Heat Tolerance Research Articles

SIRT2-mediated deacetylation of glutathione transferase alleviates oxidative damage and increases the heat tolerance of Pleurotus ostreatus

High-temperature stress (HS) severely threatens agricultural production. Pleurotus ostreatus is cultivated in many parts of the world, and its growth is strongly affected by HS. We previously reported that metabolic rearrangement occurred in HS, but the gene expression levels of several key enzymes remained unchanged. Therefore, in this study, we investigated the contribution of posttranslational modifications of proteins to HS resistance in P. ostreatus. We found that the level of acetylation of P. ostreatus decreased under short-term HS treatment and increased as the duration of HS treatment increased. Acetylation omics revealed that almost all metabolic enzymes were acetylated. We found that deacetylation under HS can improve the growth recovery ability of mycelia, the activity of matrix-degrading enzyme, and the contents of antioxidants, such as nicotinamide adenine dinucleotide phosphate (NADPH) and glutathione (GSH), but can decreased H2O2 levels. In vitro acetylation experiments and point mutations revealed that the deacetylase SIRT2 increased the activity of glutathione transferases (GSTs) by deacetylating GST1 66K, GST2 206K, and GST2 233K. Together, SIRT2 is activated by short-term HS and improves its antioxidant activity by deacetylating GSTs, thereby improving the resistance of P. ostreatus to HS. In this study, we identified new non-histone substrate proteins and new lysine acetylation sites of SIRT2 under HS. We also discovered the role of non-histone acetylation in the adaptation of organisms to HS.

Implementation of a mixed-methods heat acclimation programme in a professional soccer referee before the 2022 FIFA world cup in Qatar: a case study

ObjectivesThis case study reports the real-world practicalities of implementing a mixed-methods heat acclimation (HA) programme before the 2022 FIFA World Cup.MethodsOne male English soccer referee (age: 44 years; height: 1.82...

Gene pyramiding improved cell membrane stability under heat stress in cotton (Gossypium hirsutum L.)

Climate change has been drastically affecting cotton not only in Pakistan but also all over the world. Normally cotton is known as heat tolerant when compared with other crops, but if the high temperature occurs during flowering period the yield decreases significantly. Marker assisted gene pyramiding provides a sustainable solution to improve heat tolerance. A total of seven genotypes were developed by a series of crossing seven tolerant genotypes over the period of three years. Tolerant genotypes were selected by screening for important transcription factors (GHSP26, HSP3, HSFA2, DREB1A, HSP101, DREB2A, GhNAC2, HSPCB, GhWRKY41, TPS, GbMYB5, ANNAT8, GhMPK17, GhMKK1, GhMKK3, GhMPK2, HSC70, APX1 and GhPP2A1). The seven genotypes were evaluated under normal and heat stress in a multi-year trial. The traits related to heat tolerance, such as cell membrane stability, relative water content, excised leaf water loss, plant height, number of nodes, internodal length, number of buds, number of bolls and leaf area was observed under normal and heat stress conditions. The developed genotypes showed improvement in cell membrane stability and relative water content under heat stress. The genotypes [(VH-305×MNH-886)×MNH-1035)×NIAB-78)], [(MNH-1035×MNH-886)×MNH-886)×SM-431] and [(MNH-1035×MNH-886)×MNH-886)×SS-32] depicted heat tolerance and could be used as heat tolerant material for variety development in breeding programs.

Climate adaptive loci revealed by seascape genomics correlate with phenotypic variation in heat tolerance of the coral Acropora millepora

One of the main challenges in coral reef conservation and restoration is the identification of coral populations resilient under global warming. Seascape genomics is a powerful tool to uncover genetic markers potentially involved in heat tolerance among large populations without prior information on phenotypes. Here, we aimed to provide first insights on the role of candidate heat associated loci identified using seascape genomics in driving the phenotypic response of Acropora millepora from New Caledonia to thermal stress. We subjected 7 colonies to a long-term ex-situ heat stress assay (4 °C above the maximum monthly mean) and investigated their physiological response along with their Symbiodiniaceae communities and genotypes. Despite sharing similar thermal histories and associated symbionts, these conspecific individuals differed greatly in their tolerance to heat stress. More importantly, the clustering of individuals based on their genotype at heat-associated loci matched the phenotypic variation in heat tolerance. Colonies that sustained on average lower mortality, higher Symbiodiniaceae/chlorophyll concentrations and photosynthetic efficiency under prolonged heat stress were also the closest based on their genotypes, although the low sample size prevented testing loci predictive accuracy. Together these preliminary results support the relevance of coupling seascape genomics and long-term heat stress experiments in the future, to evaluate the effect size of candidate heat associated loci and pave the way for genomic predictive models of corals heat tolerance.

Facial cooling improves thermal perceptions and maintains the interleukin-6 response during passive heating: A sex comparison

ABSTRACT Passively elevating body temperature can trigger a potentially beneficial acute inflammatory response. However, heat therapy often causes discomfort and negative thermal perceptions, particularly in females who generally have lower heat tolerance than males. This study aimed to evaluate the impact of facial cooling on thermal comfort and interleukin-6 concentration in response to 60 minutes of dry heat exposure, and to investigate sex differences in physiological responses and perceptions. 22 healthy young adults (10 females, 12 males; age: 24.4 ± 3.3 years) completed three trials in randomized order using a dry sauna device: 1) Hyperthermia (71.1 ± 1.9°C; HEAT), 2) Hyperthermia with facial cooling via fans (71.1 ± 3.0°C; FAN), and 3) Normothermia (27.0 ± 0.9°C; CON). Blood samples to determine interleukin-6 (IL-6) plasma concentration were collected before and after exposure; basic affect and thermal comfort, rectal and skin temperature were assessed throughout the intervention. Rectal temperature following HEAT (38.0 ± 0.3°C) and FAN (37.8 ± 0.3°C) did not differ between males and females (p = 0.57). Females had higher forehead skin temperatures than males (p ≤ 0.019). Thermal comfort remained more positive in FAN compared to HEAT (p ≤ 0.002). Females felt more thermal discomfort than males in HEAT (p ≤ 0.03), but not in FAN (p = 0.28). The increase in IL-6 plasma concentration was similar between HEAT and FAN (p = 1.00), and higher than CON (p ≤ 0.02); there was no difference between males and females (p = 0.69). This study showed that facial cooling alleviated the thermal discomfort during heat exposure, particularly benefitted females, and did not impede the acute IL-6 response.

The heat is on: impact of heat waves on critical thermal maxima in larvae and adults of solitary bee Osmia bicornis (Hymenoptera: Megachilidae)

Extreme temperature events, such as heat waves, are increasing in frequency, magnitude, and duration. These events are believed to contribute to pollinator decline. Critical thermal maxima (CTmax) is a key physiological trait for understanding an organism’s ecology and predicting its responses to changes in climate. In this study, we investigated whether different life stages with distinct thermoregulatory behaviors differ in their CTmax in the solitary bee Osmia bicornis, one of the most common and important pollinators in Central Europe. Additionally, we tested the influence of excessively high temperatures, heat waves, on the CTmax in Osmia bicornis. We found CTmax varied among life stages, with adults exhibiting higher CTmax than larvae. Both females and males of adult bees showed a negative correlation between CTmax and body mass. Interestingly, adult bees exposed to different heat waves during their larval stage did not exhibit significant shifts in CTmax. These results suggest that bees may have limited capacity to enhance heat tolerance in response to prior heat exposure.

Thermal response in Boer goats differing in coat colour

Context The coat is the first defense layer protecting animals from direct sunlight, influencing radiant-heat absorption and loss. Dark coat colour may increase animal heat impact because of higher absorption of solar radiation. Aims We investigated the impact of pigmentation intensity on the heads of animals and their thermal responses to solar radiation. Furthermore, we compared the thermal responses between dark and light brown-coloured animals, to determine whether the duration of sun and shade exposure (3 h each) is sufficient to differentiate the heat gain and losses between the two groups. Methods The effect of coat colour on rectal and surface temperatures in Boer goats, classified according to their head pigmentation pattern as dark (DB, N = 11) or light brown (LB, N = 11), exposed to sun and shade, was evaluated. The animals’ body and head surface temperatures were measured the same day before, during, and after sun exposure by using infrared thermography. Individual thermographic images were analysed by body regions (rump, leg, neck) and head areas (eye, ear, upper and lower part of the head, and the muzzle). Key results During solar radiation, all measured variables increased. In the shade, the rump, leg, and neck surfaces remained elevated, whereas the head area cooled down faster, with the highest temperature changes measured for the ear of about 10%. Most surface cooling occurred within 30 min after returning to the shade. Coat colour groups differed only in higher overall muzzle temperature of DB than that of LB goats (P = 0.048). Correlations between rectal and surface temperatures were low to medium, ranging from −0.02 (eye) to 0.31 (muzzle). Conclusions The head area is suggested as the important thermal window for heat dissipation and selective brain cooling. Light brown-headed animals were more efficient in eliminating the heat gained from solar radiation when returned to shade. Implications The colouration of the animal’s head may play an important role for its heat tolerance. As an easy-to-recognise characteristic, coat colour can serve as a selection trait for local goat populations. In view of global warming, selection for lighter coat colour in domestic ruminants may also become important even under temperate climates.

Strategies, challenges, and outcomes of heat stress resilience in sub-Saharan African community-based cattle feedlots: a systematic review.

In sub-Saharan Africa, cattle feedlots face a significant challenge in dealing with heat stress. However, there is a lack of inclusive strategies for resilience in these situations. The aim of this systematic review is to investigate the strategies, challenges, and outcomes related to heat stress resilience in community-based cattle feedlots in sub-Saharan Africa. The PRISMA approach, which is a method for reporting systematic reviews and meta-analyses, was used to identify, screen, and analyze 30 peer-reviewed articles published over the last 20 years from Google Scholar and Scopus. The review found that key strategies to mitigate heat stress include providing shade through natural and artificial means, ensuring constant access to cool, clean water using water spraying systems and cooling ponds, and implementing nutritional adjustments such as high-energy feeds and electrolyte supplements. Additionally, genetic selection for heat-tolerant breeds and management practices like adjusting feeding times and improving ventilation were found to be effective in dealing with heat stress. In particular, local germplasm and genetic traits of cattle in sub-Saharan Africa play a crucial role in heat stress resilience. Indigenous breeds, which have adapted to the region's harsh climate over centuries, exhibit traits such as higher heat tolerance, better water-use efficiency, and improved feed conversion rates under heat stress conditions. This genetic resilience can be enhanced through targeted breeding programs aimed at amplifying these beneficial traits. Implementing these strategies resulted in improved cattle health and productivity, as evidenced by enhanced weight gain, better reproductive performance, and lower mortality rates. The socio-economic benefits of these strategies included reduced economic losses and increased farmer incomes, which in turn contributed to improved community health and nutrition. However, the review also identified significant challenges, including financial constraints, limited access to knowledge and training, and cultural resistance. To address these barriers, the review recommends increased investment in affordable cooling technologies, farmer education, and community-based initiatives. Additionally, leveraging the genetic strengths of local cattle breeds should be prioritized to maximize the effectiveness of heat stress resilience strategies.

Ecotypic Variation in Leaf Thermoregulation and Heat Tolerance but Not Thermal Safety Margins in Tropical Trees.

To avoid reaching lethal temperatures during periods of heat stress, plants may acclimate either their biochemical thermal tolerance or leaf morphological and physiological characteristics to reduce leaf temperature (Tleaf). While plants from warmer environments may have a greater capacity to regulate Tleaf, the extent of intraspecific variation and contribution of provenance is relatively unexplored. We tested whether upland and lowland provenances of four tropical tree species grown in a common garden differed in their thermal safety margins by measuring leaf thermal traits, midday leaf-to-air temperature differences (∆Tleaf) and critical leaf temperatures defined by chlorophyll fluorescence (Tcrit). Provenance variation was species- and trait-specific. Higher ∆Tleaf and Tcrit were observed in the lowland provenance for Terminalia microcarpa, and in the upland provenance for Castanospermum australe, with no provenance effects in the other two species. Within-species covariation of Tcrit and ∆Tleaf led to a convergence of thermal safety margins across provenances. While future studies should expand the number of provenances and species investigated, our findings suggest that lowland and upland provenances may not differ substantially in their vulnerability to heat stress, as determined by thermal safety margins, despite differences in operating temperatures and Tcrit.

Evaluating genotype by environment interaction for growth traits in Limousine cattle

Environmental conditions affect the growth and health of animals, making it crucial to quantify heat stress and the genetic basis of heat tolerance in animal breeding. The main objective of this study was to evaluate heat stress on beef cattle growth and investigate the genetic background of tolerance to harsh environmental conditions in the Italian Limousine beef cattle. Three growth traits were analysed: average daily gain (ADG), weaning weight (WW), and yearling weight (YW). Data were collected from animals raised between 1991 and 2022 and combined with 14 environmental covariates. Records for ADG, WW, and YW encompassed 108 205, 100 058, and 24 939 individuals, respectively, with 4 617, 4 670, and 2 048 genotyped individuals. Climatic variables were compared for inclusion in a linear mixed model using the Deviance Information Criterion. Multiple-trait models and genomic information incorporated environmental conditions with the largest impact on the studied traits Genotype by environment interaction (G × E) was detected in all the studied traits, showing substantial heterogeneity of the variance components across the different environments (Env). Heritability for WW remains constant among Env; instead, for ADG and YW decreased under uncomfortable environmental conditions. YW showed the lowest genetic correlation (0.28) between divergent conditions (Env 2 and Env 5,) for ADG and WW correlations dropped below 0.50 among Env. The values of genetic correlations indicate that growth traits are moderately to strongly affected by G × E. Eigenvalue decomposition of the additive genetic (co)variance matrix for ADG, WW, and YW indicated that three components accounted for over 0.80 of the proportion of the variance explained, suggesting different animal performances across Env. Spearman rank correlations showed potential re-ranking of genotyped sires, because ADG, WW, and YW showed correlations between Env below 0.80. The accuracy of single-step genomic EBV was higher compared to EBV for al traits. Overall, the result confirms the existence of G × E for growth traits in the Italian Limousine population. Including G × E in the model allows for more environment-aware predictions, helping breeders understand how different genetic bases respond to varying conditions. Genomic predictions incorporating G × E could accelerate genetic gains and improve response to selection for heat tolerance.

Heat tolerance varies considerably within a reef-building coral species on the Great Barrier Reef

Reef-building coral populations face unprecedented threats from climate warming. Standing variation in heat tolerance is crucial for evolutionary processes necessary for corals to persist. Yet, the spatial distribution of heat-tolerant corals and the underlying factors that determine heat tolerance are poorly understood from individual to ecosystem scales. Here, we show extensive variation in the heat tolerance of a foundational coral species complex across the Great Barrier Reef. Thermal thresholds of 569 individuals differed by up to 7.3 °C across scales from meters to >1250 km. Variation in thresholds among reefs was consistent with local adaptation and acclimatization to historical and recent thermal history. However, variation within reefs was sometimes greater than among reefs and largely unexplained by environmental predictors, putative host species, or symbiont communities. This indicates that within-reef heat tolerance differences may be informed primarily by other factors, such as adaptive genomic variation. We anticipate our findings will inform conservation and restoration actions, including targeting individuals for selective breeding of enhanced heat tolerance.

Genome-Wide Association Study Reveals Marker–Trait Associations for Heat-Stress Tolerance in Sweet Corn

Sweet corn (Zea mays var. rugosa Bonaf.) is a crop with a high economic benefit in tropical and subtropical regions. Heat tolerance analysis and heat-tolerant gene mining are of great significance for breeding heat-resistant varieties. By combining improved genotyping using targeted sequencing (GBTS) with liquid chip (LC) technology, a high-density marker array containing 40 K multiple single polynucleotide polymorphisms (mSNPs) was used to genotype 376 sweet corn inbred lines and their heat-stress tolerance was evaluated in the spring and summer of 2019. In general, plant height, ear height and the number of lateral branches at the first level of the male flowers were reduced by 24.0%, 36.3%, and 19.8%, respectively. High temperatures in the summer accelerated the growth process of the sweet corn, shortening the days to shedding pollen by an average of 21.6% compared to the spring. A genome-wide association study (GWAS) identified 85 significant SNPs distributed on 10 chromosomes. Phenotypes in the spring and summer were associated with the 21 and 15 loci, respectively, and significant phenotypic differences between the two seasons caused by the temperature change were associated with the 49 SNP loci. The seed setting rate (SSR) was more susceptible to heat stress. An annotation analysis identified six candidate genes, which are either heat shock transcription factors (Hsfs) or heat shock proteins (Hsps) in Arabidopsis and rice (Oryza sativa), and these candidate genes were directly and indirectly involved in the heat-resistant response in the sweet corn. The current findings provide genetic resources for improving the heat-stress tolerance of sweet corn by molecular breeding.

Seasonal and between-population variation in heat tolerance and cooling efficiency in a Mediterranean songbird

Discrete populations of widely distributed species may inhabit areas with marked differences in climatic conditions across geographic and seasonal scales, which could result in intraspecific variation in thermal physiology reflecting genetic adaptation, phenotypic plasticity, or both. However, few studies have evaluated inter-population variation in physiological responses to heat. We evaluated within- and inter-population seasonal variation in heat tolerance, cooling efficiency and other key thermoregulatory traits in two Mediterranean populations of Great tit Parus major experiencing contrasting thermal environments: a lowland population subject to hotter summers and a higher annual thermal amplitude than a montane population. Specifically, we measured heat tolerance limits (HTL), body temperature, resting metabolic rate, evaporative water loss, and evaporative cooling efficiency (the ratio between evaporative heat loss to metabolic heat production) within and above the thermoneutral zone during winter and summer. Heat tolerance during summer was greater in lowland than in montane birds; indeed, lowland birds seasonally increased this trait to a significant level, while montane ones did to a lesser extent. Besides, lowland birds showed greater evaporative cooling efficiency during summer (possibly due in part to reductions in total endogenous heat load), while surprisingly montane ones showed the opposite trend. Thus, lowland birds displayed greater seasonal flexibility in HTL, body temperature and resting metabolic rate above thermoneutrality, thus giving some support to the climatic variability hypothesis — that flexibility in thermoregulatory traits should increase with climatic variability. Our results partially support the idea that songbirds’ adaptive thermoregulation in the heat is flexible, highlighting the importance of considering intraspecific variation in thermoregulatory traits when modelling the future distribution and persistence of species under different climate change scenarios.

Temporal and trophic niche partitioning among arboreal ants in a Neotropical woodland savanna

Abstract Niche partitioning is a key mechanism for explaining species coexistence, including the coexistence of ants in trees of the Brazilian savanna (cerrado). However, we have limited information on the extent to which arboreal ant species exploit different food resources and/or have different daily foraging schedules. We tested these ideas through a baiting experiment, and by measuring the isotopic signature (δ15N) and the critical thermal maximum (CTmax) of the 14 most common species found in a typical cerrado tree species. Although most species foraged on all bait types offered, species‐specific preferences were noted for about one‐third of the species. We also found a wide variation in mean δ15N between species, reflecting interspecific differences in trophic position. Most (71.4%) species foraged predominantly on a given period of the day, ranging from strictly nocturnal species to those that foraged mainly in the afternoon. Species with a higher heat tolerance (higher CTmax) often foraged at warmer periods of the day than those with a lower tolerance. Despite the evidence of trophic and temporal niche partitioning, other mechanisms, such as nesting site specialization and behavioural trade‐offs, are required to explain species coexistence in this arboreal ant assemblage, as several species pairs largely overlapped both in their diet and time of foraging. Importantly, our results provide additional support for the idea that physiological restriction to high temperatures is important for understanding interspecific differences in foraging activity schedules.

Exploring Thinopyrum spp. Group 7 Chromosome Introgressions to Improve Durum Wheat Performance under Intense Daytime and Night-Time Heat Stress at Anthesis.

Durum wheat (DW) is one of the major crops grown in the Mediterranean area, a climate-vulnerable region where the increase in day/night (d/n) temperature is severely threatening DW yield stability. In order to improve DW heat tolerance, the introgression of chromosomal segments derived from the wild gene pool is a promising strategy. Here, four DW-Thinopyrum spp. near-isogenic recombinant lines (NIRLs) were assessed for their physiological response and productive performance after intense heat stress (IH, 37/27 °C d/n) had been applied for 3 days at anthesis. The NIRLs included two primary types (R5, R112), carriers (+) of a differently sized Th. ponticum 7el1L segment on the DW 7AL arm, and two corresponding secondary types (R69-9/R5, R69-9/R112), possessing a Th. elongatum 7EL segment distally inserted into the 7el1L ones. Their response to the IH stress was compared to that of corresponding non-carrier sib lines (-) and the heat-tolerant cv. Margherita. Overall, the R112+, R69-9/R5+ and R69-9/R112+ NIRLs exhibited a tolerant behaviour towards the applied stress, standing out for the maintenance of leaf relative water content but also for the accumulation of proline and soluble sugars in the flag leaf and the preservation of photosynthetic efficiency. As a result, all the above three NIRLs (R112+ > R69-9/R5+ > R69-9/R112+) displayed good yield stability under the IH, also in comparison with cv. Margherita. R112+ particularly relied on the strength of spike fertility/grain number traits, while R69-9/R5+ benefited from efficient compensation by the grain weight increase. This work largely confirmed and further substantiated the value of exploiting the wild germplasm of Thinopyrum species as a useful source for the improvement of DW tolerance to even extreme abiotic stress conditions, such as the severe heat treatment throughout day- and night-time applied here.

High heat tolerance and thermal safety margins in mangroves from the southwestern coast of India

Mangroves are key components of productive ecosystems that provide a multitude of ecosystem goods and services. How these species will respond to future climates with more frequent and severe extreme temperatures has not received much attention. To understand how vulnerable mangroves are to future warming, we quantified photosynthetic heat tolerance and estimated thermal safety margins for thirteen mangrove species from the southwestern Indian coast. We quantified heat tolerance as temperatures that resulted in a 5 % (T5) and 50 % (T50) decline in photosystem II function, and thermal safety margins (TSM) as the difference between T50 and maximum leaf temperatures. T50 ranged from 48.9 °C in Avicennia Marina to 55.3 °C in Bruguiera gymnorhiza, with a mean of 53.3 °C for the thirteen species. Heat tolerance was higher for species with bigger leaves which experience higher leaf temperatures, but was not related to the other leaf traits examined. Heat tolerance was exceptionally high in these mangroves compared to other woody species. With their high tolerance and large safety margins these mangroves may be relatively less vulnerable to future climates with higher temperatures.

What's the beef with gene editing? An investigation of factors influencing U.S. consumers’ acceptance of beef from gene-edited cattle

Gene-editing technology provides promising opportunities for livestock industries by enabling precise genetic modifications that enhance desirable traits such as increased disease resistance, heat tolerance, and nutritional quality. With gene-edited beef products entering the market soon, understanding consumers’ acceptance is critical. Using structural equation modeling, the study aimed to determine how key psychological and social factors influence U.S. consumers’ attitudes toward gene editing and their behavioral intentions toward ground beef from gene-edited cattle. Results indicate that knowledge, subjective social norms, and perceived benefits positively influenced attitudes, while perceived risks and food technology neophobia negatively influenced attitudes. Subjective social norms, perceived benefits, and attitudes positively influenced behavioral intentions, while perceived risks and food technology neophobia negatively influenced intentions. Attitudes acted as a partial mediator, significantly mediating the effects of subjective social norms, perceived benefits, perceived risks, and food technology neophobia on behavioral intentions. Improving consumers’ behavioral intentions toward ground beef from gene-edited cattle hinges on cultivating more favorable attitudes toward the technology. Thus, collaborative efforts by scientists, producers, policymakers, extension agents, and agricultural communicators should seek to increase consumers’ perceived benefits and improve subjective social norms, as these factors were most influential.

PSVII-5 Heat shock protein 70 gene expression and association with morphometric and heat tolerance traits in three plumage colors of Noiler chicken exposed to acute heat stress

Abstract Heat stress is one of the most difficult climatic conditions chickens faces and is a direct result of climate change. It is important to research poultry thermotolerance because it may help find genetic lines resistant to heat stress. This study investigated the influence of plumage colors on heat shock protein 70 gene expression in Noiler chickens exposed to acute heat stress. Noiler is a dual-purpose breed developed for smallholder poultry production in Nigeria. A total of 150 birds of three plumage colors (black, brown and white) of mixed sexes were used for the experiment. The birds were raised in deep litter house separated into six groups of 25 birds each and fed with commercial broiler diets from 0-8 wk and broiler finisher diets from 8 to 12 wk old. The birds were shared into treatments in 3 x 2 x 2 factorial arrangements with 3 plumage colors (black, brown, white), two temperature regimens (Control/thermoneutral, Heat stress) and sex of birds (male, female). The heat stressed birds were exposed to 41oC for 8 h from 0600 h to 1400 h for 7 d while control group maintained a thermoneutral temperature range of 30 oC to 32 oC for the same period. At 13 wk old, two birds were selected per treatment, slaughtered and the spleen removed and stored in RNA later for heat shock protein (HSP) 70 gene expression. Data collected were analyzed with Microsoft excel code for fold expression of HSP70 gene while GLM procedure in SAS was used to determine difference in expression of gene. The relative expression of HSP70 brown plumage was greater, upregulated compared with black and white. White plumage birds in control/thermoneutral group were significantly greater in HSP70 expression than other plumage colors and heat stressed birds. Association of HSP70 delta threshold cycle (DCT) values with morphometric and heat tolerance traits were investigated (Figure 1). High negative correlations emerged between HSP70DCT expression and body weight (-0.65), body temperature (-0.73) with moderate positive correlation for rectal temperature (0.55) in black birds (Table 1). HSP70 DCT positively correlated with body weight (0.70), breast/leg circumferences but negatively with wing length, suggesting reduced surface area during heat stress and a supportive role in maintaining protein integrity (Figure 2). For white Noiler birds, HSP70DCT associated negatively with body weight (-0.94) and positively with rectal temperature during heat stress (Table 2). Thermoneutral birds were positively correlated with heat tolerance traits except temperature while heat stressed birds showed low positive correlation with respiratory and pulse rates and very low positive relationship with body and rectal temperatures (Table 4). Sex-based differences emerged, with potential compromise between HSP70-mediated growth/composition in males versus muscle maintenance in females, although leg length/circumference showed shared developmental regulation (Figure 3, Table 3). These findings highlight HSP70’s versatile roles in systemic heat tolerance mechanisms influenced by plumage color, temperature regime and sex.

Black soldier fly (Hermetia illucens) larvae meal for heat-stressed broiler chicken: its effects on gut health, stress biomarkers, and growth performance

The study determined the effects of feeding black soldier fly larvae meal (BSFLM) on serum corticosterone (CORT), heat shock protein (HSP) 70, d-lactic acid (DLA), diamine oxidase (DAO) levels, gut health and performance in heat-stressed broiler chickens. Three hundred sixty-day-old male broiler chicks were assigned to BSFLM inclusion at 0% (D0) (12 replicate cages with 10 birds/cage), 5% (D5) (12 replicate cages with 10 birds/cage) or 10% (D10) (12 replicate cages with 10 birds/cage). From days 22 to 35, birds from each dietary group were exposed to either heat stress (heated) at 32 ± 1 °C for 6 h (1100 − 1700 h) or 24 ± 1 °C throughout. There were six replicate cages with 10 birds/cage per diet-temperature subgroup. Diet had no significant effect (p > 0.05) on growth performance or mortality rate. The CORT of the heated DO chickens were elevated (p < 0.05) but not their D5 and D10 counterparts. Diet did not influence HSP70, but the heat challenge increased the expression of the proteins. The unheated D0 birds showed higher (p < 0.05) DLA than the other groups. Irrespective of diet, heat exposure elevated DAO. The heat-stressed D5 and D10 birds had lower (p < 0.05) caecal E.coli and Clostridium spp. than the D0 group. The D10 chickens showed increased caecal Lactobacillus spp. counts compared to the other groups. Heat exposure but not diet was detrimental to intestinal morphology. In conclusion, BSFLM as a feed ingredient may support optimum growth performance and enhance gut health and heat tolerance in broilers.

Exploring the Genetics of Heat Tolerance through Yield Performance Evaluation in Tropical Maize (Zea mays L.)

Heat stress severely affects maize yield and productivity, making it essential to identify and select heat-tolerant genotypes. Three hundred seven testcrosses derived from a biparental population were evaluated during summer at two distinct high VPD environments along with four checks (P1844, P1855, DKC9108 and DKC9162) to know their performance and association of traits under heat stress conditions. Analysis of variance revealed significant variability among the testcrosses, indicating substantial genetic diversity. Correlation analysis identified strong positive correlations between grain yield and related traits like plant height and ears per plant, highlighting these as vital selection criteria in breeding programmes. Additionally, Best Linear Unbiased Predictors (BLUPs) were utilized to evaluate the per se performance of the testcrosses, identifying the top-performing ones with superior heat tolerance. These top testcrosses achieved an average grain yield of 3.47 t ha-1, surpassing the population mean of 3.13 t ha-1. The top 10% of selected testcross families exhibited a yield gain of 0.34 t ha-1, representing a 9.79% improvement over the population under heat stress conditions. In order to create resilient maize hybrids, the study effectively isolated 18 elite testcrosses with improved heat tolerance that outperformed the superior check P1844. This provides a mitigation method for reducing the negative effects of climate change on maize productivity.