Biochemical acclimation of metabolic enzymes in response to lowered temperature in tadpoles of Limnodynastes peronii

We measured the rate at which the metabolic enzymes lactate dehydrogenase (LDH), citrate synthase (CS), and cytochrome c oxidase (CCO) acclimate in the response to lowered temperature in the axial muscle of tadpoles of Limnodynastes peronii (Anura: Myobatrachidae) over 6 weeks. In addition, we measured growth rates of the tadpoles kept at both temperatures and examined the activities of these enzymes in the liver tissue of the control group and cold-acclimated group at the end of the experiment. We found that LDH acclimates in axial muscle; the differences between the control and cold-acclimated group became apparent after 21 days. After 42 days, the activity of LDH in axial muscle in the cold-acclimated group was 30% greater than the control group. Growth rates were maintained at 0.7 mm/week within both treatments despite the 10 degrees C difference in temperature between experimental groups. Both LDH and CS were increased in activity in the liver (5 and 1.3 times greater, respectively, in the cold-acclimated group). The thermal sensitivity (Q(10)) of LDH was between 20 and 30 degrees C in the cold-acclimated group (1.2+/-0.01) when compared to the control group (1.6+/-0.15). The rate at which acclimation in this species occurs is appropriate for seasonal changes in temperature, and these animals may not be able to respond to a rapid drop in temperature.     

Seasonal changes in thermal environment and metabolic enzyme activity in the diamondback terrapin (Malaclemys terrapin)

Diamondback terrapins experience broad fluctuations in temperature on both a daily and seasonal basis in their estuarine environment. We measured metabolic enzyme activity in terrapin muscle tissue to assess thermal dependence and the role of temperature in seasonal metabolic downregulation in this species. Activity of lactate dehydrogenase (LDH), pyruvate kinase (PK), citrate synthase (CS), and cytochrome c oxidase (CCO) was assayed at 10, 20, 30, and 40 °C for tissue collected during summer and winter. The Q(10) for enzyme activity varied between 1.31 and 2.11 within the temperature range at which terrapins were active (20-40 °C). The Q(10) for LDH, CS, and CCO varied between 1.39 and 1.76 and between 10 and 20 °C, but PK exhibited heightened thermal sensitivity within this lower temperature range, with a Q(10) of 2.90 for summer-collected tissue and 5.55 for winter-collected tissue. There was no significant effect of season on activity of LDH or PK, but activity of CS and CCO was significantly lower in winter-collected tissue compared with summer-collected tissue. Results indicate that temperature effects contribute to seasonal metabolic downregulation and dormancy in terrapins, but other environmental factors (i.e. oxygen availability), as well as seasonal shifts in blood biochemistry and circulating hormones may also play an important role.     

Seasonal metabolic changes in a year-round reproductively active subtropical tree-frog (Hypsiboas prasinus)

Although seasonal metabolic variation in ectothermic tetrapods has been investigated primarily in the context of species showing some level of metabolic depression during winter, but several species of anurans maintain their activity patterns throughout the year in tropical and subtropical areas. The tree-frog Hypsiboas prasinus occurs in the subtropical Atlantic Forest and remains reproductively active during winter, at temperatures below 10 degrees C. We compared males calling in summer and winter, and found that males of H. prasinus exhibit seasonal adjustments in metabolic and morphometric variables. Individuals calling during winter were larger and showed higher resting metabolic rates than those calling during summer. Calling rates were not affected by season. Winter animals showed lower liver and heart activity level of citrate synthase (CS), partially compensated by larger liver mass. Winter individuals also showed higher activity of pyruvate kinase (PK) and lower activity of CS in trunk muscles, and higher activity of CS in leg muscles. Winter metabolic adjustments seem to be achieved by both compensatory mechanisms to the lower environmental temperature and a seasonally oriented aerobic depression of several organs. The impact of seasonal metabolic changes on calling performance and the capacity of subtropical anurans for metabolic thermal acclimatization are also discussed.     

Aerobic and anaerobic enzyme assays in Southern California Rockfish: Proxies for physiological and ecological data

Rockfish are commercially and recreationally important, yet due to the depths they inhabit (3-500 m), little is known about their ecology. The present study examined 19 different species of Sebastes from the Southern California Bight over four seasons (late summer, fall, early winter, and spring) using metabolic enzyme assays. Enzymes used were lactate dehydrogenase (LDH), malate dehydrogenase (MDH), pyruvate kinase (PK), and citrate synthase (CS). Muscle proximate composition data (protein, water and lipid content) were also used to help interpret the enzyme data. Enzyme activity was lowest in the summer when expressed as activity per gram wet weight but when it was expressed per gram protein the trend was reversed. The rockfish have the highest protein as a percentage of wet mass (P%WM) in the spring, right before the upwelling period begins and the lowest P%WM in late summer after the peak of upwelling. Lipid content also showed a seasonal change with the highest lipid content in the late summer and the lowest in winter. The enzyme profiles have been broken into three groups which fit with their locomotory habit and their prey selection. These findings show that enzymes and muscle proximate composition can be used along with limited observational data on related species to deduce condition, seasonal impacts and ecologically important life habits in species that are difficult to observe and monitor.     

Phenotypic flexibility in passerine birds: Seasonal variation of aerobic enzyme activities in skeletal muscle

Improved winter cold tolerance is widespread among small passerines resident in cold climates and is generally associated with elevated summit metabolic rate (M_sum=maximum thermoregulatory metabolic rate) and improved shivering endurance with increased reliance on lipids as fuel. Elevated M_sum and improved cold tolerance may result from greater metabolic intensity, due to mass-specific increase in oxidative enzyme capacity, or increase in the masses of thermogenic tissues. To examine the mechanisms underlying winter increases in M_sum, we investigated seasonal changes in mass-specific and total activities of the key aerobic enzymes citrate synthase (CS) and β-hydroxyacyl CoA-dehydrogenase (HOAD) in pectoralis, supracoracoideus and mixed leg muscles of three resident passerine species, black-capped chickadee (Poecile atricapillus), house sparrow (Passer domesticus), and white-breasted nuthatch (Sitta carolinensis). Activities of CS were generally higher in winter than in summer muscles for chickadees and house sparrows, but not nuthatches. Mass-specific HOAD activity was significantly elevated in winter relative to summer in all muscles for chickadees, but did not vary significantly with season for sparrows or nuthatches, except for sparrow leg muscle. These results suggest that modulation of substrate flux and cellular aerobic capacity in muscle contribute to seasonal metabolic flexibility in some species and tissues, but such changes play varying roles among small passerines resident in cold climates.     

Correlation between immunoreactive vasotocin in optic tectum and seasonal changes in reproductive behaviors of male rough-skinned newts

Previous studies have shown that intracranial administration of the amphibian neuropeptide arginine vasotocin (AVT) to male rough-skinned newts (Taricha granulosa) can stimulate masculine sexual behaviors. The present study was conducted to determine whether concentrations of endogenous AVT in specific brain areas are correlated with seasonal changes in sexual behavior. Immunoreactive (ir) AVT was measured in the dorsal preoptic area and in the optic tectum throughout the course of the reproductive cycle. In the optic tectum, irAVT levels were low throughout the summer, fall, and winter, but rose over fivefold in the spring when sexual behaviors are most prevalent in male newts. In contrast, irAVT levels in the dorsal preoptic area were high in the summer, but declined in the fall and fluctuated widely during the winter and spring. Thus, there are site-specific changes in irAVT concentrations in the brain of male newts during the seasonal reproductive cycle. The finding that irAVT concentrations in the optic tectum are seasonally correlated with newt sexual behaviors provides further evidence that AVT in this brain area may be important in the expression of sexual behavior.     

Turtles (<Emphasis Type="Italic">Chelodina longicollis</Emphasis>) regulate muscle metabolic enzyme activity in response to seasonal variation in body temperature

Fluctuations in the thermal environment may elicit different responses in animals: migration to climatically different areas, regulation of body temperature, modification of biochemical reaction rates, or assuming a state of dormancy. Many ectothermic reptiles are active over a range of body temperatures that vary seasonally. Here we test the hypothesis that metabolic enzyme activity acclimatises seasonally in freshwater turtles (Chelodina longicollis) in addition to, or instead of, behavioural regulation of body temperatures. We measured body temperatures in free-ranging turtles (n=3) by radiotelemetry, and we assayed phosphofructokinase (PFK), lactate dehydrogenase (LDH), citrate synthase (CS) and cytochrome c oxidase (CCO) activities in early autumn (March, n=10 turtles), late autumn (May, n=7) and mid-winter (July, n=7) over a range of assay temperatures (10 °C, 15 °C, 20 °C, 25 °C). Body temperatures were either not different from, or higher than expected from a theoretical null-distribution of a randomly moving animal. Field body temperatures at any season were lower, however, than expected from animals that maximised their sun exposure. Turtles maintained constant PFK, LDH and CCO activities in different months, despite body temperature differences of nearly 13.0 °C between March (average daily body temperature=24.4 °C) and July (average=11.4 °C). CS activity did not vary between March and May (average daily body temperature=20.2 °C), but it decreased in July. Thus C. longicollis use a combination of behavioural thermoregulation and biochemical acclimatisation in response to seasonally changing thermal conditions. Ectothermic reptiles were often thought not to acclimatise biochemically, and our results show that behavioural attainment of a preferred body temperature is not mandatory for activity or physiological performance in turtles.Abbreviations CS citrate synthase - CCO cytochrome c oxidase - LDH lactate dehydrogenase - PFK phosphofructokinase Communicated by I.D. Hume     

Seasonal temperature compensation in the horse mussel, Modiolus modiolus: metabolic enzymes, oxidative stress and heat shock proteins

Seasonal collections of the subtidal horse mussel, Modiolus modiolus, from a depth of 10 m were made at the Isles of Shoals, New Hampshire to assess changes in overall energetic demand, measured as respiration, the maximal activities of rate-limiting enzymes of intermediate metabolism, level of oxidative stress, and the expression of heat shock proteins (HSP). Weighted respiration rates of mussels from winter collections were significantly lower than summer rates but decreased by less than 20%. Specific activities of several rate-limiting enzymes were measured in mussels from the summer and winter collections at the temperature of collection and the reciprocal seasonal temperature (15 and 5 degrees C). Comparisons of these enzyme activities and the protein concentrations of hexokinase and citrate synthase show that a quantitative strategy is used to acclimatize to winter temperatures by these rate-limiting enzymes of intermediate metabolism. The activities and protein concentrations of the antioxidant enzyme, Cu/Zn superoxide dismutase (SOD) is seasonally indistinguishable while the concentration of HSP 70 was greater in winter than in summer samples. These results show that mussels seasonally compensate for decreases in temperature by increasing the concentration of rate-limiting metabolic enzymes while maintaining the same level of antioxidant protection in summer and winter consistent with high aerobic metabolism in both winter and summer. Lastly, the significantly greater concentrations of HSP70 in winter samples suggests that protein chaperone functions must be maintained while other seasonal adjustments to cold temperatures are occurring.     

Strong seasonality of Bonamia sp. infection and induced Crassostrea ariakensis mortality in Bogue and Masonboro Sounds, North Carolina, USA

Asian oyster Crassostrea ariakensis is being considered for introduction to Atlantic coastal waters of the USA. Successful aquaculture of this species will depend partly on mitigating impacts by Bonamia sp., a parasite that has caused high C. ariakensis mortality south of Virginia. To better understand the biology of this parasite and identify strategies for management, we evaluated its seasonal pattern of infection in C. ariakensis at two North Carolina, USA, locations in 2005. Small (<50 mm) triploid C. ariakensis were deployed to upwellers on Bogue Sound in late spring (May), summer (July), early fall (September), late fall (November), and early winter (December) 2005; and two field sites on Masonboro Sound in September 2005. Oyster growth and mortality were evaluated biweekly at Bogue Sound, and weekly at Masonboro, with Bonamia sp. prevalence evaluated using parasite-specific PCR. We used histology to confirm infections in PCR-positive oysters. Bonamia sp. appeared in the late spring Bogue Sound deployment when temperatures approached 25 degrees C, six weeks post-deployment. Summer- and early fall-deployed oysters displayed Bonamia sp. infections after 3-4 weeks. Bonamia sp. prevalences were 75% in Bogue Sound, and 60% in Masonboro. While oyster mortality reached 100% in late spring and summer deployments, early fall deployments showed reduced (17-82%) mortality. Late fall and early winter deployments, made at temperatures <20 degrees C, developed no Bonamia sp. infections at all. Seasonal Bonamia sp. cycling, therefore, is influenced greatly by temperature. Avoiding peak seasonal Bonamia sp. activity will be essential for culturing C. ariakensis in Bonamia sp.-enzootic waters.     

Temperature dependent characteristics of intestinal glycyl-L-leucine dipeptidase in boreal zone fish

Three kinds of boreal zone fish were investigated for gastrointestinal glycyl-L-leucine (GL) dipeptide cleaving activity as a function of feeding stage and seasonal changes. The enzyme activity tested in the perch (Perca fluviatilis L.) intestine increased steadily during digestion and rapidly disappeared after completion. The temperature characteristics and the seasonal changes in dipeptide cleaving activity in pike perch (Stizostedion lucioperca L.) and bream (Abramis brama L.) were studied. In summer, the maximal activities in the pike perch and the bream were found at temperatures of 40 and 30 degrees C, respectively. In winter, the temperature of maximal activity in pike perch fell to only 30 degrees C, whereas no changes were observed in bream. The activation energies in bream and pike perch were several times lower in winter than in summer. Seasonal changes in the dipeptide cleaving activity at low temperature relative to that at the temperature of maximal activity were found. At high temperatures, the stability of the enzyme decreases in winter and increases in summer, but in the presence of a substrate the thermal stability of the enzyme increases both in winter and in summer. In our experiments, we found that in these fish, GL dipeptidase was unstable at 0 and -10 degrees C.     

Enzyme activity in the aestivating Green-striped burrowing frog (Cyclorana alboguttata)

Green-striped burrowing frogs (Cyclorana alboguttata) can depress their resting metabolism by more than 80% during aestivation. Previous studies have shown that this species is able to withstand long periods of immobilisation during aestivation while apparently maintaining whole muscle mass and contractile performance. The aim of this study was to determine the effect of prolonged aestivation on the levels of metabolic enzymes (CCO, LDH and CS) in functionally distinct skeletal muscles (cruralis, gastrocnemius, sartorius, iliofibularis and rectus abdominus) and liver of C. alboguttata. CS activity was significantly reduced in all tissues except for the cruralis, gastrocnemius and the liver. LDH activity was significantly reduced in the sartorius and rectus abdominus, but remained at control (active) levels in the other tissues. CCO activity was significantly reduced in the gastrocnemius and rectus abdominus, and unchanged in the remaining tissues. Muscle protein was significantly reduced in the sartorius and iliofibularis during aestivation, and unchanged in the remaining muscles. The results suggest that the energy pathways involved in the production and consumption of ATP are remodelled during prolonged aestivation but selective. Remodelling and subsequent down-regulation of metabolic activity seem to target the smaller non-jumping muscles, while the jumping muscles retain enzyme activities at control levels during aestivation. These results suggest a mechanism by which aestivating C. alboguttata are able to maintain metabolic depression while ensuring that the functional capacity of critical muscles is not compromised upon emergence from aestivation.     

Thermosensitivity of the lobster, Homarus americanus, as determined by cardiac assay

It is generally accepted that crustaceans detect, and respond to, changes in water temperature, yet few studies have directly addressed their thermosensitivity. In this investigation a cardiac assay was used as an indicator that lobsters (Homarus americanus) sensed a change in temperature. The typical cardiac response of lobsters to a 1-min application of a thermal stimulus, either warmer (n = 19) or colder (n = 17) than the holding temperature of 15 degrees C, consisted of a short bradycardia (39.5 +/- 8.0 s) followed by a prolonged tachycardia (188.2 +/- 10.7 s). Lobsters exposed to a range of rates of temperature change (0.7, 1.4, 2.6, 5.0 degrees C/min) responded in a dose-dependent manner, with fewer lobsters responding at slower rates of temperature change. The location of temperature receptors could not be determined, but lesioning of the cardioregulatory nerves eliminated the cardiac response. Although the absolute detection threshold is not known, it is conservatively estimated that lobsters can detect temperature changes of greater than 1 degree C, and probably as small as 0.15 degrees C. A comparison of winter and summer lobsters, both held at 15 degrees C for more than 4 weeks, revealed that although their responses to temperature changes were similar, winter lobsters (n = 18) had a significantly lower baseline heart rate (34.8 +/- 4.4 bpm) and a shorter duration cardiac response (174 s) than summer lobsters (n = 18; 49.9 +/- 5.0 bpm, and 320 s respectively). This suggests that some temperature-independent seasonal modulation of cardiac activity may be occurring.     

Metabolic disturbances in fish exposed to sodium pentachlorophenate (NaPCP) and 3,3',4,4',5-pentachlorobiphenyl (PCB126), individually or combined

The Swan River Estuary is the recipient of multiple urban and agricultural contaminants which have the potential to induce liver detoxication enzymes as well as altering the metabolism of aquatic organisms. To test if altered liver metabolism would influence liver detoxication capacities, pink snapper (Pagrus auratus) were i.p. injected with peanut oil (controls), or pentachlorobiphenyl #126 (PCB126), with sodium pentachlorophenate (NaPCP), or PCB126+NaPCP. Relative to controls, ethoxyresorufin-O-deethylase (EROD) activity was induced in the PCB126 and PCB126+NaPCP fish, but not in the NaPCP group. In the liver, cytochrome c oxidase (CCO) activity was enhanced by the treatments while citrate synthase (CS) activity remained unchanged and lactate dehydrogenase (LDH) activity was increased in the NaPCP treatment only. The results suggest that liver CCO activity may be a suitable biomarker of effect following exposure to PCBs or phenolic compounds. In the white muscle, only the PCB126+NaPCP treatment enhanced CCO activity, with all other enzymatic activities remaining unchanged. It appears that the resilience to metabolic perturbations is greater for white muscle than for liver. Low serum sorbitol dehydrogenase (sSDH) activity and histopathology of the liver indicated no significant alteration of cellular structure, albeit the lipid droplet size was increased in the PCB126 and in the PCB126+NaPCP treatments. It is concluded that the hepatic metabolic changes correspond to histopathological observations, but an altered metabolic capacity do not influence the metabolism of xenobiotics by liver enzymes, as measured by EROD activity.     

Thermal influence on metabolic rates and a bioenergetic budget for Notophthalmus viridescens from southwestern Massachusetts

Notophthalmus viridescens has been reported to overwinter on land in southwestern Massachusetts, whereas these newts hibernate in water in southwestern Ohio. Aquatic and terrestrial metabolic rates of newts from Massachusetts were measured at different exercise speeds and acclimation temperatures in order to better understand their seasonal energetic budgets. Oxygen uptake at 25°C increased with increased swimming and walking speeds and reached a plateau at speeds of 60 and 90 cm/min, whereas at 5°C, oxygen consumption linearly increased with swimming speeds. Aerobic transport costs of the newts thus decreased with increased locomotor speeds at 25°C but remained unchanged when the newts were exercised in water at 5°C. Anaerobic metabolic rates of the newts on land were little affected by acclimation temperature but also increased linearly with walking speeds at both 5°C and 25°C. Anaerobiosis contributed most of the energy for the locomotion of the newts. These newts stored an average of 12 mg lipd/g body mass, which could apparently support their survival at 5°C for 46 days without food on land but only for 18 days in water. These calculations, based on measured metabolic rates and energy reserves, support field observations of red-spotted newts hibernating on land in Massachusetts.     

Seasonal acclimation of preferred body temperatures improves the opportunity for thermoregulation in newts

Seasonal acclimation and thermoregulation represent major components of complex thermal strategies by which ectotherms cope with the heterogeneity of their thermal environment. Some ectotherms possess the acclimatory capacity to shift seasonally their thermoregulatory behavior, but the frequent use of constant acclimation temperatures during experiments and the lack of information about thermal heterogeneity in the field obscures the ecological relevance of this plastic response. We examined the experimentally induced seasonal acclimation of preferred body temperatures (T(p)) in alpine newts Ichthyosaura (formerly Triturus) alpestris subjected to a gradual increase in acclimation temperature from 5°C during the winter to a constant 15°C or diel fluctuations between 10° and 20°C during the spring/summer. Both the mean and range of T(p) followed the increase in mean acclimation temperature without the influence of diel temperature fluctuations. The direction and magnitude of this acclimatory capacity has the potential to increase the time window available for thermoregulation. Although thermoregulation and thermal acclimation are often considered as separate but coadapted adjustments to thermal heterogeneity, their combined response is employed by newts to tackle seasonal variation in a thermoregulatory-challenging aquatic environment.     

Seasonal changes in thermal responses of urban residents to cold exposure

To determine whether urban circumpolar residents show seasonal acclimatisation to cold, thermoregulatory responses and thermal perception during cold exposure were examined in young men during January-March (n=7) and August-September (n=8). Subjects were exposed for 24 h to 22 and to 10 degrees C. Rectal (T(rect)) and skin temperatures were measured throughout the exposure. Oxygen consumption (VO(2)), finger skin blood flow (Q(f)), shivering and cold (CDT) and warm detection thresholds (WDT) were assessed four times during the exposure. Ratings of thermal sensations, comfort and tolerance were recorded using subjective judgement scales at 1-h intervals. During winter, subjects had a significantly higher mean skin temperature at both 22 and 10 degrees C compared with summer. However, skin temperatures decreased more at 10 degrees C in winter and remained higher only in the trunk. Finger skin temperature was higher at 22 degrees C, but lower at 10 degrees C in the winter suggesting an enhanced cold-induced vasoconstriction. Similarly, Q(f) decreased more in winter. The cold detection threshold of the hand was shifted to a lower level in the cold, and more substantially in the winter, which was related to lower skin temperatures in winter. Thermal sensations showed only slight seasonal variation. The observed seasonal differences in thermal responses suggest increased preservation of heat especially in the peripheral areas in winter. Blunted vasomotor and skin temperature responses, which are typical for habituation to cold, were not observed in winter. Instead, the responses in winter resemble aggravated reactions of non-cold acclimatised subjects.     

Metabolic enzyme activities in black bream (Acanthopagrus butcheri) from the Swan-Canning Estuary, Western Australia

The Swan-Canning estuary, in southwestern Australia, is subject to frequent algal blooms and associated periods of hypoxia due to high levels of nutrients in stormwater runoff and sewage spills. Fish in which cellular respiration is impaired due to chronic exposure to non-nutrient pollutants in the water will have a reduced ability to survive these periods of high stress. In order to investigate if metabolic respiration in black bream (Acanthopagrus butcheri) was altered, fish were collected from five sites in the Swan-Canning estuary in summer 2001, summer 2002 and winter 2002. Aerobic and anaerobic capacities were estimated by measuring the enzymes cytochrome C oxidase (CCO) and lactate dehydrogenase (LDH). Neither seasonal or annual trends, nor upstream or downstream gradients were observed in either biomarker. The fish collected from the Barrack Street site, which is close to the Perth Central Business District, were heavily challenged in their aerobic capacity in the summer months compared to the other sites. In addition, the fish at Barrack Street displayed an altered anaerobic capacity. It is likely that the impaired metabolic capacity of the fish at Barrack Street reduces the fishes' ability to survive the frequent algal blooms within the estuary.     

Mitochondrial function in seasonal acclimatization versus latitudinal adaptation to cold in the lugworm Arenicola marina (L.)

Previous studies in marine ectotherms from a latitudinal cline have led to the hypothesis that eurythermal adaptation to low mean annual temperatures is energetically costly. To obtain more information on the trade-offs and with that the constraints of thermal adaptation, mitochondrial functions were studied in subpolar lugworms (Arenicola marina L.) adapted to summer cold at the White Sea and were compared with those in boreal specimens from the North Sea, either acclimatized to summer temperatures or to winter cold. During summer, a comparison of mitochondria from subpolar and boreal worms revealed higher succinate oxidation rates and reduced Arrhenius activation energies (Ea) in state 3 respiration at low temperatures, as well as higher proton leakage rates in subpolar lugworms. These differences reflect a higher aerobic capacity in subpolar worms, which is required to maintain motor activity at low but variable environmental temperatures--however, at the expense of an elevated metabolic rate. The lower activity of citrate synthase (CS) found in subpolar worms may indicate a shift in metabolic control within mitochondria. In contrast, acclimatization of boreal lugworms to winter conditions elicited elevated mitochondrial CS activities in parallel with enhanced mitochondrial respiration rates. With falling acclimation temperatures, the significant Arrhenius break temperature in state 3 respiration (11 degrees C) became insignificant (5 degrees C) or even disappeared (0 degrees C) at lower levels of Arrhenius activation energies in the cold, similar to a phenomenon known from hibernating vertebrates. The efficiency of aerobic energy production in winter mitochondria rose as proton leakage in relation to state 3 decreased with cold acclimation, indicated by higher respiratory control ratio values and increased adenosine diphosphate/oxygen (ADP/O) ratios. These transitions indicate reduced metabolic flexibility, possibly paralleled by a loss in aerobic scope and metabolic depression during winter cold. Accordingly, these patterns contrast those found in summer-active, cold-adapted eurytherms at high latitudes.     

Total lactate dehydrogenase activity of tail muscle is not cold-adapted in nocturnal lizards from cool-temperate habitats

The dependence of metabolic processes on temperature constrains the behavior, physiology and ecology of many ectothermic animals. The evolution of nocturnality in lizards, especially in temperate regions, requires adaptations for activity at low temperatures when optimal body temperatures are unlikely to be obtained. We examined whether nocturnal lizards have cold-adapted lactate dehydrogenase (LDH). LDH was chosen as a representative metabolic enzyme. We measured LDH activity of tail muscle in six lizard species (n = 123: three nocturnal, two diurnal and one crepuscular) between 5 and 35 °C and found no differences in LDH-specific activity or thermal sensitivity among the species. Similarly, the specific activity and thermal sensitivity of LDH were similar between skinks and geckos. Similar enzyme activities among nocturnal and diurnal lizards indicate that there is no selection of temperature specific LDH enzyme activity at any temperature. As many nocturnal lizards actively thermoregulate during the day, LDH may be adapted for a broad range of temperatures rather than adapted specifically for the low temperatures encountered when the animals are active. The total activity of LDH in tropical and temperate lizards is not cold-adapted. More data are required on biochemical adaptations and whole animal thermal preferences before trends can be established.     

Seasonal and daily changes in the capacity for nonshivering thermogenesis in the golden hamsters housed under semi-natural conditions

Nonshivering thermogenesis (NST) is a main source of heat for many small mammals. It undergoes seasonal changes, being the highest in winter and the lowest in summer. Such acclimatization can ensure winter survival for species living in moderate or cold climates. Nevertheless, not only seasonal, but also daily changes in the capacity for NST seem to be of great importance. In this study, the effects of season and time of day on the temperature of brown adipose tissue (T(BAT)), preferred ambient temperature (PT(a)) and activity after noradrenaline (NA) injections in golden hamsters (Mesocricetus auratus) housed under semi-natural conditions were investigated. Animals were kept in outdoor enclosures and experienced natural changes in both, photoperiod and ambient temperature (T(a)). NA-induced hyperthermia was the largest during autumn (mean increase in T(BAT) by 0.74+/-0.04 degrees C), while during summer increase in T(BAT) was similar to that recorded in control (saline-injected) animals (0.16+/-0.05 degrees C and 0.24+/-0.04 degrees C, respectively). In spring hyperthermia was intermediary (0.57+/-0.05 degrees C). Daily variations in the response to NA depended on the season. In summer, the largest increase in T(BAT) (0.45+/-0.1 degrees C) was recorded during the first part of the day, while in autumn-in the middle of the day and night (1.1+/-0.1 degrees C and 0.9+/-0.1 degrees C, respectively). In spring, all NA injections induced large increase in T(BAT) except for the injection in the middle of the night. The largest decrease in PT(a) after NA administration was recorded in autumn (mean decrease by 1.5+/-0.3 degrees C). Both, seasonal and daily changes in the capacity for NST reflect different demands for heat dependently on the time of the year and time of the day. It can be concluded that although long history of breeding in captivity, golden hamsters preserved ability to survive in natural environment.