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Oxidative stress is thought to be one of the main causes of ageing as it progressively damages cell components throughout life, eventually causing cellular failure and apoptosis. In many organisms, telomeres shorten throughout life under the effect of, amongst other factors, oxidative stress, and are therefore commonly used as marker of biological ageing. However, hibernators, which are regularly exposed to acute oxidative stress when rewarming from torpor, are unexpectedly long-lived. In this review, we explore the causes of oxidative stress associated with hibernation and its impact on telomere dynamics in different taxa, focussing on hibernating rodents. We then speculate on the adaptive mechanisms of hibernators to compensate for the effects of oxidative stress, which may explain their increased longevity. Because winter hibernation appears to be associated with high oxidative stress, hibernators, particularly rodents, may periodically invest in repair mechanisms and antioxidant defences, resulting in seasonal variations in telomere lengths. This research shows how species with a slow life-history strategy deal with large changes in oxidative stress, unifying evolutionary and physiological theories of ageing. Because of the marked seasonal variation in telomere length, we also draw attention when using telomeres as markers for biological aging in seasonal heterotherms and possibly in other highly seasonal species. • Hibernation tends to cause seasonal telomere shortening due to oxidative stress. • Hibernating species seem to invest in repair mechanisms during the summer. • Hibernating species express a seasonal pattern of telomere length dynamics. • A cold-induced protein could play a role in telomerase regulation in hibernators. [ABSTRACT FROM AUTHOR]

Extracellular Ca2+ plays a pivotal role in the regulation of cardiac contractility under normal and extreme conditions. Here, by using nickel chloride (NiCl 2), a non-specific blocker of extracellular Ca2+ influx, we studied the input of extracellular Ca2+ on the regulation of papillary muscle (PM) contractility under normal and hypothermic conditions in ground squirrels (GS), and rats. By measuring isometric force of contraction, we studied how NiCl 2 affects force-frequency relationship and the rest effect in PM of these species at 30 °C and 10 °C. We found that at 30 °C 1.5 mM NiCl 2 significantly reduced force of contraction across entire frequency range in active GS and rats, whereas in hibernating GS force of contraction was reduced at low and high frequency range. Additionally, NiCl 2 evoked spontaneous contractility in rats but not GS PM. The rest effect was significantly reduced by NiCl 2 for active GS and rats but not hibernating GS. At 10 °C, NiCl 2 fully reduced contractility in active GS and, to a lesser extent, in rats, whereas in hibernating GS it was significant only at 0.3 Hz. The rest effect was significantly reduced by NiCl 2 in both active and hibernating GS, whereas it was unmasked in rats that had high contractility under hypothermic conditions in control. Our results show a significant contribution of extracellular Ca2+ to myocardial contractility in GS not only in active but also in hibernating states, especially under hypothermic conditions, whereas limitation of extracellular Ca2+ influx in rats under hypothermia can play protective role for myocardial contractility. • NiCl 2 fully blocks PM contractility in active GS and rats at 30 °C. • NiCl 2 partially blocks PM contractility in hibernating GS at 30 °C. • NiCl 2 blocks PM contractility in both active and hibernating GS, and rats at 10 °C. • NiCl 2 disrupts PM contractility at 30 °C and partially restores it at 10 °C in rats. [ABSTRACT FROM AUTHOR]

Hibernators survive challenging winters by entering torpor, which lowers body temperature (T b) to ∼5 °C for 12–14 days, followed by spontaneous arousals where T b increases to ∼37 °C for 10–12 h before entering another torpor bout. This T b cycle is accompanied by significant fluctuations in metabolic rate. Little is known about the role of the liver in lipid metabolism during hibernation. In this study we measured the effect of ambient temperature on liver volume and lipid content in 13-lined ground squirrels (Ictidomys tridecemlineatus). We housed animals at thermoneutral (25 °C) or cold (5 °C) ambient temperatures, with the same photoperiod (12 h light:12 h dark) for an entire year. We determined volume and water-fat ratio of the liver using magnetic resonance imaging (MRI). Ambient temperature significantly affected both liver volume and fat content. From October to August squirrels housed at 25 °C had 25% smaller livers compared to the squirrels housed at 5 °C, but their average lipid content (13.3%) was 37% higher. Because the squirrels housed at 25 °C appeared to continue feeding throughout the winter but did not enter extended torpor, more carbohydrates may have been diverted to lipid stores. By contrast, animals housed at 5 °C did not appear to feed, and carbohydrates would likely be preferentially stored in the liver as glycogen to supply glucose for brain metabolism. These results suggest that the fat burden caused by hibernators preparing for winter can lead to symptoms of metabolic syndrome, but that these symptoms are reversible in the spring. • Ground squirrels housed at 25 °C do not enter torpor and eat throughout the winter. • Liver volume increased 23.3% in the cold-housed (5 °C) animals after hibernation. • Time and temperature significantly affect lipid content within the liver. [ABSTRACT FROM AUTHOR]

Hibernating bats optimise the duration of torpor bouts and arousals in relation to hibernaculum microclimatic conditions and fat reserves. Clustering has significant physiological and ecological benefits, promoting successful hibernation of individuals. Such aggregations may help maintain optimal temperatures, allowing better energy utilisation than in solitarily bats. However, aroused bats in a cluster could conceivably disturb those still hibernating, starting an energy-demanding arousal process. Our study was conducted over two winters in two different hibernacula (cave and mine) in the Czech Republic, where Greater mouse-eared bats (Myotis myotis) have previously been diagnosed with white-nose syndrome. In 118 arousal episodes we recorded 193 individual arousals in which a warming phase was observed, 135 (69.9%) being cold arousals, where bats ceased increasing their body temperatures at ≤ 10 °C. The remaining arousals were standard normothermic arousals, where body (fur) surface temperatures reached > 20 °C. Cold arousals occurred during the mid- and late hibernation periods, suggesting they were a response to disturbance by a neighbour in the same cluster. Arousal cascades, where bats aroused in series, were rare (12.7%) and reached a maximum in mid-January. Our data suggest that Myotis bats prolong their torpor bouts using numerous cold arousals but few arousal cascades. Upon arrival of a bat, the clustered bats show tolerance to disturbing by conspecifics. • Normothermic and cold arousals, where bats stopped their body temperatures at ≤ 10 °C, were found. • Cold arousals were a response to disturbance by a neighbour in the same cluster. • Arousal cascades, where bats aroused in series, were rare and reached a maximum in mid-January. [ABSTRACT FROM AUTHOR]

Abstract Many species use stored energy to hibernate through periods of resource limitation. Hibernation, a physiological state characterized by depressed metabolism and body temperature, is critical to winter survival and reproduction, and therefore has been extensively quantified and modeled. Hibernation consists of alternating phases of extended periods of torpor (low body temperature, low metabolic rate), and energetically costly periodic arousals to normal body temperature. Arousals consist of multiple phases: warming, euthermia, and cooling. Warming and euthermic costs are regularly included in energetic models, but although cooling to torpid body temperature is an important phase of the torpor-arousal cycle, it is often overlooked in energetic models. When included, cooling cost is assumed to be 67% of warming cost, an assumption originally derived from a single study that measured cooling cost in ground squirrels. Since this study, the same proportional value has been assumed across a variety of hibernating species. However, no additional values have been derived. We derived a model of cooling cost from first principles and validated the model with empirical energetic measurements. We compared the assumed 67% proportional cooling cost with our model-predicted cooling cost for 53 hibernating mammals. Our results indicate that using 67% of warming cost only adequately represents cooling cost in ground squirrel-sized mammals. In smaller species, this value overestimates cooling cost and in larger species, the value underestimates cooling cost. Our model allows for the generalization of energetic costs for multiple species using species-specific physiological and morphometric parameters, and for predictions over variable environmental conditions. Highlights • Hibernation models estimate the cost of warming, euthermia, cooling, torpor. • Previous models have ignored or used an assumed proportion to estimate cooling cost. • Cooling cost was derived to incorporate body size, conductance, and temperature. • Previous assumptions overestimate or underestimate costs based on body size. • Variation in cooling rate is explained by body mass and thermal conductance. [ABSTRACT FROM AUTHOR]

Small mammals hibernate to deal with environmental conditions associated with the winter season. Numerous physiological changes occur during a typical torpor-arousal cycle including variations in heart rate and blood flow. Such cycle possesses characteristics of ischemia-reperfusion cycles that can lead to oxidative stress in non-hibernating models. Interestingly, hibernators can cope with these conditions and the complete molecular picture underlying this adaptation is not fully understood. Non-coding RNAs, including microRNAs (miRNAs) and long non-coding RNAs (lncRNAs), can impact expression and activity of various targets and have been associated with oxidative stress response. This work was aimed at assessing expression of oxidative stress-associated non-coding RNAs and their targets during hibernation. Measurement of miRNAs miR-93, miR-141, miR-144 and miR-200a, lncRNAs Mhrt and ODRUL, as well as of several targets associated with the Nrf2 signaling cascade including Keap1 was conducted using qRT-PCR in hibernating hearts of the thirteen-lined ground squirrel, Ictidomys tridecemlineatus . Elevated Nrf2 levels and reduced miR-200a levels were notably observed in hibernating versus euthermic samples. Functional analysis of targets predicted to be regulated by the investigated miRNAs was performed and revealed transcriptional regulation and phosphorylation as relevant processes. These results highlight a potential interplay between non-coding RNAs and targets associated with oxidative stress response during hibernation and further strengthen the underlying importance of non-coding RNAs in cold torpor. [ABSTRACT FROM AUTHOR]

The thirteen-lined ground squirrel ( Ictidomys tridecemlineatus ) is a well-known model for studying hibernation. While in a torpid state, these animals globally suppress energy expensive processes, while supporting specialized pathways necessary for survival. Lysine acetyltransferases (KATs) play a crucial role in modulating the expression and activity of a wide-variety of cellular pathways and processes, and therefore, may play a role during hibernation when the cell is shifting to an energy conservative, cytoprotective state. Here we measured protein levels of four KATs (CBP, PCAF, GCN5L2, HAT1), total histone acetyltransferase (HAT) activity, and the levels of acetylation of histone H3 lysine 9 (H3K9ac), in multiple tissues across the torpor-arousal cycle. Our results show a tissue-specific response of KATs, particularly in the adipose tissues where specific KATs (PCAF and GCN5L2), HAT activity, and H3K9ac increased in the metabolically active BAT while HAT1, HAT activity and H3K9ac decreased in WAT. Liver showed significant increases in the KAT PCAF whereas skeletal muscle had decreased CBP and GCN5L2. Both liver and skeletal muscle showed no change in HAT activity and H3K9me3 increased in muscle during torpor. Together, these results suggest KATs may play specialized roles in the different tissues of the ground squirrel to contribute to the hibernator phenotype. [ABSTRACT FROM AUTHOR]

Ectotherms have various means of dealing with low environmental temperatures, but relatively few species have been rigorously investigated. Consequently, we have little information to predict how ectotherm populations might respond to global temperature changes. Tortoises from temperate and subtropical regions often overcome periodically cool conditions by hibernation, but speckled dwarf tortoises ( Chersobius signatus ) need to remain active to exploit ephemeral resources in their arid winter-rainfall habitat. This study investigated how dwarf tortoises cope with low temperatures in winter and spring, by measuring thermal habitat quality and thermoregulation based on differently-sized operative temperature models in sun, shade, and in deep crevices. Investigations continued in summer and autumn to obtain a year-round picture of thermoregulatory challenges. Although large models (i.e., larger than dwarf tortoises) were expected to have lower operative temperatures than smaller models, due to the former's larger thermal inertia, all model sizes had similar temperatures. Hence, the species’ small body size does not appear constrained by obtainable body temperatures in cool seasons. Nevertheless, low operative temperatures in winter posed a challenge for the tortoises, which reached their field-preferred body temperature for an average of only 0.8−0.9 h per day. Moreover, a low thermoregulation effectiveness suggested that tortoises traded-off physiological benefits of favourable body temperatures against predation risk. Spring and autumn provided higher temperatures, but summer caused the greatest thermoregulatory challenge. Although summer body temperatures were closer to field-preferred body temperature than in any other season, tortoises required rock crevices to avoid overheating. The small size of dwarf tortoises might help them utilise crevices. In summer, maximum operative temperatures in crevices were similar to field-preferred body temperature, indicating that an increase in environmental temperatures might be detrimental to dwarf tortoises. In light of projected temperature rises, future studies should assess if dwarf tortoises can cope with higher environmental temperatures in summer. [ABSTRACT FROM AUTHOR]

Evolution of heterothermy in environments with variable temperatures has allowed bats to survive food scarcity during seasonal climatic extremes by using torpor as a hibernation strategy. The controlled reduction of body temperature and metabolism through complex behavioural and physiological adaptations at organismal, organ, cellular and molecular levels includes the ability of tissues and cells to adapt to temperature alterations. Based on the prediction that cells of different tissues cultured in vitro would differ in their ability to withstand freezing and thawing of the medium, we determined the survival rate of bat-derived cells following exposure to −20 °C for 24 h in media with no cryoprotective agents or medium supplemented by glucose in concentration range 0–3333 mM. Cell survival rates were determined in relation to availability of glucose in the medium, organ origin, cell concentration and bat species. In general, increased glucose helped cells survive at sub-zero temperatures, though concentrations up to 80-fold higher than those found in chiropterans were needed. However, cells in glucose-free phosphate buffered saline also survived, suggesting that other mechanisms may be contributing to cell survival at low temperatures. Highest in vitro viability was observed in nervus olfactorius -derived cell cultures, with high survival rates and rapid re-growth under optimal conditions after exposure to −20 °C. Kidney cells from different bat species showed comparable overall survival rate patterns, though smaller chiropteran species appeared to utilise lower glucose levels as a cryoprotectant than larger species. Our in vitro data provide evidence that cells of heterothermic bats can survive sub-zero temperatures and that higher glucose levels in important tissues significantly improve hibernation survival at extremely low temperatures. • Bat cells in vitro use glucose in high concentration as an extracellular cryoprotectant. • Bat cells survive −20 °C in phosphate buffered saline without any extra added cryoprotectants. • Bat cells proliferate after freezing-thawing of the medium within a few days under optimal conditions. • Bat cells differ in their ability to withstand low temperatures depending on the tissue of origin and the species. [ABSTRACT FROM AUTHOR]

Pyruvate dehydrogenase (PDH) is a vital regulatory enzyme that catalyzes the conversion of pyruvate into acetyl-CoA and connects anaerobic glycolysis to aerobic TCA cycle. Post-translational inhibition of PDH activity via three serine phosphorylation sites (pS232, pS293, and pS300) regulate the metabolic flux through the TCA cycle, decrease glucose utilization, and facilitate lipid metabolism during times of nutrient deprivation. As metabolic readjustment is necessary to survive hibernation, the purpose of this study was to explore the post-translational regulation of pyruvate dehydrogenase and the expression levels of four mitochondrial serine/threonine kinases (PDHKs), during torpor-arousal cycles in liver, heart, and skeletal muscle of 13-lined ground squirrels. A combination of Luminex multiplex technology and western immunoblotting were used to measure the protein expression levels of total PDH, three phosphorylation sites, S232, 293, 300, and the expression levels of the corresponding PDH kinases (PDHK1-4) during euthermic control, entrance, late torpor, and interbout arousal. Liver and heart showed strong inhibitory PDH regulation, indicating a possible decrease in glucose utilization and a possible preference for β-oxidation of fatty acids during periods of low temperature and starvation. On the contrary, skeletal muscle showed limited PDH regulation via phosphorylation, possibly due to alternate controls. Phosphorylation of PDH may play an important role in regulating aerobic and anaerobic metabolic responses during hibernation in the 13-lined ground squirrel. [ABSTRACT FROM AUTHOR]

Temperature-dependent development rate, percent diapause induction (hibernation at low temperature and aestivation at high temperature), and survival of diapausing larvae of Chilo partellus (Swinhoe, 1885) were examined on 13 constant temperatures ranging from 8 to 40 °C. Development of hibernating and aestivating larvae occurred from 10 to 25 °C and 27–38 °C, respectively. However, no development occurred at 8 °C and 40 °C. To determine actual thermal conditions that affect development and trigger both kind of diapause (hibernation and aestivation), various thermal parameters were estimated by fitting the development rate data to two linear (Ordinary equation and Ikemoto & Takai) models and thirteen non-linear models. The lower thermal thresholds ( T min ) for development of diapausing larvae of C. partellus were calculated as 9.60 °C and 10.29 °C using the ordinary linear model and Ikemoto & Takai model, respectively. Similarly, the thermal constants ( K ) estimated using the ordinary linear model was 333.33 degree-days and that estimated with Ikemoto & Takai model was 338.92 degree-days. Among the non-linear models, Lactin-2 followed by Lactin-1 were found to be the best as these models estimated the critical temperatures ( T min , T max and T opt ) similar to those of observed values. Conclusively, the Ikemoto & Takai linear model and Lactin-2 followed by Lactin-1 non-linear models are useful and efficient for describing temperature-dependent development and estimating the temperature thresholds of diapausing larvae of C. partellus . Our findings provided fundamental information for estimation of thermal requirement and temperature based development models for diapausing larvae of C. partellus . This information will be highly useful for predicting the occurrence, seasonal emergence, number of generations and population dynamics of C. partellus . [ABSTRACT FROM AUTHOR]

Because body temperature is tightly coupled to physiological function, hibernating animals entering deep torpor are typically immobile. We analysed thermal behaviour and locomotory activity of hibernating greater mouse-eared bats Myotis myotis and found two types of movement behaviour related to body temperature, i.e. movement at high fur temperature and at low fur temperatures (Tflow; <5 °C). First Tflow movements appeared at the beginning of March and often occurred during long torpor bouts. In most cases, Tflow events represented slow displacements between clusters of bats. In several cases, however, departure or arrivals from and into clusters was also recorded without any elevation in body temperature. Distance travelled, flight duration and speed of locomotion during Tflow events was lower than in high fur temperature events. Such behaviour could allow bats to save energy long-term and prolong torpor bouts. Tflow movement in torpid bats significantly changes our understanding of basic hibernation principles and we strongly recommend further studies on the subject. [ABSTRACT FROM AUTHOR]

Low temperatures and the lack of food during the winter lead the marsh frog Rana ridibunda and the grass frog Rana mascareniensis to hibernate in order to survive. The present study aimed to investigate the cytoarchitecture of brain sub-regions affected by the thermal cycle's fluctuations during the hibernation and activity period, besides the regional distribution quantitative expression of Na(+)/K(+)-ATPase and Pax6 transcriptional factor, the molecular gene expressions of some heat shock proteins, uncoupling protein, and metallothionein. The two frog species were isolated from the field during summer and hibernation time in winter. During hibernation it was notable the destitution of degenerated, pyknotic and vasogenic neurons in different brain areas with high rate nearby the pallium. The immunohistochemical expression of Na+/ K+-ATPase and Pax 6 is decreased during hibernation in different brain sub-regions in the two species suggesting their tendency for energy conservation strategy during hibernation. Additionally, RT-qPCR recorded the up regulation of a number of heat shock protein genes during hibernation with sharing increase between two species for hsp90 besides and the non-significant expression in summer and hibernation periods for hsp47 for both species. Moreover, uncoupling protein (ucp1and ucp2) and metallothionein genes in olfactory bulb were with significant up regulation during the hibernation suggesting that these proteins possibly have a protective effect against reactive oxygen species ROS. So, brain adaptations to low temperature play a crucial role in coordinating stress responses. The present study shed light on the importance of the olfactory bulb in the thermoregulation and sensation of temperature elevations during the hibernation period and defended by the expression of heat shock proteins and uncoupling proteins preventing the cellular damage and proteins misfolding. Neuronal energy production and regeneration activities among amphibians are markedly reduced with decreasing body temperature. [Display omitted] • Seasonal variations have significant impact on the frog brain activity. • Harsh conditions effect frog's hibernation and their ability to regeneration. • Deacreased Na+/ K+-ATPase and Pax 6 during the hibernation periods lowering energy demands. • Olfactory bulb is crucial for the frog behavioral activities regulations. • Olfactory bulb acting firstly against cellular damage during harsh conditions. [ABSTRACT FROM AUTHOR]

Body fat storage before hibernation affects the timing of immergence in Daurian ground squirrels ( Spermophilus dauricus ). Leptin is an adipose signal and plays vital role in energy homeostasis mainly by action in brain. To test the hypothesis that leptin plays a role in facilitating the process of hibernation, squirrels were administrated with recombinant murine leptin (1 μg/day) through intracerebroventricular (ICV) injection for 12 days during fattening. From day 7 to 12, animals were moved into a cold room (5±1 °C) with constant darkness which functioned as hibernaculum. Energy intake, body mass and core body temperature (T b ) were continuously monitored throughout the course of experiment. Resting metabolic rate (RMR) was measured under both warm and cold conditions. At the end of leptin administration, we measured the serum concentration of hormones related to energy regulation, mRNA expression of hypothalamic neuropeptides and uncoupling protein 1 (UCP1) levels in brown adipose tissue (BAT). Our results showed that during leptin administration, the cumulative food intake and increase of body mass were suppressed while T b and RMR were unaltered. The proportion of torpid squirrels was not different between two groups. At the end of leptin administration, the expressions of hypothalamic neuropeptide Y and agouti gene-related protein were suppressed. There were no differences in UCP1 mRNA expression or protein content in BAT between groups. Our data suggest that leptin can affect energy intake via hypothalamic neuropeptides, but is not involved in the initiation of hibernation in fattening Daurian ground squirrels. [ABSTRACT FROM AUTHOR]

Technological innovations have made heat-sensitive data-loggers smaller, more efficient and less expensive, which has led to a growing body of literature that measures the skin- or body temperatures of small animals in their natural environments. Studies of this type on heterothermic endotherms have prompted much debate regarding how to best define 'torpor' expressions from skin- or body temperature data alone. We propose a new quantitative method for defining torpor 'entries', 'arousals' and 'stable torpor periods' whilst comparing the results to 'torpor bout' durations identified using only the torpor cut-off method. By decomposing a torpor bout into 'entries', 'stable torpor periods', and 'active arousals', we avoid biases introduced by using strict threshold temperature values for the onset of torpor, thereby allowing better insight into individual use of torpor. We present our method as an easy-to-use function written in R-code, offering an un-biased and consistent methodology to be applied on skin- or body temperature measurements across datasets and research groups. When testing the function on a large dataset of skin temperature data collected on three bat species in Norway (Plecotus auritus: N ind  = 39; Eptesicus nilssonii: N ind  = 11; Myotis brandtii: N ind  = 10), we identified 461 complete torpor bouts across species. More than 40% of the torpor bouts (N bouts  = 192) did not contain stable torpor periods, because the bats aroused before they had reached a stable skin temperature level. Furthermore, only considering 'torpid' and 'euthermic' temperature values by applying strict cut-off thresholds led to potentially large underestimations of torpor bout durations compared to our quantitative determination of the onset and termination of each torpor bout. We highlight the importance of differentiating between torpor phases, especially for active arousals that can be very energetically expensive and may alter our evaluation of the actual energetic savings gained by an individual employing torpor., Competing Interests: Declarations of competing interest We declare no conflict of interest., (Copyright © 2022 The Authors. Published by Elsevier Ltd.. All rights reserved.)

The environments in which animals have evolved and live have profound effects on all aspects of their biology. Predictable rhythmic changes in the physical environment are arguably among the most important forces shaping the evolution of behavior and physiology of animals, and to anticipate and prepare for these predictable changes, animals have evolved biological clocks. Unpredictable changes in the physical environment have important impacts on animal biology as well. The ability of animals to cope with and survive unpredictable perturbations depends on phenotypic plasticity and/or microevolution. From the time metazoans first evolved from their protistan ancestors they have lived in close association with a diverse array of microbes that have influenced, in some way, all aspects of the evolution of animal structure, function and behavior. Yet, few studies have addressed whether daily or seasonal rhythms may affect, or be affected by, an animal's microbial symbionts. This survey highlights how biologists interested in the ecological and evolutionary physiology of animals whose lifestyles are influenced by environmental cycles may benefit from considering whether symbiotic microbes have shaped the features they study. [ABSTRACT FROM AUTHOR]

Abstract: Optimal levels of unsaturated fatty acids have positive impacts on the use of prolonged bouts of hypothermia in mammalian hibernators, which generally have to face low winter ambient temperatures. Unsaturated fatty acids can maintain the fluidity of fat and membrane phospholipids at low body temperatures. However, less attention has been paid to their role in the regulation of shallow hypothermia, and in tropical species, which may be challenged more by seasonal energetic and/or water shortages than by low temperatures. The present study assessed the relationship between the fatty acids content of white adipose and liver tissues and the expression of shallow hypothermia in a tropical heterothermic primate, the gray mouse lemur (Microcebus murinus). The adipose tissue is the main tissue for fat storage and the liver is involved in lipid metabolism, so both tissues were expected to influence hypothermia dependence on fatty acids. As mouse lemurs largely avoid deep hypothermia (i.e. torpor) use under standard captive conditions, the expression of hypothermia was triggered by food-restricting experimental animals. Hypothermia depth increased with time, with a stronger increase for individuals that exhibited higher contents of unsaturated fatty acids suggesting that they were more flexible in their use of hypothermia. However these same animals delayed the use of long hypothermia bouts relative to individuals with a higher level of saturated fatty acids. This study evidences for the first time that body fatty acids unsaturation levels influence the regulation of body temperature not only in cold-exposed hibernators but also in tropical, facultative heterotherms. [Copyright &y& Elsevier]

Abstract: Hibernation researchers have long been interested in the transitions between the dissimilar states of torpor and euthermy. Natural arousal from torpor occurs spontaneously with highly predictable timing. However, animals can also be induced to arouse prematurely in response to various disturbances. While many investigations have used natural and induced arousals synonymously, direct comparisons of these two types of arousal have been limited. We address the question of whether natural and prematurely induced arousals generate the same patterns of warming at the level of the whole organism. We compare the effects of ambient temperature on the dynamics of natural versus induced arousals. Arousal duration, maximum rewarming rate, and the variance associated with increases in body temperature differed between natural and induced arousals. Prematurely inducing arousal also alters the duration of the interbout aroused (IBA) period. We recommend that careful consideration be given to experimental design and data interpretation related to the arousal phase of a torpor bout. [Copyright &y& Elsevier]

The overwintering capacity of biocontrol agents is of fundamental relevance for biological control of pests in temperate regions. In this study we tested the cold tolerance of the indigenous Drosophila pupal parasitoids Pachycrepoideus vindemmiae and Trichopria drosophilae at constant low temperature in the laboratory and exposed different preimaginal parasitoid stages in the field during winter. We evaluated whether semi-natural habitats promote overwintering via more favorable microclimatic conditions as well as higher host availability compared to orchards. Further, we studied the parasitoids' phenology in a semi-field experiment during autumn. We found that P. vindemmiae larvae and pupae were most cold tolerant under laboratory and field conditions, while all preimaginal stages of T. drosophilae displayed similar cold tolerance. Semi-natural habitats buffered temperature extremes, yet overwintering survival was not enhanced compared to orchards. Suitable overwintering hosts were present in all habitats at times when parasitoids were still active parasitizing. These results demonstrate that P. vindemmiae overwinters most likely as larva or pupa and that T. drosophilae can overwinter in a preimaginal life stage. Further, we provide evidence that both parasitoids can overwinter in a wide range of habitats and that the availability of hosts for overwintering is unlikely a limiting factor for the parasitoids during fall. • Parasitoids of D. suzukii can overwinter in semi-natural and cultivated habitats. • No effect from buffered temperature on parasitoid survival in semi-natural habitats. • Host availability not limiting for parasitoid overwintering in different habitats. • Daily temperature fluctuations affect parasitism activity, which ceased below 10°C. • Pachycrepoideus vindemmiae overwinters in the larval or pupal stage. [ABSTRACT FROM AUTHOR]

Abstract: The painted turtle (Chrysemys picta) is an especially useful organism in the study of metabolic regulation during dormancy because it is sustained by finite energy reserves from hatching until emerging from its nest, about nine months later. In this study we subjected overwintering C. picta hatchlings to 4, 10, or 15°C, temperatures simulating cold, mild, and warm winters, respectively, to investigate how various energy reserves are impacted by differential metabolic demands. An energy budget based on seasonal changes in caloric content showed that these turtles consumed an average of 0.39, 0.75, or 1.21kJg−1, respectively, during the 6-month period of simulated hibernation. These estimates of energy use agreed reasonably well with estimates based solely on respirometric data. Unexpectedly, turtles in autumn contained little residual yolk, none of which was consumed by turtles in the cold- and mild-winter groups, this finding contradicting the widely held belief that residual yolk plays an important, direct role in the survival of turtles that overwinter inside their natal nest. By contrast, a marked reduction in dry mass of both liver and carcass attested to their importance in fueling metabolism and, indeed, catabolism of substrates from these components accounted for 31–52 and 35–63%, respectively, of the energetic cost of overwintering. The greater dependence on carcass reserves and relatively poor physiological condition of turtles in the mild- and warm-winter groups implies that metabolic demands imposed by high environmental temperatures would likely constrain post-emergence fitness. [Copyright &y& Elsevier]

Abstract: Fibroblast growth factor 21 (FGF21) is a hormone released from the liver that mediates many of the physiological responses of fasting, such as lipolysis and ketogenesis. FGF21 is induced by the nuclear receptor PPARα when bound to its endogenous agonist, free fatty acid, or to the synthetic agonist, bezafibrate. To determine whether PPARα agonists mediate the metabolic suppression and accompanying fall in body temperature (T b) in a bout of torpor that occurs in mice in response to fasting, C57Bl/6J mice (wildtype) and PPARα −/− mice were implanted with temperature telemeters and fed either a control (CON) diet or one containing a PPARα agonist, bezafibrate (BEZA), for 2 weeks, followed by a fast. Wildtype mice on the BEZA diet had a striking phenotype: most entered spontaneous torpor bouts without caloric restriction towards the end of the 2 weeks. This is the first demonstration that an additive to food could induce spontaneous bouts of daily torpor. However, PPARα −/− did not express this phenotype. Moreover, wildtype mice on the BEZA diet had twice the length of torpor bouts in response to a fast as did wildtype mice on the CON diet. PPARα −/− mice did enter bouts of fasting-induced torpor, but these were unaffected by the BEZA diet. The BEZA diet induced the level of FGF21 in the blood to fasting levels only in wildtype mice. Collectively, these findings suggest that a BEZA diet mimics the fasted state in both induction of FGF21 and in thermoregulation and does so in a pathway dependent on PPARα. [Copyright &y& Elsevier]

Abstract: argue against the use of body temperature (T b) thresholds to quantify the expression of torpor in endotherms and our purpose is to provide a counterpoint argument. We contend that T b thresholds provide valuable information about ecological factors influencing the evolution of thermoregulation. We also point out shortcomings of the so-called heterothermy index proposed as an alternative. However, to be clear, we do agree with that the use of torpor thresholds can limit some aspects of the study of thermoregulation and applaud the more widespread incorporation of theoretical underpinnings proposed by and others. [Copyright &y& Elsevier]

Abstract: [(1)] Behavioural regulation of body temperature (t b) was monitored in 23 free-ranging Bufo calamita (Bc) and 17 syntopic Bufo viridis (Bv) at Urmitz (Rhineland-Palatinate, Germany) using temperature-sensitive transmitters implanted to the abdominal cavity. [(2)] In field t b varied between +0.5 and 37.4°C in Bc and between +0.6 and 33.7°C in Bv. Maximum t b of a Bc measured during an experimental trial was 38.8°C. [(3)] Natterjack toads avoided environmental temperature extremes by burrowing actively into moist sandy soil (2–90cm deep), whereas green toads hid exclusively in mammal burrows or pre-existing subterranean cavities. Shelter choice did not vary between summer and winter. [(4)] Average t b of Bc exceeded significantly that of Bv during summer (26.7°C vs. 24.7°C), while the reverse was true during winter (4.2°C vs. 7.2°C). Following hibernation the body condition of Bv was significantly lower than that of Bc. [(5)] We conclude that green toads fail to colonise regions west of the Rhine valley because of a combination of winter temperatures impeding foraging trips for prolonged periods, the choice of warm hibernacula increasing metabolic costs and/or predation risk and reduced fecundity. [Copyright &y& Elsevier]

Abstract: During times of energetic stress many small mammals reduce their body temperature and metabolic rate, a state known as torpor. Whereas torpor is effective in energy conservation it also entails costs, such as reduced foetal development in pregnant females. Because it is currently not known how subtropical bats deal with energetic challenges during the reproductive season, the thermal biology of free-ranging non-reproductive male and pregnant female Nyctophilus bifax was examined during spring. Males entered torpor much more frequently than pregnant females. However, night time activity periods were similar in both sexes. My results show that even in the subtropics torpor is used regularly during the reproductive period in spring by non-reproductive male N. bifax to conserve energy, but is used rarely by pregnant females likely to prevent slowed foetal development. [Copyright &y& Elsevier]

Abstract: [1.] Arrest temperatures and Q 10 values for extensor digitorum longus (EDL), soleus, trabecula, and jejunum muscle twitch strength, contraction time, and 0.5 relaxation time were calculated for a deep torpor hibernator, white-tailed prairie dog (WTPD) (Cynomys leucurus), a shallow torpor hibernator, black-tailed prairie dog (BTPD) (Cynomys ludovicianus), and a non-hibernator, lab rat (Rattus norvegicus) to test the hypothesis that tissue temperature tolerances limit the depth of expressed torpor. [2.] There were no temperature tolerance differences between the tissues of the two species of hibernators. Both hibernating species had arrest temperatures and Q 10 values more indicative of cold temperature tolerance than the lab rat in all tissues, with the exception of the soleus muscle. [3.] These data imply that a limited cold tolerance of contractile tissue does not preclude a shallow torpor hibernator such as the black-tailed prairie dog from expressing deep torpor patterns. Other mechanisms, such as central neural control, are more likely to be important in determining the torpor strategy utilized by hibernating species. [Copyright &y& Elsevier]

Abstract: We measured body temperatures in two large hibernating mammals, the eutherian alpine marmot (Marmota marmota) and the egg-laying echidna (Tachyglossus aculeatus) from unrestrained animals in their natural environment. In both species hibernation is broken every 13 days on average by rewarming to euthermic temperatures. We found that the time course of a rewarming could be closely fitted with a sigmoid curve, allowing calculation of peak rewarming rate and corresponding body temperature. Maximum rewarming rates were twice as high in marmots as in echidnas (12.1±1.3°Ch−1, n=10 cf. 6.2±1.2°Ch−1, n=10). Peak rewarming rates were positively correlated with body temperature in echidnas, but negatively correlated in marmots. [Copyright &y& Elsevier]

A variety of responses to climate seasonality have evolved by small mammals, including adjustments of the basal rate of metabolism (BMR) and the use of daily or seasonal torpor (here referred to as short-bout and long-bout torpor). The seasonal variation of their BMR is known to depend mainly on the concurrent variation of body mass, but it should also be affected by structural and functional changes occurring within the body that could depend on the expression of torpor. Thus it was hypothesized that BMR seasonality is related to the expression of torpor at an interspecific level. Seasonal BMR and body mass data were gathered from the literature and phylogenetic comparative analyses were done to test this hypothesis among mammals of less than 1 kg. BMR seasonality (dBMR) was quantified as the log-transformed ratio of the mean whole-animal BMR reported for the period P 2 (autumn-winter) over that for the period P 1 (spring-summer). Predictors were the seasonal body mass adjustment (dm), mean body mass (m) and torpor expression (TO , a three-level factor: no torpor, short-bout torpor, long-bout torpor). The seasonal variation of BMR was significantly related to dm but also to TO. Accounting for dm , species expressing long-bout torpor, but not those entering short-bout torpor, collectively exhibited a lower dBMR than species not entering torpor. Fat storage and use by species entering long-bout torpor, alone, could not explain their lower dBMR , as the TO:dm interaction was not significant. The low dBMR of species entering long-bout torpor may result from their collective tendency to down-regulate more strongly costly visceral organs during P 2. The dBMR of the different TO categories overlapped appreciably, which highlights our still limited knowledge of the BMR seasonality among small mammals. [Display omitted] • The seasonal variation of basal rate of metabolism (BMR) is related to torpor expression among small mammals. • Multiday, but not daily torpor affects BMR seasonality at the interspecific level. • A strong down-regulation of important functions during fall-winter must be more common in species entering multiday torpor. • Available data illustrate the high plasticity of the BMR. [ABSTRACT FROM AUTHOR]

Abstract: The African ice rat Otomys sloggetti robertsi is a small rodent confined to cold, alpine habitats. It does not hibernate and is poorly adapted physiologically to low temperatures. We predicted and showed that its fur is denser than its congeners from warmer habitats, but it had shorter fur than expected. Dense fur would provide insulation and piloerection of short fur would facilitate heat gain from solar radiation during sun basking. These traits, in addition to other behavioural and morphological traits, would assist O. s. robertsi in meeting its thermoregulatory requirements in response to low temperatures. [Copyright &y& Elsevier]

Abstract: During hibernation animals oscillate from near ambient (T a) to euthermic body temperatures (T b). As animals arouse, the rate of rewarming (RRW) might be expected to simply increase as a function of time. We monitored the T b of golden-mantled ground squirrels (Spermophilus lateralis) housed at 4, 8, 12, and 16°C during natural arousals. The maximum RRW, the time required to reach a maximum RRW, and the relative time index all demonstrated negative relationships with T a. The T b corresponding to maximal RRW demonstrated a positive relationship with T a. Squirrels reached maximal RRW when they had generated 30–40% of the heat required to reach a euthermic T b. These data suggest that arousal is more constrained than expected and that both time and temperature influence the RRW. [Copyright &y& Elsevier]

Abstract: We investigated the usefulness of body temperature (T b) as a guide to egg-laying in a monotreme mammal, the echidna, Tachyglossus aculeatus, and attempted to quantify changes in T b and relate them to specific reproductive events. Six female echidnas were implanted with temperature loggers and then radio-tracked in the wild for up to 6 years. In reproductive years there was a significant reduction in T b variability 21.7±2.5 days after final arousal from hibernation, which coincided with the time at which the female entered the nursery burrow. Egg-laying occurred within 2 days of this T b change which lasted an average of 43±4 days. [Copyright &y& Elsevier]

Abstract: [(1)] The analysis of catecholamines revealed alterations in norepinephrine levels in the blood serum and the central nervous system of the Egyptian cobra during the different phases of the hibernation cycle. This may reflect an increased central demand for norepinephrine as a mediator for adaptive changes to cold. [(2)] The low and variable concentration of dopamine suggests retarded synthesis during all the phases studied. [(3)] Serotonin may be depleted or associated with increased activity of serotonergic neurons during cold acclimation. This increases the rate of turnover of serotonin to 5-hydroxy indole acetic acid. [(4)] Cricannual measurements of cortisol and adrenocorticotrophic hormones revealed marked suppression that would clarify the direct effect of hibernation on higher centers. The decreased levels during prehibernation and hibernation were restored in normothermic animals when the pituitary–adrenal axis resumed its activity. [(5)] The decline in thyroid hormone concentrations has its behavioural and physiological responses that lead to seasonal adjustments in the hibernating cobras. [Copyright &y& Elsevier]

Abstract: [1.] The levels of water, Na, K, Ca and Mg in blood serum, brain and kidney and aldosterone level in blood of Naja haje haje were studied during the different phases of the annual cycle. [2.] The water content in the tissues studied displayed only minor changes as the animals passed from one phase to the other. [3.] A significant increase in Na was recorded in the brain during the different phases indicating a depressed sodium pump, whereas the blood Na level showed a significant decrease during hibernation. [4.] K increased in blood serum, brain and kidney during hibernation, while a nonsignificant decrease was found in blood serum during arousal. The brain may act as a potassium reservoir. [5.] An increase in Ca and Mg concentration was recorded in blood serum, brain and kidney during prehibernation and hibernation. The data suggested a homeostatic function in the transport and metabolism of these cations. [6.] Aldosterone exhibited a highly significant decrease especially during hibernation. The aldosterone regulation of ionic composition is discussed. [7.] Na/K and Ca/Mg ratios in the brain may explain the decreased excitability during winter torpor. [Copyright &y& Elsevier]

Abstract: We compared liver glycogen stores and glucose mobilization during freezing among winters in chorus frogs, Pseudacris triseriata, where populations varied in freezing survival. We also characterized tissue glycogen levels across the annual cycle. Frogs with low liver glycogen stores mobilized low amounts of glucose during freezing, and these were correlated with population variation in freezing survival. Moreover, liver glycogen stores were significantly and positively related to body mass. These data suggest that chorus frogs store liver glycogen in preparation for hibernation and that body size and glycogen stores must reach threshold levels for successful survival of freezing bouts during the winter. [Copyright &y& Elsevier]

Abstract: The relationship between sleep and natural hypothermic states, like daily torpor and hibernation, has always been of interest for sleep researchers. The three states were long considered functionally homologous. However, while investigating the effects of daily torpor on sleep in the Djungarian hamster (Phodopus sungorus), the results suggested that the animals are sleep deprived during hypothermia, and can only recover this sleep debt after return to euthermia. The data indicate that an important function of sleep cannot be fulfilled during the torpid state, a finding which may give additional insights into the processes involved in sleep regulation. [Copyright &y& Elsevier]

Abstract: Measuring the body temperature of animals living under natural conditions has gained increasing interest. This study shows in the small lemur Cheirogaleus medius that for many questions external collar transmitters can constitute an excellent alternative to implanted transmitters. During both active as well as inactive phases, data from collar transmitters precisely reflect core body temperature over a wide range of ambient temperatures. Even minor changes in the body temperature are detected, and collar transmitters are very adequate for determining general patterns of body temperature and activity in suitable species. [Copyright &y& Elsevier]

Abstract: [1.] Total lipids, free fatty acids, triglycerides, phospholipids and total cholesterol in blood serum, liver, brain, cardiac and skeletal muscles of Naja haje haje were determined during the different phases of the hibernation cycle. [2.] A sharp decrease in the level of total lipids of blood serum and all tissues occurred during hibernation. Upon arousal, lipogenesis is commonly restored. [3.] Elevated concentrations of serum free fatty acids predominated in pre-hibernation and hibernation periods, while the tissues recorded highly significant declines during hibernation. [4.] Occurrence of marked decreases in triglycerides contents of serum and tissues except the cardiac muscles in the hibernation and arousal phases. [5.] Sharp increases in the phospholipid contents of blood and the selected tissues were recorded during hibernation. The level declined in both liver and cardiac muscles in arousing animals. [6.] Total cholesterol level was lowered in blood during hibernation. The cardiac muscles showed a highly significant decrease while liver, brain and skeletal muscles showed elevations in the same phase. [Copyright &y& Elsevier]

(1) The purpose of this study was to evaluate hematological properties and blood viscosity in bullfrogs (Rana catesbeiana) submerged and exposed to prolonged low temperature. (2) Blood was collected from bullfrogs submerged in aerated water for 0, 20 or 50 days at 5°C, and those kept at 25°C. (3) No significant differences were found in hematocrit, hemoglobin, red blood cell count (RBCC), mean cell volume, apparent viscosity, plasma viscosity, or relative viscosity. (4) Plasma osmolality significantly decreased (P<0.001) in 5°C groups relative to the 25°C group. (5) Bullfrogs maintained a constant hematocrit, RBCC, and hemoglobin concentrations despite potential hemodilution, suggesting that bullfrogs could maintain a constant hematocrit during hibernation. [Copyright &y& Elsevier]

The effect of transfer from winter hibernation at 5°C to a warm temperature (20°C for 1 or 24 h) on oxidative stress and antioxidant defenses was assessed in the frog, Rana ridibunda. The temperature increase had little effect on the levels of thiobarbituric acid reactive substances but carbonylprotein levels (581, 740, 1270 and 614 pmol/mg protein in brain, liver, kidney and muscle, respectively, at 5°C) rose 3.2-fold in brain and 2.6-fold in liver after transfer to 20°C. The switch to 20°C also affected the activities of antioxidant enzymes: catalase in liver, kidney and muscle rose 33%, 55% and 126%, respectively, whereas superoxide dismutase increased 2.4-fold in liver and 2.5-fold in muscle. Glutathione reductase and glucose-6-phosphate dehydrogenase activities were also affected in some organs. The data show that recovery from winter hibernation in frogs causes increased oxidative stress and stimulates an elevation of organ antioxidant defenses. [Copyright &y& Elsevier]

Hibernation has been suggested to cause sleep debt, and since oleamide is elevated in the central nervous system of sleep-deprived mammals we hypothesized that brains from hibernating mammals would contain more oleamide than those that were not hibernating. Oleamide was 2.6-fold greater in brains of hibernating Richardson''s ground squirrel (Spermophilus richardsonii) than in euthermic brains. Additionally, brain fatty acid-binding protein did not bind oleamide and does not represent a solubilized pool of oleamide. [Copyright &y& Elsevier]

During the season of hibernation, temperate bats alternate between prolonged bouts of torpor with reduced body temperature and short arousals with a return to normothermy. Hibernating bats are sensitive to non-tactile stimuli and arouse following changes in microclimatic conditions or disturbance from other bats, potential predators, or humans. Here, we used temperature data loggers to register the skin temperature of 38 Myotis myotis bats over two winters (between January and March), during which regular visits were made to the hibernaculum. Two kinds of arousal were observed, normothermic (T sk > 25 °C) and cold (T sk < 15 °C). Although bats responded to the presence of a researcher by arousals of both kinds, cold arousals were more frequent (63.8%). We found that mass loss was not affected by the number of disturbances, however it was in positive relationship with the mass at the beginning of the observation and differed between sex and age categories. Furthermore normothermic bats crawling among cluster-mates initiated arousal cascades, which mainly consisted of cold arousals. We failed to detect any effect of age or sex on the number of arousals initiated by normothermic individuals. Warming by only a few degrees requires less energy than a normothermic arousal and we propose it is sufficient to activate the sensory system in order to assess the relevance of external stimuli. Our results indicate that cold arousals reflect a physiological and behavioural adaptation aimed at avoiding the energetic costs of disturbance that can lead to depletion of fat reserves. • Bats alternate between torpor bouts, cold and normothermic arousals. • Cold arousals were sensitive to Ta change, while Tmax of normothermic was not affected. • Cold arousals are adaptive mechanism allowing hibernators to conserve fat. • Use of cold arousals reduces disturbances and leads to successful hibernation. [ABSTRACT FROM AUTHOR]