Higher Heat Tolerance Research Articles

Leaf Pigments, Surface Wax and Spectral Vegetation Indices for Heat Stress Resistance in Pea

Pea is a grain legume crop commonly grown in semi-arid temperate regions. Pea is susceptible to heat stress that affects development and reduces yield. Leaf pigments and surface wax in a crop canopy make the primary interaction with the environment and can impact plant response to environmental stress. Vegetation indices can be used to indirectly assess canopy performance in regard to pigment, biomass, and water content to indicate overall plant stress. Our objectives were to investigate the contribution of leaf pigments and surface wax to heat avoidance in pea canopies, and their associations with spectral vegetation indices. Canopies represented by 24 pea cultivars varying in leaf traits were tested in field trials across six environments with three stress levels in western Canada. Compared with the control non-stress environments, heat stress reduced leaf lamina and petiole chlorophyll a, chlorophyll b, and carotenoid concentrations by 18–35%, and increased leaf lamina chlorophyll a/b ratio, anthocyanin and wax concentrations by 24–28%. Generally, greater leaf pigment and wax concentrations were associated with cooler canopy temperature and high heat tolerance index (HTI) values. Upright cultivars had higher HTI values, whereas the lowest HTI was associated with normal leafed vining cultivars. Vegetation indices, including photochemical reflectance index (PRI), green normalized vegetation index (GNDVI), normalized pigment chlorophyll ratio index (NPCI), and water band index (WBI), had strong correlations with HTI and with heat avoidance traits. This study highlights the contribution of pigments and wax as heat avoidance traits in crop canopies, and the potential application of spectral measurements for selecting genotypes with more heat resistant vegetation.

Mechanical, Morphological and Water absorption properties of Polypropylene based Composites

Polyethylene compounds are used instead of PE in many applications to improve the mechanical properties of PE (such as tensile strength, tensile modulus and tensile strength). Different types of combinations can be used to enhance these properties. Fibers are considered to be effective reinforcing fillers for PE. Plastic compound? Not all plastics are compounds. In fact, most plastics used in toys, water bottles and other familiar items are not composite. They are clean plastics. Polypropylene is not as solid as polyethylene. Polypropylene is harder than polyethylene and is resistant to chemicals and organic solvents. Polypropylene is pure, non-stretchable and much harder than polyethylene, commonly called fiberglass, in fact such a compound Also known As for glass-fiber reinforced plastic (GFRP), this is Specific to material properties such as tensile strength Made in different formats for permutations, stiffness, compressive strength and thermal expansion and different price points. For one, plastic deck boards are completely synthetic. It is considered safe in all plastics; it is a strong heat-resistant plastic. Due to its high heat tolerance, it is unlikely to leak even when exposed to hot or cold water. It is allowed to use with storage of food and beverages. Polypropylene (PP) is the most common in the world Is one of the thermoplastics used. Polypropylene plastic packaging, machinery and Plastic parts and threads for equipment and also used for textiles. Some plastic, BPA or other harmful chemicals in our body Or it could badly affect the world we live in. Polypropylene, a complex plastic, is common Considered safe for humans and these common ingredients are often the same Are used for products, but not theirs What are the differences? Polyester and polypropylene The main difference between the two is polyester Polypropylene is more water resistant than, It works well for athletic wear Is a quick-drying cloth. Plastic is a polymer with a large molecular weight. Polypropylene is an example of a plastic polymer. The main difference between polypropylene and plastic is that we can make crystal clear material out of polypropylene, while plastic material is generally not clear.

Forecasting Tomato Variety for Different Seasons and Regions of Bangladesh

An experiment was carried out at the "Horticulture Nursery and Germplasm Centre", of Patuakhali Science and Technology University, to find out suitable temperature, variety for winter season and promising heat tolerant variety for summer season in different regions of Bangladesh. The experiment comprised of ten varieties of tomato namely, BARI tomato 2 (Roton), BARI tomato 3, BARI tomato 9 (Lalima), BARI tomato 14, Surakkha, BARI hybrid tomato 5, BARI hybrid tomato 6, Mintoo tomato (Lal Teer Seed Ltd.), Tidy tomato (Metal Seed Ltd.) and Roma VF (ACI Seed Ltd) and three temperature conditions viz., normal temperature (10-20°C), medium temperature (21-25°C) and high temperature (26-35°C). All of the treatments were arranged into the pots. There were altogether 30 treatment combinations with three replications. The experiment was laid out in a Split-plot Design. Both different temperature conditions, varieties of tomato independently and also in combination showed significant influence on different parameters of tomato plant. Medium temperature was noticed for healthy growth and flowering but not for higher yield and yield traits. Variety engaged in vegetative acceleration (Tidy, BARI tomato 3), did not convalesced yield and yield attributes. The highest total chlorophyll (1.29 mg/gfw) in leaves and fruit weight per plant (2.06 kg) were recorded from the variety BARI tomato 2. In normal/low temperature conditions the variety Mintoo gave the highest yield (66.68 t/ha) where variety BARI tomato 2 (65.50 t/ha) was identical. Reversely, the lowest fruit weight per plant (40.23 t/ha) was found from the variety Mintoo in the high temperature but the variety BARI tomato 2 provided the highest yield (49.39 t/ha). BARI tomato 2 also afforded higher yield in medium temperature, where Roma VF and BARI tomato 3 were also closely associated. These results indicated the higher heat tolerance ability of BARI tomato 2 and lower tolerance ability of variety Mintoo. Therefore, BARI tomato 2 might be recommend for all seasons and regions of Bangladesh. Meanwhile, variety Mintoo might be recommended only for winter and for northern region whereas Roma VF and BARI tomato 3 for middle-southern region during autumn seasons of Bangladesh.

A kabuli chickpea ideotype

The concept of ‘crop ideotype’ is coined as a desirable plant model expected to better perform for seed yield, oils and other useful characteristics when developed as a cultivar, and it consists of two major approaches, namely, (i) ‘defect elimination’, that is, integration of disease resistance to a susceptible genotype from a resistant genotype and (ii) ‘selection for yield’ by improving yield after crosses between desirable parents. For consideration of these approaches, here we introduced an ideotype in kabuli chickpea (Cicer arietinum L.) which is high-yielding, extra-large-seeded, and double- or multi-podded, has high plant height and imparipinnate-leafed traits, and is heat tolerant and resistant to ascochyta blight [Ascochyta rabiei (Pass.) Labr.], which causes considerable yield losses, via marker-assisted selection. F3 and F4 lines were evaluated for agro-morphological traits divided into six classes, namely, (i) imparipinnate-leafed and single-podded progeny, (ii) imparipinnate-leafed and double-podded progeny, (iii) imparipinnate-leafed and multi-podded progeny, (iv) unifoliolate-leafed and single-podded progeny, (v) unifoliolate-leafed and double-podded progeny, (vi) unifoliolate-leafed and multi-podded progeny. F3:4 lines having 100-seed weight ≥ 45 g and double- or multi-podded traits were additionally assessed for resistance to ascochyta blight using molecular markers including SCY17590 and CaETR-1. Superior lines having higher values than their best parents were determined for all studied traits indicating that economic and important traits including yield and seed size in chickpea could be improved by crossing suitable parents. Imparipinnate-leafed and multi-podded plants had not only the highest number of pods and seeds per plant but also the highest yield. On the other hand, imparipinnate-leafed and single podded progeny had the largest seed size, followed by imparipinnate-leafed and double-podded progeny. Multi-podded plants produced 23% more seed yield than that of single-podded plants, while multi-podded plants attained 7.6% more seed yield than that of double-podded plants. SCY17590 and CaETR-1 markers located on LG4 related to QTLAR2 and QTLAR1 were found in 14 lines among 152 F3:4 lines. Six superior lines were selected for being double- or multi-podded, imparipinnate-leafed, suitable for combine harvest, heat-tolerant, and resistant to ascochyta blight, and having both of two resistance markers and extra-large seeds as high as 50–60 g per 100-seed weight. Resistance alleles from two different backgrounds for resistance to ascochyta blight were integrated with double- or multi-podded kabuli chickpea lines having high yield, extra-large seeds, high plant height, imparipinnate-leaves and high heat tolerance, playing a crucial role for future demands of population and food security. These approaches seem to be applicable in ideotype breeding for other important crop plants.

Neotropical stingless bees display a strong response in cold tolerance with changes in elevation.

Tropical pollinators are expected to experience substantial effects due to climate change, but aspects of their thermal biology remain largely unknown. We investigated the thermal tolerance of stingless honey-making bees, the most ecologically, economically and culturally important group of tropical pollinators. We assessed changes in the lower (CTMin) and upper (CTMax) critical thermal limits of 17 species (12 genera) at two elevations (200 and 1500m) in the Colombian Andes. In addition, we examined the influence of body size (intertegular distance, ITD), hairiness (thoracic hair length) and coloration (lightness value) on bees' thermal tolerance. Because stingless beekeepers often relocate their colonies across the altitudinal gradient, as an initial attempt to explore potential social responses to climatic variability, we also tracked for several weeks brood temperature and humidity in nests of three species at both elevations. We found that CTMin decreased with elevation while CTMax was similar between elevations. CTMin and CTMax increased (low cold tolerance and high heat tolerance) with increasing ITD, hair length and lightness value, but these relationships were weak and explained at most 10% of the variance. Neither CTMin nor CTMax displayed significant phylogenetic signal. Brood nest temperature tracked ambient diel variations more closely in the low-elevation site, but it was constant and higher at the high-elevation site. In contrast, brood nest humidity was uniform throughout the day regardless of elevation. The stronger response in CTMin, and a similar CTMax between elevations, follows a pattern of variation documented across a wide range of taxa that is commonly known as the Brett's heat-invariant hypothesis. Our results indicate differential thermal sensitivities and potential thermal adaptations to local climate, which support ongoing conservation policies to restrict the long-distance relocations of colonies. They also shed light on how malleable nest thermoregulation can be across elevations.

Sorghum: Nutritional Factors, Bioactive Compounds, Pharmaceutical and Application in Food Systems: A Review

After wheat, rice, maize, and barley, sorghum is the fifth most widely grown cereal on the planet. Due to its high production, drought resistance, and heat tolerance, this crop is replacing maize in some areas. Sorghum is available in a variety of colors, including cream, lemon-yellow, red, and even black. The principal grain anatomical components are pericarp, germ or embryo and endosperm. This review provides an overview of key sorghum grain components, including starches, fiber, proteins, lipids, and vitamins. Also, we summarized phenolic compounds, flavonoids, tannins, carotenoids, vitamin E, amines, Policosanols and Phytosterols in sorghum grains. Sorghum is used to manufacture bread and porridge, and it provides a significant source of energy and nutrition for humans; sorghum is extensively farmed for animal feed. However, because the natural components in sorghum are useful in the development of healthy and functional foods, sorghum farming for both biofuel production and human consumption is gaining popularity. Pigmented sorghum grain is high in antioxidants such as polyphenols, primarily tannins, which have a variety of health benefits, including antiproliferative properties linked to the prevention of certain cancers, antioxidant activities linked to the prevention of diseases linked to oxidative stress, and anti-inflammatory effects, as well as improving glucose metabolism. Because these chemicals cannot be assimilated, their application in the food business has been limited, as sorghum is regarded as a lownutritional grain due to the presence of anti-nutritional components such as strong tannins, which form complexes with proteins and iron, limiting their digestibility. This review aims to show the utilization of sorghum as a source of bioactive chemicals and the value they bestow on human health due to the general biological potential it possesses.

Consistently high heat tolerance acclimation in response to a simulated heatwave across species from the broadly distributed Acacia genus.

When leaves exceed their thermal threshold during heatwaves, irreversible damage to the leaf can accumulate. However, few studies have explored short-term acclimation of leaves to heatwaves that could help plants to prevent heat damage with increasing heatwave intensity. Here, we studied the heat tolerance of PSII (PHT) in response to a heatwave in Acacia species from across a strong environmental gradient in Australia. We compared PHT metrics derived from temperature-dependent chlorophyll fluorescence response curves (T-F 0 ) before and during a 4-day 38°C heatwave in a controlled glasshouse experiment. We found that the 15 Acacia species displayed surprisingly large and consistent PHT acclimation responses with a mean tolerance increase of 12°C (range, 7.7-19.1°C). Despite species originating from diverse climatic regions, neither maximum temperature of the warmest month nor mean annual precipitation at origin were clear predictors of PHT. To our knowledge, these are some of the largest measured acclimation responses of PHT from a controlled heatwave experiment. This remarkable capacity could partially explain why this genus has become more diverse and common as the Australian continent became more arid and suggests that the presence of Acacia in Australian ecosystems will remain ubiquitous with climate change.

Hot and sour: parasite adaptations to honeybee body temperature and pH.

Host temperature and gut chemistry can shape resistance to parasite infection. Heat and acidity can limit trypanosomatid infection in warm-blooded hosts and could shape infection resistance in insects as well. The colony-level endothermy and acidic guts of social bees provide unique opportunities to study how temperature and acidity shape insect-parasite associations. We compared temperature and pH tolerance between three trypanosomatid parasites from social bees and a related trypanosomatid from poikilothermic mosquitoes, which have alkaline guts. Relative to the mosquito parasites, all three bee parasites had higher heat tolerance that reflected body temperatures of hosts. Heat tolerance of the honeybee parasite Crithidia mellificae was exceptional for its genus, implicating honeybee endothermy as a plausible filter of parasite establishment. The lesser heat tolerance of the emerging Lotmaria passim suggests possible spillover from a less endothermic host. Whereas both honeybee parasites tolerated the acidic pH found in bee intestines, mosquito parasites tolerated the alkaline conditions found in mosquito midguts, suggesting that both gut pH and temperature could structure host-parasite specificity. Elucidating how host temperature and gut pH affect infection-and corresponding parasite adaptations to these factors-could help explain trypanosomatids' distribution among insects and invasion of mammals.

Extreme heat increases stomatal conductance and drought-induced mortality risk in vulnerable plant species.

Tree mortality during global‐change‐type drought is usually attributed to xylem dysfunction, but as climate change increases the frequency of extreme heat events, it is necessary to better understand the interactive role of heat stress. We hypothesized that some drought‐stressed plants paradoxically open stomata in heatwaves to prevent leaves from critically overheating. We experimentally imposed heat (>40°C) and drought stress onto 20 broadleaf evergreen tree/shrub species in a glasshouse study. Most well‐watered plants avoided lethal overheating, but drought exacerbated thermal damage during heatwaves. Thermal safety margins (TSM) quantifying the difference between leaf surface temperature and leaf critical temperature, where photosynthesis is disrupted, identified species vulnerability to heatwaves. Several mechanisms contributed to high heat tolerance and avoidance of damaging leaf temperatures—small leaf size, low leaf osmotic potential, high leaf mass per area (i.e., thick, dense leaves), high transpirational capacity, and access to water. Water‐stressed plants had smaller TSM, greater crown dieback, and a fundamentally different stomatal heatwave response relative to well‐watered plants. On average, well‐watered plants closed stomata and decreased stomatal conductance (g s) during the heatwave, but droughted plants did not. Plant species with low g s, either due to isohydric stomatal behavior under water deficit or inherently low transpirational capacity, opened stomata and increased g s under high temperatures. The current paradigm maintains that stomata close before hydraulic thresholds are surpassed, but our results suggest that isohydric species may dramatically increase g s (over sixfold increases) even past their leaf turgor loss point. By actively increasing water loss at high temperatures, plants can be driven toward mortality thresholds more rapidly than has been previously recognized. The inclusion of TSM and responses to heat stress could improve our ability to predict the vulnerability of different tree species to future droughts.

Limited thermal plasticity may constrain ecosystem function in a basally heat tolerant tropical telecoprid dung beetle, Allogymnopleurus thalassinus (Klug, 1855)

Tropical organisms are more vulnerable to climate change and associated heat stress as they live close to their upper thermal limits (UTLs). UTLs do not only vary little across tropical species according to the basal versus plasticity ‘trade-off’ theory but may also be further constrained by low genetic variation. We tested this hypothesis, and its effects on ecosystem function using a diurnally active dung rolling beetle (telecoprid), Allogymnopleurus thalassinus (Klug, 1855) that inhabits arid environments. Specifically, (i) we tested basal heat tolerance (critical thermal maxima [CTmax] and heat knockdown time [HKDT]), and (ii) ecological functioning (dung removal) efficiency following dynamic chronic acclimation temperatures of variable high (VT-H) (28–45 °C) and variable low (VT-L) (28–16 °C). Results showed that A. thalassinus had extremely high basal heat tolerance (> 50 °C CTmax and high HKDT). Effects of acclimation were significant for heat tolerance, significantly increasing and reducing CTmax values for variable temperature high and variable temperature low respectively. Similarly, effects of acclimation on HKDT were significant, with variable temperature high significantly increasing HKDT, while variable temperature low reduced HKDT. Effects of acclimation on ecological traits showed that beetles acclimated to variable high temperatures were ecologically more efficient in their ecosystem function (dung removal) compared to those acclimated at variable low temperatures. Allogymnopleurus thalassinus nevertheless, had low acclimation response ratios, signifying limited scope for complete plasticity for UTLs tested here. This result supports the ‘trade-off’ theory, and that observed limited plasticity may unlikely buffer A. thalassinus against effects of climate change, and by extension, albeit with caveats to other tropical ecological service providing insect species. This work provides insights on the survival mechanisms of tropical species against heat and provides a framework for the conservation of these natural capital species that inhabit arid environments under rapidly changing environmental climate.

Handling the heat - photosynthetic thermal stress in tropical trees.

Warming climate increases the risk for harmful leaf temperatures in terrestrial plants, causing heat stress and loss of productivity. The heat sensitivity may be particularly high in equatorial tropical tree species adapted to a thermally stable climate. Thermal thresholds of the photosynthetic system of sun-exposed leaves were investigated in three tropical montane tree species native to Rwanda with different growth and water use strategies (Harungana montana, Syzygium guineense and Entandrophragma exselsum). Measurements of chlorophyll fluorescence, leaf gas exchange, morphology, chemistry and temperature were made at three common gardens along an elevation/temperature gradient. Heat tolerance acclimated to maximum leaf temperature (Tleaf ) across the species. At the warmest sites, the thermal threshold for normal function of photosystem II was exceeded in the species with the highest Tleaf despite their higher heat tolerance. This was not the case in the species with the highest transpiration rates and lowest Tleaf . The results point to two differently effective strategies for managing thermal stress: tolerance through physiological adjustment of leaf osmolality and thylakoid membrane lipid composition, or avoidance through morphological adaptation and transpiratory cooling. More severe photosynthetic heat stress in low-transpiring montane climax species may result in a competitive disadvantage compared to high-transpiring pioneer species with more efficient leaf cooling.

Effect of cooling strategies on milk production, physiological variables and blood profile during hot-dry and hot-humid summer in Sahiwal cattle

The present experiment was undertaken to study the effect of misting and splashing during hot-dry and hothumid months in lactating Sahiwal cattle. The study was conducted during May, June (hot-dry) and July (hothumid) with monthly average temperature-humidity index (THI) of 79.88, 80.57 and 85.36, respectively. Eighteen lactating cattle were selected on the basis of days in milk, milk yield, and parity and then divided into three groups: control (no cooling), cooling by misting and cooling by splashing. Milk production was not affected by hot-dry and hot-humid heat stress in Sahiwal cattle. RT and RR were significantly lower in misting and splashing group as compared to control during hot-dry period. The heat stress-induced leucocytosis, lymphocytopenia and neutrophilia were significantly ameliorated by both misting and splashing during the study period. Heat stress-induced alterations in serum creatinine, sodium and ROS concentration were significantly mitigated by misting in hot-humid climate. The prolactin level significantly decreased in animals by misting during the study period. The results suggested that misting was more efficient than splashing as a cooling strategy in hot dry condition while splashing was more effective in hot-humid condition and mitigated the heat stress-induced alterations in different welfare parameters but could not fully nullify it. However, the resultant stress was not sufficient enough to decrease the milk yield in Sahiwal cattle. It may also be concluded that the Sahiwal cattle have high heat tolerance and could sustain production even in a hot-dry and hot-humid environment.

Molecular adaptations to heat stress in the thermophilic ant genus Cataglyphis.

Over the last decade, increasing attention has been paid to the molecular adaptations used by organisms to cope with thermal stress. However, to date, few studies have focused on thermophilic species living in hot, arid climates. In this study, we explored molecular adaptations to heat stress in the thermophilic ant genus Cataglyphis, one of the world's most thermotolerant animal taxa. We compared heat tolerance and gene expression patterns across six Cataglyphis species from distinct phylogenetic groups that live in different habitats and experience different thermal regimes. We found that all six species had high heat tolerance levels with critical thermal maxima (CTmax ) ranging from 43℃ to 45℃ and a median lethal temperature (LT50) ranging from 44.5℃ to 46.8℃. Transcriptome analyses revealed that, although the number of differentially expressed genes varied widely for the six species (from 54 to 1118), many were also shared. Functional annotation of the differentially expressed and co-expressed genes showed that the biological pathways involved in heat-shock responses were similar among species and were associated with four major processes: the regulation of transcriptional machinery and DNA metabolism; the preservation of proteome stability; the elimination of toxic residues; and the maintenance of cellular integrity. Overall, our results suggest that molecular responses to heat stress have been evolutionarily conserved in the ant genus Cataglyphis and that their diversity may help workers withstand temperatures close to their physiological limits.

Enhancing the heat tolerance of reef-building corals to future warming.

Reef-building corals thriving in extreme thermal environments may provide genetic variation that can assist the evolution of populations to rapid climate warming. However, the feasibility and scale of genetic improvements remain untested despite ongoing population declines from recurrent thermal stress events. Here, we show that corals from the hottest reefs in the world transfer sufficient heat tolerance to a naïve population sufficient to withstand end-of-century warming projections. Heat survival increased up to 84% when naïve mothers were selectively bred with fathers from the hottest reefs because of strong heritable genetic effects. We identified genomic loci associated with tolerance variation that were enriched for heat shock proteins, oxidative stress, and immune functions. Unexpectedly, several coral families exhibited survival rates and genomic associations deviating from origin predictions, including a few naïve purebreds with exceptionally high heat tolerance. Our findings highlight previously uncharacterized enhanced and intrinsic potential of coral populations to adapt to climate warming.

Water availability influences thermal safety margins for leaves

Abstract One application of plant physiological heat tolerance measurements is the assessment of vulnerability to increasing environmental temperatures under climatic change. A thermal safety margin (TSM), the difference between physiological tolerance and environmental temperature, is a common metric for the assessment of plant thermal vulnerability. However, there are biological and methodological aspects to consider when evaluating thermal vulnerability that have the potential to substantially alter the assessments. Two such aspects include the leaf to air temperature relationship and the scale at which air temperature data are collected. We grew plants of a desert species, Myoporum montanum, in situ under water‐stressed and well‐watered conditions, and measured their leaf temperatures and photosynthetic heat tolerance (T50 threshold) every third day over 12 days in summer. Thermal safety margins were calculated based on leaf temperatures and compared to those calculated with local and regional air temperatures. We found that heat tolerance and the thermal vulnerability assessment of a plant changed with water status. When water was readily available, plants maintained wide leaf temperature safety margins and displayed partial homeothermy. When cooling via transpiration was limited, increasing leaf temperature corresponded with occurrences of leaf poikilo‐ and megathermy, higher heat tolerance and narrower safety margins. Our study shows high physiological heat thresholds are not necessarily reflective of wide safety margins, but instead can indicate a greater vulnerability and increased risk of heat stress exposure. Calculating TSMs using air temperatures can also substantially alter margin widths. Where possible, the use of leaf temperatures in assessments of thermal vulnerability will lead to more meaningful vulnerability assessments. We recommend considering the source and temporal pairing of temperature measurements as well as plant water status, when measuring and interpreting plant TSMs. A free Plain Language Summary can be found within the Supporting Information of this article.

A compact electron beam ion trap in support of high-temperature plasma diagnostics based on conduction-cooled superconducting coils.

Spectroscopic diagnostics of future fusion reactor plasmas require information on impurity line emissions, especially for relevant high-Z metal elements (e.g., tungsten). These materials will be widely used as plasma facing components for their high heat tolerance and low sputtering yield. Based on an electron beam ion trap, a compact impurity spectra platform is developed to mimic the high-temperature environment of a fusion reactor. The proposed platform can deliver a focused e-beam at energies over 30 keV using a confining magnetic field of ∼1.0T generated by two superconducting coils (NbTi). Cooled by a closed-loop cryocooler, the coils can avoid the usage of a complicated cryogenic system involving the handling of liquid helium. For spectroscopic studies of highly charged ions, a spherically curved crystal spectrometer is proposed to measure a wavelength range around 2-4 Å covering the typical wavelength range expected to be emitted by metal ions in a fusion plasma. This paper reports the design and development progress of the platform.

The Higher the Needs, the Lower the Tolerance: Extreme Events May Select Ectotherm Recruits With Lower Metabolic Demand and Heat Sensitivity

Ongoing climate warming demands a better understanding of whether or how the ectotherms that evolved in response to fluctuating stress regimes may acquire increased heat tolerance. Using blue mussels, Mytilus spp., a globally important and well-studied species, we provide empirical evidence supporting that (i) extremely warm (future) summer conditions may select rare recruits that are more capable of expressing metabolic (feeding and respiration) suppression and recovery in response to daily thermal fluctuations in mild to critical temperature range, (ii) this higher heat tolerance can be mediated by lower baseline metabolic demand, possibly decreasing the risks of heat-induced supply and demand mismatch and its associated stress during thermal fluctuations, and (iii) the capacity to acquire such heat tolerance through acclimation is minor. We discuss our results, methodological limitations and offer a perspective for future research. Further evaluation of mechanistic hypotheses such as the one tested here (based on the role of metabolic demand) is needed to generalize the significance of drivers of fast warm adaptation in ectothermic metazoan populations.

Interspecific variation in heat tolerance and evaporative cooling capacity among sympatric temperate-latitude bats

We tested the hypothesis that interspecific variation in chiropteran heat tolerance and evaporative cooling capacity is correlated with day-roost microclimates, using three vespertilionid bats that occur sympatrically during summer in Saskatchewan, Canada. We predicted that hoary bats (Lasiurus cinereus (Palisot de Beauvois, 1796); ∼22 g) would have higher heat tolerance than little brown bats (Myotis lucifugus (Le Conte, 1831); ∼7 g) and silver-haired bats (Lasionycteris noctivagans (Le Conte, 1831); ∼13 g), as the latter two species roost in tree crevices or cavities that are more thermally buffered than the foliage roosts of hoary bats. We measured core body temperature (Tb; passive integrated transponder tags), evaporative water loss, and resting metabolic rate (flow-through respirometry) while exposing individuals to a stepped profile of increasing air temperature (Ta) from ∼30 °C in ∼2 °C increments. Experiments were terminated when individuals became hyperthermic (Tb ≈ 42.5 °C), with maximum Ta (Ta,max) ranging from 42.0 to 49.7 °C. As predicted, hoary bats had the highest heat tolerance and evaporative cooling capacity, reaching Ta,max ∼2.4 and 1.2 °C higher than little brown and silver-haired bats, respectively. Our results are consistent with the hypothesis that heat tolerance of bats is correlated with roost microclimates, although interspecific variation in body mass and phylogeny may confound these conclusions.

Thermal adaptations of adults and eggs in the Arctic seed bug Nysius groenlandicus (Insecta: Hemiptera) from South Greenland

Temperatures in Arctic and sub-Arctic regions are highly variable, with long, and cold winters, and short summers. Studies on thermal biology of ectotherms from these latitudes have mostly focused on how organisms cope with cold temperatures. However, temperatures in microhabitats such as south-facing slopes can occasionally reach high and potentially stressful temperatures. Such microclimatic conditions are challenging for organisms, since they need to time their development to coincide with the short summer, while coping with thermal extremes during summer and winter. In the present study, we investigate upper and lower thermal limits of adults and eggs in Nysius groenlandicus, a univoltine seed bug widely distributed in Greenland and alpine areas of Scandinavia and with preference for dry and sunny habitats. Secondly, we investigate the survival strategy of the overwintering egg stage during cold exposure. We found a clear association between the microhabitat temperatures experienced by each specific life stage and their heat and cold tolerance. Thus, adults and eggs, which are both exposed to high summer temperatures, showed a high heat tolerance. Adults which do not overwinter had very poor cold tolerance, whereas eggs produced in autumn were very cold hardy (with some survival at − 21 °C). Cold tolerance of the eggs of N. groenlandicus was based on freeze avoidance through extensive supercooling and by conserving water. These results suggest life stage-specific adaptation to heat and cold stress in Arctic and sub-Arctic insects, and highlight new research avenues addressing adaptation to higher and more variable temperatures in Arctic and sub-Arctic regions.

Effect of Short-Time High-Temperature Treatment on the Photosynthetic Performance of Different Heat-Tolerant Grapevine Cultivars.

To explore the photosynthetic response of short-term high-temperature treatments to the leaves of different grape varieties (Shenyue and Shenfeng), we performed 45°C treatments on annual potted grapes in an artificial climate chamber to simulate the summer high-temperature period. We measured the rapid A-Ci response curve, 1,5-ribulose bisphosphate carboxylase/oxygenase (Rubisco) activity and chlorophyll a fluorescence. Photosynthetic performance-related parameters of grapevine leaves were found to be adversely affected by high temperature; the maximum rates of carboxylation of Rubisco and ribulose diphosphate regeneration and Rubisco activity were all significantly reduced. The JI of the JIP-test curve disappeared under high-temperature treatment, and the K peak appeared, indicating that the oxygen-evolving complex (OEC) had been destroyed. Principal component analysis showed that PSII activity (Fv /Fm , DFABS , φEo , ABS/RC) was greatly affected by high temperature. It was also found that the Rubisco activity and OEC destruction strength were greater in one of the cultivars, and we were able to determine heat resistance based on the phenotype and photosynthetic performance. It can be seen from the above that Shenyue leaves have higher heat tolerance and stronger photosynthetic performance than Shenfeng leaves. This shows that photosynthetic performance is strongly correlated with a grapevine's tolerance to abiotic stress.