Responses to Rapid Temperature Change in Vertebrate Ectotherms

Vertebrate ectotherms often encounter rapid, large scale changesin body temperature. In this paper, I discuss the direct effectsof changing body temperature on physiological parameters, aswell as corrective responses initiated by the animal. For manybiological functions, mean body temperature provides a usefulmeasure of the thermal effects produced by an altered environmentaltemperature. Under most conditions, the fins and body surfaceof fish are more important avenues of heat exchange than thegills. The local thermal sensitivity of peripheral blood vesselsresults in vasomotor adjustments which can alter thermal conductivity.Acid-base balance is challenged by changes in body temperature.Shifts in body temperature also alter metabolic demands, enzymeconformation, ionic and osmotic relationships, spontaneous activitylevels and nervous system function. Compensatory mechanismsinclude behavioral thermoregulation, by which animals seek toavoid stressful thermal environments, and autonomic restorativeresponses such as high temperature panting in reptiles. Waterbreathers may initiate anticipatory responses to minimize arterialoxygen fluctuations during termperature change. The organizationof the central neuronal network underlying the above regulatoryresponses is unclear. Both air and water breathers are ableto initiate compensatory acid-base responses, but the strategiesutilized by the two groups are quite different. Altered bodytemperature initiates long-term acclimation responses, and ifrapid, can also trigger stress responses.     

Progressive enhancement of body temperature responses to consecutive exercise-bouts of the same intensity in dogs

Progressive enhancement of body temperature responses to consecutive exercise-bouts of the same intensity in dogs. Acta physiol. pol., 1985, 36 (3): 165-174. Changes in rectal (Tre), muscle (Tm), and hypothalamic (Thy) temperatures, plasma osmolality, and some intermediary metabolic variables were examined in dogs performing four successive exercise-bouts of the same intensity. During the rest-intervals separating the exercise-bouts body temperatures returned to initial levels and water losses were replaced. Tm and Tre responses to consecutive exercise-bouts were progressively increasing. Similar tendency was found in Thy changes. Cardiac and respiratory frequencies attained the same levels in all four exercise-bouts, while blood lactate and FFA concentrations were increasing and blood glucose level was decreasing progressively. No changes in plasma osmolality was noted. Exercise-induced increases in Tm correlated positively with plasma FFA concentration (r = 0.68). Body temperature responses to exercise were reduced by beta-adrenergic blockade. It is concluded that the enhancement of the thermal responses to consecutive exercise-bouts can be related to the metabolic action of catecholamines.     

Intraspecific temperature dependence of the scaling of metabolic rate with body mass in fishes and its ecological implications

Metabolism constitutes a fundamental property of all organisms. Metabolic rate is commonly described to scale as a power function of body size and exponentially with temperature, thereby treating the effects of body size and temperature independently. Mounting evidence shows that the scaling of metabolic rate with body mass itself depends on temperature. Across‐species analyses in fishes suggest that the mass‐scaling exponent decreases with increasing temperature. However, whether this relationship holds at the within‐species level has rarely been tested. Here, we re‐analyse data on the metabolic rates of four freshwater fish species, two coregonids and two cyprinids, that cover wide ranges of body masses and their naturally experienced temperatures. We show that the standard metabolic rate of the coregonids is best fit when accounting for a linear temperature dependence of the scaling of metabolic rate with body mass, whereas a constant mass‐scaling exponent is supported in case of the cyprinids. Our study shows that phenotypic responses to temperature can result in temperature‐dependent scaling relationships at the species level and that these responses differ between taxa. Together with previous findings, these results indicate that evolutionarily adaptive and phenotypically plastic responses to temperature affect the scaling of metabolic rate with body mass in fishes.     

Respiratory responses of the mysid Gastrosaccus brevifissura (Peracarida: Mysidacea), in relation to body size,temperature and salinity

The mysid Gastrosaccus brevifissura (Peracarida: Mysidacea) is widely distributed in southern Africa and is thought to be important in the functioning of estuarine systems. This mysid may experience highly variable physicochemical conditions, and its physiological responses to these are of interest considering its ecological role. This study presents data on the metabolic physiology in relation to body length, temperature (15-30 degrees C) and salinity (15-35 psu) of a G. brevifissura population on the sub-tropical eastern seaboard of South Africa. Oxygen consumption rate was linearly related to size (for body lengths ranging from 3 to 10 mm) and varied among individuals from 0.67 to 6.51 microgram h(-1), dependent on environmental conditions. Oxygen consumption rate was largely independent of salinity variation between 20 and 35 psu, although was significantly depressed at 15 psu. Aerobic rate generally increased with an acute increase in temperature (Q(10)=2.147), but was not affected by 7 days of acclimation at either 15 or 25 degrees C. The lack of a metabolic adjustment to meet the additional energetic demands associated with a decline in salinity may well be a factor limiting the estuarine distribution of G. brevifissura. Even though feeding behaviour substantially changes between summer and winter, this may best be explained by food availability or other ecological factors, rather than a metabolic adjustment, considering the apparent lack of metabolic acclimation.     

Idiosyncratic species effects confound size-based predictions of responses to climate change

Understanding and predicting the consequences of warming for complex ecosystems and indeed individual species remains a major ecological challenge. Here, we investigated the effect of increased seawater temperatures on the metabolic and consumption rates of five distinct marine species. The experimental species reflected different trophic positions within a typical benthic East Atlantic food web, and included a herbivorous gastropod, a scavenging decapod, a predatory echinoderm, a decapod and a benthic-feeding fish. We examined the metabolism–body mass and consumption–body mass scaling for each species, and assessed changes in their consumption efficiencies. Our results indicate that body mass and temperature effects on metabolism were inconsistent across species and that some species were unable to meet metabolic demand at higher temperatures, thus highlighting the vulnerability of individual species to warming. While body size explains a large proportion of the variation in species'' physiological responses to warming, it is clear that idiosyncratic species responses, irrespective of body size, complicate predictions of population and ecosystem level response to future scenarios of climate change.     

Thermoregulatory consequences of long-term microwave exposure at controlled ambient temperatures

This study was designed to identify and measure changes in thermoregulatory responses, both behavioral and physiological, that may occur when squirrel monkeys are exposed to 2450-MHz continuous wave microwaves 40 hr/week for 15 weeks. Power densities of 1 or 5 mW/cm2 (specific absorption rate = 0.16 W/kg per mW/cm2) were presented at controlled environmental temperatures of 25, 30, or 35 degrees C. Standardized tests, conducted periodically, before, during, and after treatment, assessed changes in thermoregulatory responses. Dependent variables that were measured included body mass, certain blood properties, metabolic heat production, sweating, skin temperatures, deep body temperature, and behavioral responses by which the monkeys selected a preferred environmental temperature. Results showed no reliable alteration of metabolic rate, internal body temperature, blood indices, or thermoregulatory behavior by microwave exposure, although the ambient temperature prevailing during chronic exposure could exert an effect. An increase in sweating rate occurred in the 35 degrees C environment, but sweating was not reliably enhanced by microwave exposure. Skin temperature, reflecting vasomotor state, was reliably influenced by both ambient temperature and microwaves. The most robust consequence of microwave exposure was a reduction in body mass, which appeared to be a function of microwave power density.     

Metabolic and febrile responses to typhoid vaccine in humans: effect of beta-adrenergic blockade.

Fever and activation of acute phase responses were induced in human volunteers by intramuscular injection of typhoid vaccine. Vaccine injection caused a rapid (within 1 h) and sustained rise in metabolic rate (peak response 16%, 6-8 h), followed by later increases in white blood cell count (3-4 h), skin temperature (4-5 h), oral temperature (5-6 h), heart rate (6-8 h), and plasma cortisol (5-8 h). A peak fever [1.2 +/- 0.2 degree C (SE) rise] was recorded 12 h after vaccine injection. The involvement of the sympathetic nervous system in the development of these responses was investigated by the oral administration of propranolol before (80 mg) and 3 h after (40 mg) vaccine injection. Propranolol prevented the increases in metabolic rate, heart rate, and skin temperature but did not inhibit the rise in oral temperature or white cell count after vaccine administration. These data indicate that the sympathetic nervous system is responsible for the rise in energy expenditure associated with fever in humans. However, the rise in body temperature can develop in the absence of this increase in metabolic rate possibly by changes in heat loss.     

Influence of sleep on the cardiovascular and metabolic responses to a decrease in ambient temperature in lambs

Experiments were done on seven lambs between the ages of 10 and 24 days to investigate the effects of sleep on the cardiovascular and metabolic responses to a decrease in ambient temperature. Each lamb was anesthetized and instrumented for recordings of electrocorticogram, electro-oculogram, and nuchal electromyograms and measurements of cardiac output, systemic and pulmonic pressures and hemoglobin oxygen saturations as well as body core temperature. No sooner than three days after surgery, measurements were made during periods of quiet wakefulness, quiet sleep and active sleep at ambient temperatures of 25 degrees C and 18 degrees C. Decreasing the environmental temperature from 25 degrees C to 18 degrees C elicited a similar thermogenic response during quiet wakefulness, quiet sleep and active sleep as evidenced by an increase in total body oxygen consumption. The increased metabolic oxygen demand was met by an increase in systemic oxygen transport as well as by an increase in total body oxygen extraction. Since shivering was absent during active sleep, it is likely that nonshivering thermogenesis played a major role in the metabolic response. Our data provide evidence that sleep does not significantly alter the cardiovascular and metabolic responses to a modest decrease in ambient temperature in young lambs.     

Limits to exhaustive exercise in fish

Exercise to exhaustion leads to severe metabolic, acid-base and ionic changes in fish. It has been shown that several abiotic and biotic factors can limit burst exercise performance and the recovery process in fish. This article reviews the importance of body size, temperature, fasting/starvation and training on the ability of fish to perform and recover from exhaustive exercise. It is concluded that the constraints placed on a fish prior to and following exercise reflects the large intra-specific variability in the physiological response to exercise in fish.     

Relative contribution of core and cutaneous temperatures to thermal comfort and autonomic responses in humans.

Subjective thermal comfort plays a critical role in body temperature regulation since this represents the primary stimulus for behavioral thermoregulation. Although both core (Tc) and skin-surface (Tsk) temperatures are known afferent inputs to the thermoregulatory system, the relative contributions of Tc and Tsk to thermal comfort are unknown. We independently altered Tc and Tsk in human subjects while measuring thermal comfort, vasomotor changes, metabolic heat production, and systemic catecholaminergic responses. Multiple linear regression was used to determine the relative Tc/Tsk contribution to thermal comfort and the autonomic thermoregulatory responses, by using the ratio of regression coefficients for Tc and Tsk. The Tc/Tsk contribution ratio was relatively lower for thermal comfort (1:1) than for vasomotor changes (3:1; P = 0.008), metabolic heat production (3.6:1; P = 0.001), norepinephrine (1.8:1; P = 0.03), and epinephrine (3:1; P = 0.006) responses. Thus Tc and Tsk contribute about equally toward thermal comfort, whereas Tc predominates in regulation of the autonomic and metabolic responses.     

Thermal sensation and thermophysiological responses to metabolic step-changes

This study investigated the effect on thermal perception and thermophysiological variables of controlled metabolic excursions of various intensities and durations. Twenty-four subjects were alternately seated on a chair or exercised by walking on a treadmill at a temperature predicted to be neutral at sedentary activity. In a second experimental series, subjects alternated between rest and exercise as well as between exercise at different intensities at two temperature levels. Measurements comprised skin and oesophageal temperatures, heart rate and subjective responses. Thermal sensation started to rise or decline immediately (within 1 min) after a change of activity, which means that even moderate activity changes of short duration affect thermal perceptions of humans. After approximately 15–20 min under constant activity, subjective thermal responses approximated the steady-state response. The sensitivity of thermal sensation to changes in core temperature was higher for activity down-steps than for up-steps. A model was proposed that estimates transient thermal sensation after metabolic step-changes. Based on predictions by the model, weighting factors were suggested to estimate a representative average metabolic rate with varying activity levels, e.g. for the prediction of thermal sensation by steady-state comfort models. The activity during the most recent 5 min should be weighted 65%, during the prior 10–5 min 25% and during the prior 20–10 min 10%.     

Resource allocation in yolk-feeding fish

An insight is made into the main processes that occur in fish during endogenous feeding period. The ways in which yolk absorption rate can be measured are evaluated. Essential amino acids and polyunsaturated fatty acids are preferentially retained for incorporation into body tissue. Profound physiological and anatomical changes in yolk and a sequence of slow, fast, and a second period of slow absorption occur during the endogenous feeding period. Attempts to quantify the ontogenetic sequence are reviewed. Various methods of body size assessment are compared, and sources of bias in individual and population growth estimates are discussed. Several calorimetric methods are compared of which direct calorimetry using an oxygen bomb is the reference method. An advanced elemental analysis (CHNS) is a reliable technique that is adequate for early stages. Indices of growth potential are reviewed including a comparison of different measures, models and approaches used to estimate growth. Changes in body hydration, caloric value, content of lipids, protein, free amino acids (FAA) and minerals, and in content of RNA and DNA occur in early ontogeny. Ways to quantify metabolic rate are identified. Mean relative respiration rate of initial egg before activation is very low, about 20 mm³ g⁻¹ h⁻¹. Ontogenetic sequence in absolute metabolic rate of fish embryos and yolk-feeding larvae involves an increase through hatching to a peak at the time of first feeding ability, and a decrease under starvation. Models predicting the relationship between oxygen consumption and age in yolk-feeding fish are reviewed. Sequence of metabolic fuels begins with use of small molecules as carbohydrates, soon switched to FAA. Later lipids are progressively used, they provide energy for swimming activity. After yolk depletion body protein-bound amino acids are mobilised. In this review I focused on the major environmental variables as temperature, oxygen, salinity, pH, toxic xenobiotics, light, UV radiation, magnetic field and substrate, along with intrinsic factors as egg or body size, sex and genetic factors. A question was posed on how the extrinsic and intrinsic factors determine yolk absorption, growth and metabolic rates in yolk-feeding fish. Special attention is devoted to fish body size attained exclusively on yolk. A considerable variety of body size responses to temperature was found, for which several explanations are forwarded. Methodological progress made recently is characterised and the most conspicious advances in understanding of fish early life history are highlighted. Information derived from these studies can be used in management of fish populations in the field and to optimise activities in aquaculture.     

Global patterns in lake ecosystem responses to warming based on the temperature dependence of metabolism

Climate warming is expected to have large effects on ecosystems in part due to the temperature dependence of metabolism. The responses of metabolic rates to climate warming may be greatest in the tropics and at low elevations because mean temperatures are warmer there and metabolic rates respond exponentially to temperature (with exponents >1). However, if warming rates are sufficiently fast in higher latitude/elevation lakes, metabolic rate responses to warming may still be greater there even though metabolic rates respond exponentially to temperature. Thus, a wide range of global patterns in the magnitude of metabolic rate responses to warming could emerge depending on global patterns of temperature and warming rates. Here we use the Boltzmann–Arrhenius equation, published estimates of activation energy, and time series of temperature from 271 lakes to estimate long‐term (1970–2010) changes in 64 metabolic processes in lakes. The estimated responses of metabolic processes to warming were usually greatest in tropical/low‐elevation lakes even though surface temperatures in higher latitude/elevation lakes are warming faster. However, when the thermal sensitivity of a metabolic process is especially weak, higher latitude/elevation lakes had larger responses to warming in parallel with warming rates. Our results show that the sensitivity of a given response to temperature (as described by its activation energy) provides a simple heuristic for predicting whether tropical/low‐elevation lakes will have larger or smaller metabolic responses to warming than higher latitude/elevation lakes. Overall, we conclude that the direct metabolic consequences of lake warming are likely to be felt most strongly at low latitudes and low elevations where metabolism‐linked ecosystem services may be most affected.     

The TRPM2 channel: A thermo-sensitive metabolic sensor

Living organisms continually experience changes in ambient temperature. To detect such temperature changes for adaptive behavioral responses, we evolved the ability to sense temperature. Thermosensitive transient receptor potential (TRP) channels, so-called thermo-TRPs, are involved in many physiologic functions in diverse organisms and constitute important temperature sensors. One of the important roles of thermo-TRPs is detecting ambient temperature in sensory neurons. Importantly, the functional expression of thermo-TRPs is observed not only in sensory neurons but also in tissues and cells that are not exposed to drastic temperature changes, indicating that thermo-TRPs are involved in many physiologic functions within the body's normal temperature range. Among such thermo-TRPs, this review focuses on one thermo-sensitive metabolic sensor in particular, TRPM2, and summarizes recent progress to clarify the regulatory mechanisms and physiologic functions of TRPM2 at body temperature under various metabolic states.     

Size matters: plasticity in metabolic scaling shows body-size may modulate responses to climate change

Variability in metabolic scaling in animals, the relationship between metabolic rate (R) and body mass (M), has been a source of debate and controversy for decades. R is proportional to M^b, the precise value of b much debated, but historically considered equal in all organisms. Recent metabolic theory, however, predicts b to vary among species with ecology and metabolic level, and may also vary within species under different abiotic conditions. Under climate change, most species will experience increased temperatures, and marine organisms will experience the additional stressor of decreased seawater pH (‘ocean acidification’). Responses to these environmental changes are modulated by myriad species-specific factors. Body-size is a fundamental biological parameter, but its modulating role is relatively unexplored. Here, we show that changes to metabolic scaling reveal asymmetric responses to stressors across body-size ranges; b is systematically decreased under increasing temperature in three grazing molluscs, indicating smaller individuals were more responsive to warming. Larger individuals were, however, more responsive to reduced seawater pH in low temperatures. These alterations to the allometry of metabolism highlight abiotic control of metabolic scaling, and indicate that responses to climate warming and ocean acidification may be modulated by body-size.     

Ventilatory and metabolic responses to hypoxia in the smallest simian primate, the pygmy marmoset.

The pygmy marmoset (Cebuella pygmaea) is the smallest New World Monkey (average body mass of 120-130 g). As such, it faces possible challenges to thermoregulation. Small mammals (e.g., rats) are well known to lower body temperature and metabolism in response to hypoxia; however, small primates have not been studied in this respect nor have, in general, the interactions between metabolism and ventilation. Because little is known about these responses in small primates, it seemed of great interest to assess the hypoxia-induced metabolic depression and drop in body temperature and the associated ventilatory requirements in this species under hypoxic conditions. Exposure to graded hypoxia (30 min at each of 18, 16, 14, 12, and 10% O(2)) caused body temperature to drop from the normoxic value of 39 to 37 degrees C. This was accompanied by a marked metabolic depression (O(2) consumption was approximately 68% of the normoxic value, implying a suppression of metabolism greater than that predicted from a typical value of the effect of 10 degrees C change on metabolism of 2-3 times). Minute ventilation declined in parallel to metabolism, maintaining a constant air-convection requirement during hypoxia; thus this species did not show the typical mammalian hyperventilation. Acute exposure to 10% O(2) led to a similar overall decline in metabolism and body temperature and qualitative differences in the timing of these changes. The pygmy marmoset shares some similarities in its hypoxic metabolic response with other mammals of similar size yet appears to be unique in its much diminished ventilatory response to hypoxia.     

Metabolic and hormonal acclimation to heat stress in domesticated ruminants

Environmentally induced periods of heat stress decrease productivity with devastating economic consequences to global animal agriculture. Heat stress can be defined as a physiological condition when the core body temperature of a given species exceeds its range specified for normal activity, which results from a total heat load (internal production and environment) exceeding the capacity for heat dissipation and this prompts physiological and behavioral responses to reduce the strain. The ability of ruminants to regulate body temperature is species- and breed-dependent. Dairy breeds are typically more sensitive to heat stress than meat breeds, and higher-producing animals are more susceptible to heat stress because they generate more metabolic heat. During heat stress, ruminants, like other homeothermic animals, increase avenues of heat loss and reduce heat production in an attempt to maintain euthermia. The immediate responses to heat load are increased respiration rates, decreased feed intake and increased water intake. Acclimatization is a process by which animals adapt to environmental conditions and engage behavioral, hormonal and metabolic changes that are characteristics of either acclimatory homeostasis or homeorhetic mechanisms used by the animals to survive in a new 'physiological state'. For example, alterations in the hormonal profile are mainly characterized by a decline and increase in anabolic and catabolic hormones, respectively. The response to heat load and the heat-induced change in homeorhetic modifiers alters post-absorptive energy, lipid and protein metabolism, impairs liver function, causes oxidative stress, jeopardizes the immune response and decreases reproductive performance. These physiological modifications alter nutrient partitioning and may prevent heat-stressed lactating cows from recruiting glucose-sparing mechanisms (despite the reduced nutrient intake). This might explain, in large part, why decreased feed intake only accounts for a minor portion of the reduced milk yield from environmentally induced hyperthermic cows. How these metabolic changes are initiated and regulated is not known. It also remains unclear how these changes differ between short-term v. long-term heat acclimation to impact animal productivity and well-being. A better understanding of the adaptations enlisted by ruminants during heat stress is necessary to enhance the likelihood of developing strategies to simultaneously improve heat tolerance and increase productivity.     

Physiological genetics of dietary restriction: uncoupling the body temperature and body weight responses

Numerous physiological and molecular changes accompany dietary restriction (DR), which has been a major impediment to elucidating the causal basis underlying DR's many health benefits. Two major metabolic responses to DR that potentially underlie many of these changes are the body temperature (T(b)) and body weight (BW) responses. These responses also represent an especially difficult challenge to uncouple during DR. We demonstrate in this study, using two recombinant inbred (RI) panels of mice (the LXS and LSXSS) that naturally occurring genetic variation serves as a powerful tool for modulating T(b) and BW independently during DR. The correlation coefficient between the two responses was essentially zero, with R = -0.04 in the LXS and -0.03 in the LSXSS, the latter averaged across replicate cohorts. This study is also the first to report that there is highly significant (P = 10(-10)) strain variation in the T(b) response to DR in the LXS (51 strains tested), with strain means ranging from 2 to 4 degrees C below normal. The results suggest that the strain variation in the T(b) response to DR is largely due to differences in the rate of heat loss rather than heat production (i.e., metabolic rate). This variation can thus be used to assess the long-term effects of lower T(b) independent of BW or metabolic rate, as well as independent of food intake and motor activity as previously shown. These results also suggest that murine genetic variation may be useful for uncoupling many more responses to DR.     

Effects of temperature and oxygen depletion on metabolic rates of tomato and carrot cell cultures and cuttings measured by calorimetry

Abstract. Isothermal heat-conductance calorimetry was used to monitor responses of tomato and carrot metabolism to changes in temperature and oxygen concentrations. Calorimetric measurements of metabolic heat evolution from tissue segments and cultured cells was found to be a sensitive, nondestructive estimate of metabolic rates. Short-term measurements of metabolic rates of cells in culture correlate well with calorimetric measurements made on tissue sections. The results accurately predict the growth properties of intact plants based on the generally recognized characteristics of these two species. The calorimetric method provides another means for rapid evaluation of plant responses to physical and chemical stresses and is of value for screening and selection.     

Changes in cold tolerance due to a 14-day stay in the Canadian Arctic

Responses to cold exposure tests both locally and of the whole body were examined in subjects who stayed in the Arctic (average maximum and minimum temperatures –11 and –21° C respectively) for 14 days of skiing and sleeping in tents. These changes were compared to responses in subjects living working in Ottawa, Canada (average max. and min. temperatures –5 and –11° C respectively). The tests were done before the stay in the Arctic (Pre), immediately after the return (Post 1) and approximately 32 days after the return (Post 2). For the whole-body cold exposure each subject, wearing only shorts and lying on a rope mesh cot, was exposed to an ambient temperature of 10° C. There was no consistent response in the changes of metabolic or body temperature to this exposure in either of groups and, in addition, the changes over time were variable. Cold induced vasodilatation (CIVD) was determined by measuring temperature changes in the middle finger of the nondominant hand upon immersion in ice water for 30 min. CIVD was depressed after the Arctic exposure whilst during the Post 2 testing, although variable, did not return to the Pre values; the responses of the control group were similar. These results indicate that normal seasonal changes may be as important in adaptation as a stay in the Arctic. Caution is advised in the separation of seasonal effects when examining the changes in adaptation after exposure to a cold environment.