C bats increased dry thermal conductance and evaporative heat loss compared to lower Ta. At 45°C dry thermal conductance was lower than at 40°C and evaporative heat loss was 132% of metabolic heat production. At high Ta there was only a slight increase in metabolic rate despite the employment of evaporative cooling mechanisms and an increa...
TL;DR: Analysis of footprints on the surface of a sand dune to estimate maximal running speeds and the incidence of bipedality in nature, as well as to investigate the effects of incline on the escape locomotion of the lizard Callisaurus draconoides, found that only 11% of all strides were greater than 90% of maximal speed of C.dragonoides.
Abstract: We analyzed footprints on the surface of a sand dune to estimate maximal running speeds and the incidence of bipedality in nature, as well as to investigate the effects of incline on the escape locomotion of the lizard Callisaurus draconoides. Previous laboratory tests predicted that inclines would negatively affect sprinting performance in C. draconoides. Although physiologists commonly assume that escape locomotion will be near maximal capacity, we found that only 11% of all strides were greater than 90% of maximal speed of C. draconoides. Escape paths averaged 10 m in length and were generally straight. Approximately 30% of the strides taken by C. draconoides were bipedal, and this value was three times greater than previously found for the closely related species Uma scoparia. The modal value of bipedal stride lengths was greater than that for quadrupedal strides. Inclines negatively affected velocity of only the first meter of C. draconoides escape paths. The location of nearest cover had be...
TL;DR: This study extends the examination of CA to a temperate anemone, Anthopleura elegantissima, and documents symbiosis‐enhanced production of CA at the biochemical and molecular level, and reports the first direct evidence that the presence of symbionts affects the expression of a host cnidarian gene.
Abstract: Endosymbiotic dinoflagellates resident within cnidarian hosts are extremely productive primary producers. This high productivity may be due in part to an inorganic carbon transport system, present in host tissue, that accelerates carbon delivery to the algae. The enzyme carbonic anhydrase (CA; EC 4.2.1.1) has been shown to be important in this transport system in a variety of tropical symbiotic cnidarians. This study extends the examination of CA to a temperate anemone, Anthopleura elegantissima, and documents symbiosis‐enhanced production of CA at the biochemical and molecular level. Depending on light availability, A. elegantissima can occur naturally with (symbiotic) or without (aposymbiotic) dinoflagellates, making it an ideal study organism for symbiosis‐enhanced gene expression. We compared (1) CA activities, (2) quantities of CA using an anti‐human CA immunoprobe, and (3) quantities of transcript using a semiquantitative PCR in symbiotic versus aposymbiotic A. elegantissima host tissue. Am...
TL;DR: Increased (compensatory) consumption appears to be the primary mechanism by which caterpillars consuming low‐protein food maintained growth rates.
Abstract: For many insect herbivores, variation in protein availability is a pervasive part of the environment. I explore how variable protein availability affects growth rates of fifth‐instar Manduca sexta caterpillars and how growth is related to behavior and physiology. Groups of larvae were reared on low‐ or high‐protein artificial diets (5.9% and 17.7% casein by dry weight, respectively) and then transferred in the fifth instar to the same or opposite diet. During or after the 24‐h period following transfer, I measured growth rate, consumption rate, growth efficiency, midgut proteolytic activity, and masses of midgut contents and tissues. Fifth‐instar caterpillars reared in earlier instars on high‐protein diet grew about 20% more rapidly over 24 h than did caterpillars reared on low‐protein diet. This growth pattern appears to be caused by differences in consumption and growth efficiency: caterpillars reared on high protein consumed more food, and used it more efficiently, than did caterpillars reared...
TL;DR: It is found that food intake, gut mass, and cardiopulmonary organ mass increased in mice living at high altitudes, and RMR was not correlated with organ mass differences along the altitudinal gradient.
Abstract: Individuals within a species, living across a wide range of habitats, often display a great deal of phenotypic plasticity for organ mass and function. We investigated the extent to which changes in organ mass are variable, corresponding to environmental demand, across an altitudinal gradient. Are there changes in the mass of oxygen delivery organs (heart and lungs) and other central processing organs (gut, liver, kidney) associated with an increased sustainable metabolic rate that results from decreased ambient temperatures and decreased oxygen availability along an altitudinal gradient? We measured food intake, resting metabolic rate (RMR), and organ mass in captive deer mice (Peromyscus maniculatus bairdii) at three sites from 1,200 to 3,800 m above sea level to determine whether energy demand was correlated with organ mass. We found that food intake, gut mass, and cardiopulmonary organ mass increased in mice living at high altitudes. RMR was not correlated with organ mass differences along the...
TL;DR: European starlings (Sturnus vulgaris) were fed either a low‐ or high‐quality diet to test the effects of dietary quality on basal metabolic rate (BMR) and internal morphology, and dry matter digestibility and energy digestibility were lower for starlings fed the low‐ quality diet.
Abstract: European starlings (Sturnus vulgaris) were fed either a low‐ or high‐quality diet to test the effects of dietary quality on basal metabolic rate (BMR) and internal morphology. Basal metabolic rate did not differ significantly between the two dietary groups, but internal morphology differed greatly. Starlings fed the low‐quality diet had heavier gastrointestinal tracts, gizzards, and livers. Starlings fed the high‐quality diet had heavier breast muscles. Starlings on the low‐quality diet maintained mass, while starlings on the high‐quality diet gained mass. Dry matter digestibility and energy digestibility were lower for starlings fed the low‐quality diet, and their food and water intake were greater than starlings on the high‐quality diet. The lack of dietary effect on BMR may be the result of increased energy expenditure of digestive organs paralleling a reduction of energy expenditure of organs and tissues not related to digestion (i.e., skeletal muscle). This trade‐off in energy allocation amo...
TL;DR: It is suggested that a general model for genetically linked differences in the growth rate of bivalve molluscs will need to include the processes of metabolic control rather than relying solely on an analysis of the individual components of the energetics of growth.
Abstract: Pacific oysters (Crassostrea gigas) of identical age from two genetically distinct lines, one fast growing and the other slow growing, were held at three levels of ration and analysed for physiological traits to explain differences in their rates of growth. The data supported three hypotheses; faster growth was associated with faster rates of consumption of food, reduced metabolic rate at maintenance (i.e., at zero growth), and reduced metabolic costs of growth. A comparison with the Sydney rock oyster, Saccostrea commercialis, based on similar experiments on the two species, indicated that faster growth of Pacific oysters depended on similar physiological differences; the mean metabolic costs of growth, however, were similar in the two species. It is suggested that a general model for genetically linked differences in the growth rate of bivalve molluscs will need to include the processes of metabolic control rather than relying solely on an analysis of the individual components of the energetics...
TL;DR: The investigation tests two hypotheses: that previous estimates of the scaling exponents for the DGC and its characteristics are more broadly applicable to insects, and that, in response to temperature, both DGC frequency and the quantity of CO2 emitted during the open (O) phase (O‐phase emission volume) are modulated.
Abstract: Although discontinuous gas exchange cycles (DGC) are known from many insects, the effects of body size and temperature on DGC have not been widely examined. Here, these effects are investigated in five Scarabaeus dung beetle species from mesic and xeric habitats. The investigation tests two hypotheses: that previous estimates of the scaling exponents for the DGC and its characteristics are more broadly applicable to insects, and that, in response to temperature, both DGC frequency and the quantity of CO2 emitted during the open (O) phase (O‐phase emission volume) are modulated. Like previous workers, we find that \documentclass{aastex} \usepackage{amsbsy} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{bm} \usepackage{mathrsfs} \usepackage{pifont} \usepackage{stmaryrd} \usepackage{textcomp} \usepackage{portland,xspace} \usepackage{amsmath,amsxtra} \usepackage[OT2,OT1]{fontenc}
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TL;DR: The results suggest that embryonic hypoxia may negatively affect survival and fitness in these species.
Abstract: Oxygen available to amphibian embryos fluctuates widely and is often very low. We investigated the effects of oxygen partial pressure (1.3–16.9 kPa) on embryonic development and hatching of two salamander (Ambystoma) and two frog (Rana) species. In Ambystoma, chronic hypoxia resulted in slowed development, delayed hatching, and embryos that were less developed at the time of hatching. Although hypoxia was not lethal to embryos, temporary developmental abnormalities were observed in Ambystoma at oxygen partial pressures of 3.8 kPa and below. Posthatching survival decreased below 3.3 kPa. In Rana, hypoxia did not affect developmental rate, presumably because hatching occurs at a very early stage of development relative to Ambystoma. However, Rana embryos hatched sooner in hypoxia than in normoxia, resulting in less developed embryos at the time of hatching. The results suggest that embryonic hypoxia may negatively affect survival and fitness in these species.
TL;DR: A gut dispersion index that measured degree of axial mixing was positively correlated with mean retention time, indicating that higher retention times are accompanied by increased axialmix, and a modification of the assumptions of the original model is proposed.
Abstract: We explored modulation of retention time in cedar waxwings (Bombycilla cedrorum) by feeding them diets varying in hexose concentration. Our goals were to (1) test three predictions of a chemical reactor–based model of how guts might respond optimally to diet shifts; (2) determine whether modulation of retention time can occur quickly, thereby facilitating rapid changes in diet; (3) tease apart the relative influence of ingestion rate and nutrient concentration on retention time; and (4) examine the degree of axial mixing in the intestine and its relationship with retention time. The model's predictions were rejected: mean retention time did not decrease, ingestion rate did not increase, and glucose assimilation efficiency did not decrease with increased hexose concentration of the diet. Instead, birds displayed maximal intake rate at intermediate sugar concentration, and mouth to cloaca mean retention times increased with hexose concentration. Significant modulation of retention time occurred qui...
TL;DR: Findings indicate that a depression of ADP‐dependent respiration in liver mitochondria occurs during torpor and is reversed during the interbout arousals to euthermia, indicating that alterations in proton leak are not contributing appreciably to downregulation of resppiration in hibernation.
Abstract: The biochemical mechanisms by which hibernators cool as they enter torpor are not fully understood. In order to examine whether rates of substrate oxidation vary as a function of hibernation, liver mitochondria were isolated from telemetered ground squirrels (Spermophilus lateralis) in five phases of their annual hibernation cycle: summer active, and torpid, interbout aroused, entrance, and arousing hibernators. Rates of state 3 and state 4 respiration were measured in vitro at 25°C. Relative to mitochondria from summer‐active animals, rates of state 3 respiration were significantly depressed in mitochondria from torpid animals yet fully restored during interbout arousals. These findings indicate that a depression of ADP‐dependent respiration in liver mitochondria occurs during torpor and is reversed during the interbout arousals to euthermia. Because this inhibition was determined to be temporally independent of entrance and arousal, it is unlikely that active suppression of state 3 respiration ...
TL;DR: Energy expenditure is widely used in the study of ecological phenomena, in evolutionary theory, and as a subject of interest in its own right.
Abstract: Energy expenditure is widely used in the study of ecological phenomena, in evolutionary theory, and as a subject of interest in its own right. Many analyses of physiological and ecological phenomena have depended on a correlation with body mass that is parallel to the correlation of rate of metabolism with body mass. Therefore, our understanding of these phenomena has often depended on our analysis of the correlation of rate of metabolism with body mass. Because total rates of metabolism are proportional to body mass (m) raised to a power (b) !1.0, mass-specific rates of metabolism decrease with an increase in mass. That is, if when has the units of cm O2 h 1 and m is in b Vo = am Vo 2 2
TL;DR: The relative insensitivity of the ionoregulatory system of tambaqui to low pH indicates that this is a feature of fish native to blackwater systems rather than one that is common to all Amazon fish.
Abstract: Sensitivity to acid water was assessed in three species of Amazonian fish that encounter naturally acidic blackwaters to differing degrees in the wild: tambaqui (Colossoma macropomum), matrincha (Brycon erythropterum), and tamoata (Hoplosternum littorale), in decreasing order of occurrence in blackwater. Fish were exposed to a graded reduction in water pH, from pH 6 to 5 to 4 to 3.5, followed by return to pH 6. Fish were exposed to each new pH for 24 h. During these exposures, net transfers of ions (Na+, K+, Cl−, and Ca2+) and acid‐base equivalents to and from the external water were used as physiological indicators of acid tolerance. Exposure to pH 5 had a minimal effect on net ion fluxes. Significant net losses of all ions (except Ca2+) were recorded in all three species during the first few hours of exposure to pH 4. However, ion balance was usually restored within 18 h at pH 4. Exposure to pH 3.5 caused even greater ion losses in all three species and proved to be acutely lethal to tamoata. M...
TL;DR: Results indicate that egg temperatures induced positive metabolic compensation in both sexes in hatchling snapping turtles, indicating that the effects of embryonic temperature on metabolic physiology, in combination with effects on sex, may be important to the ecology and evolution of TSD.
Abstract: Temperature acclimation of adult vertebrates typically induces changes in metabolic physiology. During early development, such metabolic compensation might have profound consequences, yet acclimation of metabolism is little studied in early life stages. We measured the effect of egg incubation temperature on resting metabolic rate (RMR) and blood thyroid hormone levels of hatchling snapping turtles (Chelydra serpentina). Like many reptiles, snapping turtles have temperature‐dependent sex determination (TSD), in which embryonic temperature determines sex. Therefore, we designed the experiments to separately measure effects of temperature and of sex on the response variables. We incubated eggs in the laboratory at 21.5°, 24.5°, 27.5°, and 30.5°C, producing both sexes, all males, both sexes, and all females, respectively. Hatchling RMR, when measured at a common temperature (either 25° or 31°C), was negatively correlated with egg temperature in both males and females, such that RMR of turtles from 2...
TL;DR: It is suggested that sea lions can depress their resting metabolism in response to decreases in energy intake or body mass, regardless of satiation level.
Abstract: Diets of six Steller sea lions (Eumetopias jubatus) were switched between a high (herring) and a low (squid) energy density food for 14 d to determine the effects on ingested prey mass, body mass, resting metabolic rate, and the heat increment of feeding. Body mass was measured daily, and resting metabolism was measured weekly by gas respirometry. Ingested food mass did not differ significantly between the squid diet and the control or the recovery herring diet periods. As a result of differences in energy density, gross energy intake was significantly lower during the squid diet phase than during either the control or recovery periods. As a result, sea lions lost an average of 1.1 kg/d, totaling 12.2% of their initial body mass by the end of the experimental period. The heat increment of feeding for a 4‐kg squid meal was significantly lower than for a similarly sized meal of herring. Decreases in both absolute (24.0 to 18.0 MJ/d, −24%) and mass‐corrected (903 to 697 kJ/d/kg0.67, −20%) metabolism...
TL;DR: Data suggest that the observed NST in the marsupial bettong is not attributable to BAT, a specialized thermogenic effector, and the presence of BAT was evaluated by examining the expression of the uncoupling protein 1 (UCP1) with both rat cDNA and oligonucleotide probes.
Abstract: The Tasmanian bettong (Bettongia gaimardi, a marsupial) is a rat‐kangaroo that increases nonshivering thermogenesis (NST) in response to norepinephrine (NE). This study attempted to assess whether brown adipose tissue (BAT), a specialized thermogenic effector, is involved in NST in the bettong. Regulatory NST, indicated by resting oxygen consumption (Vo2) of the whole body, was measured under conscious conditions at 20°C with various stimuli: cold (4°–5°C) or warm (25°C) acclimation, NE injection, and the β3‐adrenoceptor agonist (BRL) 37344. In line with the functional studies in vivo, the presence of BAT was evaluated by examining the expression of the uncoupling protein 1 (UCP1) with both rat cDNA and oligonucleotide probes. Both NE and BRL 37344 significantly stimulated NST in the bettong. After cold acclimation of the animals (at 4°–5°C for 2 wk), the resting Vo2 was increased by 15% and the thermogenic effect of NE was enhanced; warm‐acclimated animals showed a slightly depressed response. H...
TL;DR: Exposing only a small part of their body when in water (20%) slowed heat loss considerably, allowing crocodiles to spend more time in the water while maintaining body temperature within their preferred body temperature range.
Abstract: I recorded body temperature and behaviour of eight Crocodylus johnstoni in the wild over a 2-yr period in order to quantify the effect of posturing on body temperature and to provide a mechanistic explanation of how behaviour affects body temperature. Behaviour was categorised according to the proportion of a crocodile's surface area exposed from the water (0% exposed [=diving] to 100% exposed [=basking]). Crocodiles did not simply shuttle between the extremes of 100% exposed and diving but showed an array of intermediate postures. Rates of body temperature change were negative for exposures less than 40% and positive for 60%-100% exposed. This was due to the difference between operative temperature and body temperature, which was negative during diving but increased with the percentage of exposure, up to 25 degrees-30 degrees C during basking. For any particular posture, the rate of body temperature change decreased with increasing mass. Thermal time constants were shortest during diving and longest during basking. A heat-transfer equation predicted the rate of body temperature change well, except that it underestimated the rate of body temperature change during 80% and 100% exposed. Exposing only a small part of their body when in water (20%) slowed heat loss considerably, allowing crocodiles to spend more time in the water while maintaining body temperature within their preferred body temperature range.
TL;DR: The hypothesis that pine warblers modulate the activity of digestive enzymes in proportion to demand from substrates in the diet is supported, supporting the hypothesis that Pine warblersModulation of gut function is important in an ecological and evolutionary context.
Abstract: Modulation of gut function is important in an ecological and evolutionary context because it likely determines what food items an animal can and cannot eat. We examined how diet affects activity of digestive enzymes in an omnivorous bird, the pine warbler (Dendroica pinus). Pine warblers were fed insect‐based, fruit‐based, and seed‐based diets for ∼54 d. We then measured activity of amylase, maltase, sucrase, aminopeptidase‐N, trypsin, chymotrypsin, carboxypeptidase A, carboxypeptidase B, pancreatic lipase, and carboxyl ester lipase. We predicted that carbohydrase activities would be highest in birds fed the diet highest in carbohydrates (fruit based), protease activities would be highest in those fed the diet highest in protein (insect based), and lipase activities would be highest in those fed the diets highest in lipid (insect based and seed based). Also, we predicted that pine warblers would exhibit greater dietary modulation of enzyme activity than reported for a less omnivorous congener, th...
TL;DR: First instars of Carausius morosus provide a good model for morphometric evaluation of the diffusing capacity between the tracheal system and hemolymph: air sacs are lacking, tracheoles do not penetrate the organs and muscles, and entire animals can be evaluated electron microscope without subsampling.
Abstract: First instars of Carausius morosus provide a good model for morphometric evaluation of the diffusing capacity between the tracheal system and hemolymph: air sacs are lacking, tracheoles do not penetrate the organs and muscles, and entire animals can be evaluated electron microscopically without subsampling. The tracheal volume makes up 1.3% of the volume of the whole insect excluding appendages. We calculated the lateral diffusing capacity for oxygen and carbon dioxide for five classes of tracheae according to their diameters, from 0.2 μm to 35 μm. The harmonic mean thickness of the tracheal epithelium is lowest in smallest tracheae and increases with increasing tracheal diameter. Although the smallest tracheae make up 70% (O2) and 60% (CO2) of the total diffusing capacity, the proximal four classes may also be significant in diffusion of oxygen and particularly of carbon dioxide. The suppression of the development of respiratory pigments in the evolution of terrestrial insects may have increased...