Variation In Heat Tolerance Research Articles

Effects of balancing selection and microhabitat temperature variations on heat tolerance of the intertidal black mussel Septifer virgatus

Realistic assessments of the impacts of global warming on population extinction risk are likely to require an integrated analysis of the roles of standing genetic variation, microhabitat thermal complexity, and the inter-individual variation of heat tolerance due to both genetic differences and seasonal acclimatization effects. Here, we examine whether balancing selection and microhabitat temperature heterogeneity can interact to enhance the population persistence to thermal stress for the black mussel Septifer virgatus. We deployed biomimetic data loggers on the shore to measure the microhabitat-specific thermal variation from June 2014 to April 2016. Thermal tolerance of specimens was indexed by measuring effects of temperature on heart rate. Genotyping of specimens was performed using double digestion restriction association RADSeq (ddRADseq). Our results show that inter-individual variations in thermal tolerance correlate significantly with genetic differences at some specific gene loci, and that heterozygotes have higher thermal tolerances than homozygotes. The observed seasonal changes in genotype frequency suggest that these loci are under balancing selection. The ability of thermally resistant heterozygotes to survive in sun-exposed microhabitats acts to balance the loss of homozygotes during summer and enable the persistence of genetic polymorphisms. Population persistence of the mussel is also facilitated by the micro-scale variation in temperature, which provides refugia from thermal stress. Our results emphasize that inter-individual variation in thermal tolerance and in microhabitat heterogeneity in temperature are important for the persistence of populations in rocky shore habitats.

Rain shadow effects predict population differences in thermal tolerance of leaf‐cutting ant workers (Atta cephalotes)

AbstractTests of hypotheses for the evolution of thermal physiology often rely on mean temperatures, but mounting evidence suggests geographic variation in temperature extremes is also an important predictor of species’ thermal tolerances. Although the tropics are less thermally variable than higher latitude regions, rain shadows on the leeward sides of mountains can experience greater diel and seasonal variation in temperature than windward sites. Rain shadows provide opportunities to test predictions about the relationships of extreme temperatures with thermal physiology while controlling for latitude. We tested the hypothesis that populations of leaf‐cutting ants (Atta cephalotes) in leeward, montane, and windward sites in Costa Rica would differ in upper thermal tolerances (CTmax) of workers. As predicted from rain shadow effects via extreme high temperatures, the leeward rain shadow site yielded the highest mean CTmax (rain shadow site 42.1 ± 0.3°C, Montane site 38.2 ± 0.5°C, and windward site 38.2 ± 0.3°C). This suggests that high‐temperature extremes in tropical rain shadow forests can select for higher thermal tolerances. CTmax increased with worker body size within sites, but CTmax increased with body size more gradually at the two lowland sites, as predicted if local high temperatures selected more strongly on the most thermally vulnerable society members (small workers). This suggests that warmer lowland climates selected for colonies with less variation in heat tolerance than cooler high elevation climates.Abstract in Spanish is available with online material.

Obligate bacterial endosymbionts limit thermal tolerance of insect host species

The thermal tolerance of an organism limits its ecological and geographic ranges and is potentially affected by dependence on temperature-sensitive symbiotic partners. Aphid species vary widely in heat sensitivity, but almost all aphids are dependent on the nutrient-provisioning intracellular bacterium Buchnera, which has evolved with aphids for 100 million years and which has a reduced genome potentially limiting heat tolerance. We addressed whether heat sensitivity of Buchnera underlies variation in thermal tolerance among 5 aphid species. We measured how heat exposure of juvenile aphids affects later survival, maturation time, and fecundity. At one extreme, heat exposure of Aphis gossypii enhanced fecundity and had no effect on the Buchnera titer. In contrast, heat suppressed Buchnera populations in Aphis fabae, which suffered elevated mortality, delayed development and reduced fecundity. Likewise, in Acyrthosiphon kondoi and Acyrthosiphon pisum, heat caused rapid declines in Buchnera numbers, as well as reduced survivorship, development rate, and fecundity. Fecundity following heat exposure is severely decreased by a Buchnera mutation that suppresses the transcriptional response of a gene encoding a small heat shock protein. Similarly, absence of this Buchnera heat shock gene may explain the heat sensitivity of Ap. fabae Fluorescent in situ hybridization revealed heat-induced deformation and shrinkage of bacteriocytes in heat-sensitive species but not in heat-tolerant species. Sensitive and tolerant species also differed in numbers and transcriptional responses of heat shock genes. These results show that shifts in Buchnera heat sensitivity contribute to host variation in heat tolerance.

Variation for Heat Tolerance During Seed Germination in Diverse Carrot [Daucus carota (L.)] Germplasm

Carrot production is constrained by high levels of heat stress during the germination stage in many global regions. Few studies have been published evaluating the effect of heat stress on carrot seed germination or screening for genetic heat stress tolerance. The objectives of this study were to evaluate the response of diverse carrot germplasm to heat stress, identify heat-tolerant germplasm that may be used by plant breeders, and define the appropriate temperature for assessing heat tolerance in germinating carrot seed. To identify an appropriate screening temperature, three commercial hybrids and an open pollinated variety were evaluated at five temperatures (24, 32.5, 35, 37.5, and 40 °C). In preliminary studies, 35 °C was identified as the optimal temperature for screening heat tolerance of carrot seed. Cultivated and wild carrot plant introductions (PIs) (n = 270) from the U.S. Department of Agriculture (USDA) National Plant Germplasm System (NPGS) representing 41 countries, inbred lines from the USDA Agricultural Research Service (n = 15), and widely grown commercial hybrids (n = 8) were evaluated for heat tolerance under heat stress and nonstress conditions (35 °C and 24 °C, respectively) by calculating absolute decrease in percent germination (AD), inhibition index (II), relative heat tolerance (RHT), and heat tolerance index (HTI). All measurements of heat tolerance identified significant differences among accessions; AD ranged from −13.0% to 86.7%, II ranged from 35.7% to 100.0%, RHT ranged from 0 to 1.36, and HTI ranged from 0.0 to 1.45. The broad-sense heritability (H2) calculations ranged from 0.64 to 0.86 for different traits, indicating a moderately strong genetic contribution to the phenotypic variation. Several wild carrot accessions and inbred lines displayed low levels of heat tolerance, whereas cultivated accessions PI 643114 (United States), PI 652400 and PI 652403 (Turkey), PI 652208 (China), and PI 652403 (Russia) were most heat tolerant. This is the first evaluation of heritability for heat stress tolerance during carrot seed germination, the first measure of HTI, and the first correlation calculation between heat and salt tolerance during germination in carrot.

Evolutionary potential of thermal preference and heat tolerance in Drosophila subobscura.

Evolutionary change of thermal traits (i.e., heat tolerance and behavioural thermoregulation) is one of the most important mechanisms exhibited by organisms to respond to global warming. However, the evolutionary potential of heat tolerance, estimated as narrow-sense heritability, depends on the methodology employed. An alternative adaptive mechanism to buffer extreme temperatures is behavioural thermoregulation, although the association between heat tolerance and thermal preference is not clearly understood. We suspect that methodological effects associated with the duration of heat stress during thermal tolerance assays are responsible for missing this genetic association. To test this hypothesis, we estimated the heritabilities and genetic correlations for thermal traits in Drosophila subobscura, using high-temperature static and slow ramping assays. We found that heritability for heat tolerance was higher in static assays (h2 =0.134) than in slow ramping assays (h2 =0.084), suggesting that fast assays may provide a more precise estimation of the genetic variation of heat tolerance. In addition, thermal preference exhibited a low heritability (h2 =0.066), suggesting a reduced evolutionary response for this trait. We also found that the different estimates of heat tolerance and thermal preference were not genetically correlated, regardless of how heat tolerance was estimated. In conclusion, our data suggest that these thermal traits can evolve independently in this species. In agreement with previous evidence, these results indicate that methodology may have an important impact on genetic estimates of heat tolerance and that fast assays are more likely to detect the genetic component of heat tolerance.

Elevated temperatures cause loss of seed set in common bean (Phaseolus vulgaris L.) potentially through the disruption of source-sink relationships

BackgroundClimate change models predict more frequent incidents of heat stress worldwide. This trend will contribute to food insecurity, particularly for some of the most vulnerable regions, by limiting the productivity of crops. Despite its great importance, there is a limited understanding of the underlying mechanisms of variation in heat tolerance within plant species. Common bean, Phaseolus vulgaris, is relatively susceptible to heat stress, which is of concern given its critical role in global food security. Here, we evaluated three genotypes of P. vulgaris belonging to kidney market class under heat and control conditions. The Sacramento and NY-105 genotypes were previously reported to be heat tolerant, while Redhawk is heat susceptible.ResultsWe quantified several morpho-physiological traits for leaves and found that photosynthetic rate, stomatal conductance, and leaf area all increased under elevated temperatures. Leaf area expansion under heat stress was greatest for the most susceptible genotype, Redhawk. To understand gene regulatory responses among the genotypes, total RNA was extracted from the fourth trifoliate leaves for RNA-sequencing. Several genes involved in the protection of PSII (HSP21, ABA4, and LHCB4.3) exhibited increased expression under heat stress, indicating the importance of photoprotection of PSII. Furthermore, expression of the gene SUT2 was reduced in heat. SUT2 is involved in the phloem loading of sucrose and its distal translocation to sinks. We also detected an almost four-fold reduction in the concentration of free hexoses in heat-treated beans. This reduction was more drastic in the susceptible genotype.ConclusionsOverall, our data suggests that while moderate heat stress does not negatively affect photosynthesis, it likely interrupts intricate source-sink relationships. These results collectively suggest a physiological mechanism for why pollen fertility and seed set are negatively impacted by elevated temperatures. Identifying the physiological and transcriptome dynamics of bean genotypes in response to heat stress will likely facilitate the development of varieties that can better tolerate a future of elevated temperatures.

Differential Heat‐Induced Changes in Phenolic Acids Associated with Genotypic Variations in Heat Tolerance for Hard Fescue

Secondary metabolites, including phenolic acids, play important roles in plant defense against abiotic stress. The objectives of this study were to evaluate the response of phenolic acids to short‐term heat shock (7 h) and long‐term heat stress (21 d) in hard fescue [Festuca trachyphylla (Hack.) Krajina] and to identify constituents of phenolic acids associated with genotypic variation in heat tolerance. Plants of the heat‐tolerant cultivar ‘Reliant IV’ and heat‐sensitive cultivar ‘Predator’ were exposed to heat stress at 38/33°C (day/night) or nonstress temperature conditions at 22/18°C. Four phenolic acids (salicylic acid, homovanillic acid, caffeic acid, and ferulic acid) showed significant increases in content under short‐term heat shock. Seven phenolic acids (3,4‐dyhydroxybenzoic acid, 4‐hydroxybenzoic acid, coumaric acid, gallic acid, cinnamic acid, benzoic acid, and vanillic acid) showed significant increases in content after long‐term heat stress. Increases in the content of homovanillic acid (by 118%) and caffeic acid (by 117%) were observed in Reliant IV under short‐term heat shock compared with the untreated control, whereas 3,4‐dyhydroxybenzoic acid showed greater accumulation in Reliant IV (by 214%) than Predator (by 148%) under long‐term heat stress. These differentially accumulated phenolic acids could be associated with the contrasting levels of heat tolerance between the two cultivars. The transient increases in response to short‐term heat shock indicate their potential roles as stress signaling molecules, and their dramatic accumulation after long‐term heat stress suggests protective roles under heat stress.

Bed bugs (Cimex lectularius L.) exhibit limited ability to develop heat resistance.

The global population growth of the bed bug, Cimex lectularius (L.), is attributed to their cryptic behavior, diverse insecticide resistance mechanisms, and lack of public awareness. Bed bug control can be challenging and typically requires chemical and non-chemical treatments. One common non-chemical method for bed bug management is thermal remediation. However, in certain instances, bed bugs are known to survive heat treatments. Bed bugs may be present after a heat treatment due to (i) abiotic factors associated with the inability to achieve lethal temperatures in harborage areas for a sufficient time period, (ii) re-infestation from insects that escaped to cooler areas during a heat treatment or (iii) development of physiological resistance that allows them to survive heat exposure. Previous research has investigated the optimal temperature and exposure time required for either achieving complete mortality or sublethally affecting their growth and development. However, no research has examined bed bug populations for their ability to develop resistance to heat exposure and variation in thermo-tolerance between different bed bug strains. The goals of this study were: i) to determine if bed bugs could be selected for heat resistance under a laboratory selection regime, and ii) to determine if bed bug populations with various heat exposure histories, insecticide resistance profiles, and geographic origins have differential temperature tolerances using two heat exposure techniques (step-function and ramp-function). Selection experiments found an initial increase in bed bug survivorship; however, survivorship did not increase past the fourth generation. Sublethal exposure to heat significantly reduced bed bug feeding and, in some cases, inhibited development. The step-function exposure technique revealed non-significant variation in heat tolerance between populations and the ramp-function exposure technique provided similar results. Based on these study outcomes, the ability of bed bugs to develop heat resistance appears to be limited.

Oxidative damage and antioxidant mechanism in tomatoes responding to drought and heat stress

Abiotic stresses especially combined stress such as concurrence of drought and heat will influence crop production more seriously in the near future. Reactive oxygen species (ROS) worked as signal transduction molecule to accelerate plant response at abiotic stress conditions, the accumulation of which caused oxidative damage. Understanding the underlying effect of combined stress on the ROS metabolism and antioxidant mechanism in plant is a prerequisite for crop improvement in a changing climate. We aimed to explore the distinct response of the ROS production and its scavenging system in tomato at single and combined stress and to elucidate the crosstalk of tolerance mechanism. Thereby, dynamic changes in ROS metabolism and antioxidant mechanism in tomatoes at control, drought, heat and drought + heat (combined stress) were investigated. Two tomato cultivars (Sufen 14: CV1, Jinlingmeiyu: CV2) were applied to compare the cultivar difference. 6 days of drought and combined stress led to a sharp increase in H2O2 (hydrogen peroxide) content and O2·− (superoxide radicals) production speed of both cultivars even though there were fluctuations from day 1 to day 5. Dramatic increase of SOD and APX activity and significant decrease of CAT activity occurred in both cultivars at all stresses on day 3. In contrast, combined stress significantly depressed the POD and CAT activity in both cultivars on day 6. The significant increase in MDA content was observed in CV1 at drought and combined stress and in CV2 at three stresses. Meanwhile, combined stress induced significant decrease in proline content only in CV1. The canopy area and stem diameter of both cultivars at the combined stress were smaller than single stress. We found that there was cultivar variation in heat tolerance but not in drought and combined stress tolerance. In conclusion, the stress tolerance of tomatoes at drought and heat is closely associated with its ability to respond to oxidative damage and regulation of ROS scavenging system with unique ROS response induced by the combined stress. This study not only increases our understanding of the complex ROS responses in plants to abiotic stress, but also provides knowledge to improve crop tolerance.

Identification and characterization of novel homeodomain leucine zipper (HD-Zip) transcription factors associated with heat tolerance in perennial ryegrass

The homeodomain leucine zipper (HD-Zip) family transcription factors play roles in regulating plant development and responses to abiotic stress; however, how HD-Zip genes are associated with plant heat tolerance is unclear. The objectives of this study were to characterize HD-Zip I genes in perennial ryegrass (Lolium perenne), analyze the expression pattern under different abiotic stresses and identify novel HD-Zip I members associated with genetic variations in heat tolerance. A total of 13 HD-Zip I genes were identified in the transcriptome of perennial ryegrass. A comprehensive phylogenetic tree of HD-Zip I proteins in perennial ryegrass, Arabidopsis and rice was constructed. Motif analysis between LpHD-Zip I and OsHD-Zip I by MEME was characterized. LpHD-Zip I had close evolutionary relationship to OsHD-Zip I, and HD-Zip I may be subject to functional differentiation between monocotyledons and dicotyledons. qPCR analysis of 13 HD-Zip I genes showed these genes expressed at different levels in roots and leaves. These genes also showed various expression levels under different abiotic stresses (cold, heat, salt and osmotic). Physiological responses of heat-sensitive lines (321681 and 418714) and heat-tolerant lines (231565 and 275660) of perennial ryegrass to heat stress were evaluated. Differential expression levels of four genes (LpHOX6, -8, -21 and -24) were detected between heat-sensitive and heat-tolerant lines. LpHOX6, -8 and -24 expression levels were negatively associated with heat tolerance while LpHOX21 was positively associated with heat tolerance of perennial ryegrass. This is the first study demonstrating the association of four members of the HD-Zip I family (LpHOX6, -8, -21, and -24) with genetic variations in heat tolerance.

Intraspecific variation in lizard heat tolerance alters estimates of climate impact.

Research addressing the effects of global warming on the distribution and persistence of species generally assumes that population variation in thermal tolerance is spatially constant or overridden by interspecific variation. Typically, this rationale is implicit in sourcing one critical thermal maximum (CTmax ) population estimate per species to model spatiotemporal cross-taxa variation in heat tolerance. Theory suggests that such an approach could result in biased or imprecise estimates and forecasts of impact from climate warming, but limited empirical evidence in support of those expectations exists. We experimentally quantify the magnitude of intraspecific variation in CTmax among lizard populations, and the extent to which incorporating such variability can alter estimates of climate impact through a biophysical model. To do so, we measured CTmax from 59 populations of 15 Iberian lizard species (304 individuals). The overall median CTmax across all individuals from all species was 42.8°C and ranged from 40.5 to 48.3°C, with species medians decreasing through xeric, climate-generalist and mesic taxa. We found strong statistical support for intraspecific differentiation in CTmax by up to a median of 3°C among populations. We show that annual restricted activity (operative temperature > CTmax ) over the Iberian distribution of our study species differs by a median of >80hr per 25-km2 grid cell based on different population-level CTmax estimates. This discrepancy leads to predictions of spatial variation in annual restricted activity to change by more than 20days for six of the study species. Considering that during restriction periods, reptiles should be unable to feed and reproduce, current projections of climate-change impacts on the fitness of ectotherm fauna could be under- or over-estimated depending on which population is chosen to represent the physiological spectra of the species in question. Mapping heat tolerance over the full geographical ranges of single species is thus critical to address cross-taxa patterns and drivers of heat tolerance in a biologically comprehensive way.

Differences in heat tolerance within a Daphnia magna population: the significance of body PUFA content

In this study, we use the model organism Daphnia magna to determine variation in heat tolerance within a natural population and relate this to variation in body fatty acid content and composition. As a proxy for heat tolerance we measured time to immobilization (Timm) for 25 clonal lineages isolated from a single lake. The clonal lineages were grown on Chlamydomonas reinhardii at 15°C. Upon deposition of the first clutch, Timm and body fatty acids were determined. We report significant differences of Timm and of the content of PUFAs and of eicosapentaenoic acid (EPA) among the D. magna clonal lineages. Timm was negatively related to total PUFA-content, indicating that increased body PUFA-content may be detrimental for membrane properties at high temperatures. Juvenile somatic growth varied significantly among clonal lineages, and was not related to total body PUFA-content, hence body PUFA-content was no proxy for PUFA-limitation. No correlative evidence for an impact of body EPA-content on Timm or juvenile growth was obtained. We hypothesize that the observed intra-population variability of body PUFA-content might be related to potentially different amplitudes in diel vertical migration in response to fish. These different amplitudes would mean differences in the extent of diurnal temperature fluctuations among the clonal lineages.

The role of tolerance variation in vulnerability forecasting of insects.

Quantifying the amount of climatic change organisms can withstand before exceeding their physiological tolerance is a cornerstone of vulnerability forecasting. Yet most work in this area treats tolerance as a fixed trait. We review recent work that quantifies variation in high temperature tolerance across bioclimatic gradients, and we explore the implications for vulnerability to climate change. For some sources of variation, including differences in the evolutionary potential of heat tolerance across latitude, the typical biogeographic pattern of high vulnerability in the tropics is exacerbated. For other sources of variation, including certain types of plastic variation in heat tolerance, the biogeographic pattern of high tropical vulnerability is diminished. As a consequence, thermal tolerance variation should not be ignored in vulnerability forecasting.

Capturing genetic variability and selection of traits for heat tolerance in a chickpea recombinant inbred line (RIL) population under field conditions

Chickpea is the most important pulse crop globally after dry beans. Climate change and increased cropping intensity are forcing chickpea cultivation to relatively higher temperature environments. To assess the genetic variability and identify heat responsive traits, a set of 296 F8–9 recombinant inbred lines (RILs) of the cross ICC 4567 (heat sensitive) × ICC 15614 (heat tolerant) was evaluated under field conditions at ICRISAT, Patancheru, India. The experiment was conducted in an alpha lattice design with three replications during the summer seasons of 2013 and 2014 (heat stress environments, average temperature 35 °C and above), and post-rainy season of 2013 (non-stress environment, max. temperature below 30 °C). A two-fold variation for number of filled pods (FPod), total number of seeds (TS), harvest index (HI), percent pod setting (%PodSet) and grain yield (GY) was observed in the RILs under stress environments compared to non-stress environment. A yield penalty ranging from 22.26% (summer 2013) to 33.30% (summer 2014) was recorded in stress environments. Seed mass measured as 100-seed weight (HSW) was the least affected (6 and 7% reduction) trait, while %PodSet was the most affected (45.86 and 44.31% reduction) trait by high temperatures. Mixed model analysis of variance revealed a high genotypic coefficient of variation (GCV) (23.29–30.22%), phenotypic coefficient of variation (PCV) (25.69–32.44%) along with high heritability (80.89–86.89%) for FPod, TS, %PodSet and GY across the heat stress environments. Correlation studies (r = 0.61–0.97) and principal component analysis (PCA) revealed a strong positive association among the traits GY, FPod, VS and %PodSet under stress environments. Path analysis results showed that TS was the major direct and FPod was the major indirect contributors to GY under heat stress environments. Therefore, the traits that are good indicators of high grain yield under heat stress can be used in indirect selection for developing heat tolerant chickpea cultivars. Moreover, the presence of large genetic variation for heat tolerance in the population may provide an opportunity to use the RILs in future-heat tolerance breeding programme in chickpea.

Differential Responses of Amino Acids and Soluble Proteins to Heat Stress Associated with Genetic Variations in Heat Tolerance for Hard Fescue

Amino acid and protein metabolism are interrelated and both play important roles in plant adaptation to heat stress. The objective of this study was to identify amino acids and soluble proteins associated with genetic variation in heat tolerance of hard fescue (Festuca trachyphylla). According to a previous screening experiment, the hard fescue cultivars Reliant IV and Predator were selected as heat-tolerant and heat-sensitive cultivars, respectively. Plants of these two hard fescue cultivars were exposed to heat stress at 38/33 °C (day/night) or optimal temperature at 21/18 °C in growth chambers. Each cultivar had four replications under each temperature, and the experimental design was a split-plot design, temperature as the main plots and cultivars as the subplots. Under heat stress, ‘Reliant IV’ exhibited higher turf quality (TQ) and greater membrane stability than ‘Predator’. In response to heat stress, total amino acid content increased, whereas total soluble protein content decreased in both cultivars. The greater accumulation of amino acids in ‘Reliant IV’ was contributed by the greater increase of proteins involved in the glycolysis and the tricarboxylic acid (TCA) cycle that provided carbon skeleton for amino acid synthesis. ‘Reliant IV’ leaves exhibited greater extent of increases in the content of six individual amino acids (histidine, glutamine, proline, threonine, aspartate, and tryptophan) than ‘Predator’ under heat stress. Several soluble proteins were upregulated in response to heat stress, to a greater extent in ‘Reliant IV’ than ‘Predator’, including the proteins involved in photosynthesis, protein folding, redox hemostasis, stress signaling, stress defense, cell organization, and metabolism. These differentially accumulated free amino acids and soluble proteins could be associated with the genetic variation in heat tolerance of hard fescue.

Candidate Genes and Molecular Markers Correlated to Physiological Traits for Heat Tolerance in Fine Fescue Cultivars.

Heat stress is one of the major abiotic factors limiting the growth of cool-season grass species during summer season. The objectives of this study were to assess genetic variations in the transcript levels of selected genes in fine fescue cultivars differing in heat tolerance, and to identify single nucleotide polymorphism (SNP) markers associated with candidate genes related to heat tolerance. Plants of 26 cultivars of five fine fescue species (Festuca spp.) were subjected to heat stress (38/33 °C, day/night temperature) in controlled environmental growth chambers. Physiological analysis including leaf chlorophyll content, photochemical efficiency, and electrolyte leakage demonstrated significant genetic variations in heat tolerance among fine fescue cultivars. The transcript levels of selected genes involved in photosynthesis (RuBisCO activase, Photosystem II CP47 reaction center protein), carbohydrate metabolism (Sucrose synthase), energy production (ATP synthase), growth regulation (Actin), oxidative response (Catalase), and stress protection (Heat shock protein 90) were positively correlated with the physiological traits for heat tolerance. SNP markers for those candidate genes exhibited heterozygosity, which could also separate heat-sensitive and heat-tolerant cultivars into clusters. The development of SNP markers for candidate genes in heat tolerance may allow marker-assisted breeding for the development of new heat-tolerant cultivars in fine fescue and other cool-season grass species.

Heated communities: large inter- and intraspecific variation in heat tolerance across trophic levels of a soil arthropod community

Temperature extremes are predicted to increase in frequency, intensity and duration under global warming and are believed to significantly affect community composition and functioning. However, the effect of extreme climatic events on communities remains difficult to predict, especially because species can show dissimilar responses to abiotic changes, which may affect the outcome of species interactions. To anticipate community responses we need knowledge on within and among species variation in stress tolerance. We exposed a soil arthropod community to experimental heat waves in the field and measured heat tolerance of species of different trophic levels from heated and control plots. We measured the critical thermal maximum (CTmax) of individuals to estimate inter- and intraspecific variation in heat tolerance in this community, and how this was affected by experimental heat waves. We found interspecific variation in heat tolerance, with the most abundant prey species, the springtail Isotoma riparia, being more sensitive to high temperatures than its predators (various spider species). Moreover, intraspecific variation in CTmax was substantial, suggesting that individuals within a single species were unequally affected by heat extremes. However, heat tolerance of species did not increase after being exposed to an experimental heat wave. We conclude that interspecific variation in tolerance traits potentially causes trophic mismatches during extreme events, but that intraspecific variation could lessen these effects by enabling partial survival of populations. Therefore, ecophysiological traits can provide a better understanding of abiotic effects on communities, not only within taxonomic or functional groups, but also when comparing different trophic levels.

Genetic Variation for Tolerance to Terminal Heat Stress in Dasypyrum villosum

Heat stress substantially reduces the grain yield and quality of wheat (Triticum aestivum L., 2n = 6x = 42, AABBDD genome) and poses a major challenge to sustaining productivity because of global warming. Across wheat‐growing regions in the United States and globally, wheat often experiences terminal heat stress during the postflowering period. Dasypyrum villosum, a wild relative of wheat, has been a useful genetic resource for the improvement of several traits in wheat. Here we report a first survey of terminal heat tolerance in D. villosum. Twenty accessions of D. villosum from seven countries and three common wheat cultivars (checks) were compared. Agronomic traits including single kernel weight, total grain weight, grain number, and shoot weight were evaluated in both nonstress (22°C day, 17°C night) and heat stress (36°C day, 30°C night) conditions in two independent experiments. The results showed that there was significant genetic variation for heat tolerance during the grain‐filling period in D. villosum and that single kernel weight was less affected by heat stress in D. villosum than in common wheat. Three accessions, TA10228 and TA10225 originating in Italy and TA2172 in Turkey, showed the highest terminal heat tolerance. This work suggests that D. villosum may be a useful novel resource for the improvement of heat tolerance in common wheat.

Differential profiles of membrane proteins, fatty acids, and sterols associated with genetic variations in heat tolerance for a perennial grass species, hard fescue (Festuca Trachyphylla)

Cellular membrane composition controls membrane stability, affecting plant tolerance to abiotic stress. The objectives of this study were to examine differential changes in membrane constituents (sterol, fatty acid and membrane protein) in response to heat stress for a cool-season perennial grass species, hard fescue (Festuca trachyphylla) and identify major membrane constituents associated with the genetic variations in heat tolerance for two varieties contrasting in heat tolerance. Plants of heat-tolerant ‘Reliant IV’ and heat-sensitive ‘Predator’ were exposed to heat stress at 38/33°C (day/night) in growth chambers. Under heat stress, ‘Reliant IV’ showed better turf quality, greater membrane stability and higher photochemical efficiency compared to ‘Predator’. Leaf membranes of ‘Reliant IV’ showed greater increase of ethyl sterols (fucosterol, stigmasterol, sitosterol and avenasterol), and two fatty acids [oleic acid (18:1) and linoleic acid (18:2)] under heat stress compared to those for ‘Predator’. Several membrane proteins were less down-regulated or more up-regulated by heat stress in ‘Reliant IV’ than in ‘Predator’, including down-regulated proteins involved in electron transport of photosynthesis (ATP synthase subunits and cytochrome b6-f complex iron-sulfur subunit), signaling (lectin-domain containing receptor kinase A4.2), and protein modification (S-acyltransferase), and up-regulated proteins involved in carboxylation in photosynthesis (Rubisco activase beta form) and stress defense (disease resistance protein 1). These differentially accumulated sterols, fatty acids, and proteins in cellular membranes could contribute to the differential level of heat tolerance between the two varieties of hard fescues. These compounds could be used as biomarkers to select for heat-tolerant germplasm in hard fescues.

How are endemic and widely distributed bromeliads responding to warming temperatures? A case study in a Brazilian hotspot

The increase in mean global temperature is causing extensive changes in ecosystems. However, little is yet known about the heat tolerance of neotropical plant species. Here, we investigate heat tolerance variation in both restricted and widely distributed bromeliad species co-occurring in campo rupestre, a megadiverse ecosystem in central and eastern Brazil. We determined the heat tolerance of the photosynthetic apparatus using chlorophyll fluorescence measurements to test if the endemic species Vriesea minarum is more heat sensitive than two widely distributed species, Vriesea bituminosa and Aechmea nudicaulis. Furthermore, we tested if the distinct photosynthetic metabolisms of the species, sun exposure, and rainfall seasonality of campo rupestre influence this outcome. Our results show that, contrary to our expectations, the endemic campo rupestre species did not show the greatest heat sensitivity, but did have one of the lowest heat tolerance plasticities. The CAM bromeliad A. nudicaulis was more heat tolerant than the other bromeliad species, but both heat tolerance and its plasticity are highly affected by sun exposure and the rainfall seasonality of campo rupestre. The low values and plasticity of V. minarum thermal tolerance could indicate that the threat of global warming could be greater for this campo rupestre endemic species. Our results also indicate that heat tolerance, especially the ability to withstand stressful temperatures for a long time, is an important parameter that differentiates the ecological strategies of these bromeliads species.