Thermoregulation in free-ranging Nycteris thebaica (Nycteridae) during winter : no evidence of torpor

Bats are among the most heterothermic mammals, with nearly all species investigated under free-ranging conditions to date exhibiting some degree of daily torpor and/or hibernation. We investigated thermoregulation during late winter by seven Nycteris thebaica in a warm, semi-arid habitat in northern South Africa, using temperature-sensitive transmitters to measure skin temperature (Tskin). Unexpectedly, we found no evidence for any expression of daily torpor or hibernation based on a total of 86 days of data from 7 bats (one male and six females), despite air temperatures as low as ∼10 ◦C. Instead, daytime Tskin was distributed unimodally with most values in the 33–35 ◦C range, and a minimum Tskin of 28.4 ◦C at a roost temperature of 24.6 ◦C. There are several possible reasons why N. thebaica may avoid torpor, including predation in roosts, and the long nightly foraging periods of this species compared to many others.http://www.elsevier.com/locate /mambiohb201

Thermoregulation in desert birds : scaling and phylogenetic variation in heat tolerance and evaporative cooling

Evaporative heat dissipation is a key aspect of avian thermoregulation in hot environments.We quantified variation in avian thermoregulatory performance at high air temperatures (Ta) using published data on body temperature (Tb), evaporative water loss (EWL) and resting metabolic rate (RMR) measured under standardized conditions of very low humidity in 56 arid-zone species. Maximum Tb during acute heat exposure varied from 42.5±1.3°C in caprimulgids to 44.5±0.5°C in passerines. Among passerines, both maximum Tb and the difference between maximum and normothermic Tb decreased significantly with body mass (Mb). Scaling exponents for minimum thermoneutral EWL and maximum EWL were 0.825 and 0.801, respectively, even though evaporative scope (ratio of maximum to minimum EWL) varied widely among species. Upper critical limits of thermoneutrality (Tuc) varied by >20°C and maximumRMR during acute heat exposure scaled toMb 0.75 in both the overall data set and among passerines. The slope of RMR at Ta>Tuc increased significantly with Mb but was substantially higher among passerines, which rely on panting, comparedwith columbids, in which cutaneous evaporation predominates. Our analysis supports recent arguments that interspecific within-taxon variation in heat tolerance is functionally linked to evaporative scope and maximum ratios of evaporative heat loss (EHL) to metabolic heat production (MHP). We provide predictive equations for most variables related to avian heat tolerance. Metabolic costs of heat dissipation pathways, rather than capacity to increase EWL above baseline levels, appear to represent the major constraint on the upper limits of avian heat tolerance.The National Research Foundation and the National Science Foundation.http://jeb.biologists.orgam2022Zoology and Entomolog

The influence of transition metal solutes on dislocation core structure and values of Peierls stress and barrier in tungsten

Several transition metals were examined to evaluate their potential for improving the ductility of tungsten. The dislocation core structure and Peierls stress and barrier of $1/2$ screw dislocations in binary tungsten-transition metal alloys (W$_{1-x}$TM$_{x}$) were investigated using first principles electronic structure calculations. The periodic quadrupole approach was applied to model the structure of $1/2$ dislocation. Alloying with transition metals was modeled using the virtual crystal approximation and the applicability of this approach was assessed by calculating the equilibrium lattice parameter and elastic constants of the tungsten alloys. Reasonable agreement was obtained with experimental data and with results obtained from the conventional supercell approach. Increasing the concentration of a transition metal from the VIIIA group, i.e. the elements in columns headed by Fe, Co and Ni, leads to reduction of the $C^\prime$ elastic constant and increase of elastic anisotropy A=$C_{44}/C^\prime$. Alloying W with a group VIIIA transition metal changes the structure of the dislocation core from symmetric to asymmetric, similar to results obtained for W$_{1-x}$Re$_{x}$ alloys in the earlier work of Romaner {\it et al} (Phys. Rev. Lett. 104, 195503 (2010))\comments{\cite{WRECORE}}. In addition to a change in the core symmetry, the values of the Peierls stress and barrier are reduced. The latter effect could lead to increased ductility in a tungsten-based alloy\comments{\cite{WRECORE}}. Our results demonstrate that alloying with any of the transition metals from the VIIIA group should have similar effect as alloying with Re.Comment: 12 pages, 8 figures, 3 table

Hyperglycaemia aversion in type 1 diabetes: A grounded theory study

Objective: Very little is known about the circumstances under which hyperglycaemia aversion develops and is maintained. The present study aimed to identify psychological factors involved in the process of hyperglycaemia aversion and to understand how it affects people's self‐management of type 1 diabetes. Design: Qualitative, in‐depth interviews were used. Methods: A constructivist grounded theory study, using semi‐structured participant interviews, was undertaken to build a theoretical model of the process of hyperglycaemia aversion. Results: Eighteen participants were interviewed. Fifteen were considered hyperglycaemia averse and included in the analysis. A theoretical model was developed to describe and explain processes involved in hyperglycaemia aversion. Many participants held very high standards for themselves and often had a strong preference for control. While some participants described anxiety associated with higher blood glucose, the most proximal driver of their approach was self‐criticism and frustration associated with not meeting their own high standards for blood glucose. A number of attentional processes and beliefs, mostly related to hypoglycaemia, maintained and reinforced their blood glucose preference. Diabetes technology served as an enabler, raiser of standards, and additional critical judge of participants' hyperglycaemia aversion. Conclusions: The trans‐diagnostic concept of emotional over‐control is used to understand the proposed model of processes of hyperglycaemia aversion. The present study offers new insight which will aid clinicians in identifying and supporting those who may be at risk of psychological distress and harm associated with a preference for avoidance of higher blood glucose levels

Torpor in dark times : patterns of heterothermy are associated with the lunar cycle in a nocturnal bird

Many studies have shown that endotherms become more heterothermic when the costs of thermoregulation are high and /or when limited energy availability constrains thermoregulatory capacity. However, the roles of many ecological variables, including constraints on foraging opportunities and/ or success, remain largely unknown. To test the prediction that thermoregulatory patterns should be related to foraging opportunities in a heterothermic endotherm, we examined the relationship between the lunar cycle and heterothermy in Freckled Nightjars (Caprimulgus tristigma), which are visually orienting, nocturnal insectivores that are dependent on ambient light to forage. This model system provides an opportunity to assess whether variation in foraging opportunities influences the expression of heterothermy. The nightjars were active and foraged for insects when moonlight was available but become inactive and heterothermic in the absence of moonlight. Lunar illumination was a much stronger predictor of the magnitude of heterothermic responses than was air temperature (Ta). Our data suggest that heterothermy was strongly related to variation in foraging opportunities associated with the lunar cycle, even though food abundance appeared to remain relatively high throughout the study period. Patterns of thermoregulation in this population of Freckled Nightjars provide novel insights into the environmental and ecological determinants of heterothermy, with the lunar cycle, and not Ta, being the strongest predictor of torpor use.The University of Pretoria; the Natural Sciences and Engineering Research Council, Canada; and the DST/NRF Centre of Excellence at the Percy FitzPatrick Institute.http://www.uk.sagepub.com/journals/Journal200933ab201

Avian thermoregulation in the heat : efficient evaporative cooling in two southern African nightjars

Please read abstract in the article.The DST-NRF Center of Excellence at the Percy FitzPatrick Institute and University of Pretoria.http://link.springer.com/journal/3602018-04-30hj2018Zoology and Entomolog

Mapping evaporative water loss in desert passerines reveals an expanding threat of lethal dehydration

Extreme high environmental temperatures produce a variety of consequences for wildlife, including mass die-offs. Heat waves are increasing in frequency, intensity, and extent, and are projected to increase further under climate change. However, the spatial and temporal dynamics of die-off risk are poorly understood. Here, we examine the effects of heat waves on evaporative water loss (EWL) and survival in five desert passerine birds across the southwestern United States using a combination of physiological data, mechanistically informed models, and hourly geospatial temperature data. We ask how rates of EWL vary with temperature across species; how frequently, over what areas, and how rapidly lethal dehydration occurs; how EWL and die-off risk vary with body mass; and how die-off risk is affected by climate warming. We find that smaller-bodied passerines are subject to higher rates of mass-specific EWL than larger-bodied counterparts and thus encounter potentially lethal conditions much more frequently, over shorter daily intervals, and over larger geographic areas. Warming by 4 °C greatly expands the extent, frequency, and intensity of dehydration risk, and introduces new threats for larger passerine birds, particularly those with limited geographic ranges. Our models reveal that increasing air temperatures and heat wave occurrence will potentially have important impacts on the water balance, daily activity, and geographic distribution of arid-zone birds. Impacts may be exacerbated by chronic effects and interactions with other environmental changes. This work underscores the importance of acute risks of high temperatures, particularly for small-bodied species, and suggests conservation of thermal refugia and water sources

Dehydration risk is associated with reduced nest attendance and hatching success in a cooperatively breeding bird, the southern pied babbler Turdoides bicolor

incubation in birds. Understanding the mechanisms driving these impacts requires comprehensive knowledge of animal physiology and behaviour under natural conditions. We used a novel combination of a non-invasive doubly labelled water (DLW) technique, nest temperature data and field-based behaviour observations to test effects of temperature, rainfall and group size on physiology and behaviour during incubation in southern pied babblers Turdoides bicolor, a cooperatively breeding passerine endemic to the arid savanna regions of southern Africa. The proportion of time that clutches were incubated declined as air temperatures increased, a behavioural pattern traditionally interpreted as a benefit of ambient incubation. However, we show that (i) clutches had a <50% chance of hatching when exposed to daily maximum air temperatures of >35.3◦C; (ii) pied babbler groups incubated their nests almost constantly (99% of daylight hours) except on hot days; (iii) operative temperatures in unattended nests frequently exceeded 40.5◦C, above which bird embryos are at risk of death; (iv) pied babblers incubating for long periods of time failed to maintain water balance on hot days; and (v) pied babblers from incubating groups lost mass on hot days. These results suggest that pied babblers might leave their nests during hot periods to lower the risk of dehydration associated with prolonged incubation at high operative temperatures. As mean air temperatures increase and extreme heat events become more frequent under climate change, birds will likely incur ever greater thermoregulatory costs of incubation, leading to compromised nest attendance and increased potential for eggs to overheat, with implications for nest success and, ultimately, population persistence.Australian Research Council, BBSRC David Phillips Fellowship, e British Ornithologists’ Union, DST-NRF Centre of Excellence, Oppenheimer Memorial Trust and University of Cape Town and the National Research Foundation of South Africa.http://conphys.oxfordjournals.orgdm2022Zoology and Entomolog

Role of Akt signaling pathway regulation in the speckled mousebird (Colius striatus) during torpor displays tissue specific responses

Pronounced heterothermic responses are relatively rare among birds. Along with taxa such as hummingbirds and caprimulgids, the order Coliiformes (mousebirds) is known to possess the physiological capacity for torpor. During torpor, body temperature is greatly reduced and a bird becomes unresponsive to external stimuli until ambient temperatures return to more favorable conditions. Under such conditions, these birds are forced to rely only on their internal fuel storage for energy and show great reduction in metabolic rates by decreasing energy-expensive processes. This study investigated the role of the key insulin-Akt signaling kinase pathway involved in regulating energy metabolism and protein translation in the liver, kidney, heart, skeletal muscle, and brain of the speckled mousebird (Colius striatus). The degree of phosphorylation of well-conserved target residues with important regulatory function was examined in both the euthermic control and torpid birds. The results demonstrated marked differences in responses between the tissues with decreases in RPS6 S235/236 phosphorylation in the kidney (0.52 fold of euthermic) and muscle (0.29 fold of euthermic) as well as decreases in GS3K3β S9 in muscle (0.60 fold of euthermic) and GSK3α S21 (0.71 fold of euthermic) phosphorylation in kidney during torpor, suggesting a downregulation of this pathway. Interestingly, the liver demonstrated an increase in RPS6 S235/236 (2.89 fold increase) and P70S6K T412 (1.44 fold increase) phosphorylation in the torpor group suggesting that protein translation is maintained in this tissue. This study demonstrates that avian torpor is a complex phenomenon and alterations in this signaling pathway follow a tissue specific pattern.Supplementary material 1: Western blots for quantifying the relative levels of phosphorylated S209 eIF-4E and total mTOR levels in euthermic and torpid C. striatus tissuesSupplementary material 2: Sequence alignment of mousebird protein targets involved in the Akt signaling kinase pathway and protein translation in comparison to human sequencesThe Natural Sciences and Engineering Research Council of Canada (NSERC), the Canada Research Chair in Molecular Physiology, an NSERC funded Alexander Graham Bell Canada Graduate Scholarship, an Ontario Graduate Scholarship and the National Research Foundation of South Africa.https://www.elsevier.com/locate/cellsig2021-11-01hj2020Zoology and Entomolog

Phosphorylation status of pyruvate dehydrogenase in the mousebird Colius striatus undergoing torpor

DATA AVAILABILITY STATEMENT : Data available on request from the authors.Torpor is a heterothermic response that occurs in some animals to reduce metabolic expenditure. The speckled mousebird (Colius striatus) belongs to one of the few avian taxa possessing the capacity for pronounced torpor, entering a hypometabolic state with concomitant decreases in body temperature in response to reduced food access or elevated thermoregulatory energy requirements. The pyruvate dehydrogenase complex (PDC) is a crucial site regulating metabolism by bridging glycolysis and the Krebs cycle. Three highly conserved phosphorylation sites are found within the E1 enzyme of the complex that inhibit PDC activity and reduce the flow of carbohydrate substrates into the mitochondria. The current study demonstrates a marked increase in S232 phosphorylation during torpor in liver, heart, and skeletal muscle of C. striatus. The increase in S232 phosphorylation during torpor was particularly notable in skeletal muscle where levels were ~49-fold higher in torpid birds compared to controls. This was in contrast to the other two phosphorylation sites (S293 and S300) which remained consistently phosphorylated regardless of tissue. The relevant PDH kinase (PDHK1) known to phosphorylate S232 was found to be substantially upregulated (~5-fold change) in the muscle during torpor as well as increasing moderately in the liver (~2.2-fold increase). Additionally, in the heart, a slight (~23%) decrease in total PDH levels was noted. Taken together the phosphorylation changes in PDH suggest that inhibition of the complex is a common feature across several tissues in the mousebird during torpor and that this regulation is mediated at a specific residue.Natural Sciences and Engineering Research Council of Canada and National Research Foundation of South Africa.http://wileyonlinelibrary.com/journal/jezhj2023Zoology and Entomolog