Lethal Temperature Research Articles

Abstract 10771: Avoidance of Lethal Isotherm Formation in Esophageal Tissue with an Active Cooling Device Under High-Power, Short-Duration Ablation

Introduction: Atrioesophageal fistula (AEF) is a severe complication of left atrial ablation for the treatment of atrial fibrillation. Thermal injury is the proposed mechanism, and a potential pathway occurs through exceeding the lethal isotherm of esophageal tissue in contact with the left atrial posterior wall. Active cooling with a novel cooling device has been shown to significantly reduce thermal injury, with no AEFs encountered after more than 4200 treatments worldwide. We aimed to evaluate the effects of active cooling when specifically using newer high-power short-duration (HPSD) ablation settings to further estimate the protective mechanisms of this novel approach to reduce serious injury. Hypothesis: Active cooling may preclude attainment of a lethal isotherm in esophageal tissue under HPSD ablation. Methods: We developed a model of the left atrium and esophagus, and simulated radiofrequency (RF) ablation of the left atrium under HPSD settings. Tissue thickness was set to typical posterior-wall parameters (Figure). Power settings were evaluated at 50 W for 10 seconds, and 90 W for 4 seconds. Active cooling was set to a typical 4 °C coolant temperature. Lethal isotherm temperature was taken as 50 °C. Results: In both scenarios of HPSD ablation, the peak esophageal mucosal temperature reached 39° C in control conditions, using no active cooling. With active cooling in place, peak temperatures remained below 11 °C (Figure). Peak temperatures at the epi-esophageal region of esophageal tissue exceeded the lethal isotherm of 50 °C in control conditions, but remained at or below the lethal isotherm with active cooling in place. Conclusions: Based on our mathematical modeling, esophageal cooling significantly reduced temperature rise and prevented the achievement of temperatures thought to be lethal to esophageal tissue. This finding may offer a mechanistic rationale for the absence of serious esophageal injury encountered to date using this approach.

Extreme minimum temperatures in the Great Lakes region of the United States: A climatology with implications for insect mortality

AbstractWinter‐season extreme minimum temperatures may play a major role in limiting population growth and spread of the hemlock woolly adelgid (HWA) (Adelges tsugae Annand) (Hemiptera: Adelgidae), an invasive sap‐feeding insect that has caused extensive mortality of hemlock trees (Tsuga spp.) in many eastern United States (US) forests. This atypical insect feeds throughout the winter but populations can sustain high mortality when winter‐season extreme minimum temperatures drop below −20 to −30°C. Detection of HWA in Michigan during 2015 motivated interest in HWA winter survival in the US Great Lakes region. Here, we used the parameter‐elevation regressions on independent slopes model (PRISM) gridded daily minimum temperature dataset to construct a 1981–2018 climatology of extreme minimum temperatures in the Great Lakes region, the first such effort for this region. Metrics examined include absolute and mean annual extreme minimum temperatures (defined as the lowest daily minimum temperature during the study period and the study‐period mean lowest daily minimum temperature during each calendar year, respectively), and the frequency of daily minimum temperatures below −20 and −30°C. Minimum temperature patterns we identified support the following two hypotheses: first, proximity to water, surface elevation and latitude are the principal controls for extreme minimum temperatures in the Great Lakes region; second, the modifying influence of the relatively warm Lake Michigan serves to protect locations within about 10–25 km of the lakeshore from severe and potentially lethal temperatures for HWA. Analysis of projected minimum temperatures at the end of the 21st century (2080–2099) reveals a range of HWA distribution expansion scenarios. Although the original motivation for this study arose from interest in potential HWA mortality, a climatological study of extreme minimum temperatures has potentially broad relevance to, for example, human health and safety and forest ecology.

Using upper thermal limits of Lampsilis bracteata (Texas fatmucket) from the North Llano and San Saba rivers, Texas to inform water management practices in the Edwards Plateau

Abstract Overexploitation of freshwater resources coupled with climate change can affect the flow and temperature regimes in rivers, which can be catastrophic for aquatic biota. The San Saba and Llano rivers, located in central Texas, are experiencing low flows and stream dewatering owing to over‐allocation. Both systems harbour imperilled species, including Lampsilis bracteata, Texas fatmucket, which has been proposed for listing under the US Endangered Species Act. It is suspected that elevated water temperatures are a contributing factor in its decline. The upper thermal tolerances of glochidia and juvenile life stages were evaluated within each river. Mussels were acclimated to 27°C and tested across a range of temperatures (30–39°C) in 24 h (glochidia) and 96 h (juveniles) laboratory tests. The resulting tolerances were related to in situ water temperature and discharge using a uniform continuous above‐threshold analysis. In the Llano, the 24 h LT50 (lethal temperature resulting in 50% mortality) was 31.8°C (95% CI 31.5–32.1°C), whereas the 96 h LT50 was 32.4°C (95% CI 32.1–32.7°C). In the San Saba, the 24 h LT50 was 34.7°C (95% CI 34.5–35.0°C), whereas the 96 h LT50 was 32.5°C (95% CI 32.2–32.9°C). LT50 thresholds were not exceeded for L. bracteata within the San Saba, but LT05 (lethal temperature resulting in 5% mortality) thresholds were exceeded. Water temperature loggers were lost in the Llano River as a result of a large flood; however, samples reported by the Texas Commission on Environmental Quality show that the LT05 and LT50 for both glochidia and juveniles were exceeded. Findings from this study indicate that thermal tolerances of L. bracteata vary by population and that low flows may be contributing to its decline. Our approach is non‐species and region specific, which means that the methods presented should help managers and conservationists evaluate whether reduced water quantity and elevated temperatures are exerting impacts on aquatic species within their region.

Actual tissue temperature during ablation index-guided high-power short-duration ablation versus standard ablation: Implications in terms of the efficacy and safety of atrial fibrillation ablation.

Actual in vivo tissue temperatures and the safety profile during high-power short-duration (HPSD) ablation of atrial fibrillation have not been clarified. We conducted an animal study in which, after a right thoracotomy, we implanted 6-8 thermocouples epicardially in the superior vena cava, right pulmonary vein, and esophagus close to the inferior vena cava. We recorded tissue temperatures during a 50 W-HPSD ablation and 30 W-standard ablation targeting an ablation index (AI) of 400 (5-15 g contact force). Maximum tissue temperatures reached with HSPD ablation were significantly higher than that reached with standard ablation (62.7 ± 12.5 vs. 52.7 ± 11.4°C, p = 0.033) and correlated inversely with the distance between the catheter tip and thermocouple, regardless of the power settings (HPSD: r = -0.71; standard: r = -0.64). Achievement of lethal temperatures (≥50°C) was within 7.6 ± 3.6 and 12.1 ± 4.1 s after HPSD and standard ablation, respectively (p = 0.003), and was best predicted at cutoff points of 5.2 and 4.4 mm, respectively. All HPSD ablation lesions were transmural, but 19.2% of the standard ablation lesions were not (p = 0.011). There was no difference between HPSD and standard ablation regarding the esophageal injury rate (30% vs. 33.3%, p > 0.99), with the injury appearing to be related to the short distance from the catheter tip. Actual tissue temperatures reached with AI-guided HPSD ablation appeared to be higher with a greater distance between the catheter tip and target tissue than those with standard ablation. HPSD ablation for <7 s may help prevent collateral tissue injury when ablating within a close distance.

Functional implication of heat shock protein 70/90 and tubulin in cold stress of Dermacentor silvarum

BackgroundThe tick Dermacentor silvarum Olenev (Acari: Ixodidae) is a vital vector tick species mainly distributed in the north of China and overwinters in the unfed adult stage. The knowledge of the mechanism that underlies its molecular adaptation against cold is limited. In the present study, genes of hsp70 and hsp90 cDNA, named Dshsp70 and Dshsp90, and tubulin were cloned and characterized from D. silvarum, and their functions in cold stress were further evaluated.MethodsThe genome of the heat shock proteins and tubulin of D. silvarum were sequenced and analyzed using bioinformatics methods. Each group of 20 ticks were injected in triplicate with Dshsp90-, Dshsp70-, and tubulin-derived dsRNA, whereas the control group was injected with GFP dsRNA. Then, the total RNA was extracted and cDNA was synthesized and subjected to RT-qPCR. After the confirmation of knockdown, the ticks were incubated for 24 h and were exposed to − 20 °C lethal temperature (LT50), and then the mortality was calculated.ResultsResults indicated that Dshsp70 and Dshsp90 contained an open reading frame of 345 and 2190 nucleotides that encoded 114 and 729 amino acid residues, respectively. The transcript Dshsp70 showed 90% similarity with that identified from Dermacentor variabilis, whereas Dshsp90 showed 85% similarity with that identified from Ixodes scapularis. Multiple sequence alignment indicates that the deduced amino acid sequences of D. silvarum Hsp90, Hsp70, and tubulin show very high sequence identity to their corresponding sequences in other species. Hsp90 and Hsp70 display highly conserved and signature amino acid sequences with well-conserved MEEVD motif at the C-terminal in Hsp90 and a variable C-terminal region with a V/IEEVD-motif in Hsp70 that bind to numerous co-chaperones. RNA interference revealed that the mortality of D. silvarum was significantly increased after injection of dsRNA of Dshsp70 (P = 0.0298) and tubulin (P = 0.0448), whereas no significant increases were observed after the interference of Dshsp90 (P = 0.0709).ConclusionsThe above results suggested that Dshsp70 and tubulin play an essential role in the low-temperature adaptation of ticks. The results of this study can contribute to the understanding of the survival and acclimatization of overwintering ticks.Graphical abstract

Dry-Heat Tolerance of Egg Sacs of Invasive Latrodectus Spiders (Araneae: Theridiidae) in Japan: Implications for Efficient Control/Extermination.

Strategic responses to invasive Latrodectus widow spiders are a global challenge due to the risks they pose to health and ecosystems. Chemical strategies involving the use of pyrethroids are effective against adult spiders, but as their populations rebound, chemical control becomes costly and unsustainable for eradication. A major obstacle is the inefficacy of insecticides against eggs, which are covered by a protective silk egg sac. Eradication of invasive spiders must focus on destroying progeny. Here, the responses of eggs in egg sacs of two invasive Latrodectus spiders in Japan (Latrodectus hasseltii (Thorell) and Latrodectus geometricus (C.L. Koch)) to short-term dry-heat exposure were examined. To test whether the dry-heat tolerance of the egg sacs of both spider species differed, lethal temperature (LT) was determined based on the hatching rate of eggs from egg sacs subjected to a range of temperatures. Hatching in both species failed completely when the egg sacs were exposed to temperatures of 55°C and above for 10 min, but the LT to reduce hatching by 90% (LT90) differed significantly between L. hasseltii (50. 9°C) and L. geometricus (52. 8°C). Our study highlights the efficacy of dry heat in suppressing hatching and thus shows the possibility for effective extermination of these noxious invasive pests. Further exploration and investigation of the effects of humidity and heat exposure time on egg sacs under field conditions are needed to guide Latrodectus spider control strategies.

Heat memory in plants: histone modifications, nucleosome positioning and miRNA accumulation alter heat memory gene expression.

Plant adaptation to high temperature, often referred to as heat acclimation, is a process in which exposure to moderately high temperatures increases a plant's tolerance to subsequent (normally) lethal high temperatures. Plants store heat experience information (heat memory) obtained from previous exposure to high temperatures for several days and develop future temperature responsiveness. However, our understanding of heat acclimation is very limited. In the model plant Arabidopsis thaliana, changes in the expression patterns of heat memory genes play a central role in regulating plant survival and adaptation to recurring heat stress. Heat stress-related transcription factors and histone-modifying enzymes function in the sensitized expression of heat memory genes via the deposition and removal of histone modifications. Chromatin-remodeling complexes and miRNA accumulation also trigger the sustained expression of heat memory genes. In this review, I describe studies of heat acclimation that have provided important insights into the molecular mechanisms that lead to flexible and reversible gene expression upon heat stress in plants.

Vertical Fine-Scale Distribution of Calanus sinicus in the Yellow Sea Cold Water Mass During the Over-Summering Process

Calanus sinicus, a temperate copepod with a lethal temperature &amp;gt;27°C, is one of the key species in Chinese coastal marine ecosystems. The C. sinicus population increases in spring and declines in early summer annually due to increasing water temperature. Numerous C. sinicus individuals then congregate in the Yellow Sea Cold Water Mass (YSCWM) and remain under the thermocline from early summer to early autumn. Development and reproduction is halted in this cold and foodless bottom water and they avoid ascending to the hot surface water, which is regarded as an over-summering strategy. Based on discrete water sampling approaches, previous studies demonstrated that higher chlorophyll a (Chl a) levels appeared in the mixed hot surface water layer; however, the subsurface chlorophyll a maximum layer (SCML) has seldom been described. In the present study, various probes and a visual plankton recorder (VPR) were used to determine the fine vertical distributions of environmental factors and C. sinicus. VPR observations showed the ecological responses in fine scale and indicated that few C. sinicus individuals ascend at night, the main population preferred to remain below the SCML all day long. The results demonstrated that a constant thin SCML existed in the YSCWM area, and that the SCML location coincided with or was beneath the thermocline and halocline layers, where the temperature was suitable for C. sinicus. The relationship between abundance and Chl a, showed the diel vertical migration trend of C. sinicus to feed at night in the YSCWM area. In addition to temperature as a main influencing factor, dissolved oxygen concentrations and column depth were also influencing factors. Therefore, in addition to avoiding high surface temperature, energy supplement may be an important driving force confining the diel vertical migration of C. sinicus in the Yellow Sea in summer.

Cardiac and respiratory metabolic analysis of low-temperature tolerance in two geographic genotypes of Haliotis diversicolor and the hybrid

Evident survival heterosis exists in the hybrid (HdDY) of two Haliotis diversicolor geographic genotypes (maternal genotype HdTW and paternal genotype HdJP). To explore the physiological basis underlying the heterosis, we compared the survival rate, cardiac performance, oxygen consumption rate, and ammonia excretion rate of the three H. diversicolor genotypes at the low temperature. After one year of cultivation in the abalone farm, the survival rates of HdTW, HdJP, and HdDY were 27.76%, 86.90%, and 88.57%, respectively. The 50% lethal low temperature (LLT50) of HdTW was higher than HdJP and HdDY. During low-temperature exposure, the abalone’s heartbeat variation pattern appeared as three stages: the heartbeat decreasing stage, arrhythmia stage, and cardiac recovery stage. Four cardiac indices were developed to compare the three genotypes’ cardiac differences: the low-temperature heartbeat decreasing rate (LDR), cardiac arrhythmia temperature (CAT), low-temperature heartbeat recovering rate (LRR), and cardiac recovery time (CRT). HdTW had lower LDR and higher CAT than HdJP and HdDY, while HdJP had lower LRR and higher CRT than HdTW and HdDY, suggesting the hybrid’s cardiac function is parent-like in low-temperature tolerance and mother-like in low-temperature recovery. Meanwhile, the heart rates of HdJP and HdDY were always higher than HdTW at both normal temperature (20 °C) and low temperature (12 °C). The oxygen consumption rate and ammonia excretion rate of HdJP and HdDY were also higher than HdTW after low-temperature exposure. The results indicate the hybrid’s advantageous respiratory and metabolic functions at low temperatures, which could be a vital physiological mechanism of the hybrid’s survival heterosis. This study elucidates the cardiac and respiratory metabolic differences among different abalone genotypes at low temperatures, which may help us understand the physiological basis of mollusks’ low-temperature tolerance. The evaluation protocol and indices developed in this study could be helpful in mollusks’ physiological researches, such as the low-temperature tolerance heterosis, low-temperature adaption, and habitat differentiation.

Preanthesis changes in freeze resistance, relative water content, and ovary growth preempt bud phenology and signify dormancy release of sour cherry floral buds.

Growing degree hours (GDH) predicted floral bud development of 'Montmorency' sour cherry and explained changes in lethal temperatures (LT50) that preempted any visible changes in bud phenology. The gradual warming during late winter and early spring promotes floral bud development and, concomitantly, the de-acclimation of Prunus sp. flowers. In fact, once ecodormancy releases, an approximate 20°C loss of hardiness occurs prior to any distinguishable changes in external bud phenology. The aim of the following work was to characterize the physiological changes of 'Montmorency' sour cherry floral buds as they transition from endo- and ecodormancy and resume growth, and to determine whether physiological and anatomical characteristics within the buds preempt or signify dormancy release to enable a better prediction of freeze susceptibility. Here, we present a developmental timeline of the preanthesis changes of 'Montmorency' floral buds, ovaries and anthers over 2 years following their completion of chilling and relate these changes to growing degree hours (GDH) and the lethal temperature (LT50) of flowers. Changes in bud dry weight (DW), fresh weight (FW), volume, and external phenology stage including the percentage of green color development of bud scales were predicted by heat accumulation but were not early predictors of the increasing freeze susceptibility of pistils. Between endodormancy and green tip stage, ovary volume increased nearly threefold and relative water content (RWC) increased from ~ 45 to 70% in both years. A linear mixed regression model indicated that RWC and the interaction between RWC and ovary growth were significant predictors of LT50. Importantly, the loss of ~ 20°C of freeze resistance occurred between 45 and 57% RWC and preceded any detectable changes in bud phenology. Microsporogenesis was observed after dormancy release when measurable changes in the ovary and bud RWC had already occurred. A GDH model estimated freeze sensitivity of pistils and explained 93% of the variation in LT50 during preanthesis development. A simple GDH model to predict critical freeze temperature of pistils should aid producers to manage frost protection.

Physiological and Transcriptional Responses to Acute and Chronic Thermal Stress in the Ark Shell Scapharca subcrenata

Ark shells (Scapharca subcrenata) grown on the tidal flats are often exposed to high temperature stresses in summer. In order to better understand their adaption to extreme or natural high temperature, we first determined the 96-h upper lethal temperature of ark shell and then investigated their physiological and transcriptional responses to acute or chronic thermal stress at the 96-h upper median lethal temperature (32°C). A significantly higher cumulative mortality (52% in 96 h) was observed in the acute heating treatment (AHT) group than that (22% in 7 days) in the chronic heating treatment (CHT) group. The apoptosis and necrosis rates of hemocytes were increased significantly in a time-dependent manner under both thermal stress strategies. Activities of antioxidant enzymes [superoxide dismutase (SOD) and catalase (CAT)] increased dramatically in a short time followed by a quick decline and reached to a lower level within 12 h in the AHT group, but maintain relatively high levels over a long period in the CHT group. The contents of malondialdehyde (MDA) were increased significantly firstly and restored to the original later in both acute and chronic thermal stress. Moreover, expression of the genes related to heat shock proteins (HSPs; HSP90, HSP70, HSP20, and sHSP), apoptosis [TNF receptor-associated factor 6 (TRAF6), glucose regulated protein 78 kD (GRP78), and caspase-3 (Casp-3)] and antioxidant responses [glutathione S-transferase (GST) and multidrug resistance protein (MRP)] could be induced and up-regulated significantly by thermal stress, however, expression of regucalcin (RGN), metallothionein (MT), and peroxiredoxin (PRX) was down-regulated dramatically under the two heating treatments. These results suggested that anti-apoptotic system, antioxidant defense system and HSPs could play important roles in thermal tolerance of ark shells, and the heat-resistant ark shell strains could be selected continuously by properly chronic thermal stress.

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

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

Horticultural Characterization of Wild Hydrangea quercifolia Seedlings Collected Throughout the Species Native Range

Oakleaf hydrangea (Hydrangea quercifolia Bartr.) is an understory shrub native to the southeastern United States. Hydrangeas are popular ornamental landscape plants; however, little is known about the diversity in horticulturally important traits for oakleaf hydrangea. Information regarding the variation in important traits could guide future breeding efforts for the species. Seed was collected from 55 populations throughout the range of the species for the purpose of conducting a horticultural characterization of the species compared with select cultivars. Plant architecture was characterized as plant height, number of nodes, internode length, number of branches, and plant width. Plant architecture was measured for container-grown and field-grown plants in two locations (Minnesota and Tennessee). Tolerance to leaf spot (Xanthomonas campestris L.) was characterized for wild-collected seedlings and cultivars by measuring disease severity under exposure to ambient inoculum. Cold hardiness was characterized during two winters with a controlled freezing experiment. During the first winter, seedlings were tested in January; during the second winter, seedlings and cultivars were tested monthly from October through April. Plant architecture varied by environment, with plants growing larger in Tennessee than in Minnesota. The heights of container-grown and field-grown plants were correlated with the collection site latitude (r = −0.66), with populations from the northeastern extent of the range of the species being the most compact, and populations from Florida being the tallest. Leaf spot severity varied significantly among populations and cultivars and was also correlated with latitude for the seedlings (r = 0.70). Two populations in Florida were identified as sources of high tolerance to leaf spot, whereas ‘Flemygea’ and ‘Alice’ were identified as having moderate tolerance to leaf spot. Cold hardiness varied among populations and cultivars and among months of the winter. The overall maximum cold hardiness was observed in February [mean lethal temperature (LT50) = −33.7 °C], and several populations maintained an extreme level of cold hardiness into late winter. Midwinter cold hardiness also varied by latitude (r = −0.65), with northern populations showing higher levels of cold hardiness. These results indicate that certain wild oakleaf hydrangea populations will be useful for introgressing novel variation into breeding programs.

Reproduction of the Androgenetic Population of the Asian Corbicula Clam (Bivalvia: Cyrenidae) in the Northern Dvina River Basin, Russia

The Corbicula clam is one of the most successful invaders of aquatic ecosystems and has invaded all continents except Antarctica. The natural dispersion of Corbicula seems to be limited by low winter temperatures that fall below the lower lethal temperatures (0 to +2 °C). However, Corbicula can be found in colder regions, taking refuge in waters heated by thermal power plants. The purpose of this investigation was to study the gonadal histology, reproductive cycle, and the seasonal changes of shell size structure of the Corbicula clam populations in the warm water discharge of the Arkhangelsk thermal power plant (Northwest Russia). Samples were collected monthly from January 2017 to December 2018 and processed using traditional histological and morphological techniques. The number of reproductive periods varied from year to year. It was established that the Corbicula clam has a continuous reproduction period which may be adaptive in unstable environmental conditions. This reproductive strategy is probably aimed at increasing the reproductive success of the population. Our data expand the understanding of reproductive features of the Corbicula clam in harsh environmental conditions. These results could be applied to control, monitoring, and management measures.

Are succulence or trait combinations related to plant survival on hot and dry green roofs?

The many ecosystem services that green roofs can provide rely on good plant coverage and plant survival, which is challenging in hot and dry climates. While true succulents like Sedum spp. have been shown to survive well on green roofs, there are limited studies relating individual traits or trait combinations to survival in other life-forms. Succulence is a rarely studied trait that describes plant water storage in leaves, stems and roots, regardless of life-form. This means that succulence can occur in plants which are not considered to be true succulents like Sedum or Crassula species. Improving water availability through succulence may improve survival on unirrigated green roofs, but succulence, as a trait, has rarely been investigated in plants which are not true succulents. We investigated whether succulence or trait combinations can relate well with survival and could be used to improve plant selection for different substrate depths on hot and dry green roofs. We conducted two experiments with the same 11 Mediterranean species (five herbs, three sub-shrubs and three shrubs); (1) a pot experiment to determine traits under well-watered conditions including: succulence, leaf lethal temperature, water use, root:shoot ratio and leaf area. These individual traits and the combinations of all these traits were used in the analyses of this experiment; and (2) a green-roof module experiment to determine survival in four substrate depths (10, 15, 20, and 25 cm). Survival was not related to succulence, indicating that increased internal water storage in non-succulent plants does not per se lead to greater survival in extreme conditions. Survival was also not related to individual traits relating to water use and leaf heat tolerance or trait combinations. Nevertheless, plants in the same functional groups had similar survival, which suggests plants with similar trait combinations can have similar survival on green roofs.

Lethal temperature and toxicity of ammonia in juveniles of Curimbatá (Prochilodus lineatus)

The maintenance of quality parameters in fish farming is fundamental to the success of production systems. Ammonia is toxic when present in high concentrations, causing inadequate development, loss of growth, and mortality in fish. Temperature can also cause biochemical and physiological changes in organisms and cause mortality. Curimbatá Prochilodus spp. have the potential to be used in fish farming in polycultures in Brazil. However, few studies have been carried out regarding adequate water quality parameters for the production of Curimbatá. Thus, the present study determined the lower and upper lethal temperatures (LT50), as well as the lethal concentration (LC50), and sublethal and toxic effects of ammonia on juveniles of Curimbatá Prochilodus lineatus through tests of acute exposure for 96 h. In the lethal temperature test, the fish were subjected to treatments of 10 °C, 15 °C, 20 °C, 25 °C, 30 °C, 35 °C, and 40 °C. Temperatures of 10 °C and 40 °C were lethal at 36 and 24 h, respectively. The lower and upper LT50 were 13.8 ± 1.14 and 39.7 ± 1.59 °C at 36 and 12 h, respectively. For the determination of lethal and sublethal concentrations of ammonia (NH3), the fish were subjected to treatments 0.00, 0.75, 1.14, 1.47, 1.82, and 2.21 (mg/L NH3). The LC50 determined for 96 h was 0.62 mg/L and the LC10 for 24 h was 0.93 mg/L. In addition, histopathological evaluation of the gills was adequate to observe the effects of acute ammonia concentrations. Ammonia concentrations above 0.75 mg/L caused irreversible histological changes. The results of the study indicates that the ideal temperature range for breeding Curimbatá is 25 °C to 30 °C, since this variation did not influence fish survival. In addition, Curimbatá should be grown in water with concentrations below 0.75 mg/L of ammonia.

Tree crown injury from wildland fires: causes, measurement and ecological and physiological consequences.

SummaryThe dead foliage of scorched crowns is one of the most conspicuous signatures of wildland fires. Globally, crown scorch from fires in savannas, woodlands and forests causes tree stress and death across diverse taxa. The term crown scorch, however, is inconsistently and ambiguously defined in the literature, causing confusion and conflicting interpretation of results. Furthermore, the underlying mechanisms causing foliage death from fire are poorly understood. The consequences of crown scorch – alterations in physiological, biogeochemical and ecological processes and ecosystem recovery pathways – remain largely unexamined. Most research on the topic assumes the mechanism of leaf and bud death is exposure to lethal air temperatures, with few direct measurements of lethal heating thresholds. Notable information gaps include how energy transfer injures and kills leaves and buds, how nutrients, carbohydrates, and hormones respond, and what physiological consequences lead to mortality. We clarify definitions to encourage use of unified terminology for foliage and bud necrosis resulting from fire. We review the current understanding of the physical mechanisms driving foliar injury, discuss the physiological responses, and explore novel ecological consequences of crown injury from fire. From these elements, we propose research needs for the increasingly interdisciplinary study of fire effects.

Development of a method for heat shock stress assessment in yeast based on transcription of specific genes.

All living cells, including yeast cells, are challenged by different types of stresses in their environments and must cope with challenges such as heat, chemical stress, or oxidative damage. By reversibly adjusting the physiology while maintaining structural and genetic integrity, cells can achieve a competitive advantage and adapt environmental fluctuations. The yeast Saccharomyces cerevisiae has been extensively used as a model for study of stress responses due to the strong conservation of many essential cellular processes between yeast and human cells. We focused here on developing a tool to detect and quantify early responses using specific transcriptional responses. We analyzed the published transcriptional data on S.cerevisiae DBY strain responses to 10 different stresses in different time points. The principal component analysis (PCA) and the Pearson analysis were used to assess the stress response genes that are highly expressed in each individual stress condition. Except for these stress response genes, we also identified the reference genes in each stress condition, which would not be induced under stress condition and show stable transcriptional expression over time. We then tested our candidates experimentally in the CEN.PK strain. After data analysis, we identified two stress response genes (UBI4 and RRP) and two reference genes (MEX67 and SSY1) under heat shock (HS) condition. These genes were further verified by real-time PCR at mild (42°C), severe (46°C), to lethal temperature (50°C), respectively.

THE USE OF COOLING AND FREEZING FOR ANESTHESIA OF Phrynops geoffroanus TURTLES (PLEURODIRA: CHELIDAE) AND THE ESTABLISHMENT OF LOW INCIPIENT LETHAL TEMPERATURE

The use of hypothermia for anesthesia and euthanasia in ectothermic individuals has promoted many discussions, especially in the last four decades, and yet it continues today as a method that is prohibited or restricted to certain procedures. Despite this, some studies have shown satisfactory results in obtaining anesthetic plans, raising questions about the real possibility of using this method in research. The aim of the present experiment was to determine the time patterns to generate anesthesia and low incipient lethal temperature in Phrynops geoffroanus through cooling and freezing. Turtles reached the anesthesia grade nine within 30 minutes, making ease handling due to muscle relaxation, and, in 80 minutes, they reached anesthesia grade 11, becoming insensitive. The low incipient lethal temperature (LILT) shows that 1°C is the limit freezing from where the turtle can recover its motor activities while lower temperatures cause death. The low incipient lethal temperature was determined in a 300-minute period independently of the individual's size or weight.

Forecasting overwintering mortality of Spathius galinae in North America

Evaluating the cold tolerance of biological control agents is often necessary to optimize their release and performance. We used field and laboratory assays to determine the cold hardiness of the parasitoid Spathius galinae Belokobylskij & Strazanac, an approved classical biological control agent of emerald ash borer (Agrilus planipennis Fairmaire) in North America. Supercooling points and lower lethal temperature of mature (cocooned) S. galinae larvae were measured in controlled cooling assays in the laboratory. Most S. galinae larvae died after reaching their supercooling point, which occurred at −25.0 °C on average. Several larvae, however, initiated freezing but later eclosed, suggesting S. galinae may be partially freeze tolerant. Supercooling points were not affected by chilling rate. In the winter of 2019 – 2020, we monitored development of mature S. galinae larvae in ash segments above and beneath the snow in three locations in Minnesota, USA. Nearly 100% of S. galinae larvae died after air temperatures reached −29 °C in Minnesota. Using models developed from our data, we forecast eclosion rates of S. galinae based on minimum winter temperatures across the range of ash (Fraxinus spp.) in North America. Our results indicate that S. galinae populations may suffer high overwintering mortality in areas where winter temperatures regularly decrease below −28 °C, but a small portion of the population may be able to survive lower temperatures.