Range Of Body Temperatures Research Articles

Metabolic rate and foraging behaviour: a mechanistic link across body size and temperature gradients

The mechanistic link between metabolic rate and foraging behaviour is a crucial aspect of several energy‐based ecological theories. Despite its importance to ecology however, it remains unclear whether and how energy requirements and behavioural patterns are mechanistically connected. Here we aimed to assess how modes of behaviour, including cumulative space use, patch selection and time spent in an experimental resource‐patchy environment, are related to a forager's standard metabolic rate (SMR) and its main determinants, i.e. body mass and temperature. We tested the individual behavioural patterns and metabolic rates of a model organism, the amphipod Gammarus insensibilis, across a range of body masses and temperatures. We demonstrated quantitatively that body mass and temperature exert a major influence on foraging decisions and space use behaviour via their effects on metabolic rates and the marginal value of energy. Individual cumulative space use was found to scale allometrically with body mass and exponentially with temperature, with patch giving‐up time falling as body mass and temperature increased. In response to warmer temperatures, the specimens adaptively intensified their foraging effort and explored larger spaces to offset the elevated SMR. Our results showed that SMR explained more variation than body mass and temperature combined, and had greater predictive power for behavioural patterns. Furthermore, foraging decisions regarding patch choice and partitioning were strongly related to mass‐and‐temperature‐adjusted SMR (residual), which is a component of metabolic phenotype. Individuals with higher M–T adjusted SMR initially preferred the most profitable patch and, as time progressed, abandoned the patch earlier and explored more space than the others. These results demonstrate that foraging decisions are intimately associated with variations in standard metabolic rate, whether phenotypic or due to size and temperature combined. This, in turn, sheds light on higher‐order energy‐based ecological processes.

High phenotypic diversity correlated with genomic variation across the European Batrachochytrium salamandrivorans epizootic.

Recognizing the influence of pathogen diversity on infection dynamics is crucial for mitigating emerging infectious diseases. Characterising such diversity is often complex, for instance when multiple pathogen variants exist that interact differently with the environment and host. Here, we explore genotypic and phenotypic variation of Batrachochytrium salamandrivorans (Bsal), an emerging fungal pathogen that is driving declines among an increasing number of European amphibian species. For thirteen isolates, spanning most of the known temporal and geographical Bsal range in Europe, we mapped phenotypic diversity through numerous measurements that describe varying reproductive rates in vitro across a range of temperatures. Bsal isolates are revealed to have different thermal optima and tolerances, with phenotypic variation correlating with genomic diversity. Using a mechanistic niche model of the fire salamander (Salamandra salamandra) as an example, we illustrate how host steady-state body temperature and Bsal thermal range variation may influence pathogen growth through space and time across Europe. Our combined findings show how the identity of emergent pathogen variants may strongly influence when and which host populations are most at risk.

Analysis of subcellular energy metabolism in five Lacertidae lizards across varied environmental conditions

Aerobic respiration is the main energy source for most eukaryotes, and efficient mitochondrial energy transfer greatly influences organismal fitness. To survive environmental changes, cells have evolved to adjust their biochemistry. Thus, measuring energy metabolism at the subcellular level can enhance our understanding of individual performance, population dynamics, and species distribution ranges. We investigated three important metabolic traits at the subcellular level in five lacertid lizard species sampled from different elevations, from sea level up to 2000 m. We examined hemoglobin concentration, two markers of oxidative stress (catalase activity and carbonyl concentration) and maximum rate of metabolic respiration at the subcellular level (potential metabolic activity at the electron transport system). The traits were analysed in laboratory acclimated adult male lizards to investigate the adaptive metabolic responses to the variable environmental conditions at the local sampling sites. Potential metabolic activity at the cellular level was measured at four temperatures – 28 °C, 30 °C, 32 °C and 34 °C – covering the range of preferred body temperatures of the species studied. Hemoglobin content, carbonyl concentration and potential metabolic activity did not differ significantly among species. Interspecific differences were found in the catalase activity, Potential metabolic activity increased with temperature in parallel in all five species. The highest response of the metabolic rate with temperature (Q10) and Arrhenius activation energy (Ea) was recorded in the high-mountain species Iberolacerta monticola.

Trimodality applications validation of near-infrared persistent luminescence nanoparticles

Here, we introduced Cr ion, as emission center, to achieve the NIR emission for MgGa2O4, while Zn ion is used to increase oxygen vacancy to improve the emission intensity. Thus, Mg0.9Zn0.1Ga2O4: 0.006 Cr3+ (MZGC) was prepared as the optimal composite with the enhanced NIR emission at 708 nm, while the host, Mg0.9Zn0.1Ga2O4 (MZG), exhibited the afterglow emission at 425 nm under 224 nm excitation. The result from density functional theory confirmed Cr and Zn ions occupied in the octahedral coordination to improve the optical behaviors. The NIR emission of MZGC was applied for bioimaging as confirmed with mice model under both visible and NIR excitation. We proposed MZGC strategy for fingerprint imaging and recognition with their resistance to stray light interference. By applying the mixture of MZGC and MZG, we realized ratiometric temperature sensing at 35–40 °C within body temperature range. The optical mechanism clearly illustrated for tri-modality applications as bioimaging, fingerprint recognition, and temperature sensing. This work provides a reliable method for the improvement of optical properties and thus extend the applications of persistent luminescence nanoparticles.

Do Bewick´s Wren (Thryomanes bewickii) nestlings experience thermal stress in nest-boxes in a tropical urban city?

Urban areas present thermal environments that may be challenging for altricial nestlings, particularly in early development. We aimed to evaluate whether altricial Bewick's Wren (Thryomanes bewickii) nestlings experienced thermal stress in the nest-box during the early- and late-developmental stages. We determined the thermoregulatory set point (thermoneutral range) of nestlings by measuring cloacal body temperature of five nestlings from three nests, every other day from hatching until they fledged. We also exposed nestlings to a thermal challenge from day 5 to determine the age of endothermy. We used dataloggers to determine the thermal environment inside and outside of three nest-boxes, and obtained the operative temperature for nestlings in the nest-box using 3D-printed models corresponding to early- and late-developmental stages. Ambient temperatures inside the nest box fluctuated throughout the day, being colder at night just before day-break (min range: 10.4°C – 10.8°C), and hotter in the afternoon (max range: 25.8°C - 28.3°C). However, temperatures in the nest-box did not reach the extreme high and low outside temperatures, and were warmer at night. Nestlings reached age of endothermy at 9 ± 2.3 days after hatching, and showed a thermoneutral range of body temperature above ambient temperatures in the nest-box. Operative temperatures of models in the nest-box closely followed ambient temperatures, and were below nestlings´ thermoneutral range. Therefore, nestlings could experience thermal stress when parents do not provide additional buffering while off the nest for foraging. Although nest-boxes provide limited thermal benefits for nesting birds in tropical cities, they still provide valuable nesting and roosting sites where natural cavities are limited in availability.

UM FILME DE POLIURETANO DE BASE AQUOSA CONTENDO ÓLEO DE MAMONA E NANOPARTÍCULAS DE PRATA INDUZIU A INIBIÇÃO DE BIOFILME BACTERIANO IN VITRO

Healthcare-related infections (HAIs) are a huge global issue. In 2020, about 11,124 patients (12.7%) with an ICU (intensive care unit) stay of over two days developed at least one ICU-acquired healthcare-associated infection (European Centre for Disease Prevention and Control, 2024). Hospital-acquired infections are mainly caused by contamination of these facilities, which often involves the transmission of microorganisms through contact with contaminated surfaces. In this context, the advancement of novel strategies to mitigate the contamination of medical devices, biomaterials, and hospital equipment is crucial and drives the demand for advancements in materials sciences. The application of antimicrobial polymers to coat medical devices and other hospital equipment has emerged as a promising approach, reducing the risk of healthcare-related contamination. The main goal of this research was to incorporate silver nanoparticles (Ag-NPs) into a waterborne castor oil-based polyurethane (PU) suspension to produce a film coating and evaluate its effectiveness in preventing bacterial adhesion. The films of pristine polyurethane (WBPU) and polyurethane containing Ag-NPs were subjected to physicochemical characterization and antimicrobial assays. Thermogravimetric analysis showed that no decomposition occurs below 200 oC, and the PU can be used in materials at the body temperature range. The WBPU film with 0.4% (w/w) Ag-NPs exhibited 36.4% inhibition of Staphylococcus aureus adhesion and 20.5% inhibition of biofilm formation. This castor oil-based polyurethane antimicrobial film is a promising alternative for coating the surfaces of equipment and devices used in the healthcare sector.

An arctic breeding songbird overheats during intense activity even at low air temperatures

Birds maintain some of the highest body temperatures among endothermic animals. Often deemed a selective advantage for heat tolerance, high body temperatures also limits birds’ thermal safety margin before reaching lethal levels. Recent modelling suggests that sustained effort in Arctic birds might be restricted at mild air temperatures, which may require reductions in activity to avoid overheating, with expected negative impacts on reproductive performance. We measured within-individual changes in body temperature in calm birds and then in response to an experimental increase in activity in an outdoor captive population of Arctic, cold-specialised snow buntings (Plectrophenax nivalis), exposed to naturally varying air temperatures (− 15 to 36 °C). Calm buntings exhibited a modal body temperature range from 39.9 to 42.6 °C. However, we detected a significant increase in body temperature within minutes of shifting calm birds to active flight, with strong evidence for a positive effect of air temperature on body temperature (slope = 0.04 °C/ °C). Importantly, by an ambient temperature of 9 °C, flying buntings were already generating body temperatures ≥ 45 °C, approaching the upper thermal limits of organismal performance (45–47 °C). With known limited evaporative heat dissipation capacities in these birds, our results support the recent prediction that free-living buntings operating at maximal sustainable rates will increasingly need to rely on behavioural thermoregulatory strategies to regulate body temperature, to the detriment of nestling growth and survival.

Advances in 4D printing of biodegradable photopolymers

AbstractOver the past decade, 4D printing has revolutionized the field of advanced manufacturing by fabricating structures that dynamically respond to environmental stimuli. During this process, shape‐memory polymers (SMPs) stand out, enabling transformations triggered by temperature, light, or other environmental factors, and show great potential for applications in biomedicine and beyond. Notably, biodegradable SMPs offer a compelling advantage in medical devices due to their ability to adapt within the body's temperature range and to be absorbed by tissues, reducing the risks associated with permanent implants. While extrusion techniques have laid the groundwork for 4D printing in biomedicine, vat photopolymerization methods like stereolithography and digital light processing are now at the forefront, favored for their high printing resolution and flexibility in material design. However, the search for suitable biodegradable materials for these advanced techniques continues, with current research focusing on developing systems that meet both the mechanical demands and degradation profiles required for medical applications. This review aims to critically analyze the advancements in biodegradable 4D photopolymers, particularly biodegradable elastomers, and discuss the challenges that lie ahead for their clinical translation.

Shape-Persistent Conductive Nerve Guidance Conduits for Peripheral Nerve Regeneration.

To solve the problems of slow regeneration and mismatch of axon regeneration after peripheral nerve injury, nerve guidance conduits (NGCs) have been widely used to promote nerve regeneration. Multichannel NGCs have been widely studied to mimic the structure of natural nerve bundles. However, multichannel conduits are prone to structural instability. Thermo-responsive shape memory polymers (SMPs) can maintain a persistent initial structure over the body temperature range. Electrical stimulation (ES), utilized within nerve NGCs, serves as a biological signal to expedite damaged nerve regeneration. Here, an electrospun shape-persistent conductive NGC is designed to maintain the persistent tubular structure in the physiological temperature range and improve the conductivity. The physicochemical and biocompatibility of these P, P/G, P/G-GO, and P/G-RGO NGCs are conducted in vitro. Meanwhile, to evaluate biocompatibility and peripheral nerve regeneration, NGCs are implanted in subcutaneous parts of the back of rats and sciatic nerves assessed by histology and immunofluorescence analyses. The conductive NGC displays a stable structure, good biocompatibility, and promoted nerve regeneration. Collectively, the shape-persistent conductive NGC (P/G-RGO) is expected to promote peripheral nerve recovery, especially for long-gap and large-diameter nerves.

In situ temperature determination using magnetic resonance spectroscopy thermometry for noninvasive postmortem examinations.

Magnetic resonance spectroscopy (MRS) thermometry offers a noninvasive, localized method for estimating temperature by leveraging the temperature-dependent chemical shift of water relative to a temperature-stable reference metabolite under suitable calibration. Consequentially, this technique has significant potential as a tool for postmortem MR examinations in forensic medicine and pathology. In these examinations, the deceased are examined at a wide range of body temperatures, and MRS thermometry may be used for the temperature adjustment of magnetic resonance imaging (MRI) protocols or for corrections in the analysis of MRI or MRS data. However, it is not yet clear to what extent postmortem changes may influence temperature estimation with MRS thermometry. In addition, N-acetylaspartate, which is commonly used as an in vivo reference metabolite, is known to decrease with increasing postmortem interval (PMI). This study shows that lactate, which is not only present in significant amounts postmortem but also has a temperature-stable chemical shift, can serve as a suitable reference metabolite for postmortem MRS thermometry. Using lactate, temperature estimation in postmortem brain tissue of severed sheep heads was accurate up to 60 h after death, with a mean absolute error of less than 0.5°C. For this purpose, published calibrations intended for in vivo measurements were used. Although postmortem decomposition resulted in severe metabolic changes, no consistent deviations were observed between measurements with an MR-compatible temperature probe and MRS thermometry with lactate as a reference metabolite. In addition, MRS thermometry was applied to 84 deceased who underwent a MR examination as part of the legal examination. MRS thermometry provided plausible results of brain temperature in comparison with rectal temperature. Even for deceased with a PMI well above 60 h, MRS thermometry still provided reliable readings. The results show a good suitability of MRS thermometry for postmortem examinations in forensic medicine.

A preliminary study of ecosmart intra venous system on patients’ comfort

Intravenous fluid therapy may cause discomfort to patients most of the time. More research and innovation are needed to develop infusion devices to provide a more comfortable feeling for patients receiving the therapy. This preliminary study analyzed the effect of economical and smart (ecosmart) infusion systems on comfort in healthy adults. The one-group post-test-only design was used in this pre-experimental investigation. A range of ages, gender, body weight, body temperature, and normal blood pressure selected participants. An independently created, valid, and reliable tool was used to measure comfort. Data analysis employed a t-test on a single sample. Fifteen nursing students are participating as sampling objects. The average comfort score for the study's participants was 11.2 (SD = 2.5967; p < 0.05). The result indicates that the participants are at ease using the ecosmart system. The respondents' sense of comfort related to the instrument showed comfort or relaxation.
 Keywords: Nursing care; ecosmart; comfort; patient-centered care; hospital; fluid therapy

High toughness, ultra-sensitive, and extreme environment resistant fabric temperature sensors based on supramolecular-polymer dual network ionic conductive elastomers

Liquid-free ionic conductive elastomers (ICEs) show great potential for next-gen wearable electronics, free from issues like solvent evaporation and freezing. However, crafting ICEs with both strength and temperature sensitivity remains a significant challenge. In this study, a supramolecular gel based on 1,3:2,4-bis (3,4-dimethylbenzene methylene) sorbitol (DMBS) is selected as the first network, and poly(ethylene glycol) methyl ether methacrylate (PEGMA) copolymerized with diallyl dimethyl bis (trifluoromethyl sulfonyl)imide (DADMATFSI) is added as the second network, with the addition of lithium bis(trifluoromethyl sulfonyl)imide (LiTFSI). The supramolecular-polymer dual network ion-conductive elastomer SP-DN-LiTFSI is created. The elastomer exhibits exceptional mechanical characteristics, including a maximum tensile stress of 1591.1 kPa and an impressive strain of 2361 %. Additionally, it demonstrates an extraordinarily high toughness of 33.121 MJ m−3. Moreover, this elastomer-based temperature sensor is responsive to external stimuli, such as blowing, and boasts an outstanding temperature sensing coefficient (S) of 0.114 °C−1 within the range of 30–60 °C. Remarkably, it can discern even the slightest temperature variations as low as 0.5 °C within the typical human body temperature range. This work represents an innovative integration of a dual network structure and two strategies for elastomer fabrication. It provides a novel approach for developing highly sensitive wearable temperature measurement devices that exhibit exceptional resistance to mechanical wear.

Cycling temperature treatments affect estimates of digestive performance in prairie lizards (Sceloporus consobrinus).

In nature, many organisms experience a daily range of body temperatures. Thermal performance at stable temperatures is often extrapolated to predict function in cyclical environments. However, temperature order and cyclicity may influence physiological processes. The current study compared energy intake, digestive passage time and energy budgets at a stable temperature (33°C) and two temperature cycles in lizards (Sceloporus consobrinus), to determine (1) whether stable treatments adequately project performance in a cycling environment and (2) whether temperature order influences performance. Cycles had a mean temperature of 33°C, and rotated through 30°C, 33°C and 36°C daily, with equal durations of time at each temperature but differing temperature order, with warm days and cool nights in cycle 1 and cool days and warm nights in cycle 2. For analyses, performance in the stable treatment was compared with that during cycles. If temperature is the primary factor regulating performance, then performance from the stable treatment and cycles should compare favorably. However, physiological performance varied based on temperature treatment. Energy intake and budgets were similar between the stable trial and cycle 1 but not cycle 2. However, passage time did not differ. Notably, the two cycling regimes consistently varied in performance, indicating that temperature order plays a primary role in regulating performance. Physiological data collection requires careful consideration of effects of cycling versus stable temperature treatments. Stable temperatures do not consistently represent performance in cycling regimes and consideration should be paid not only to which temperatures animals experience but also to how temperature is experienced in nature.

Textile‐Based Flexible Temperature Sensors for Wearable and Sports Applications

Flexible textile‐based sensors are versatile alternatives that can be comfortably worn and can detect a broad range of body and environment temperatures. Furthermore, they become more essential due to the recent rise in the use of wearable customized gadgets, wearable clothing, sports, medical, and soft robotics. Typically made from rigid materials like metals or semiconductors, traditional temperature sensors are heavy, inflexible, and difficult to wear since they can only endure very slight variations in their physical shape to be placed on any irregularly shaped object. In this review, developments in textile temperature sensors are discussed with a focus on their performance, fabrication techniques, advances in various materials, and applications, such as wearable monitoring and sports. Moreover, an in‐depth analysis of different performance parameters is also presented. Lastly, to provide useful guidance and directions for future study, it is concluded by outlining the current limitations of this field, and future recommendations for the scientific community to further explore other facets of textile temperature devices.

Stimuli‐responsive properties of double network hydrogels derived from κ‐carrageenan and poly (acrylamide)

AbstractThe utilization of stretchable, antifreezing hydrogels is imperative when using them as electrolyte membranes and ionic conductors for flexible energy storage devices or electronic skin. However, a problem still persists in the formation of a functional hydrogel with comprehensive performance including antifreezing, temperature‐sensitive, favorable reusability, and self‐healing properties. Herein, through anionic κ‐carrageenan (κ‐CG) as the physical noncovalent crosslinking network of the hydrogel, and acrylamide (AM) as monomers forming the second network through chemical crosslinking, κ‐CG‐Li+/PAM double‐network (DM) hydrogels were obtained by one‐pot thermally initiated polymerization. The DM structure showed excellent fracture strain and strong breaking stress, and lithium ions ensure its good electrical conductivity. The transparency of the hydrogel could reach above 91.0%, and the freezing point of the resultant gel was −34.9°C, which was measured by differential scanning calorimetry at low temperature. The as‐synthesized DM gel exhibited robust tensile properties with tensile elongation of 1840% and fracture energy of 967.3 kJ/m3. The response sensitivity of the hydrogel as a wearable sensor in different environments was explored. κ‐CG‐Li+/PAM could not only respond in the large strain range of 100%–400% but also capture the change in 0.1% strain. The deformation sensitivity was GF = 1.83 at 200% compressive strain range, and the hydrogel had a pressure sensitivity of 2.71 kPa−1 over the pressure range of 0–5 kPa. In addition to the properties of ionic conductive hydrogels, the hydrogel demonstrated outstanding temperature sensitivity in the human body temperature range of 35°C–40°C or in the range of 20°C–60°C (TCR = 1.628/°C).

Myosin and tropomyosin-troponin complementarily regulate thermal activation of muscles.

Contraction of striated muscles is initiated by an increase in cytosolic Ca2+ concentration, which is regulated by tropomyosin and troponin acting on actin filaments at the sarcomere level. Namely, Ca2+-binding to troponin C shifts the "on-off" equilibrium of the thin filament state toward the "on" state, promoting actomyosin interaction; likewise, an increase in temperature to within the body temperature range shifts the equilibrium to the on state, even in the absence of Ca2+. Here, we investigated the temperature dependence of sarcomere shortening along isolated fast skeletal myofibrils using optical heating microscopy. Rapid heating (25 to 41.5°C) within 2 s induced reversible sarcomere shortening in relaxing solution. Further, we investigated the temperature-dependence of the sliding velocity of reconstituted fast skeletal or cardiac thin filaments on fast skeletal or β-cardiac myosin in an in vitro motility assay within the body temperature range. We found that (a) with fast skeletal thin filaments on fast skeletal myosin, the temperature dependence was comparable to that obtained for sarcomere shortening in fast skeletal myofibrils (Q10 ∼8), (b) both types of thin filaments started to slide at lower temperatures on fast skeletal myosin than on β-cardiac myosin, and (c) cardiac thin filaments slid at lower temperatures compared with fast skeletal thin filaments on either type of myosin. Therefore, the mammalian striated muscle may be fine-tuned to contract efficiently via complementary regulation of myosin and tropomyosin-troponin within the body temperature range, depending on the physiological demands of various circumstances.

Chitosan-PEG Gels Loaded with Jatropha mollissima (Pohl) Baill. Ethanolic Extract: An Efficient and Effective Biomaterial in Hemorrhage Control.

A lack of control over blood loss can have catastrophic implications, including death. Although several hemostatic medications have been employed to reduce bleeding, a vast majority of them are ineffective, expensive, or pose health risks to the patient. To overcome these constraints, chitosan-polyethylene glycol (CS-PEG) hemostatic gels loaded with ethanolic extract of Jatropha mollissima sap (EES) were prepared and their hemostatic, physicochemical, and cytotoxic properties were evaluated. The gels were produced by mixing CS with PEG (an external plasticizer) and EES. The phytochemical analysis revealed a significant concentration of total polyphenols and tannins content in the extract and catechin was identified as one of the key compounds of EES. Infrared spectroscopy analysis revealed the presence of EES in the gels, as well as the chemical interaction between CS and PEG. The gels were thermally stable between 25 and 37 °C (ambient and human body temperature range), had pseudoplastic deformation behavior (rheological properties preserved after shearing), were simple to inject (compression force 30 N), and were biocompatible. In vivo experiments showed that both CS-PEG-EES gels exhibited greater hemostatic action in preventing tail hemorrhage in Wistar rats, with decreased bleeding time and blood weight compared with unloaded CS-PEG gels (control groups) and Hemostank, a commercial product. However, the gel prepared with acetic acid was more efficient in controlling bleeding. These findings reveal that CS-PEG-EES gels can reduce hemorrhages and are a potent, simple, and safe hemostatic agent.

Body Temperature Manipulation Increases Salivary Cortisol Independent of Exercise

The vast majority of circulating cortisol in the blood is bound and inactivated by binding proteins like corticosteroid-binding globulin (CBG) and albumin. The cortisol that is free of these binding proteins is secreted via saliva and other body fluids. Ex-vivo studies have shown that CBG binding to cortisol is temperature-dependent within the physiological range of human core body temperatures. Exercise is a standard experimental paradigm for inducing cortisol responses. However, these studies rarely consider that exercise-induced changes in core body temperature might increase free cortisol independent of psychological stress or physical exertion. We tested the effect of heat exposure without exertion or other stressors on saliva cortisol. 26 Participants (18 healthy and 8 with Major Depression MDD) sat motionless in a dry infrared sauna set to 65.5 degrees C (150 F). They had their tympanic membrane temperature and salivary cortisol measured as their body temperature increased. Exposure to exogenous heat significantly increased core body temperature from 36.93 C/98.48 F (95% CI 36.79-37.07 C, 98.23-98.73 F) to 38.42 C /101.16 F (95% CI 38.24-38.6 C, 100.83-101.48 F) after 45 minutes of heat exposure, F(15,42.33)=43.509, p<0.001. Concurrently saliva cortisol also increased significantly from 4.00 nmol/l (95%CI 1.89-6.11) to 9.87 nmol/l (95% CI 5.58-14.17), F(1,33.17)=6.64, p=0.015. Elevations in core body temperature can significantly increase free cortisol levels even in the absence of exercise or overt psychological stressors.

Contrasting Effects of Temperature on Human Arylamine N-Acetyltransferase and Acetyl Coenzyme A Hydrolase Activities.

There are two human arylamine N-acetyltransferases (NAT1 and NAT2) that have evolved separately and differ in their substrate specificity and tissue localization. In addition to its acetyltransferase activity, NAT1 can hydrolyze acetyl coenzyme A to coenzyme A in the presence of folate. Here, we show that NAT1 is rapidly inactivated at temperatures above 39 °C whereas NAT2 is more stable. NAT1 acetyltransferase activity is also rapidly lost in whole cells at a rate similar to that of recombinant protein, suggesting it is not protected by intracellular chaperones. By contrast, the hydrolase activity of NAT1 is resistant to heat-induced inactivation, in part because folate stabilizes the protein. Heat generated by mitochondria following the dissipation of the inner membrane potential was sufficient to inactivate NAT1 in whole cells. Within the physiological range of core body temperatures (36.5-37.5 °C), NAT1 acetyltransferase activity decreased by 30% while hydrolase activity increased by >50%. This study demonstrates the thermal regulation of NAT1, but not NAT2, and suggests that NAT1 may switch between an acetyltransferase and a hydrolase within a narrow temperature range in the presence of folate.

Hummingbirds use insulated nests to save energy for the clutch

All wild animals need to perform a balancing act with the energy they take in and the energy they burn. To save energy, hummingbirds can use torpor, a process where they decrease their body temperature and metabolism. However, mothers only use torpor in an emergency, as their eggs and chicks are sensitive to low temperatures. Erich Eberts, from Loyola Marymount University, USA, and an international team of colleagues from various US and Canadian universities set out to determine how female Allen’s hummingbirds (Selasphorus sasin) manage their energy budget at night-time while incubating chicks and, importantly, whether their nests provide energy savings.From January to May in 2017 and 2018, the team located more than 60 Allen’s hummingbird nests with eggs or chicks in the suburbs around Loyola Marymount University in Los Angeles, CA, USA. The researchers then monitored 56 of the nests until the chicks fledged (40 nests), were killed by predators (12 nests) or failed for some other unknown reason (4 nests). To measure the temperatures of the hummingbird mothers, the researchers placed thermal cameras 0.5-1 m away from nests, programmed to capture one image every minute, successfully collecting thermal images on 108 nights from 14 of the 56 nests they were monitoring. The researchers then used the thermal images to determine the mother’s body temperature, and the temperature of a nearby branch or leaf to measure the local environmental temperature.For their analysis, the team then defined the thermal states of the hummingbirds as either normal body temperature, deep torpor (low body temperature), shallow torpor (moderately low body temperature) or the transition to or from torpor. Then, in a separate series of theoretical models, the researchers estimated the energetic costs of the hummingbirds under a range of conditions, with either torpid or normal body temperatures for 0, 2, 6, 10 or 12 h, and either nesting or completely exposed to the surrounding air.The researchers found that on 103 nights (of the total 108), the hummingbird mothers maintained normal body temperatures, and failed to enter torpor to conserve energy. However, one hummingbird did enter deep torpor on two nights in February, decreasing its skin temperature to 14°C, and two other hummingbirds used shallow torpor on three nights, decreasing skin temperatures to approximately 19°C. However, the chicks of the mothers that sporadically used torpor still developed successfully and took flight when they were old enough. The researchers concluded that hummingbird mothers rarely enter torpor to protect their chicks from nocturnal low temperatures, although they do resort to using torpor in exceptional circumstances.Nevertheless, the team discovered that the temperatures within the nest remained approximately 7.5°C higher than the surrounding air, thanks to the insulation they provided, which allowed the roosting mothers to conserve energy. In one of the teams’ energetic models, a nesting mother maintaining a normal body temperature for 12 h could save around 24% of her energy thanks to her nest compared with a mother exposed to the environment. Yet, if nesting hummingbirds used torpor for 6 h, they could save 41% of the energy they would expend maintaining a normal body temperature in the open.Overall, Eberts and colleagues successfully used a non-invasive method to determine that mother Allen’s hummingbirds almost always forgo torpor when nesting. The mothers prioritize the health of their chicks, instead of saving energy for themselves. In addition, hummingbird mothers can depend on their well-constructed, insulated nests to provide a warm home and save energy when raising their young.