Heat Tolerance Research Articles

Selective breeding enhances coral heat tolerance to marine heatwaves

Marine heatwaves are becoming more frequent, widespread and severe, causing mass coral bleaching and mortality. Natural adaptation may be insufficient to keep pace with climate warming, leading to calls for selective breeding interventions to enhance the ability of corals to survive such heatwaves, i.e., their heat tolerance. However, the heritability of this trait–a prerequisite for such approaches–remains unknown. We show that selecting parent colonies for high rather than low heat tolerance increased the tolerance of adult offspring (3–4-year-olds). This result held for the response to both 1-week +3.5 °C and 1-month +2.5 °C simulated marine heatwaves. In each case, narrow-sense heritability (h2) estimates are between 0.2 and 0.3, demonstrating a substantial genetic basis of heat tolerance. The phenotypic variability identified in this population could theoretically be leveraged to enhance heat tolerance by up to 1 °C-week within one generation. Concerningly, selective breeding for short-stress tolerance did not improve the ability of offspring to survive the long heat stress exposure. With no genetic correlation detected, these traits may be subject to independent genetic controls. Our finding on the heritability of coral heat tolerance indicates that selective breeding could be a viable tool to improve population resilience. Yet, the moderate levels of enhancement we found suggest that the effectiveness of such interventions also demands urgent climate action.

Urbanization drives partner switching and loss of mutualism in an ant-plant symbiosis.

Mutualistic interactions between species underpin biodiversity and ecosystem function, but may be lost when partners respond differently to abiotic conditions. Except for a few prominent examples, effects of global anthropogenic change on mutualisms are poorly understood. Here we assess the effects of urbanization on a symbiosis in which the plant Cordia nodosa house ants in hollow structures (domatia) in exchange for defense against herbivores. We expected to find that mutualist ants would be replaced in the city by heat-tolerant opportunists, leaving urban plants vulnerable to herbivory. In five protected forest sites and five urban forest fragments in southeast Perú, we recorded the identity and heat tolerance (CTmax) of ant residents of C. nodosa. We also assayed their plant-defensive behaviors and their effects on herbivory. We characterized the urban heat-island effect in ambient temperatures and within domatia. Forest plants housed a consistent ant community dominated by three specialized plant ants, whereas urban plants housed a suite of 10 opportunistic taxa that were, collectively, about 13 times less likely than forest ants to respond defensively to plant disturbance. In the forest, ant exclusion had the expected effect of increasing herbivory, but in urban sites, exclusion reduced herbivory. Despite poor ant defense in urban sites, we detected no difference in total standing herbivory, perhaps because herbivores themselves also declined in the city. Urban sites were warmer than forest sites (daily maxima in urban domatia averaged 1.6°C hotter), and the urban ant community as a whole was slightly more heat tolerant. These results illustrate a case of mutualism loss associated with anthropogenic disturbance. If urbanization is representative of increasing anthropogenic stressors more broadly, we might expect to see destabilization of myrmecophytic mutualisms in forest ecosystems in the future.

A high-throughput protocol for testing heat-stress tolerance in pollen

AbstractViable pollen is crucial for fertilization, but pollen is generally highly susceptible to heat stress. A quick, reliable method for testing the heat-stress tolerance of pollen is needed to improve the heat-stress tolerance in plants, but current methods require considerable space and labor. In addition, many such methods only test tolerance to a single constant temperature, making it time-consuming to screen heat tolerance over a wide temperature range and to examine the dynamics of pollen viability at different temperatures. To address this issue, we aimed to: (1) develop an easy, reliable method for measuring pollen viability at different temperatures; and (2) identify the best temperature range for screening pollen with high heat-stress tolerance. We harvested mature pollen from wheat (Triticum aestivum) plants and transferred it to a 96-well plate filled with liquid medium containing sucrose. We placed the plate in a PCR machine operating under a gradient PCR program to simultaneously test a range of temperatures. After incubating the pollen for 4 h, at temperatures ranging from 21.9 to 47 °C, we examined the pollen grains under a light microscope and employed a specific image analysis pipeline to assess the effects of temperature on pollen morphology, germination, and tube growth. This method facilitated the high-throughput screening of many pollen samples, enabling rapid, reliable, and precise analysis of pollen viability in response to temperature. Our approach should be applicable to other plant species and could be used to identify quantitative trait loci or genes influencing heat stress tolerance in pollen for breeding programs.

Selection for heat tolerance in Atlantic salmon (Salmo salar) using reaction norms

Selection for heat tolerance is a key strategy for aquaculture to cope with the effects of climate change. Different alternatives exist to select aquatic species for heat tolerance. Here, we investigated the feasibility of applying reaction norms in summer growth of Atlantic salmon (Salmo salar) naturally exposed to diverse heat loads as a strategy to genetically improve heat tolerance. For this, summer growth of 40,044 fish from 2685 families and 21 cohorts, distributed across 14 years and 2 sites in Tasmania, was analysed under different reaction norm models (RNM), using a function of the average daily seawater temperature during the summer period (ranging from 12.8 to 19.7 °C) as the environment descriptor (heat load). RNM results unravelled substantial genotype by environment interaction for summer growth, specially between intermediate and high heat loads. Quadratic and spline linear-linear RNM outperformed linear RNM, showing a non-linear behaviour of the additive genetic effect on summer growth across different heat load gradients. The predictive ability of breeding values from RNM revealed opportunities to select for heat tolerance either for the highest heat load or for sensitivity to thermal variation (slope of RNM). Genomic-based breeding values presented better statistical properties than pedigree-based breeding values, highlighting the importance of using genomic information for a better predictive ability of heat tolerance. Genome-wide association analysis reinforced the polygenic nature of heat tolerance, indicating genomic selection as a more effective strategy to improve heat tolerance in Atlantic salmon, compared to strategies targeting specific genomic regions/genes.

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

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

Marker assisted selection and genome recovery for heat tolerance in segregants of rice (Oryza sativa L.)

Abstract In the present global warming scenario, it is urgent to impart heat tolerance into the popular high yielding rice (Oryza sativa L.) varieties to reduce yield loss to a great extent. Uma (a prevalent red-grained rice variety in Kerala) was crossed with Nagina 22 (N22), the popular donor for heat tolerance. From the seven promising heat-tolerant F3 plants previously identified through marker assisted selection and field screening, F4 lines (58 nos.) were raised and characterised morphologically. Heat tolerance was scored under natural heat stress during hot summer months in field conditions. Among the evaluated F4 progenies, 26 promising plants registered >75% spikelet fertility. Double panicles were observed in some of the tillers of fourteen F4 plants. During the selection with reported polymorphic markers between parents, all the 26 F4 plants produced the corresponding amplicon for RM5749 (linked marker for heat tolerance in the parental cross Uma x N22) and also for RM9, RM201, RM208, RM225, RM242, RM495, RM3586, RM6100, RM6836, and RM26212, corresponding to the heat tolerant parent N22. Genomic analysis revealed 64% recovery of the Uma genome in seven F4 plants, with maximum genomic regions of Uma on the chromosomes 3 and 5. These promising F4 plants could be forwarded to generate stable and high yielding heat tolerant rice varieties. The identified markers could be used for linkage analysis and QTL mapping in future. Keywords: Heat stress; Rice; spikelet fertility; SSR; QTL

Genotype-by-environment interactions in beef and dairy cattle populations: A review of methodologies and perspectives on research and applications.

Modern livestock production systems are characterized by a greater focus on intensification, involving managing larger numbers of animals to achieve higher productive efficiency and animal health and welfare within herds. Therefore, animal breeding programs need to be strategically designed to select animals that can effectively enhance production performance and animal welfare across a range of environmental conditions. Thus, this review summarizes the main methodologies used for assessing the levels of genotype-by-environment interaction (G × E) in cattle populations. In addition, we explored the importance of integrating genomic and phenotypic information to quantify and account for G × E in breeding programs. An overview of the structure of cattle breeding programs is provided to give insights into the potential outcomes and challenges faced when considering G × E to optimize genetic gains in breeding programs. The role of nutrigenomics and its impact on gene expression related to metabolism in cattle are also discussed, along with an examination of current research findings and their potential implications for future research and practical applications. Out of the 116 studies examined, 60 and 56 focused on beef and dairy cattle, respectively. A total of 83.62% of these studies reported genetic correlations across environmental gradients below 0.80, indicating the presence of G × E. For beef cattle, 69.33%, 24%, 2.67%, 2.67%, and 1.33% of the studies evaluated growth, reproduction, carcass and meat quality, survival, and feed efficiency traits, respectively. By contrast, G × E research in dairy cattle populations predominantly focused on milk yield and milk composition (79.36% of the studies), followed by reproduction and fertility (19.05%), and survival (1.59%) traits. The importance of G × E becomes particularly evident when considering complex traits such as heat tolerance, disease resistance, reproductive performance, and feed efficiency, as highlighted in this review. Genomic models provide a valuable avenue for studying these traits in greater depth, allowing for the identification of candidate genes and metabolic pathways associated with animal fitness, adaptation, and environmental efficiency. Nutrigenetics and nutrigenomics are emerging fields that require extensive investigation to maximize our understanding of gene-nutrient interactions. By studying various transcription factors, we can potentially improve animal metabolism, improving performance, health, and quality of products such as meat and milk.

On the use of rapid acute heat tolerance assays to resolve ecologically relevant differences among corals

On the use of rapid acute heat tolerance assays to resolve ecologically relevant differences among corals

Assessment of genetic variability, heritability and correlation in advanced breeding lines of bread wheat (Triticum aestivum) under heat stress condition

Abstract An experiment was conducted under normal (with six irrigation during crop period) and stressed condition during Rabi 2019 in All India Coordinated Research Project (AICRP) on Wheat, MARS, Dharwad, Karnataka with the view of assessing genetic variability, heritability and expected genetic advance in 104 F4 families of the cross HD2864 × DBW14. The progenies exhibited wide range of variation for all the traits indicating the presence of enough genetic variability in the material under study. Under timely sown condition, the traits like leaf waxyness, NDVI at different stages, SPAD at different stages, number of productive tillers per plant, seeds per spike, grain filling duration, spike length, thousand grains weight and seed set percentage showed high variability. The traits like plant height, canopy temperature at different stages and membrane stability index showed low variability. Under late sown condition, the traits like leaf waxyness, plant height, NDVI at different stages, SPAD at different stages, number of productive tillers per plant, seeds per spike, yield per plant, row bulk yield and seed set percentage showed high variability. The traits like days to maturity, spike length and membrane stability index showed low variability. The findings shows that all traits related to crop yield are positively linked, except for canopy temperature at different growth stages. Promising lines identified through Heat susceptibility index (HSI) and Heat tolerance index (HTI) can be utilized in future breeding programs to enhance crop productivity. Keywords: Variability, Coefficient of variation, Heritability, Genetic advance.

Assessing the thermal limits and metabolic profiles of small indigenous fish species: Informing conservation and aquaculture in a changing climate

This study explored the thermal tolerance and routine metabolic rate of ten small indigenous fish species from Northeast India: Amblypharyngodon mola, Esomus danrica, Puntius sophore, Gudusia chapra, Heteropneustes fossilis, Botia dario, Lepidocephalichthys guntea, Mystus cavasius, Aplocheilus panchax, and Glossogobius giuris. Fish were acclimated to 20°C, 25°C, and 30°C for two weeks prior to experiments and assessed for critical thermal maxima (CTmax), critical thermal minima (CTmin), lethal thermal maxima (LTmax), oxygen consumption rates, and respiratory quotients using standardized methods. The results revealed significant interspecific variations: CTmax ranged from 36.4°C to 41.7°C, CTmin from 8.7°C to 15.2°C, and LTmax from 41.5°C to 44.9°C. Oxygen consumption rates varied between 0.26 and 1.07 mg O₂/g/h, with respiratory quotients ranging from 0.76 to 1.01. Heteropneustes fossilis (CTmax: 41.7°C at 30°C acclimation) exhibited the highest thermal tolerance, while Amblypharyngodon mola had the lowest (CTmax: 38.2°C at 30°C acclimation). Differences in thermal tolerance between species were statistically significant (p<0.05). Notably, CTmax was positively correlated with oxygen consumption rates, suggesting a connection between metabolic rate and heat tolerance. These findings enhance our understanding of the physiological adaptations of these species to their thermal environments and underscore their conservation needs amidst climate change.

Physiological responses, ethology, and ingestive behavior of Anglo-Nubiana goats submitted to different air temperatures

The objective of this study was to evaluate the physiological parameters and ingestive behavior of Anglo-Nubian goats as a function of air temperature, as well as the correlation of these variables. Six male goats were distributed in a completely randomized design in a climate chamber. The treatments consisted of four different controlled AT (20, 24, 28 and 32 °C). The physiological responses: heart rate (HR), respiratory rate (RR) and rectal temperature (RT) were collected at three different times of the day (8 am, 12 pm and 4 pm). The behavioral responses evaluated were: lying inactive, standing inactive, feeding, standing ruminating and lying ruminating. The feed intake decreased linearly in the hours of 4–7 AM, according to the increase in AT. The time spent in the lying ruminating activity decreased linearly (P<0.05) with the increase in AT. The intake and the rate of dry matter intake decreased linearly (P<0.05) with the increase in AT and the water intake increased linearly (P<0.05). The overall results provide information that can be used in heat tolerance studies, helping livestock farmers around the world to plan and make decisions. In addition to contributing to the development of strategies, national and international guidelines for mitigation and accurate assessment of thermal stress.

Evaluating Heat Stress Effects on Growth in Tunisian Local Kids: Enhancing Breeding Strategies for Arid Environments.

This study evaluates the impact of thermal load on the weights of Tunisian local kids using 24 models with cubic and quadratic Legendre polynomials, based on daily temperatures (Tmin, Tmax, and Tavg) on the day of weight recording and averaged over 7, 14, and 21 days before weighing. The deviance information criterion (DIC) consistently shows that cubic polynomial models offer a better fit than quadratic models, highlighting their superior accuracy in studying the effects of thermal load on kid weights. The models with the best fit utilized average or maximum temperatures over 14 or 21 days. The patterns of response were similar across the temperature variables and periods, showing a stable weight response at lower temperatures (thermoneutral region) followed by a decline as the temperatures increased. The weight loss was -125 g/°C beyond the moderate heat stress threshold (Tavg21 = 17.7 °C) and -450 g/°C beyond the severe heat stress threshold (Tavg21 = 25.3 °C) for Tavg21. The heat stress thresholds for moderate heat stress (HS1) were 8.6 °C for Tmin14, 27.4 °C for Tmax14, and 18.6 °C for Tavg14; moreover, for acute heat stress (HS2), they were 17.2 °C for Tmin14, 32.4 °C for Tmax14, and 25.5 °C for Tavg14. High variability in individual responses was observed, with differences in the slope of response ranging from 2.0 kg/°C for moderate heat stress to around 3.0 kg/°C for severe heat stress for Tavg. The correlations between the weights under different temperatures were low, indicating that rankings based on weight could change with varying heat conditions. The animals with larger weight levels generally demonstrated better heat tolerance, and those with good heat tolerance under moderate conditions were also likely to have good tolerance under severe conditions.

Chlorophyll Fluorescence in Wheat Breeding for Heat and Drought Tolerance

The constantly growing need to increase the production of agricultural products in changing climatic conditions makes it necessary to accelerate the development of new cultivars that meet the modern demands of agronomists. Currently, the breeding process includes the stages of genotyping and phenotyping to optimize the selection of promising genotypes. One of the most popular phenotypic methods is the pulse-amplitude modulated (PAM) fluorometry, due to its non-invasiveness and high information content. In this review, we focused on the opportunities of using chlorophyll fluorescence (ChlF) parameters recorded using PAM fluorometry to assess the state of plants in drought and heat stress conditions and predict the economically significant traits of wheat, as one of the most important agricultural crops, and also analyzed the relationship between the ChlF parameters and genetic markers.

The ZmHSF08-ZmUGT92A1 module regulates heat tolerance by altering reactive oxygen species levels in maize

GTs (Glycosyltransferases) are important in plant growth and abiotic stresses. However, its role in maize heat response is far from clear. Here, we describe the constitutively expressed UDP-glycosyltransferase ZmUGT92A1, which has a highly conserved PSPG box and is localized in chloroplasts, is induced under heat stress. Functional disruption of ZmUGT92A1 leads to heat sensitivity and reactive oxygen species accumulation in maize. Metabolomics analysis revealed that ZmUGT92A1 affected multiple metabolic pathways and altered the metabolic homeostasis of flavonoids under heat stress. In vitro assay showed ZmUGT92A1 exhibits glycosyltransferase activity on flavonoids and hormones. Additionally, we identified a rapidly heat-induced transcription factor, ZmHSF08, which can directly bind and repress the promoter region of ZmUGT92A1. The ZmHSF08 overexpression line exhibits heat sensitivity and reactive oxygen species accumulation. These findings reveal that the ZmHSF08-ZmUGT92A1 module plays a role in heat tolerance in maize and provide candidate strategies for the development of heat-tolerant varieties.

Nuclear integration of MYB36 and APX-1 genes impart heat tolerance in wheat.

Elevated temperatures during grain filling stage, exceeding the optimal range by 3-4°C, not only results in a substantial yield reduction in wheat by 10-50% but activates disease and insect infestation. In this research, we introduced heat-tolerant MYB36 and APX-1 gene cassettes into wheat, employing an efficient Agrobacterium mediated transformation protocol, demonstrating higher transformation efficiency. The study encompassed the assembly of MYB36 and APX-1 gene cassettes, and confirmation of gene products in Agrobacterium, followed by the transformation of the MYB36 and APX-1 genes into wheat explants. We were able to select transgenic plant with various combinations. The transgenic plants with APX-1 gene alone produced medium sized grain and spike whereas with both APX-1 and MYB36 genes expressed individually under SPS and rd29a promoter respectively showed good tolerance to heat at 32oC at grain filling/milking stage and produced relatively bold grains. While non-transgenic plants grains were wrinkled with thin spike showing susceptibility to heat. This research contributes to the broader scientific understanding of plant stress responses and the combined effectiveness of MYB36 and APX-1 genes in crop improvement without disturbing normal nutritional values. The gene integration can serve as a valuable tool in breeding programs aimed at developing heat-tolerant wheat varieties. These findings also advance our comprehension of the functions of heat-induced genes and lay the foundation for selecting optimal candidates for in-depth functional studies of heat-responsive MYB36 and APX-1 genes in wheat.

Phenological Adaptation Is Insufficient to Offset Climate Change-Induced Yield Losses in US Hybrid Maize.

Climate change is projected to decrease maize yields due to warmer temperatures and their consequences. Studies using crop growth models (CGMs), however, have predicted that, through a combination of alterations to planting date, flowering time, and maturity, these yield losses can be mitigated or even reversed. Here, we examine three assumptions of such studies: (1) that climate has driven historical phenological trends, (2) that CGM ensembles provide unbiased estimates of yields under high temperatures, and (3) that the effects of temperature on yields are an emergent property of interactions between phenology and environment. We used data on maize phenology from the United States Department of Agriculture, a statistical model of maize hybrid heat tolerance derived from 80 years of public yield trial records across four US states, and outputs of an ensemble of CMIP6 climate models. While planting dates have advanced historically, we found a trend toward later planting dates after 2005 and no trend for silking or maturity, shifting more time into the reproductive period. We then projected maize yields using the historical model and crop calendars devised using three previously proposed adaptation strategies. In contrast to studies using CGMs, our statistical yield model projected severe yield losses under all three strategies. Finally, we projected maize yields accounting for historical genetic variability for heat tolerance, discovering that it was insufficient to overcome the negative effects of projected warming. These projections are driven by greater heat stress exposure under all crop calendars and climate scenarios. Combined with analysis of the internal sensitivities of CGMs to temperature, our results suggest that current projections do not adequately account for the effects of increasing temperatures on maize yields. Climate adaptation in the US Midwest must utilize a richer set of strategies than phenological adaptation, including improvements to heat tolerance and crop diversification.

Evaluate the Genetic Divergence and Principal Component Analysis in Bread Wheat (Triticum aestivum L.)

The current investigation was carried out on some bread wheat (Triticum aestivum L.) genotypes throughout spring season to evaluate their heat tolerance via Cluster Analysis and principal component analysis (PCA). The experiment was accomplished in an augmented block design with 60 genotypes and three replications. Evaluations were carried out on 26 quantitative traits. Cluster analysis showed five clusters, cluster I with 56 genotypes and clusters II, III, IV and V with only one genotype each. The clusters II, III, IV and V have only one genotype each, so their intra-cluster distances were zero. The intra-cluster distance for cluster I was 57.879. The maximum and minimum inter cluster distance was found between cluster II and III (267.377) and between cluster I and II (86.469), respectively. Cluster I showed the earliest (76.689 days) average for early maturity (days to 50% heading) and cluster III showed the maximum (27.664) average for grain yield (grain yield per plant). PCA indicated that the five principal components (PC1 to PC5) accounted for 65.61% of the total variance. PC1 accounted for 11.51% of the total variance and showed positive factor loading for almost traits. Harvest index, grain yield per plant, flag leaf width and leaf rolling showed the highest factor loadings for PC1. As a result of the foregoing data and analysis, it is possible to conclude that there is great potential for effective genetic improvement for grain yield and correlated traits in the present wheat genotypes.

Searching for variables representing the response to cold stress in Mediterranean Geotrupinae reveals an association between heat and cold tolerances

Searching for variables representing the response to cold stress in Mediterranean Geotrupinae reveals an association between heat and cold tolerances

Association analysis of different wheat genotypes for heat tolerance for yield and its attributing characters

Association analysis of different wheat genotypes for heat tolerance for yield and its attributing characters

The genome of a giant clam zooxanthella (Cladocopium infistulum) offers few clues to adaptation as an extracellular symbiont with high thermotolerance

BackgroundCladocopium infistulum (Symbiodiniaceae) is a dinoflagellate specialized to live in symbiosis with western Pacific giant clams (Tridacnidae). Unlike coral-associated symbionts, which reside within the host cells, C. infistulum inhabits the extracellular spaces of the clam’s digestive diverticula. It is phylogenetically basal to a large species complex of stress-tolerant Cladocopium, many of which are associated with important reef-building corals in the genus Porites. This close phylogenetic relationship may explain why C. infistulum exhibits high thermotolerance relative to other tridacnid symbionts. Moreover, past analyses of microsatellite loci indicated that Cladocopium underwent whole-genome duplication prior to the adaptive radiations that led to its present diversity.ResultsA draft genome assembly of C. infistulum was produced using long- and short-read sequences to explore the genomic basis for adaptations underlying thermotolerance and extracellular symbiosis among dinoflagellates and to look for evidence of genome duplication. Comparison to three other Cladocopium genomes revealed no obvious over-representation of gene groups or families whose functions would be important for maintaining C. infistulum’s unique physiological and ecological properties. Preliminary analyses support the existence of partial or whole-genome duplication among Cladocopium, but additional high-quality genomes are required to substantiate these findings.ConclusionAlthough this investigation of Cladocopium infistulum revealed no patterns diagnostic of heat tolerance or extracellular symbiosis in terms of overrepresentation of gene functions or genes under selection, it provided a valuable genomic resource for comparative analyses. It also indicates that ecological divergence among Cladocopium species, and potentially among other dinoflagellates, is partially governed by mechanisms other than gene content. Thus, additional high-quality, multiomic data are needed to explore the molecular basis of key phenotypes among symbiotic microalgae.