Mechanisms Of Thermal Tolerance Research Articles

Regulatory network in heat stress response in parasitoid wasp focusing on Xap5 heat stress regulator

Insects are susceptible to elevated temperatures, resulting in impaired fertility, and shortened lifespan. This study investigated the genetic mechanisms underlying heat stress effects. We conducted RNA sequencing on Pteromalus puparum exposed to 25°C and 35°C, revealing transcriptional signatures. Weighted Gene Co-expression Network Analysis uncovered heat stress-associated modules, forming a regulatory network of 113 genes. The network is naturally divided into two subgroups, one linked to acute heat stress, including heat shock proteins (HSPs), and the other to chronic heat stress, involving lipogenesis genes. We identified an Xap5 Heat Shock Regulator (XHSR) gene as a crucial network component, validated through RNA interference and quantitative PCR assays. XHSR knockdown reduced wasps' lifespan while directly inducing HSPs and mediating lipogenesis gene induction. CRISPR/Cas9-mediated knockout of the Drosophila XHSR homolog reduced mutants' survival, highlighting its conserved role. This research sheds light on thermal tolerance mechanisms, offering potential applications in pest control amid global warming.

Time of day-dependent effects of heat treatment on thermal tolerance and sex differentiation in Nile tilapia (Oreochromis niloticus)

The present research aimed to determine the influence of the time of day at which heat treatment (HT) is applied to sexual differentiation and thermal tolerance mechanisms in Nile tilapia (Oreochromis niloticus). To this end, fish larvae were subjected to HT (36 °C) for 12 days at different times of the day during the thermosensitive period (i.e. 11–23 days post-fertilization, dpf). The heat treatment was applied during the light phase (L-HT); during the dark phase (D-HT), or during both light-dark phases (LD-HT). A control group maintained at constant rearing temperature (28 °C, CTRL) was also used. At 25 dpf, thermal tolerance was determined (survival) and whole larvae samples were collected for the mRNA expression analysis (qPCR). There after, all the groups remained at constant temperature until 270 dpf, when some fish were sacrificed and each individual's gonadal lobules were collected for histological and qPCR analyses. At the same time, each experimental group was subjected to acute heat shock (HS; 36 °C for 2 h) in either the mid-light (ML) or the mid-dark (MD) phase. When HS exposure finished, adults' brains were extracted to determine the HS response by qPCR. The expression of the genes involved in female (cyp19a1a, foxl2, era) and male (amh, ara, sox9a, dmrt1) sexual differentiation and thermal tolerance (hsp70, hsp90a, hsp27) in the 25 dpf larvae and adults was studied. The results revealed that all the HT-treated larvae showed an up-regulation of testicular differentiation gene expression and inhibition of ovarian differentiation gene expression, which resulted in a higher percentage of males. The time of day of HT during development influenced thermotolerance in the larval and adult stages, with the lowest survival and highest cellular stress (higher HSPs expression) observed in the larvae of the D-HT and LD-HT groups. These findings reveal the need to further investigate the link between sexual differentiation and thermotolerance daily rhythms in thermal biology research. These results may be useful for optimizing masculinization protocols in the tilapia industry, while ensuring animal welfare and minimizing negative HT effects on fish physiology.

Comparative chromatin dynamics reveal differential thermal tolerance mechanisms between two congeneric oyster species

Oysters, being globally farmed bivalve of significant economic and ecological value, are increasingly confronted with heat stress induced by global warming, such as the frequent occurrence of mass summer mortality events worldwide. The role of epigenetics in adapting to high-temperature environments has garnered growing attention; however, its application in oysters remains poorly understood. In this study, we conducted a comparative analysis between two closely related oyster species (the relatively thermosensitive Crassostrea gigas and the relatively thermotolerant Crassostrea angulata) using ATAC-Seq and RNA-Seq to reveal the differential thermal tolerance mechanisms at the chromatin dynamics level in response to high-temperature stress. The comparative analysis showed that the inhibitor of apoptosis protein (IAP) family and its associated apoptosis pathways were the major divergent pathway between the two species. The promoter regions of differentially expressed genes in C. gigas under heat stress were found to be enriched with motifs such as Foxp1, Foxk2, Myc, Cebpd, Foxo3, and Hsf1 motifs and expressed genes related to molecular chaperones, including heat shock protein family. And C. angulata activated the genes related to anti-apoptosis, DNA damage repair, and fatty acid synthesis (decreasing fatty acid unsaturation of membrane to regulate membrane fluidity). These findings suggest that C. angulata may have evolved a more centralized and energy-efficient transcriptional regulatory network at the genomic level, thereby facilitating its long-term adaptation to relatively high temperature environments. Furthermore, the key transcription factor Hsf1, involved in heat shock responses, may contribute to the differential heat response patterns in C. gigas and C. angulata through divergent expression levels of its alternatively spliced isoforms (Hsf1a and Hsf1d). Our work will contribute to predicting the adaptive potential of oysters and other marine invertebrates in facing future global warming, and provide a theoretical foundation for genetic improvement of resistance traits and sustainable development of oyster industry.

A bioenergetics approach to modelling tolerance limits under acute thermal stress in farmed finfish

Pinpointing thermal tolerance thresholds for commercially important species, such as aquaculture finfish, under acute and chronic thermal stress is becoming increasingly relevant in the context of climate change. While experimental research, traditionally quantified by the determination of the Critical Thermal Maximum (CTmax), offers valuable insights, it is necessary to further develop appropriate tools to provide predictions and shed light on the underlying mechanisms of thermal tolerance. Bioenergetic models have long been used to study the effects of temperature on fish metabolism under chronic, but rarely under acute, scales. In this study, we present a modelling approach based on the Dynamic Energy Budget (DEB) theory that describes the tolerance limits of fish under acute thermal stress in bioenergetics terms. It adopts the notion of an energy-dependent tolerance to stress and defines acute tolerance limits at the intersection of fundamental energy fluxes, namely those relating to the mobilization of energy and to maintenance costs. To showcase this approach, DEB models for two finfish, the European sea bass (Dicentrarchus labrax) and the meagre (Argyrosomus regius) were used to run acute thermal challenge simulations and study shifts in the critical temperature achieved by the fish. The results suggest that the model can adequately capture the general tolerance patterns observed experimentally for the two species as well as pinpoint the parameters that may influence them. In particular, the simulations showed a positive relation between acclimation temperature and tolerance while the opposite stands for the body size of the fish, with smaller fish achieving higher critical temperatures than their larger counterparts. Also, tolerance limits were affected by the state of internal reserves, with well-fed fish exhibiting higher values. Finally, the potential application of this modelling approach on higher taxonomic scales was evaluated, by running simulations on species belonging to major fish orders. The preliminary results suggest that the method can capture differences among groups that are consistent with literature, suggesting it may be a realistic mechanistic approach for studying thermal tolerance in ectotherms.

Thermal acclimation results in persistent phosphoproteome changes in the freshwater planarian Crenobia alpina (Tricladida: Planariidae)

Understanding the molecular mechanisms underlying thermal tolerance of aquatic invertebrates can inform predictions about the effects of thermal regime changes on these species. While gene expression and protein abundance changes underlie compensatory responses, little is known about the role of post-translational modifications as thermal tolerance mechanisms. To test the hypothesis that protein phosphorylation changes in response to thermal acclimation, we studied the phosphoproteome of the freshwater planarian Crenobia alpina. This species has a supposedly limited thermal tolerance and is found in cold-stable habitats. We systematically investigated phosphopeptide abundances following 168 h acclimation to 11, 14, 17, and 20 °C, using label-free quantitative phosphoproteomics. We provide a comparative analysis of 2115 phosphosites from 1049 phosphoproteins, whereby little to no differences could be observed between 11, 14, and 17 °C. However, more than 130 phosphopeptides were significantly more abundant and 40 were less abundant following acclimation to 20 °C. These phosphoproteins were functionally associated with the regulation of neuronal processes, cilia, DNA damage repair, aquaporins, and mitochondrial fission and fusion. These data support the hypothesis that phosphorylation plays a role in thermal acclimation responses, suggesting that PTMs are of significance in invertebrate thermal acclimation. PTMs may therefore offer an alternative route of transient protein adaptation to temperature increase in invertebrates, and should not be neglected when trying to understand how molecular system dynamics in response to elevated temperatures.

Heat shock protein gene expression varies among tissues and populations in free-living birds

Abstract Climate change is dramatically altering our planet, yet our understanding of mechanisms of thermal tolerance is limited in wild birds. We characterized natural variation in heat shock protein (HSP) gene expression among tissues and populations of free-living Tree Swallows (Tachycineta bicolor). We focused on HSPs because they prevent cellular damage and promote recovery from heat stress. We used quantitative PCR to measure gene expression of 3 HSPs, including those in the HSP70 and HSP90 families that have robust experimental connections to heat in past literature. First, to evaluate how tissues and, by extension, the functions that they mediate, may vary in their thermal protection, we compared HSP gene expression among neural and peripheral tissues. We hypothesized that tissues with particularly vital functions would be more protected from heat as indicated by higher HSP gene expression. We found that brain tissues had consistently higher HSP gene expression compared to the pectoral muscle. Next, we compared HSP gene expression across 4 distinct populations that span over 20° of latitude (>2,300 km). We hypothesized that the more southern populations would have higher HSP gene expression, suggesting greater tolerance of, or experience with, warmer local conditions. We observed largely higher HSP gene expression in more southern populations than northern populations, although this pattern was more striking at the extremes (southern Indiana vs. Alaska), and it was stronger in some brain areas than others (ventromedial telencephalon vs. hypothalamus). These results shed light on the potential mechanisms that may underlie thermal tolerance differences among populations or among tissues.

Contrasting heat stress response patterns of coral holobionts across the Red Sea suggest distinct mechanisms of thermal tolerance.

Corals from the northern Red Sea, in particular the Gulf of Aqaba (GoA), have exceptionally high bleaching thresholds approaching >5℃ above their maximum monthly mean (MMM) temperatures. These elevated thresholds are thought to be due to historical selection, as corals passed through the warmer Southern Red Sea during recolonization from the Arabian Sea. To test this hypothesis, we determined thermal tolerance thresholds of GoA versus central Red Sea (CRS) Stylophora pistillata corals using multi-temperature acute thermal stress assays to determine thermal thresholds. Relative thermal thresholds of GoA and CRS corals were indeed similar and exceptionally high (~7℃ above MMM). However, absolute thermal thresholds of CRS corals were on average 3℃ above those of GoA corals. To explore the molecular underpinnings, we determined gene expression and microbiome response of the coral holobiont. Transcriptomic responses differed markedly, with a strong response to the thermal stress in GoA corals and their symbiotic algae versus a remarkably muted response in CRS colonies. Concomitant to this, coral and algal genes showed temperature-induced expression in GoA corals, while exhibiting fixed high expression (front-loading) in CRS corals. Bacterial community composition of GoA corals changed dramatically under heat stress, whereas CRS corals displayed stable assemblages. We interpret the response of GoA corals as that of a resilient population approaching a tipping point in contrast to a pattern of consistently elevated thermal resistance in CRS corals that cannot further attune. Such response differences suggest distinct thermal tolerance mechanisms that may affect the response of coral populations to ocean warming.

Saturation of thylakoid-associated fatty acids facilitates bioenergetic coupling in a marine diatom allowing for thermal acclimation.

In a rapidly warming world, we ask, "What limits the potential of marine diatoms to acclimate to elevated temperatures?," a group of ecologically successful unicellular eukaryotic photoautotrophs that evolved in a cooler ocean and are critical to marine food webs. To this end, we examined thermal tolerance mechanisms related to photosynthesis in the sequenced and transformable model diatom Phaeodactylum tricornutum. Data from transmission electron microscopy (TEM) and fatty acid methyl ester-gas chromatography mass spectrometry (FAME-GCMS) suggest that saturating thylakoid-associated fatty acids allowed rapid (on the order of hours) thermal tolerance up to 28.5°C. Beyond this critical temperature, thylakoid ultrastructure became severely perturbed. Biophysical analyses revealed that electrochemical leakage through the thylakoid membranes was extremely sensitive to elevated temperature (Q10 of 3.5). Data suggest that the loss of the proton motive force (pmf) occurred even when heat-labile photosystem II (PSII) was functioning, and saturation of thylakoid-associated fatty acids was active. Indeed, growth was inhibited when leakage of pmf through thylakoid membranes was insufficiently compensated by proton input from PSII. Our findings provide a mechanistic understanding of the importance of rapid saturation of thylakoid-associated fatty acids for ultrastructure maintenance and a generation of pmf at elevated temperatures. To the extent these experimental results apply, the ability of diatoms to generate a pmf may be a sensitive parameter for thermal sensitivity diagnosis in phytoplankton.

Stimulation of isoprene emissions and electron transport rates as key mechanisms of thermal tolerance in the tropical species Vismia guianensis.

Tropical forests absorb large amounts of atmospheric CO2 through photosynthesis, but high surface temperatures suppress this absorption while promoting isoprene emissions. While mechanistic isoprene emission models predict a tight coupling to photosynthetic electron transport (ETR) as a function of temperature, direct field observations of this phenomenon are lacking in the tropics and are necessary to assess the impact of a warming climate on global isoprene emissions. Here we demonstrate that in the early successional species Vismia guianensis in the central Amazon, ETR rates increased with temperature in concert with isoprene emissions, even as stomatal conductance (gs ) and net photosynthetic carbon fixation (Pn ) declined. We observed the highest temperatures of continually increasing isoprene emissions yet reported (50°C). While Pn showed an optimum value of 32.6±0.4°C, isoprene emissions, ETR, and the oxidation state of PSII reaction centers (qL ) increased with leaf temperature with strong linear correlations for ETR (ƿ=0.98) and qL (ƿ=0.99) with leaf isoprene emissions. In contrast, other photoprotective mechanisms, such as non-photochemical quenching, were not activated at elevated temperatures. Inhibition of isoprenoid biosynthesis repressed Pn at high temperatures through a mechanism that was independent of stomatal closure. While extreme warming will decrease gs and Pn in tropical species, our observations support a thermal tolerance mechanism where the maintenance of high photosynthetic capacity under extreme warming is assisted by the simultaneous stimulation of ETR and metabolic pathways that consume the direct products of ETR including photorespiration and the biosynthesis of thermoprotective isoprenoids. Our results confirm that models which link isoprene emissions to the rate of ETR hold true in tropical species and provide necessary "ground-truthing" for simulations of the large predicted increases in tropical isoprene emissions with climate warming.

Does social thermal regulation constrain individual thermal tolerance in an ant species?

In ants, social thermal regulation is the collective maintenance of a nest temperature that is optimal for individual colony members. In the thermophilic ant Aphaenogaster iberica, two key behaviours regulate nest temperature: seasonal nest relocation and variable nest depth. Outside the nest, foragers must adapt their activity to avoid temperatures that exceed their thermal limits. It has been suggested that social thermal regulation constrains physiological and morphological thermal adaptations at the individual level. We tested this hypothesis by examining the foraging rhythms of six populations of A. iberica, which were found at different elevations (from 100 to 2,000m) in the Sierra Nevada mountain range of southern Spain. We tested the thermal resistance of individuals from these populations under controlled conditions. Janzen's climatic variability hypothesis (CVH) states that greater climatic variability should select for organisms with broader temperature tolerances. We found that the A. iberica population at 1,300m experienced the most extreme temperatures and that ants from this population had the highest heat tolerance (LT50=57.55°C). These results support CVH's validity at microclimatic scales, such as the one represented by the elevational gradient in this study. Aphaenogaster iberica maintains colony food intake levels across different elevations and mean daily temperatures by shifting its rhythm of activity. This efficient colony-level thermal regulation and the significant differences in individual heat tolerance that we observed among the populations suggest that behaviourally controlled thermal regulation does not constrain individual physiological adaptations for coping with extreme temperatures.

Comparative Transcriptome Analysis of the Heat Stress Response in Monochamus alternatus Hope (Coleoptera: Cerambycidae).

Temperature is a critical factor of insect population abundance and distribution. Monochamus alternatus Hope (Coleoptera: Cerambycidae) is a significant concern since it is transmitted vector of the pinewood nematode posing enormous economic and environmental losses. This pest shows tolerance to heat stress, especially extremely high temperatures. Exposing for 6, 12, 24, 48, or 96 h, the 50% median lethal temperatures (Ltem50) for fourth-instar larvae were 47.5, 45.5, 43.9, 43.4, and 42.3°C, respectively. A total of 63,360 unigenes were obtained from complementary DNA libraries of M. alternatus fourth-instar larvae (kept at 25°C and exposed to 40°C for 3 h) and annotated with six databases. Five hundred sixty-one genes were significantly upregulated, and 245 genes were downregulated after heat stress. The Gene Ontology enrichment analysis showed that most different expression genes are categorized into “protein folding” and “unfold protein binding” terms. In addition, “Longevity regulating pathway-multiple species,” “Antigen processing and presentation” as well as “MAPK signaling pathway” were significantly enriched Kyoto Encyclopedia of Genes and Genomes pathways. Further analysis of different expression genes showed that metabolism processes were suppressed, while ubiquitin proteolytic system, heat shock proteins, immune response, superoxide dismutase, cytochrome P450s, and aldehyde dehydrogenase were induced after heat shock. The stress signaling transduction pathways such as MAPK, Hippo, and JAK-STAT might be central convergence points in M. alternatus heat tolerance mechanism. The expression levels from quantitative real-time PCR of 13 randomly selected genes were consistent with the transcriptome results. These results showed that M. alternatus possessed strong heat tolerance and genes related to protein activity, immune response, and signal transduction composed of a complicated heat tolerance mechanism of M. alternatus. This research provided new insights into the mechanisms of thermal tolerance in other insects and aided in exploring the function of heat resistance-related genes.

RNAi based transcriptome suggests genes potentially regulated by HSF1 in the Pacific oyster Crassostrea gigas under thermal stress

BackgroundThe Pacific oyster Crassostrea gigas is an important fishery resource that is sensitive to temperature fluctuations. Thus, it has evolved a protection mechanism against heat stress by increasing the expression of the gene coding for heat shock protein (HSP) 70 under elevated temperatures. In other animals, heat shock response is a transcriptional response driven by the heat shock transcription factor 1 (HSF1) and thermal stress can trigger HSP70 expression to protect the organism via HSF1. However, the regulatory relationship between HSF1 and HSP remains unclear in Pacific oyster. Therefore, in the present study, we examined the transcriptomic response of several to thermal stress following HSF1 interference.ResultsWe identified 150 genes responsive to heat shock including seven HSP genes, six of which belonging to the group of 17 HSP genes enriched in response to heat shock, according to weighted gene co-expression network analysis (WGCNA). The other gene was enriched in the module correlated with HSF1 interference. In addition, we found 48 and 47 genes that were upregulated and downregulated by HSF1 in response to heat shock, respectively. In the upregulated genes, we identified one HSP70 potentially regulated by HSF1 in response to heat shock. Furthermore, based on differentially expressed genes and WGCNA analyses, we found that the hypoxia signaling pathway was enriched under heat shock conditions. Five genes were then selected to detect dynamic changes through time. The results suggested that gene expression was correlated with HSF1 expression. The regulation of HSP70 by HSF1 was preliminarily confirmed by binding site predictions and by a dual luciferase assay.ConclusionsOur results revealed that the expression of HSP70 and HSP20 was initially triggered after 2 h of heat shock, and one of the HSP70 genes was potentially regulated by HSF1. From these results, it is evident that not all heat-inducible genes were triggered simultaneously in response to heat shock stress. Overall, the results revealed a possible HSF1–HSP regulatory relationship in Pacific oyster, providing valuable information on the mechanisms of thermal tolerance in this commercially important oyster.

Evolution of thermal tolerance in multifarious environments.

Species extinction rates are many times greater than the direst predictions made two decades ago by environmentalists, largely because of human impact. Major concerns are associated with the predicted higher recurrence and severity of extreme events, such as heat waves. Although tolerance to these extreme events is instrumental to species survival, little is known whether and how it evolves in natural populations, and to what extent it is affected by other environmental stressors. Here, we study physiological and molecular mechanisms of thermal tolerance over evolutionary times in multifarious environments. Using the practice of "resurrection ecology" on the keystone grazer Daphnia magna, we quantified genetic and plastic differences in physiological and molecular traits linked to thermal tolerance in historical and modern genotypes of the same population. This population experienced an increase in average temperature and occurrence of heat waves, in addition to dramatic changes in water chemistry, over five decades. On genotypes resurrected across the five decades, we measured plastic and genetic differences in CTmax , body size, Hb content and differential expression of four heat shock proteins after exposure to temperature as single stress and in combination with food levels and insecticide loads. We observed evolution of the critical thermal maximum and plastic response in body size, HSP expression and Hb content over time in a warming only scenario. Molecular and physiological responses to extreme temperature in multifarious environments were not predictable from the response to warming alone. Underestimating the effect of multiple stressors on thermal tolerance can lead to wrong estimates of species evolvability and persistence.

Mechanisms of Thermal Tolerance in Reef-Building Corals across a Fine-Grained Environmental Mosaic: Lessons from Ofu, American Samoa

Environmental heterogeneity gives rise to phenotypic variation through a combination of phenotypic plasticity and fixed genetic effects. For reef-building corals, understanding the relative roles of acclimatization and adaptation in generating thermal tolerance is fundamental to predicting future response of coral populations to future climate change. The temperature mosaic in the lagoon of Ofu Island, American Samoa, represents an ideal natural laboratory for studying thermal tolerance in corals. Two adjacent back-reef pools 500 meters apart have different temperature profiles: the highly variable (HV) pool experiences temperatures that range from 24.5°C to 35°C, whereas the moderately variable (MV) pool ranges from 25°C to 32°C. Standardized heat stress tests have shown that corals native to the HV pool have consistently higher levels of bleaching resistance than those in the MV pool. In this review, we summarize research into the mechanisms underlying this variation in bleaching resistance, focusing on the important reef-building genus Acropora. Both acclimatization and adaptation occur strongly and define thermal tolerance differences between pools. Most individual corals shift physiology to become more heat resistant when moved into the warmer pool. Lab based tests show that these shifts begin in as little as a week and are equally sparked by exposure to periodic high temperatures as constant high temperatures. Genome-wide data on gene expression show that a wide variety of genes are co-regulated in expression modules that change expression after experimental heat stress, after acclimatization, and even after short term environmental fluctuations. Population genetic scans have shown associations between a corals’ thermal environmental and its alleles at 100s to 1000s of nuclear genes and no single gene confers strong environmental effects within or between species. Symbionts also tend to differ between pools and species, and the thermal tolerance of a coral is a reflection of individual host genotype and specific symbiont types. We conclude the review by placing this work in the context of parallel research going on in other species, reefs and ecosystems around the world and into the broader framework of reef coral resilience in the face of near future climate change.

Evaluation and directed evolution for thermostability improvement of a GH 13 thermostable α-glucosidase from Thermus thermophilus TC11.

BackgroundThermal stable α-glucosidases with transglycosylation activity could be applied to the industrial production of oligosaccharides as well as conjugation of sugars to biologically useful materials. Therefore, α-glucosidases isolated from thermophiles have gained attention over the past decade. In this study, the characterization of a highly thermostable α-glucosidase and its thermostability improved mutant from newly isolated strain Thermus thermophilus TC11 were investigated.ResultsThe recombinant α-glucosidase (TtAG) from Thermus thermophilus TC11 was expressed in Escherichia coli BL21 (DE3) and purified. The purified enzyme had a molecular mass of 184 kDa and consisted of 59-kDa subunits; it showed hydrolytic activity for pNP-α-d-glucopyranoside (pNPG), sucrose, trehalose, panose, and isomaltooligosaccharides and very low activity for maltose. The highest specific activity of 288.96 U/mg was observed for pNPG at 90 °C and pH 5.0; Pb2+ provided a 20 % activity increase. TtAG was stable at 70 °C for more than 7 h and had a half-life of 195 min at 80 °C and 130 min at 90 °C. Transglycosylation activity was also observed with sucrose and trehalose as substrates. TtAG showed differences on substrate specificity, transglycosylation, multimerization, effects of metal ions and optimal pH from other reported Thermus α-glucosidases. One single-substitution TtAG mutant Q10Y with improved thermostability was also obtained from random mutagenesis library. The site-saturation mutagenesis and structural modelling analysis indicated that Q10Y substitution stabilized TtAG structure via additional hydrogen bonding and hydrophobic interactions.ConclusionOur findings indicate that TtAG is a highly thermostable and more acidic α-glucosidase distinct from other reported Thermus α-glucosidases. And this work also provides new insights into the catalytic and thermal tolerance mechanisms of α-glucosidases, which may guide molecular engineering of α-glucosidase and other thermostable enzymes for industrial application.Electronic supplementary materialThe online version of this article (doi:10.1186/s12896-015-0197-x) contains supplementary material, which is available to authorized users.

Thermal tolerance traits of juveniles of the ayu Plecoglossus altivelis and Japanese flounder Paralichthys olivaceus evaluated by their caudal fin cells

The thermal tolerances of the ayu Plecoglossus altivelis and Japanese flounder Paralichthys olivaceus were evaluated by assaying the primary culture cells and the free cells from their caudal fins (at 43 °C for 2 h) in comparison with the whole body tolerances of juveniles (at 30 °C for the ayu and 32 °C for the Japanese flounder). Primary culture cells and free cells were assayed separately and similar results were obtained for each type of cells. The thermal tolerance values observed in the whole body were significantly correlated with the values obtained from both the primary culture cells and the free cells. These results suggest that there is a significant correlation between the in vivo and in vitro thermal tolerances in these fish. In the case of the ayu, significant differences were observed between two lines for the mean tolerance values evaluated by all three methods. This finding suggests that cell assays with primary culture cells or free cells from a caudal fin clip could be useful for evaluating the genetic variation and genetic mechanisms of thermal tolerance of fish.