The effects of two different types of clothing on seasonal warm acclimatization

The work described in this paper investigates the effects of two types of clothing leaving the legs covered or uncovered, on seasonal warm acclimatization in women. Experiments were carried out to observe the differences in thermal responses between two groups of subjects who dressed themselves in trousers or kneelength skirts during the daytime for 3 months from April to June. Rectal temperatures in the subjects wearing skirts were found to be shifted to higher levels when the season gradually became warmer from spring to summer. The results suggest that the clothing type worn in daily life may play an important role in the seasonal warm acclimatization of thermal responses in humans.     

The effects of two types of clothing on seasonal cold tolerance

This study investigated the effects of two types of clothing, leaving legs covered or uncovered, on seasonal cold tolerance in women. Experiments were carried out to compare cold tolerance at an ambient temperature (T _a) of 10° C in December between two groups of subjects, who wore either knee-length skirts (skirt group) or full-length trousers (trouser group) for 3 months from September to November. The main results are summarized as follows: rectal temperatures continued to fall for 40 min in the trouser group when the subjects were covered by a blanket, while it became stable in 30 min in the skirt group; rectal temperatures showed greater increases in the skirt group when the blanket was removed after 40 min exposure to T _a of 10° C; metabolic heat production was kept significantly lower in the skirt group when uncovered or covered by a blanket at T _a of 10° C; metabolic heat production was negatively correlated with mean skin temperature and was always higher in the trouser group when measured at the same mean skin temperature; in the uncovered condition diastolic blood pressure increased significantly in the trouser group but not in the skirt group. These results would suggest that the subjects who wore skirts for 3 months from September to November had improved their ability to tolerate the cold.     

Limited plasticity of low temperature tolerance in an Australian cantharid beetle Chauliognathus lugubris

Spatial and/or taxonomic bias in thermal tolerance and plasticity data can severely impact projections of climate change responses and limit the understanding of the evolution of thermal performance curves. Thus, further data from under‐represented groups and geographical locations are important for synthesizing and predicting the physiological responses of insects to climate variability. For example, the magnitude of rapid cold‐hardening (RCH) and seasonal acclimatization of low temperature tolerance are typically poorly documented for nondipteran species from the southern Hemisphere. Moreover, few studies assess RCH responses under different acclimation regimes. To address this paucity of data, the low temperature survival, RCH and acclimation ability of Chauliognathus lugubris (F.) are assessed from an adult aggregation collected in Armidale, New South Wales, Australia. Beetles are acclimated to either 27 or 20 °C for 1 week and then tested for their ability to survive cold shock or rapidly cold‐harden. There is no effect of acclimation on low temperature survival (mean survival range at ?5.4 °C for 2 h: 4–52% in 27 and 20 °C acclimation groups). In addition, beetles show no significant improvement in survival after acute thermal pretreatments. In conclusion, these data suggest a generally poor acclimation potential of low temperature survival and no RCH responses in adult Australian cantharid beetles, which is accordance with what might be expected given the microclimate experienced, their ability for behavioural regulation and the life history of the species.     

Seasonal variation in basal and plastic cold tolerance: Adaptation is influenced by both long‐ and short‐term phenotypic plasticity

Understanding how thermal selection affects phenotypic distributions across different time scales will allow us to predict the effect of climate change on the fitness of ectotherms. We tested how seasonal temperature variation affects basal levels of cold tolerance and two types of phenotypic plasticity in Drosophila melanogaster. Developmental acclimation occurs as developmental stages of an organism are exposed to seasonal changes in temperature and its effect is irreversible, while reversible short‐term acclimation occurs daily in response to diurnal changes in temperature. We collected wild flies from a temperate population across seasons and measured two cold tolerance metrics (chill‐coma recovery and cold stress survival) and their responses to developmental and short‐term acclimation. Chill‐coma recovery responded to seasonal shifts in temperature, and phenotypic plasticity following both short‐term and developmental acclimation improved cold tolerance. This improvement indicated that both types of plasticity are adaptive, and that plasticity can compensate for genetic variation in basal cold tolerance during warmer parts of the season when flies tend to be less cold tolerant. We also observed a significantly stronger trade‐off between basal cold tolerance and short‐term acclimation during warmer months. For the longer‐term developmental acclimation, a trade‐off persisted regardless of season. A relationship between the two types of plasticity may provide additional insight into why some measures of thermal tolerance are more sensitive to seasonal variation than others.     

Evolution of thermotolerance in seasonal environments: the effects of annual temperature variation and life-history timing in Wyeomyia smithii

In organisms with complex life cycles, the adaptive value of thermotolerance depends on life-history timing and seasonal temperature profiles. We illustrate this concept by examining variation in annual thermal environments and thermal acclimation among four geographic populations of the pitcher plant mosquito. Only diapausing larvae experience winter, whereas both postdiapause and nondiapause adults occur only during the growing season. Thus, adults experience transient cold stress primarily during the spring. We show that adult cold tolerance (chill coma recovery) is enhanced in spring-like conditions via thermal acclimation but is unaffected by diapause state. Moreover, adult mosquitoes from northern populations were more cold tolerant than those from southern populations largely because acclimation responses were steeper in the north. In contrast to cold tolerance, there was no significant acclimation of heat tolerance (heat knockdown), and no significant differences in heat tolerance between northern and southern populations. Field temperature data show that because of evolved differences in diapause timing, adult exposure to cold stress is remarkably consistent across geography. This suggests that geographic variation in cold tolerance may not be the result of direct selection on adults. Our results illustrate the importance of the interplay between phenological and thermal adaptation for understanding variation along climatic gradients.     

Thermoregulatory and subjective responses of clothed men in the cold during continuous and intermittent exercise

Thermoregulatory and thermal subjective responses were studied in ten male, clothed subjects during continuous (C) and intermittent (I) exercise at the same average level of oxygen consumption. The subjects performed both I and C twice, dressed in two different three-layer cold-protective clothing ensembles of two thermal insulation levels [total clothing insulation = 2.59 clo (L) and 3.20 clo (H)]. Experiments were carried out at an ambient temperature of -10 degrees C. Rectal temperatures increased similarly in both types of exercise. Mean skin temperature (Tsk) was lower in I compared to C with both levels of clothing insulation. Over the last 0.5 h of the experiment Tsk was approximately 1.3 degrees C lower in I than in C for clothing L. The skin evaporation rate was higher in clothing H than L but did not differ between I and C. Subjective ratings for thermal sensations of the whole body (BTS) and hands were close to neutral in I and around slightly warm in C. The BTS was lower in I than in C and was lower in L compared to H. It was concluded that, at equal average energy expenditure, thermal responses to intermittent and continuous exercise in the cold differ in clothed subjects, principally as a result of different patterns of heat exchange.     

How consistent are the transcriptome changes associated with cold acclimation in two species of the Drosophila virilis group?

For many organisms the ability to cold acclimate with the onset of seasonal cold has major implications for their fitness. In insects, where this ability is widespread, the physiological changes associated with increased cold tolerance have been well studied. Despite this, little work has been done to trace changes in gene expression during cold acclimation that lead to an increase in cold tolerance. We used an RNA-Seq approach to investigate this in two species of the Drosophila virilis group. We found that the majority of genes that are differentially expressed during cold acclimation differ between the two species. Despite this, the biological processes associated with the differentially expressed genes were broadly similar in the two species. These included: metabolism, cell membrane composition, and circadian rhythms, which are largely consistent with previous work on cold acclimation/cold tolerance. In addition, we also found evidence of the involvement of the rhodopsin pathway in cold acclimation, a pathway that has been recently linked to thermotaxis. Interestingly, we found no evidence of differential expression of stress genes implying that long-term cold acclimation and short-term stress response may have a different physiological basis.     

Effects of thermal environment on sleep and circadian rhythm

ABSTRACT: The thermal environment is one of the most important factors that can affect human sleep. The stereotypical effects of heat or cold exposure are increased wakefulness and decreased rapid eye movement sleep and slow wave sleep. These effects of the thermal environment on sleep stages are strongly linked to thermoregulation, which affects the mechanism regulating sleep. The effects on sleep stages also differ depending on the use of bedding and/or clothing. In semi-nude subjects, sleep stages are more affected by cold exposure than heat exposure. In real-life situations where bedding and clothing are used, heat exposure increases wakefulness and decreases slow wave sleep and rapid eye movement sleep. Humid heat exposure further increases thermal load during sleep and affects sleep stages and thermoregulation. On the other hand, cold exposure does not affect sleep stages, though the use of beddings and clothing during sleep is critical in supporting thermoregulation and sleep in cold exposure. However, cold exposure affects cardiac autonomic response during sleep without affecting sleep stages and subjective sensations. These results indicate that the impact of cold exposure may be greater than that of heat exposure in real-life situations; thus, further studies are warranted that consider the effect of cold exposure on sleep and other physiological parameters.     

Onset of freezing tolerance in birch (Betula pubescens Ehrh.) involves LEA proteins and osmoregulation and is impaired in an ABA-deficient genotype

In many woody plants a short photoperiod triggers the onset of cold acclimation, but the nature of this process has remained obscure. We aimed to establish which physiological and genetic factors have a role in short-day-induced acclimation by comparing two types of birch, Betula pubescens Ehrh. and B. pubescens f. hibernifolia Ulv., the latter being unable to increase its abscisic acid (ABA) levels. In the wild type, short-day or natural autumn conditions in the field appeared to elevate the ABA levels before acclimation, which was accompanied by tissue desiccation, osmotic adjustments and accumulation of Group 2 LEA proteins [responsive to ABA (RAB) 16-like; 24, 30 and 33 kDa] and Group 4 LEA proteins [late embryogenesis abundant (LEA) 14-like; 19 kDa]. Under similar conditions the ABA-deficient birch showed reduced water loss, defective osmoregulation, absence of inducible Group 2 LEA proteins, and delayed or reduced tolerance to freezing. In contrast, both birch genotypes showed similar seasonal production patterns of Group 4 LEA proteins. Our results demonstrate that onset of cold acclimation in birch is based on multiple mechanisms, including molecular pathways that are typical of stress responses. ABA may be important for the accurate timing of cold acclimation in trees that are sensitive to photoperiod.     

Review on modeling heat transfer and thermoregulatory responses in human body

Several mathematical models of human thermoregulation have been developed, contributing to a deep understanding of thermal responses in different thermal conditions and applications. In these models, the human body is represented by two interacting systems of thermoregulation: the controlling active system and the controlled passive system. This paper reviews the recent research of human thermoregulation models. The accuracy and scope of the thermal models are improved, for the consideration of individual differences, integration to clothing models, exposure to cold and hot conditions, and the changes of physiological responses for the elders. The experimental validated methods for human subjects and manikin are compared. The coupled method is provided for the manikin, controlled by the thermal model as an active system. Computational Fluid Dynamics (CFD) is also used along with the manikin or/and the thermal model, to evaluate the thermal responses of human body in various applications, such as evaluation of thermal comfort to increase the energy efficiency, prediction of tolerance limits and thermal acceptability exposed to hostile environments, indoor air quality assessment in the car and aerospace industry, and design protective equipment to improve function of the human activities.     

Extensive Acclimation in Ectotherms Conceals Interspecific Variation in Thermal Tolerance Limits

Species’ tolerance limits determine their capacity to tolerate climatic extremes and limit their potential distributions. Interspecific variation in thermal tolerances is often proposed to indicate climatic vulnerability and is, therefore, the subject of many recent meta-studies on differential capacities of species from climatically different habitats to deal with climate change. Most studies on thermal tolerances do not acclimate animals or use inconsistent, and insufficient, acclimation times, limiting our knowledge of the shape, duration and extent of acclimation responses. Consequently patterns in thermal tolerances observed in meta-analyses, based on data from the literature are based on inconsistent, partial acclimation and true trends may be obscured. In this study we describe time-course of complete acclimation of critical thermal minima in the tropical ectotherm Carlia longipes and compare it to the average acclimation response of other reptiles, estimated from published data, to assess how much acclimation time may contribute to observed differences in thermal limits. Carlia longipes decreased their lower critical thermal limits by 2.4°C and completed 95% of acclimation in 17 weeks. Wild populations did not mirror this acclimation process over the winter. Other reptiles appear to decrease cold tolerance more quickly (95% in 7 weeks) and to a greater extent, with an estimated average acclimation response of 6.1°C. However, without data on tolerances after longer acclimation times available, our capacity to estimate final acclimation state is very limited. Based on the subset of data available for meta-analysis, much of the variation in cold tolerance observed in the literature can be attributed to acclimation time. Our results indicate that (i) acclimation responses can be slow and substantial, even in tropical species, and (ii) interspecific differences in acclimation speed and extent may obscure trends assessed in some meta-studies. Cold tolerances of wild animals are representative of cumulative responses to recent environments, while lengthy acclimation is necessary for controlled comparisons of physiological tolerances. Measures of inconsistent, intermediate acclimation states, as reported by many studies, represent neither the realised nor the potential tolerance in that population, are very likely underestimates of species’ physiological capacities and may consequently be of limited value.     

Fall field crickets did not acclimate to simulated seasonal changes in temperature

In nature, many organisms alter their developmental trajectory in response to environmental variation. However, studies of thermal acclimation have historically involved stable, unrealistic thermal treatments. In our study, we incorporated ecologically relevant treatments to examine the effects of environmental stochasticity on the thermal acclimation of the fall field cricket (Gryllus pennsylvanicus). We raised crickets for 5 weeks at either a constant temperature (25°C) or at one of three thermal regimes mimicking a seasonal decline in temperature (from 25 to 12°C). The latter three treatments differed in their level of thermal stochasticity: crickets experienced either no diel cycle, a predictable diel cycle, or an unpredictable diel cycle. Following these treatments, we measured several traits considered relevant to survival or reproduction, including growth rate, jumping velocity, feeding rate, metabolic rate, and cold tolerance. Contrary to our predictions, the acclimatory responses of crickets were unrelated to the magnitude or type of thermal variation. Furthermore, acclimation of performance was not ubiquitous among traits. We recommend additional studies of acclimation in fluctuating environments to assess the generality of these findings.     

A proposed role for the anaerobic pathway during low-temperature sweetening in tubers of Solanum tuberosum

Survival and growth of temperate zone woody plants under changing seasonal conditions is dependent on proper timing of cold acclimation and development of vegetative dormancy, shortening photoperiod being an important primary signal to induce these adaptive responses. To elucidate the physiological basis for climatic adaptation in trees, we have characterized photoperiodic responses in the latitudinal ecotypes of silver birch ( Betula pendula Roth) exposed to gradually shortening photoperiod under controlled conditions. In all ecotypes, shortening photoperiod triggered growth cessation, cold acclimation and dormancy development, that was accompanied by increases in endogenous abscisic acid (ABA) and decreases in indole-3-acetic acid (IAA). There were distinct differences between the ecotypes in the rates and degrees of these responses. The critical photoperiod and the photoperiodic sensitivity for growth cessation varied with latitudinal origin of the ecotype. The northern ecotype had a longer critical photoperiod and a greater photoperiodic sensitivity than the southern ecotype. Compared with the southern ecotypes, the northern ecotype was more responsive to shortening photoperiod, resulting in earlier cold acclimation, dormancy development, increase in ABA content and decrease in IAA content. However, at the termination of the experiment, all the ecotypes had reached approximately the same level of cold hardiness (−12 to −14°C), ABA content (2.1–2.3 µg g⁻¹ FW) and IAA content (17.2–20.3 ng g⁻¹ FW). In all ecotypes, increase in ABA levels preceded development of bud dormancy and maximum cold hardiness. IAA levels decreased more or less parallel with increasing cold hardiness and dormancy, suggesting a role of IAA in the photoperiodic control of growth, cold acclimation and dormancy development in birch.     

Does declining carbon‐use efficiency explain thermal acclimation of soil respiration with warming?

Enhanced soil respiration in response to global warming may substantially increase atmospheric CO₂ concentrations above the anthropogenic contribution, depending on the mechanisms underlying the temperature sensitivity of soil respiration. Here, we compared short‐term and seasonal responses of soil respiration to a shifting thermal environment and variable substrate availability via laboratory incubations. To analyze the data from incubations, we implemented a novel process‐based model of soil respiration in a hierarchical Bayesian framework. Our process model combined a Michaelis–Menten‐type equation of substrate availability and microbial biomass with an Arrhenius‐type nonlinear temperature response function. We tested the competing hypotheses that apparent thermal acclimation of soil respiration can be explained by depletion of labile substrates in warmed soils, or that physiological acclimation reduces respiration rates. We demonstrated that short‐term apparent acclimation can be induced by substrate depletion, but that decreasing microbial biomass carbon (MBC) is also important, and lower MBC at warmer temperatures is likely due to decreased carbon‐use efficiency (CUE). Observed seasonal acclimation of soil respiration was associated with higher CUE and lower basal respiration for summer‐ vs. winter‐collected soils. Whether the observed short‐term decrease in CUE or the seasonal acclimation of CUE with increased temperatures dominates the response to long‐term warming will have important consequences for soil organic carbon storage.     

Effect of fasting and thermal acclimation on metabolism of juvenile axolotls (Ambystoma mexicanum)

Juvenile axolotls were acclimated to 15○C or 25○C and either fed or fasted at both temperatures, to study the interaction of thermal acclimation and nutritional state on metabolism. Fasting but not thermal acclimation significantly increased oxygen consumption at 15○C. Fasting also increased the specific activities of two oxidative metabolic enzymes – citrate synthase and cytochrome oxidase – but not that of the glycolytic enzyme lactic dehydrogenase. The specific activity of cytochrome oxidase was further stimulated by cold acclimation. Triglycerides and fatty acids were severely depleted in fasted animals, but thermal acclimation had no significant effect on lipid stores. This study illustrates: (1) the differential nature of various metabolic responses to fasting; and (2) the confounding interaction of the nutritional state on thermal acclimation experiments in an ectotherm.     

Changes in carbohydrates, ABA and bark proteins during seasonal cold acclimation and deacclimation in Hydrangea species differing in cold hardiness

Cold injury is frequently seen in the commercially important shrub Hydrangea macrophylla but not in Hydrangea paniculata. Cold acclimation and deacclimation and associated physiological adaptations were investigated from late September 2006 to early May 2007 in stems of field-grown H. macrophylla ssp. macrophylla (Thunb.) Ser. cv. Blaumeise and H. paniculata Sieb. cv. Kyushu. Acclimation and deacclimation appeared approximately synchronized in the two species, but they differed significantly in levels of mid-winter cold hardiness, rates of acclimation and deacclimation and physiological traits conferring tolerance to freezing conditions. Accumulation patterns of sucrose and raffinose in stems paralleled fluctuations in cold hardiness in both species, but H. macrophylla additionally accumulated glucose and fructose during winter, indicating species-specific differences in carbohydrate metabolism. Protein profiles differed between H. macrophylla and H. paniculata, but distinct seasonal patterns associated with winter acclimation were observed in both species. In H. paniculata concurrent increases in xylem sap abscisic acid (ABA) concentrations ([ABA](xylem)) and freezing tolerance suggests an involvement of ABA in cold acclimation. In contrast, ABA from the root system was seemingly not involved in cold acclimation in H. macrophylla, suggesting that species-specific differences in cold hardiness may be related to differences in [ABA](xylem). In both species a significant increase in stem freezing tolerance appeared long after growth ceased, suggesting that cold acclimation is more regulated by temperature than by photoperiod.     

Some aspects of the mechanism of thermal acclimation in the earthworm Lampito mauritii

Summary Inorganic ions (Ca, Mg, Na, K, Cl, SO₄) and free amino acids of the body fluids of the normal, cold and warm acclimated worms (laboratory as well as seasonal populations) are estimated. Calcium increased and chloride and sodium decreased on both cold and warm acclimation in relation to normal. But magnesium and sulphate and free amino acids increased on warm acclimation whereas potassium increased and magnesium decreased on cold acclimation. Changes in different ions in the same direction are observed in the seasonal populations. Attention is drawn to the adaptive significance of these changes in the different ions during thermal acclimation.Changes in the glycogen, RNA, protein and non-protein nitrogen, and water content in the tissues of normal and acclimated worms are studied. Glycogen increased on warm and cold acclimation, whereas RNA content, protein nitrogen and dry weight of the cold worms increased over normal. No change is observed in non-protein nitrogen on thermal acclimation. The role of these substances and the significance of the changes observed, in the operation of homeostatic mechanism compensating to temperature changes in the metabolic rate of the worms, are also discussed.Changes in the pattern of neurosecretory activity are followed with thermal acclimation and it is shown that the activity of the neurosecretory cells increased on cold and warm acclimation, but the positions of these cells, which are active, are different from normal worms in warm acclimated worms.Studies on the effect of the body fluids of acclimated worms on the tissues of normal and acclimated worms showed that the body fluids of cold acclimated worms increased the respiration of the tissues of normal and warm acclimated worms and vice-versa.     

Evolutionary Analyses of Morphological and Physiological Plasticity in Thermally Variable Environments

SYNOPSIS. Morphological and physiological plasticity is oftenthought to represent an adaptive response to variable environments.However, determining whether a given pattern of plasticity isin fact adaptive is analytically challenging, as is evaluatingthe degree of and limits to adaptive plasticity. Here we describea general methodological framework for studying the evolutionof plastic responses. This framework synthesizes recent analyticaladvances from both evolutionary ecology and functional biology,and it does so by integrating field experiments, functionaland physiological analyses, environmental data, and geneticstudies of plasticity. We argue that studies of plasticity inresponse to the thermal environment may be particularly valuablein understanding the role of environmental variation in theevolution of plasticity: not only can thermally-relevant traitsoften be mechanistically and physiologically linked to the thermalenvironment, but also the variability and predictability ofthe thermal environment itself can be quantified on ecologicallyrelevant time scales. We illustrate this approach by reviewinga case study of seasonal plasticity in the extent of wing melanizationin Western White Butterflies (Pontia occidentalis). This reviewdemonstrates that 1) wing melanin plasticity is heritable, 2)plasticity does increase fitness in nature, but the effect variesbetween seasons and between years, 3) selection on existingvariation in the magnitude of plasticity favors increased plasticityin one melanin trait that affects thermoregulation, but 4) themarked unpredictability of short-term (within-season) weatherpatterns substantially limits the capacity of plasticity tomatch optimal wing phenotypes to the weather conditions actuallyexperienced. We complement the above case study with a casualreview of selected aspects of thermal acclimation responses.The magnitude of thermal acclimation ("flexibility") is demonstrablymodest rather than fully compensatory. The magnitude of geneticvariation (crucial to evolutionary responses to selection) inthermal acclimation responses has been investigated in onlya few species to date. In conclusion, we suggest that an understandingof selection and evolution of thermal acclimation will be enhancedby experimental examinations of mechanistic links between traitsand environments, of the physiological bases and functionalconsequences of acclimation, of patterns of environmental variabilityand predictability, of the fitness consequences of acclimationin nature, and of potential genetic constraints.     

The persistence of short‐term cold acclimation in Drosophila melanogaster (Diptera: Drosophilidae)

Daily and seasonal fluctuations in temperature present significant challenges for the survival of many ectothermic species that can be tempered via thermal acclimation. In the present study, we use multiple naturally derived genotypes of Drosophila melanogaster to determine the persistence of beneficial short‐term thermal acclimation on subsequent survival after cold shock. We found that the benefit of short‐term acclimation persisted for 2 h in most genotypes after a rapid cold hardening treatment. Genotype did not directly influence the persistence of short‐term acclimation benefits, indicating that environmental variation may be more important for the persistence of acclimation benefits rather than genetic capacity for acclimation. The present study extends the current understanding of the limits and importance of short‐term acclimation events, providing greater detail on the timing of the loss of short‐term acclimation benefits in a genetically variable natural population.     

Hardening trumps acclimation in improving cold tolerance of Drosophila melanogaster larvae

Abstract Chill‐susceptible insects are able to improve their survival of acute cold exposure over both the short term (i.e. hardening at a relatively severe temperature) and longer term (i.e. acclimation responses at milder temperatures over a longer time frame). However, the mechanistic overlap of these responses is not clear. Four larval stages of four different strains of Drosophila melanogaster are used to test whether low temperature acclimation (10 °C for 48 h) improves the acute cold tolerance (LT₉₀, ～2 h) of larvae, and whether acclimated larvae still show hardening responses after brief exposures to nonlethal cold or heat, or a combination of the two. Acclimation results in increased cold tolerance in three of four strains, with variation among instars. However, if acclimation is followed by hardening pre‐treatments, there is no improvement in acute cold survival. It is concluded that short‐term thermal responses (e.g. hardening) may be of more ecological relevance to short‐lived life stages such as larvae, and that the mechanisms of low temperature hardening and acclimation in D. melanogaster may be antagonistic, rather than complementary.