Increased Heat Tolerance Research Articles

Heat-absorbing sexual coloration co-adapts with increased heat tolerance in dragonflies

Heat-absorbing sexual coloration co-adapts with increased heat tolerance in dragonflies

OsRHS Negatively Regulates Rice Heat Tolerance at the Flowering Stage by Interacting With the HSP Protein cHSP70-4.

Heat stress at the flowering stage significantly impacts rice grain yield, yet the number of identified genes associated with rice heat tolerance at this crucial stage remains limited. This study focuses on elucidating the function of the heat-induced gene reduced heat stress tolerance 1 (OsRHS). Overexpression of OsRHS leads to reduced heat tolerance, while RNAi silencing or knockout of OsRHS enhances heat tolerance without compromising yield, as assessed by the seed setting rate. OsRHS is localized in the cytoplasm and mainly expressed in the glume and anther of spikelet. Moreover, OsRHS was found to interact with the HSP protein cHSP70-4, and the knockout of cHSP70-4 resulted in increased heat tolerance. Complementation assays revealed that the knockout of cHSP70-4 could restore the compromised heat tolerance in OsRHS overexpression plants. Additional investigation reveals that elevated temperatures can amplify the bond between OsRHS and cHSP70-4 within rice. Furthermore, our findings indicate that under heat stress conditions during the flowering stage, OsRHS plays a negative regulatory role in the expression of many stress-related genes. These findings unveil the crucial involvement of OsRHS and cHSP70-4 in modulating heat tolerance in rice and identify novel target genes for enhancing heat resilience during the flowering phase in rice.

Bat thermoregulation in the heat: seasonal variation in evaporative cooling capacities in four species of European bats

Phenotypic flexibility is an important source of physiological variation in endotherms and plays an integral role in species’ response to rapid environmental changes. Studies of phenotypic flexibility have focused on winter acclimatization and cold endurance, and there are fewer data on summer acclimatization and adjustments in heat dissipation capacity, especially in Temperate-Zone species. We used indirect calorimetry and thermometry to test if thermoregulation at high air temperatures (Ta) varies between spring and summer in four species of European vespertilionid bats: Nyctalus noctula, Pipistrellus nathusii, P. pygmaeus, and P. pipistrellus. We measured subcutaneous body temperature (Tsub), evaporative water loss, and resting metabolic rate while exposing bats to a stepped profile of increasing Ta, from 28 °C–48 °C. We predicted that during summer, bats increase heat tolerance and evaporative cooling capacity, to better tolerate hotter Tas. In contrast, we found lower maximum ratios of evaporative heat loss (EHL) to metabolic heat production (MHP) during summer, but no seasonal differences in maximum Ta tolerated or Tsub. The main cause of this seasonal difference in maximum EHL/MHP seems to be from bats increasing EWL more gradually with increasing Ta in summer than spring, particularly in the smaller Pipistrellus species. Therefore, this seasonal variation in heat-dissipation strategies may reflect enhanced water conservation during summer to avoid dehydration, as bats are confined to roosts for longer and hotter days compared to spring.

Integration of C3H15-mediated transcriptional and post-transcriptional regulation confers plant thermotolerance in Arabidopsis.

Heat stress is an environmental factor that significantly threatens crop production worldwide. Nevertheless, the molecular mechanisms governing plant responses to heat stress are not fully understood. Plant zinc finger CCCH proteins have roles in stress responses as well as growth and development through protein-RNA, protein-DNA, and protein-protein interactions. Here, we reveal an integrated multi-level regulation of plant thermotolerance that is mediated by the CCCH protein C3H15 in Arabidopsis. Heat stress rapidly suppressed C3H15 transcription, which attenuated C3H15-inhibited expression of its target gene HEAT SHOCK TRANSCRIPTION FACTOR A2 (HSFA2), a central regulator of heat stress response (HSR), thereby activating HEAT SHOCK COGNATE 70 (HSC70.3) expression. The RING-type E3 ligase MED25-BINDING RING-H2 PROTEIN 2 (MBR2) was identified as an interacting partner of C3H15. The mbr2 mutant was susceptible to heat stress compared to wild-type plants, whereas plants overexpressing MBR2 showed increased heat tolerance. MBR2-dependent ubiquitination mediated the degradation of phosphorylated C3H15 protein in the cytoplasm, which was enhanced by heat stress. Consistently, heat sensitivities of C3H15 overexpression lines increased in MBR2 loss-of-function and decreased in MBR2 overexpression backgrounds. Heat stress-induced accumulation of HSC70.3 promoted MBR2-mediated degradation of C3H15 protein, implying that an auto-regulatory loop involving C3H15, HSFA2, and HSC70.3 regulates HSR. Heat stress also led to the accumulation of C3H15 in stress granules (SGs), a kind of cytoplasmic RNA granule. This study advances our understanding of the mechanisms plants use to respond to heat stress, which will facilitate technologies to improve thermotolerance in crops.

Pollution offsets the rapid evolution of increased heat tolerance in a natural population

Despite the increasing evidence for rapid thermal evolution in natural populations, evolutionary rescue under global warming may be constrained by the presence of other stressors. Highly relevant in our polluted planet, is the largely ignored evolutionary trade-off between heat tolerance and tolerance to pollutants. By using two subpopulations (separated 40 years in time) from a resurrected natural population of the water flea Daphnia magna that experienced a threefold increase in heat wave frequency during this period, we tested whether rapid evolution of heat tolerance resulted in reduced tolerance to the widespread metal zinc and whether this would affect heat tolerance upon exposure to the pollutant. Our results revealed rapid evolution of increased heat tolerance in the recent subpopulation. Notably, the sensitivity to the metal tended to be stronger (reduction in net energy budget) or was only present (reductions in heat tolerance and in sugar content) in the recent subpopulation. As a result, the rapidly evolved higher heat tolerance of the recent subpopulation was fully offset when exposed to zinc. Our results highlight that the many reports of evolutionary rescue to global change stressors may give a too optimistic view as our warming planet is polluted by metals and other pollutants.

Tadpoles Develop Elevated Heat Tolerance in Urban Heat Islands Regardless of Sex

The ability of wildlife to endure the effects of high temperatures is increasingly important for biodiversity conservation under climate change and spreading urbanization. Organisms living in urban heat islands can have elevated heat tolerance via phenotypic or transgenerational plasticity or microevolution. However, the prevalence and mechanisms of such thermal adaptations are barely known in aquatic organisms. Furthermore, males and females can differ in heat tolerance, which may lead to sex-biased mortality, yet it is unknown how sex differences in thermal biology influence urban phenotypic divergence. To address these knowledge gaps, we measured critical thermal maxima (CTmax) in male and female agile frog (Rana dalmatina) tadpoles captured from warm urban ponds and cool woodland ponds, and in a common-garden experiment where embryos collected from both habitat types were raised in the laboratory. We found higher CTmax in urban-dwelling tadpoles compared to their counterparts living in woodland ponds. This difference was reversed in the common-garden experiment: tadpoles originating from urban ponds had lower CTmax than tadpoles originating from woodland ponds. We found no effect of sex on CTmax or its difference between habitats. These results demonstrate that aquatic amphibian larvae can respond to the urban heat island effect with increased heat tolerance similarly to other, mostly terrestrial taxa studied so far, and that phenotypic plasticity may be the main driver of this response. Our findings also suggest that heat-induced mortality may be independent of sex in tadpoles, but research is needed in many more taxa to explore potentially sex-dependent urban thermal responses.

Melatonin Application Induced Physiological and Molecular Changes in Carnation (Dianthus caryophyllus L.) under Heat Stress

Carnation is one of the most important ornamental plants worldwide; however, heat stress is a problem, which affects carnation cultivation. The harmful effects of heat stress include impaired vegetative development and reduced floral induction. In this study, to enhance carnation growth under conditions of heat stress, various concentrations of melatonin were added to in vitro culture media. The mechanism by which melatonin reduced heat stress damage was then studied by taking measurements of morphological parameters, levels of reactive oxygen species (ROS), antioxidant enzymes, and malondialdehyde (MDA), as well as differential gene expression, in carnation plants during in vitro culture. These data revealed that untreated carnation plants were more harmed by conditions of heat stress than plants treated with melatonin. Melatonin at concentrations of 5 and 10 mM increased chlorophyll content, fresh weight, and plant height to a greater extent than other concentrations. Melatonin may, thus, be used to alleviate damage to carnations caused by heat stress. The application of melatonin was also found to reduce oxidative damage and enhance antioxidant defense mechanisms. In addition, the expression of heat-related genes was found to be upregulated; in melatonin-treated plants, an upregulation was recorded in the expression of GAPDH, DcPOD1, DcPOD2, DcPOD3, Gols1, MBF1c, HSF30, HSP101, HSP70, and sHSP (MT) genes. In short, we found that melatonin treatment increased heat tolerance in carnation plants. The data presented here may serve as a reference for those seeking to enhance the growth of plants in conditions of heat stress.

Skin transcriptomic analysis reveals candidate genes and pathways associated with thermotolerance in hair sheep.

The skin plays an important role in thermoregulation. Identification of genes on the skin that contribute to increased heat tolerance can be used to select animals with the best performance in warm environments. Our objective was to identify candidate genes associated with the heat stress response in the skin of Santa Ines sheep. A group of 80 sheep assessed for thermotolerance was kept in a climatic chamber for 8days at a stress level temperature of 36°C (10 am to 04pm) and a maintenance temperature of 28°C (04pm to 10 am). Two divergent groups, with seven animals each, were formed after ranking them by thermotolerance using rectal temperature. Fromskin biopsy samples,total RNA was extracted, quantified, and used for RNA-seq analysis. 15,989 genes were expressed in sheep skin samples, of which 4 genes were differentially expressed (DE; FDR < 0.05) and 11 DE (FDR 0.05-0.177) between the two divergent groups. These genes are involved in cellular protection against stress (HSPA1A and HSPA6), ribosome assembly (28S, 18S, and 5S ribosomal RNA), and immune response (IGHG4, GNLY, CXCL1, CAPN14, and SAA-4). The candidate genes and main pathways related to heat tolerance in Santa Ines sheep require further investigation to understand their response to heat stress in different climatic conditions and under solar radiation. It is essential to verify whether these genes and pathways are present in different breeds and to understand the relationship between heat stress and other genes identified in this study.

Continent-wide parallel urban evolution of increased heat tolerance in a common moth.

Urbanization and its urban-heat-island effect (UHI) have expanding footprints worldwide. The UHI means that urban habitats experience a higher mean and more frequent extreme high temperatures than rural habitats, impacting the ontogeny and resilience of urban biodiversity. However, many organisms occupy different microhabitats during different life stages and thus may experience the UHI differently across their development. While evolutionary changes in heat tolerance in line with the UHI have been demonstrated, it is unknown whether such evolutionary responses can vary across development. Here, using common-garden-reared Chiasmia clathrata moths from urban and rural populations from three European countries, we tested for urban evolution of heat shock tolerance in two life stages: larvae and adults. Our results indicate widespread urban evolution of increased heat tolerance in the adult stage only, suggesting that the UHI may be a stronger selective agent in adults. We also found that the difference in heat tolerance between urban and rural populations was similar to the difference between Mid- and North-European regions, suggesting similarity between adaptation to the UHI and natural, latitudinal temperature variation. Our observations incentivize further research to quantify the impact of these UHI adaptations on fitness during urbanization and climate change, and to check whether life-stage-specific adaptations in heat tolerance are typical of other ectothermic species that manage to survive in urbanized settings.

Genome-wide analysis of ALDH gene family in jujube and identification of ZjALDH3F3 for its important role in high-temperature tolerance

Aldehyde dehydrogenases (ALDHs) are NAD(P)-dependent enzymes that oxidize aliphatic and aromatic aldehydes. They play crucial roles in various biological processes and plant responses to stress. The impact of high temperatures on jujube quality and yield has been well documented. Nevertheless, the involvement of ALDHs in the response to heat stress remains poorly understood. This study aimed to identify ZjALDHs in the jujube genome (Ziziphus jujuba var. spinosa) and conducted in silico analyses. Phylogenetic analyses indicated that ALDHs in plants, including jujube, can be divided into ten families, and members from the same family share conserved gene and protein structures. Quantitative real-time PCR (qRT-PCR) and β-glucuronidase (GUS) histochemical staining were used to analyze the expression patterns of ZjALDHs in response to elevated temperatures. We identified a ZjALDH (ZjALDH3F3) gene displaying a significant upregulation and down-regulation, respectively in heat-resistant (HR) and heat-sensitive (HS) jujube in response to heat treatments. Such specific responses are probably attributed to the different heat-responsive cis-elements of ZjALDH3F3 in HR and HS jujubes. ZjALDH3F3 over-expressed in tobacco increased heat tolerance, as evidenced by the reduced accumulation of reactive oxygen species (ROS) and elevated activity of antioxidant enzymes. The qRT-PCR results indicated that the expression of antioxidant enzymes, abscisic acid (ABA), and stress-responsive genes was enhanced in transgenic tobacco. This study sheds novel light on the function of ZjALDHs in heat resistance of jujube.

Tunable rice protein–starch composite soft gels: Structural role of ultrasound-modified protein

Soft composite gels were prepared with ultrasound-treated rice protein (URP, 4%) and rice starch (RS, 6%). The compositional and physical attributes of URP were elucidated, and the textural, rheological and structural properties of the composite gels were characterized. URP showed a reduced particle size, improved solubility, and increased heat tolerance. Cooked (65 °C for 20 min, then heated to 95 °C at 1 °C/min) RS + URP gels displayed a homogeneous and smooth texture with a range of reduced hardness (62%–78.3%) compared with RS gel while largely retaining the water-holding capacity. The viscosity and shear moduli (Gʹ and G′′) of the gels decreased correspondingly, and starch retrogradation was partially inhibited by the interaction with URP. A salient amorphous state revealed by X-ray diffraction confirmed weaker amylose association, in corroboration with non-covalent interactions between RS and URP shown by FTIR spectroscopy. These findings suggest that URP can be a functional ingredient for the development of soft, protein-rich, starch-based gel products suitable for the dysphagia diet.

Assessing the contribution of bacteria to the heat tolerance of experimentally evolved coral photosymbionts.

Coral reefs are extremely vulnerable to ocean warming, which triggers coral bleaching-the loss of endosymbiotic microalgae (Symbiodiniaceae) from coral tissues, often leading to death. To enhance coral climate resilience, the symbiont, Cladocopium proliferum was experimentally evolved for >10 years under elevated temperatures resulting in increased heat tolerance. Bacterial 16S rRNA gene metabarcoding showed the composition of intra- and extracellular bacterial communities of heat-evolved strains was significantly different from that of wild-type strains, suggesting bacteria responded to elevated temperatures, and may even play a role in C. proliferum thermal tolerance. To assess whether microbiome transplantation could enhance heat tolerance of the sensitive wild-type C. proliferum, we transplanted bacterial communities from heat-evolved to the wild-type strain and subjected it to acute heat stress. Microbiome transplantation resulted in the incorporation of only 30 low-abundance strains into the microbiome of wild-type cultures, while the relative abundance of 14 pre-existing strains doubled in inoculated versus uninoculated samples. Inoculation with either wild-type or heat-evolved bacterial communities boosted C. proliferum growth, although no difference in heat tolerance was observed between the two inoculation treatments. This study provides evidence that Symbiodiniaceae-associated bacterial communities respond to heat selection and may contribute to coral adaptation to climate change.

Elderly residents’ uses of fragmented outdoor spaces in public housing estates in Hong Kong——Decoding causality and heat-risk exposure

Well-designed open/semi-open spaces in public housing estates (PHEs) are important urban living rooms for urban residents to enhance well-beings, relieve from cramped homes, and cope with hotter climate. In order to understand the elderly residents' space use in light of space/neighbourhood attributes and microclimates, mobile field tests including physical measurement, passive observation, and questionnaire survey were carried out in 33 fragmented outdoor spaces (FOSs) in Choi Hung Estate (CHE) and Upper Ngau Tou Kok Estate (UNTKE) in Hong Kong from June to early October 2022. GIS application was adopted to map the vitality in association with microclimates. The ordered probit model and multilevel regression model were employed to explore the contributions of factors to the elderly's FOSs use. It is shown that the time of the day, microclimate (mPET—modified PET for hot-humid regions & wind speed), FOSs attributes (SVF, nature view, functionality, size), and neighbourhood attributes (accessibility & building density) significantly influence elderly attendance in FOSs. One degree increase in mPET is associated with around 4.7% decrease in the elderly's FOSs use. The elderly is likely exposed to unconscious heat risks under the compensatory effects of space and neighbourhood building attributes on the thermal environment of a FOS, and popular FOSs contribute to an increase in heat tolerance by approximately 5 °C in terms of mPET. A FOS that maintains mPET between 30.8 °C and 33.1 °C in summer, along with other favourable attributes (SVF, accessibility & functionality) may help mitigate the heat risks and increase overall usage rate.

Environmental drivers and species traits of mesophication and xerophication in forests of western New York State

Forests of the eastern US have exhibited widespread taxonomic shifts involving decreasing abundances of many species of Quercus, Pinus and Carya and increasing abundances of many species of Acer, Fagus, Prunus as well as other genera. These taxonomic changes have been called mesophication and explained variously as decreased tolerance of fire, drought, and heat; decreased palatability for deer browsing; and increased tolerance of shade. The major driver of those shifts in taxonomy and ecological traits has been attributed to decreased surface burning due to Native American depopulation, cessation of settler-colonial land clearance, larger deer populations, and decreased drought, among other drivers. We endeavored to test which traits exhibited the most mesophication and which environmental factors best predicted that mesophication. We collected size-stratified taxonomic data for 2488 trees from 160 plots, converted that into measures of mesophyticness for each trait in each plot, and then inferred mesophication in each plot as the difference between the mesophyticness of small trees and large trees. Mesophyticness of each trait ranged from zero for a xerophytic trait to one for a mesophytic trait. We also collected site-specific data for 22 potential environmental predictors of trait changes (including abiotic, biotic, anthropogenic, and spatial predictors). All traits exhibited strong mesophication; these are, in descending order of percent of sites with strong mesophication: fire tolerance, white-tailed deer browse preference, Native American diet tree, cold tolerance, shade tolerance, drought tolerance, and general browse preference. For all traits, mesophication of small relative to large trees was greatest in plots where large trees were xerophytic, and least where large trees were mesophytic. We further found that mesophication was similar for plots regardless of the abundance or presence of Quercus, indicating that mesophication is not the same as oak decline. A diverse set of predictors best explained mesophication of taxonomic and ecological traits, but three were consistently chosen: cooler summer temperature, higher small tree density, and shorter distance to pre-1700 Native American towns. In addition to mesophication, there was also some evidence of xerophication, most strongly for an increase in heat tolerance as might be expected due to recent climate change. Our results show that forest mesophication is a complex syndrome involving changes in independent species traits that are driven by many environmental factors, creating a challenge for land managers.

Increase in heat tolerance following a period of heat stress in a naturally occurring insect species.

Climate warming is the defining environmental crisis of the 21st century. Elucidating whether organisms can adapt to rapidly changing thermal environments is therefore a crucial research priority. We investigated warming effects on a native Hemipteran insect (Murgantia histrionica) that feeds on an endemic plant species (Isomeris arborea) of the California coastal sage scrub. Experiments conducted in 2009 quantified the temperature responses of juvenile maturation rates and stage-specific and cumulative survivorship. The intervening decade has seen some of the hottest years ever recorded, with increasing mean temperatures accompanied by an increase in the frequency of hot extremes. Experiments repeated in 2021 show a striking change in the bugs' temperature responses. In 2009, no eggs developed past the second nymphal stage at 33°C. In 2021, eggs developed into reproductive adults at 33°C. Upper thermal limits for maturation and survivorship have increased, along with a decrease in mortality risk with increasing age and temperature, and a decrease in the temperature sensitivity of mortality with increasing age. While we cannot exclude the possibility that other environmental factors occurring in concert could have affected our findings, the fact that all observed trait changes are in the direction of greater heat tolerance suggests that consistent exposure to extreme heat stress may at least be partially responsible for these changes. Harlequin bugs belong to the suborder Heteroptera, which contains a number of economically important pests, biological control agents and disease carriers. Their differential success in withstanding warming compared to beneficial holometabolous insects such as pollinators may exacerbate the decline of beneficial insects due to other causes (e.g. pollution and pesticides) with potentially serious consequences on both biodiversity and ecosystem functioning.

AtMYBS1 negatively regulates heat tolerance by directly repressing the expression of MAX1 required for strigolactone biosynthesis in Arabidopsis

Heat stress caused by global warming requires the development of thermotolerant crops to sustain yield. It is necessary to understand the molecular mechanisms that underlie heat tolerance in plants. Strigolactones (SLs) are a class of carotenoid-derived phytohormones that regulate plant development and responses to abiotic or biotic stresses. Although SL biosynthesis and signaling processes are well established, genes that directly regulate SL biosynthesis have rarely been reported. Here, we report that the MYB-like transcription factor AtMYBS1/AtMYBL, whose gene expression is repressed by heat stress, functions as a negative regulator of heat tolerance by directly inhibiting SL biosynthesis in Arabidopsis. Overexpression of AtMYBS1 led to heat hypersensitivity, whereas atmybs1 mutants displayed increased heat tolerance. Expression of MAX1, a critical enzyme in SL biosynthesis, was induced by heat stress and downregulated in AtMYBS1-overexpression (OE) plants but upregulated in atmybs1 mutants. Overexpression of MAX1 in the AtMYBS1-OE background reversed the heat hypersensitivity of AtMYBS1-OE plants. Loss of MAX1 function in the atmyb1 background reversed the heat-tolerant phenotypes of atmyb1 mutants. Yeast one-hybrid assays, chromatin immunoprecipitation‒qPCR, and transgenic analyses demonstrated that AtMYBS1 directly represses MAX1 expression through the MYB binding site in the MAX1 promoter in vivo. The atmybs1d14 double mutant, like d14 mutants, exhibited hypersensitivity to heat stress, indicating the necessary role of SL signaling in AtMYBS1-regulated heat tolerance. Our findings provide new insights into the regulatory network of SL biosynthesis, facilitating the breeding of heat-tolerant crops to improve crop production in a warming world.

Heat stress in wheat: a global challenge to feed billions in the current era of the changing climate

Crop failure is largely caused by various climate hazards, and among them, heat stress is the primary factor hindering crop production. The significant global loss of crop yield is primarily due to heat-related damage during the reproductive phase. Terminal heat stress has been well documented in wheat, causing morphophysiological alterations, biochemical disruptions, and reduction of genetic potential. The formation of shoots and roots, the effect on the double ridge stage, and early biomass in the vegetative stage are also impacted by heat stress. The final negative outcomes of heat stress include reduced grain number and weight, slower grain filling rate, reduced grain quality, and shorter grain filling duration. Plants have developed mechanisms to adapt to heat stress through modifications in their morphological or growth responses, physiological and biochemical pathways, and changes in enzyme reactions. Numerous heat tolerance genes have been identified in wheat, but the more extensive study is needed to increase heat tolerance in crops to satisfy the food demands of the world’s growing population. The global food policy needs to prioritize and promote additional joint research and the development of heat-tolerant wheat breeding to ensure the world’s food security.

Brook trout can handle some heat…given enough time

On average, the world is getting warmer, and heatwaves are becoming more common and unpredictable – especially in areas closer to the Earth's poles. Warming near the poles may be bad news for animals, such as brook trout, living in these areas. Luckily, many animals have evolved ways to deal with heat, which could give them a buffer against severe weather. Some animals can adjust how their bodies work when the environment gets warmer, which can help them better handle brief periods of extreme heat. But these internal adjustments take time and may depend on what temperatures the animal has experienced recently. Predicting how animals will handle temperature changes is hard, because the ability to modify body function varies across the animal kingdom, and often we do not know how long it takes to make these adjustments. Erin Stewart and Graham Raby at Trent University, Canada, and Chris Wilson and Vince Frasca at the Ontario Ministry of Natural Resources and Forestry, Canada, wanted to know whether living in warmer conditions helps brook trout to better tolerate extreme temperatures and, if so, how long it takes for their tolerance to develop.To answer these questions, Stewart and colleagues used aquarium heaters and a slow, steady flow of water from a nearby creek to create three naturally fluctuating temperatures: unheated, warmed (+3°C) and warmer still (+6°C). All the water temperatures used in the experiment were within the 10–20°C range that brook trout typically survive best in. To find the hottest temperature that brook trout from each water temperature could stand before losing control of their body movements, Stewart slowly heated up an insulated tank of water containing a small number of trout until the fish reached the point where they began floating on their sides. After this, the trout were placed in a cool tank of water and monitored until they recovered. Almost all the trout survived this brush with extreme heat. To figure out whether the length of time a trout spent living in each creek water temperature (unheated or heated) influenced its heat tolerance, Stewart measured the heat tolerance of different fish from each group after 1, 4, 8, 16 and 30 days.The team found that living in warmer water improved the ability of the brook trout to handle hotter temperatures, but that it took time for the fish to adjust. Trout from the warmest treatment (+6°C) showed a marked increase in heat tolerance after only a single day of living in these warmer conditions. In contrast, trout from the warm group (+3°C) took about 8 days before they showed an improvement in survival over fish living in unheated creek water. Stewart and colleagues also found that the heat tolerance of both warmed groups continued to improve throughout the 30 days of living in the different creek water temperatures.These results suggest that brook trout can adjust to warming environments, within reasonable limits. More importantly, this study highlights an often-overlooked factor that applies to the study of heat tolerance for all animals, not just fish: how long these adjustments take. With climates changing faster than ever in history, many scientists are turning their attention to studying the heat sensitivity of animals. But, if we, as researchers and conservationists, want to use our finite time and resources wisely, we need to account for the fact that biological adjustments to warming temperatures take time.

Shotgun proteomics reveals changes in the pectoralis major muscle of broilers supplemented with passion fruit seed oil under cyclic heat stress conditions

The aim of this study was to characterize the proteins differentially expressed in the pectoralis major muscle of broilers supplemented with passion fruit seed oil (PFSO) under cyclic heat stress conditions. Ninety one-day-old male chicks were housed in cages arranged in a climatic chamber, where they were kept under cyclic heat stress for eight hours a day from the beginning to the end of the experiment. The birds were divided into two experimental groups, one group supplemented with 0.9% PFSO and a control group (CON) without PFSO supplementation. At 36 days of age, 18 birds were slaughtered to collect muscle samples. From pools of breast fillet samples from each group, proteolytic cleavage of the protein extracts was performed, and later, the peptides were analyzed by liquid chromatography-tandem mass spectrometry (LC-MS/MS). The 0.9% PFSO supplementation revealed the modulation of 57 proteins in the pectoralis major muscle of broilers exposed to cyclic heat stress. Among them, four proteins were upregulated, and 46 proteins were downregulated. In addition, seven proteins were expressed only in the CON group. These results suggest that PFSO may increase heat tolerance, with a possible reduction in oxidative stress, activation of neuroprotective mechanisms, protection against apoptosis, decrease in inflammatory responses, and regulation of energy metabolism.

Heat hardening of a larval amphibian is dependent on acclimation period and temperature.

Plasticity in heat tolerance provides ectotherms the ability to reduce overheating risk during thermal extremes. However, the tolerance-plasticity trade-off hypothesis states that individuals acclimated to warmer environments have a reduced plastic response, including hardening, limiting their ability to further adjust their thermal tolerance. Heat hardening describes the short-term increase in heat tolerance following a heat shock that remains understudied in larval amphibians. We sought to examine the potential trade-off between basal heat tolerance and hardening plasticity of a larval amphibian, Lithobates sylvaticus, in response to differing acclimation temperatures and periods. Lab-reared larvae were exposed to one of two acclimation temperatures (15°C and 25°C) for either 3 or 7 days, at which time heat tolerance was measured as critical thermal maximum (CTmax ). A hardening treatment (sub-critical temperature exposure) was applied 2 h before the CTmax assay for comparison to control groups. We found that heat-hardening effects were most pronounced in 15°C acclimated larvae, particularly after 7 days of acclimation. By contrast, larvae acclimated to 25°C exhibited only minor hardening responses, while basal heat tolerance was significantly increased as shown by elevated CTmax temperatures. These results are in line with the tolerance-plasticity trade-off hypothesis. Specifically, while exposure to elevated temperatures inducesacclimation in basal heat tolerance, shifts towards upper thermal tolerance limits constrain the capacity for ectotherms to further respond to acute thermal stress.