The ΔT thermal dose concept 1: in vivo teratogenesis

This project was an initial test of the hypothesis that there would be a ΔT thermal dose relationship for birth defects in rats (Rattus norvegicus) during neural tube closure (NTC). Additionally, the same thermal dose as applied during NTC in utero in vivo, was also applied to exteriorized (i.e., ex vivo) in utero pregnant uterine horns at a comparable stage of organogenesis. Since the yields of the two regimens were comparable, the hyperthermia-induced teratogenic effects appear to result from the thermal dosing of the in utero embryos and not the elevated temperature of the mother. The hypothesis was supported.     

Is there plasticity in developmental instability? The effect of daily thermal fluctuations in an ectotherm

Diversified bet‐hedging (DBH) by production of within‐genotype phenotypic variance may evolve to maximize fitness in stochastic environments. Bet‐hedging is generally associated with parental effects, but phenotypic variation may also develop throughout life via developmental instability (DI). This opens for the possibility of a within‐generation mechanism creating DBH during the lifetime of individuals. If so, DI could in fact be a plastic trait itself; if a fluctuating environment indicates uncertainty about future conditions, sensing such fluctuations could trigger DI as a DBH response. However, this possibility has received little empirical attention. Here, we test whether fluctuating environments may elicit such a response in the clonally reproducing crustacean Daphnia magna. Specifically, we exposed genetically identical individuals to two environments of different thermal stability (stable vs. pronounced daily realistic temperature fluctuations) and tested for effects on DI in body mass and metabolic rate shortly before maturation. Furthermore, we also estimated the genetic variation in DI. Interestingly, fluctuating temperatures did not affect body mass, but metabolic rate decreased. We found no evidence for plasticity in DI in response to environmental fluctuations. The lack of plasticity was common to all genotypes, and for both traits studied. However, we found considerable evolvability for DI, which implies a general evolutionary potential for DBH under selection for increased phenotypic variance.     

Do thick leaves avoid thermal damage in critically low wind speeds?

Transient lulls in air movement are rarely measured, but can cause leaf temperature to rise rapidly to critical levels. The high heat capacity of thick leaves can damp this rapid change in temperature. However, little is known about the extent to which increased leaf thickness can reduce thermal damage, or how thick leaves would need to be to have biological significance. We evaluated quantitatively the contribution of small increases in leaf thickness to the reduction in thermal damage during critically low wind speeds under desert conditions. We employed a numerical model to investigate the effect of thickness relative to transpiration, absorptance and leaf size on damage avoidance. We used measured traits and thermotolerance thresholds of real leaves to calculate the leaf temperature response to naturally occurring variable low wind speed. Our results demonstrated that an increase in thickness of only fractions of a millimetre can prevent excursions to damaging high temperatures. This damping effect of increased thickness was greatest when other means of reducing leaf temperature (transpiration, reflectance or reduced size) were lacking. For perennial desert flora, we propose that increased leaf thickness is important in decreasing the incidence of extreme heat stress and, in some species, in enhancing long-term survival.     

The ΔT thermal dose concept 2: in vitro cellular effects

The results of this project provide proof of concept for an analysis of hyperthermia-induced in vitro cellular effects in relation to a thermal dose determination with a temperature-differential basis from each cell line's historical physiological temperature (HPT). Human (Homo sapiens) fetal cells, whose HPT was assumed to be 37°C, and guinea pig (Cavia porcellus) fetal cells, whose HPT was assumed to be 39.5°C, were used. It was hypothesized that in vitro cellular functionality (e.g., fastest cell doubling time) would be maximal at each line's respective HPT and decrease with temperatures above and below each line's HPT. The hypothesis was supported.     

Why collagens best survived in fossils? Clues from amino acid thermal stability

Explaining why type I collagens are preferentially preserved in the geological time scale remains a challenge. Several pieces of evidence indicate that its rich content in the bone and its unique, stable structure played key roles in its preservation. By considering the distinct thermal stability of amino acids, we reveal that the elevated abundance of thermostable amino acid residues in type I collagens also contribute to its survival.     

Subjective estimation of thermal environment in recreational urban spaces—Part 1: investigations in Szeged,Hungary

During two investigation periods in transient seasons (14 weekdays in autumn 2009 and 15 weekdays in spring 2010) 967 visitors in two inner city squares of Szeged (Hungary) were asked about their estimation of their thermal environment. Interrelationships of subjective assessments—thermal sensation, perceptions and preferences for individual climate parameters—were analyzed, as well as their connections with the prevailing thermal conditions [air temperature, relative humidity, wind velocity, mean radiant temperature and physiologically equivalent temperature (PET)]. Thermal sensation showed strong positive relationships with air temperature and solar radiation perception, while wind velocity and air humidity perception had a negative (and weaker) impact. If a parameter was perceived to be low or weak, then it was usually desired to be higher or stronger. This negative correlation was weakest in the case of humidity. Of the basic meteorological parameters, Hungarians are most sensitive to variations in wind. Above PET?=?29°C, people usually prefer lower air temperature and less solar radiation. The temperature values perceived by the interviewees correlated stronger with PET, but their means were more similar to air temperature. It was also found that the mean thermal sensation of Hungarians in transient seasons depends on PET according to a quadratic function (R ²?=?0.912) and, consequently, the thermal comfort ranges of the locals differ from that usually adopted.     

A perspective on insect–microbe holobionts facing thermal fluctuations in a climate-change context

Temperature influences the ecology and evolution of insects and their symbionts by impacting each partner independently and their interactions, considering the holobiont as a primary unit of selection. There are sound data about the responses of these partnerships to constant temperatures and sporadic thermal stress (mostly heat shock). However, the current understanding of the thermal ecology of insect–microbe holobionts remains patchy because the complex thermal fluctuations (at different spatial and temporal scales) experienced by these organisms in nature have often been overlooked experimentally. This may drastically constrain our ability to predict the fate of mutualistic interactions under climate change, which will alter both mean temperatures and thermal variability. Here, we tackle down these issues by focusing on the effects of temperature fluctuations on the evolutionary ecology of insect–microbe holobionts. We propose potentially worth-investigating research avenues to (i) evaluate the relevance of theoretical concepts used to predict the biological impacts of temperature fluctuations when applied to holobionts; (ii) acknowledge the plastic (behavioural thermoregulation, physiological acclimation) and genetic responses (evolution) expressed by holobionts in fluctuating thermal environments; and (iii) explore the potential impacts of previously unconsidered patterns of temperature fluctuations on the outcomes and the dynamic of these insect–microbe associations.     

Is telomere length a molecular marker of past thermal stress in wild fish?

Telomeres protect eukaryotic chromosomes; variation in telomere length has been linked (primarily in homoeothermic animals) to variation in stress, cellular ageing and disease risk. Moreover, telomeres have been suggested to function as biomarker for quantifying past environmental stress, but studies in wild animals remain rare. Environmental stress, such as extreme environmental temperatures in poikilothermic animals, may result in oxidative stress that accelerates telomere attrition. However, growth, which may depend on temperature, can also contribute to telomere attrition. To test for associations between multitissue telomere length and past water temperature while accounting for the previous individual growth, we used quantitative PCR to analyse samples from 112 young‐of‐the‐year brown trout from 10 natural rivers with average water temperature differences of up to 6°C (and an absolute maximum of 23°C). We found negative associations between relative telomere length (RTL) and both average river temperature and individual body size. We found no indication of RTL–temperature association differences among six tissues, but we did find indications for differences among the tissues for associations between RTL and body size; size trends, albeit nonsignificant in their differences, were strongest in muscle and weakest in fin. Although causal relationships among temperature, growth, oxidative stress, and cross‐sectional telomere length remain largely unknown, our results indicate that telomere‐length variation in a poikilothermic wild animal is associated with both past temperature and growth.     

Exploring the thermal stability and activity of α-chymotrypsin in the presence of spermine

Polyamines such as spermine can have interaction with protein. The aim of the present study was to investigate how spermine could influence the structure, thermal stability, and the activity of α-chymotrypsin. Kinetics, thermodynamics, molecular dynamics (MD), and docking simulations studies were conducted to investigate the effect of spermine on the activity and structure of α-Chymotrypsin (α-Chy) in 50 mM Tris–HCl buffer, with the pH 8, using different spectroscopic techniques as well as molecular docking and MD simulations. The stability and activity of α-Chy were increased in the presence of spermine. The results of the kinetic study showed that the activity of spermine was increased. Enzyme activation was accompanied by changes on the α-Chy conformation. Fluorescence intensity changes showed dynamic quenching during spermine binding. The fluorescence quenching of the α-Chy suggested the more polar location of Trp residues. Near-UV and Far-UV circular dichroism studies also demonstrated the transfer of Trp, Phe, and Tyr residues to a more flexible environment. The increase in the absorption of α-Chy in the presence of spermine was as a result of the formation of spermine–α-Chy complex. Molecular docking results revealed the presence of one binding site with a negative value for the Gibbs free energy of the binding of spermine to α-Chy. Docking study also revealed that van der Waals interactions and hydrogen bonds played a major role in stabilizing the complex.     

Redistribution of GFAP and αB-crystallin after thermal stress in C6 glioma cell line

Summary Some intermediate filament (IF) proteins expressed in the development of glia include nestin, vimentin, and glial fibrillary acidic protein (GFAP). However, GFAP is the major intermediate filament protein of mature astrocytes. To determine the organization of GFAP in glial cells, rat GFAP cDNA tagged with enhanced green fluorescent protein (EGFP) was transfected into the rat C6 glioma cell line. After selection, two stable C6-EGFP-GFAP cell lines were established. Stable C6-EGFP-GFAP cell lines with or without heat shock treatment were analyzed by immunocytochemistry, electron microscopy, and Western blot analysis. In the transient transfection study, EGFP-GFAP transiently expressed in C6 cells formed punctate aggregations in the cytoplasm right after transfection, but gradually a filamentous structure of EGFP-GFAP was observed. The protein level of nestin in the C6-EGFP-GFAP stable clone was similar to that in the pEGFP-C1 transfected C6 stable clones and non-transfected C6 cells, whereas the level of vimentin was reduced in Western blotting. Interestingly, the expression level of small heat shock protein αB-crystallin in C6-EGFP-GFAP cells was also enhanced after transfection. Immunostaining patterns of C6-EGFP-GFAP cells showed that GFAP was dispersed as a fine filamentous structure. However, after heat shock treatment, GFAP formed IF bundles in C6-EGFP-GFAP cells. In the meantime, αB-crystallin also colocalized with IF bundles of GFAP in C6-EGFP-GFAP cells. The heat-induced GFAP reorganization we found suggested that small heat shock protein αB-crystallin may play a functional role regulating the cytoarchitecture of GFAP.     

Sensory recovery in a split skin graft: pinprick or a thermal sensory analyzer?

Sensory return in a split skin graft is an important factor in the protection of this graft from injury. Hence, three tests were compared: (1) the standard pain test using a simple pin, (2) the cold pain test, and (3) the hot pain test. Both the hot and cold pain tests were performed using the thermal sensory analyzer device. Thirteen patients were investigated; all had split skin grafts applied directly onto deep fascia after malignant melanoma excision on the lower limb. The period after grafting ranged from 4 to 15 years, and the mean age was 46.5 years. The normal contralateral side of each patient was used as the control for that patient. The results were collected in simple data tables and were analyzed using paired t tables for small samples with the level of significance set at p < 0.05. The standard pain test demonstrated that the split skin grafts applied on deep fascia did not recover sensation, even 15 years after surgery (p < 0.001). The hot and cold pain tests were both in agreement with the standard pain test at p < 0.001 and p < 0.03, respectively. The standard pain test is usually performed, as described in this study, using a pin, which is cheap and readily available in any plastic surgery and burn clinic. However, the cold and hot pain tests as performed here using the thermal sensory analyzer device are accurate but are costly, cumbersome, and not available in all clinics except for highly specialized units. Hence, the author would like to dispel the myth that the standard pain test is inaccurate. This might be so in testing sensation in "normal" skin but not in testing the recovery of sensation in a skin graft.     

Modeling thermal sensation in a Mediterranean climate—a comparison of linear and ordinal models

A simple thermo-physiological model of outdoor thermal sensation adjusted with psychological factors is developed aiming to predict thermal sensation in Mediterranean climates. Microclimatic measurements simultaneously with interviews on personal and psychological conditions were carried out in a square, a street canyon and a coastal location of the greater urban area of Athens, Greece. Multiple linear and ordinal regression were applied in order to estimate thermal sensation making allowance for all the recorded parameters or specific, empirically selected, subsets producing so-called extensive and empirical models, respectively. Meteorological, thermo-physiological and overall models - considering psychological factors as well - were developed. Predictions were improved when personal and psychological factors were taken into account as compared to meteorological models. The model based on ordinal regression reproduced extreme values of thermal sensation vote more adequately than the linear regression one, while the empirical model produced satisfactory results in relation to the extensive model. The effects of adaptation and expectation on thermal sensation vote were introduced in the models by means of the exposure time, season and preference related to air temperature and irradiation. The assessment of thermal sensation could be a useful criterion in decision making regarding public health, outdoor spaces planning and tourism.     

‘Optimal thermal range’ in ectotherms: Defining criteria for tests of the temperature-size-rule

Thermal performance curves for population growth rate r (a measure of fitness) were estimated over a wide range of temperature for three species: Coleps hirtus (Protista), Lecane inermis (Rotifera) and Aeolosoma hemprichi (Oligochaeta). We measured individual body size and examined if predictions for the temperature-size rule (TSR) were valid for different temperatures. All three organisms investigated follow the TSR, but only over a specific range between minimal and optimal temperatures, while maintenance at temperatures beyond this range showed the opposite pattern in these taxa. We consider minimal and optimal temperatures to be species-specific, and moreover delineate a physiological range outside of which an ectotherm is constrained against displaying size plasticity in response to temperature. This thermal range concept has important implications for general size-temperature studies. Furthermore, the concept of 'operating thermal conditions' may provide a new approach to (i) defining criteria required for investigating and interpreting temperature effects, and (ii) providing a novel interpretation for many cases in which species do not conform to the TSR.     

Coral mortality associated with thermal fluctuations in the Phoenix Islands, 2002�C2005

The Phoenix Islands (Republic of Kiribati, 172–170°W and 2.5–5°S) experience intra- and inter-annual sea surface temperature variability of ≈2°C and have few local anthropogenic impacts. From July 2002, a thermal stress event occurred, which peaked at 21 Degree Heating Weeks (DHW) in January 2003 and persisted for 4 years. Such thermal stress was greater than any thermal event reported in the coral reef literature. Reef surveys were conducted in July 2000, June 2002, and May 2005, for six of the eight islands. Sampling was stratified by exposure (windward, leeward, and lagoon) and depth (5, 10, 15, and 25 m). The thermal stress event caused mass coral mortality, and coral cover declined by approximately 60% between 2002 and 2005. However, mortality varied among sites (12–100%) and among islands (42–79%) and varied in accordance with the presence of a lagoon, island size, and windward vs. leeward exposure. Leeward reefs experienced the highest and most consistent decline in coral cover. Island size and the presence of a lagoon showed positive correlations with coral mortality, most likely because of the longer water residence time enhancing heating. Windward reefs showed cooler conditions than leeward reefs. Recently dead corals were observed at depths >35 m on windward and >45 m on leeward reefs. Between-island variation in temperature had no effect on between-island variation in coral mortality. Mortality levels reported here were comparable to those reported for the most extreme thermal stress events of 9–10 DHW in other regions. These results highlight the high degree of acclimation and/or adaptation of the corals in the Phoenix Islands to their local temperature regime, and their consequent vulnerability to anomalous events. Moreover, the results suggest the need to adjust thermal stress calculations to reflect local temperature variation.     

Subjective estimations of thermal environment in recreational urban spaces—Part 2: international comparison

The present paper is the second part of our study in which we compare the results obtained in Szeged (Hungary) with those achieved through earlier outdoor thermal comfort projects based on simultaneous questionnaire surveys and on-site meteorological measurements. The main characteristics of the selected studies—conducted in Hungary, Sweden, Portugal, Canada, Taiwan and across Europe in the frame of project RUROS—are reviewed, emphasizing the common features and also the discrepancies in the applied methodology. We discuss their potential effects on the evolution and interpretation of the results concerning the subjective assessment of the thermal environment. Another aspect of the comparison focuses on the regional climatic differences naturally ensuing from the various locations, which left their marks on the results related to both physiological acclimatization and mental adaptation. The compared results of different studies include correlation coefficients expressing interrelationships between the different aspects of subjective estimations (thermal sensation, perceptions, preferences) and also between subjective assessments and the corresponding meteorological parameters. We compare neutral temperatures (expressed in physiological equivalent temperature, PET) which arose for Taiwan and Hungary, as well as thermal sensation zones for local inhabitants. Subjectively assessed temperature values of Sweden and Hungarians are analyzed according to the measured air temperature. According to our experiences the methodology should be standardized for the level of field surveys and also for the level of data processing in order to make the data collected in different locations comparable.     

Orexin inputs to caudal raphé neurons involved in thermal,cardiovascular, and gastrointestinal regulation

Orexin-expressing neurons in the lateral hypothalamus with their wide projections throughout the brain are important for the regulation of sleep and wakefulness, ingestive behavior, and the coordination of these behaviors in the environmental context. To further identify downstream effector targets of the orexin system, we examined in detail orexin-A innervation of the caudal raphé nuclei in the medulla, known to harbor sympathetic preganglionic motor neurons involved in thermal, cardiovascular, and gastrointestinal regulation. All three components of the caudal raphé nuclei, raphé pallidus, raphé obscurus, and parapyramidal nucleus, are innervated by orexin-A-immunoreactive fibers. Using confocal microscopy, we demonstrate close anatomical appositions between varicose orexin-A immunoreactive axon profiles and sympathetic premotor neurons identified with either a transneuronal retrograde pseudorabies virus tracer injected into the interscapular brown fat pads, or with in situ hybridization of pro-TRH mRNA. Furthermore, orexin-A injected into the fourth ventricle induced c-Fos expression in the raphé pallidus and parapyramidal nucleus. These findings suggest that orexin neurons in the hypothalamus can modulate brown fat thermogenesis, cardiovascular, and gastrointestinal functions by acting directly on neurons in the caudal raphé nuclei, and support the idea that orexins simultaneous stimulation of food intake and sympathetic activity might have evolved as a mechanism to stay alert while foraging.     

Is DNA damage the signal for induction of thermal resistance? induction by radiation in yeast

Yeast, as well as higher eukaryotes, are induced to increase thermal resistance (thermotolerance) by prior exposure to a heat stress. Prior exposure to an acute dose of either 60Co gamma or 254-nm ultraviolet radiation, at sublethal or fractionally lethal doses, is shown to cause a marked increase in the resistance of Saccharomyces cerevisiae to killing by heat. Following a radiation exposure, thermal resistance increased with time during incubation in nutrient medium, and the degree of resistance reached was proportional to the dose received. Partial induction by radiation followed by maximum induction by heat did not produce an additive response when compared to a maximum induction by heat alone, suggesting that the same process was induced by both heat and radiation. Irradiation with 254-nm uv light followed by an immediate, partial photoreversal of the pyrimidine dimers with long-wavelength uv light resulted in a reduced level of resistance compared to cells not exposed to the photoreversal light, indicating that the cells specifically recognized pyrimidine dimers as a signal to increase their thermal resistance. Exposure to 254-nm uv or ionizing radiation induced thermal resistance in mutants defective in either excision repair (rad3, uv-sensitive) or recombinational repair (rad52, gamma-sensitive), suggesting that recognition and repair of DNA damage by these systems are not a part of the signal which initiates an increase in resistance to heat. The amount of induction, per unit dose, was greater in the DNA repair-deficient mutants than in the wild-type cells, suggesting that an increase in the length of time during which damage remains in the DNA results in an increase in the effectiveness of the induction. These data indicate that types of DNA damage as diverse as those produced by ionizing radiation and by ultraviolet light are recognized as a signal by the yeast cell to increase its thermal resistance. It is therefore suggested that heat-induced alterations in DNA or in DNA-dependent chromosomal organization may be the signal for heat induction of thermotolerance in this and other eukaryotes.