Drosophila Embryogenesis Scales Uniformly across Temperature in Developmentally Diverse Species

Temperature affects both the timing and outcome of animal development, but the detailed effects of temperature on the progress of early development have been poorly characterized. To determine the impact of temperature on the order and timing of events during Drosophila melanogaster embryogenesis, we used time-lapse imaging to track the progress of embryos from shortly after egg laying through hatching at seven precisely maintained temperatures between 17.5°C and 32.5°C. We employed a combination of automated and manual annotation to determine when 36 milestones occurred in each embryo. D. melanogaster embryogenesis takes 33 hours at 17.5°C, and accelerates with increasing temperature to a low of 16 hours at 27.5°C, above which embryogenesis slows slightly. Remarkably, while the total time of embryogenesis varies over two fold, the relative timing of events from cellularization through hatching is constant across temperatures. To further explore the relationship between temperature and embryogenesis, we expanded our analysis to cover ten additional Drosophila species of varying climatic origins. Six of these species, like D. melanogaster, are of tropical origin, and embryogenesis time at different temperatures was similar for them all. D. mojavensis, a sub-tropical fly, develops slower than the tropical species at lower temperatures, while D. virilis, a temperate fly, exhibits slower development at all temperatures. The alpine sister species D. persimilis and D. pseudoobscura develop as rapidly as tropical flies at cooler temperatures, but exhibit diminished acceleration above 22.5°C and have drastically slowed development by 30°C. Despite ranging from 13 hours for D. erecta at 30°C to 46 hours for D. virilis at 17.5°C, the relative timing of events from cellularization through hatching is constant across all species and temperatures examined here, suggesting the existence of a previously unrecognized timer controlling the progress of embryogenesis that has been tuned by natural selection as each species diverges.     

Tropical Strains of Ralstonia solanacearum Outcompete Race 3 Biovar 2 Strains at Lowland Tropical Temperatures

Bacterial wilt, caused by members of the heterogenous Ralstonia solanacearum species complex, is an economically important vascular disease affecting many crops. Human activity has widely disseminated R. solanacearum strains, increasing their global agricultural impact. However, tropical highland race 3 biovar 2 (R3bv2) strains do not cause disease in tropical lowlands, even though they are virulent at warm temperatures. We tested the hypothesis that differences in temperature adaptation and competitive fitness explain the uneven geographic distribution of R. solanacearum strains. Using three phylogenetically and ecologically distinct strains, we measured competitive fitness at two temperatures following paired-strain inoculations of their shared host, tomato. Lowland tropical strain GMI1000 was only weakly virulent on tomato under temperate conditions (24°C for day and 19°C for night [24/19°C]), but highland tropical R3bv2 strain UW551 and U.S. warm temperate strain K60 were highly virulent at both 24/19°C and 28°C. Strain K60 was significantly more competitive than both GMI1000 and UW551 in tomato rhizospheres and stems at 28°C, and GMI1000 also outcompeted UW551 at 28°C. The results were reversed at cooler temperatures, at which highland strain UW551 generally outcompeted GMI1000 and K60 in planta. The superior competitive index of UW551 at 24/19°C suggests that adaptation to cool temperatures could explain why only R3bv2 strains threaten highland agriculture. Strains K60 and GMI1000 each produced different bacteriocins that inhibited growth of UW551 in culture. Such interstrain inhibition could explain why R3bv2 strains do not cause disease in tropical lowlands.     

Thermal performance of the Chagas disease vector,Triatoma infestans,under thermal variability

Vector-borne diseases (VBD) are particularly susceptible to climate change because most of the diseases’ vectors are ectotherms, which themselves are susceptible to thermal changes. The Chagas disease is one neglected tropical disease caused by the protozoan parasite, Trypanosoma cruzi. One of the main vectors of the Chagas disease in South America is Triatoma infestans, a species traditionally considered to be restricted to domestic or peridomestic habitats, but sylvatic foci have also been described along its distribution. The infestation of wild individuals, together with the projections of environmental changes due to global warming, urge the need to understand the relationship between temperature and the vector’s performance. Here, we evaluated the impact of temperature variability on the thermal response of T. infestans. We acclimated individuals to six thermal treatments for five weeks to then estimate their thermal performance curves (TPCs) by measuring the walking speed of the individuals. We found that the TPCs varied with thermal acclimation and body mass. Individuals acclimated to a low and variable ambient temperature (18°C ± 5°C) exhibited lower performances than those individuals acclimated to an optimal temperature (27°C ± 0°C); while those individuals acclimated to a low but constant temperature (18°C ± 0°C) did not differ in their maximal performance from those at an optimal temperature. Additionally, thermal variability (i.e., ± 5°C) at a high temperature (30°C) increased performance. These results evidenced the plastic response of T. infestans to thermal acclimation. This plastic response and the non-linear effect of thermal variability on the performance of T. infestans posit challenges when predicting changes in the vector’s distribution range under climate change.     

Temperature Effects on Development of Meloidogyne Enterolobii and M. Floridensis

Meloidogyne enterolobii and M. floridensis are virulent species that can overcome root-knot nematode resistance in economically important crops. Our objectives were to determine the effects of temperature on the infectivity of second-stage juveniles (J2) of these two species and determine differences in duration and thermal-time requirements (degree-days [DD]) to complete their developmental cycle. Florida isolates of M. enterolobii and M. floridensis were compared to M. incognita race 3. Tomato cv. BHN 589 seedlings following inoculation were placed in growth chambers set at constant temperatures of 25°C, and 30°C, and alternating temperatures of 30°C to 25°C (day–night). Root infection by the three nematode species was higher at 30°C than at 25°C, and intermediate at 30°C to 25°C, with 33%, 15%, and 24% infection rates, respectively. There was no difference, however, in the percentages of J2 that infected roots among species at each temperature. Developmental time from infective J2 to reproductive stage for the three species was shorter at 30°C than at 25°C, and 30°C to 25°C. The shortest time and DD to egg production for the three species were 13 days after inoculation (DAI) and 285.7 DD, respectively. During the experimental timeframe of 29 d, a single generation was completed at 30°C for all three species, whereas only M. floridensis completed a generation at 30°C to 25°C. The number of days and accumulated DD for completing the life cycle (from J2 to J2) were 23 d and 506.9 DD for M. enterolobii, and 25 d and 552.3 DD for M. floridensis and M. incognita, respectively. Exposure to lower (25°C) and intermediate temperatures (30°C to 25°C) decreased root penetration and slowed the developmental cycle of M. enterolobii and M. floridensis compared with 30°C.     

Temperature-Regulated Formation of Mycelial Mat-Like Biofilms by Legionella pneumophila

Fifty strains representing 38 species of the genus Legionella were examined for biofilm formation on glass, polystyrene, and polypropylene surfaces in static cultures at 25°C, 37°C, and 42°C. Strains of Legionella pneumophila, the most common causative agent of Legionnaires' disease, were found to have the highest ability to form biofilms among the test strains. The quantity, rate of formation, and adherence stability of L. pneumophila biofilms showed considerable dependence on both temperature and surface material. Glass and polystyrene surfaces gave between two- to sevenfold-higher yields of biofilms at 37°C or 42°C than at 25°C; conversely, polypropylene surface had between 2 to 16 times higher yields at 25°C than at 37°C or 42°C. On glass surfaces, the biofilms were formed faster but attached less stably at 37°C or 42°C than at 25°C. Both scanning electron microscopy and confocal laser scanning microscopy revealed that biofilms formed at 37°C or 42°C were mycelial mat like and were composed of filamentous cells, while at 25°C, cells were rod shaped. Planktonic cells outside of biofilms or in shaken liquid cultures were rod shaped. Notably, the filamentous cells were found to be multinucleate and lacking septa, but a recA null mutant of L. pneumophila was unaffected in its temperature-regulated filamentation within biofilms. Our data also showed that filamentous cells were able to rapidly give rise to a large number of short rods in a fresh liquid culture at 37°C. The possibility of this biofilm to represent a novel strategy by L. pneumophila to compete for proliferation among the environmental microbiota is discussed.     

16S rRNA Sequences and Differences in Bacteria Isolated from the Muztag Ata Glacier at Increasing Depths

Small subunit 16S rRNA sequences, growth temperatures, and phylogenetic relationships have been established for 129 bacterial isolates recovered under aerobic growth conditions from different regions of a 22-m ice core from the Muztag Ata Mountain glacier on the Pamirs Plateau (China). Only 11% were psychrophiles (grew at 2°C or −2°C up to ~20°C), although the majority (82%) were psychrotolerant (grew at 2°C or −2°C up to 37°C). The majority of the isolates had 16S rRNA sequences similar to previously determined sequences, ranging from 85% to 100% identical to database sequences. Based on their 16S rRNA sequences, 42.6% of the isolates were high-G+C (HGC) gram-positive bacteria, 23.3% were γ-Proteobacteria, 14.7% were α-Proteobacteria, 14.7% were Flavobacteria, and 4.7% were low-G+C (LGC) gram-positive bacteria. There were clear differences in the depth distribution, with Proteobacteria, HGC/Cytophaga-Flavobacterium-Bacteroides (CFB), Proteobacteria, LGC/CFB/HGC, Cryobacterium psychrophilum, HGC/CFB, Proteobacteria/HGC/CFB, and HGC/CFB being the predominant isolates from ice that originated from 2.7 to 3.8, 6.2, 7.5, 8.3, 9.0, 9.7, 12.5, and 15.3 m below the surface, respectively. This layered distribution of bacterial isolates presumably reflects both differences in bacteria inhabiting the glacier's surface, differences in bacteria deposited serendipitously on the glacier's surface by wind and snowfall, and nutrient availability within the ice.     

Kinetics of Thermal Denaturation and Aggregation of Bovine Serum Albumin

Thermal aggregation of bovine serum albumin (BSA) has been studied using dynamic light scattering, asymmetric flow field-flow fractionation and analytical ultracentrifugation. The studies were carried out at fixed temperatures (60°C, 65°C, 70°C and 80°C) in 0.1 M phosphate buffer, pH 7.0, at BSA concentration of 1 mg/ml. Thermal denaturation of the protein was studied by differential scanning calorimetry. Analysis of the experimental data shows that at 65°C the stage of protein unfolding and individual stages of protein aggregation are markedly separated in time. This circumstance allowed us to propose the following mechanism of thermal aggregation of BSA. Protein unfolding results in the formation of two forms of the non-native protein with different propensity to aggregation. One of the forms (highly reactive unfolded form, U_hr) is characterized by a high rate of aggregation. Aggregation of U_hr leads to the formation of primary aggregates with the hydrodynamic radius (R_h,1) of 10.3 nm. The second form (low reactive unfolded form, U_lr) participates in the aggregation process by its attachment to the primary aggregates produced by the U_hr form and possesses ability for self-aggregation with formation of stable small-sized aggregates (A_st). At complete exhaustion of U_lr, secondary aggregates with the hydrodynamic radius (R_h,2) of 12.8 nm are formed. At 60°C the rates of unfolding and aggregation are commensurate, at 70°C the rates of formation of the primary and secondary aggregates are commensurate, at 80°C the registration of the initial stages of aggregation is complicated by formation of large-sized aggregates.     

Effect of Conditioning Treatments on the Survival of Radopholus similis at High Temperatures

Heat treatments are an environmentally safe method for eliminating quarantine pests from tropical foliage. Conditioning heat treatments can induce thermotolerance against subsequent and otherwise phytotoxic temperatures in tropical foliage, allowing heat treatments to be even more effective. However, if thermotolerance is also induced in nematodes of quarantine significance like Radopholus similis, heat treatments would be rendered ineffective. A lethal thermal death point (LT_99.9) was established for R. similis by recording mortality at 25 (control temperature), 43°C, 45°C, 47°C, or 49°C after a 0, 1-, 2-, 4-, 6-, 8-, 10-, 12-, or 15-minute exposure. In a second experiment, nematodes were conditioned at 35, 40, or 45°C for 0, 15, 30, 60, 120, and 180 minutes, allowed to rest for 3 hours, and then challenged at 47°C for 5 minutes. No nematodes survived the challenge heat treatment; rather, nematode mortality was hastened by the conditioning treatment itself. In a third experiment, R. similis inside anthurium roots were conditioned at 25°C or 40°C for 15 minutes and then treated at 45°C for up to 8 minutes. Mortality of conditioned and unconditioned nematodes was similar (P > 0.1). Conditioning treatments increase plant thermotolerance but do not induce thermotolerance in R. similis. Heat treatments have promise as disinfection protocols for quarantines.     

Seed dormancy,germination and storage behavior of Magnolia sinica,a plant species with extremely small populations of MagnoliaceaeOA

Magnolia sinica is one of the most endangered Magnoliaceae species in China. Seed biology information concerning its long-term ex situ conservation and utilization is insufficient. This study investigated dormancy status, germination requirements and storage behavior of M. sinica. Freshly matured seeds germinated to ca. 86.5% at 25/15°C but poorly at 30°C; GA3 and moist chilling promoted germination significantly at 20°C. Embryos grew at temperatures(alternating or constant) between 20°C and 25°...     

Factors influencing range contraction of a rodent herbivore in a steppe grassland over the past decades

1. Climate warming and human disturbance are known to be key drivers in causing range contraction of many species, but quantitative assessment on their distinctive and interactive effects on local disappearance is still rare.
2. In this study, we examined the association of climate warming and human disturbance stressors with local disappearance probability of Brandt''s voles (Lasiopodomys brandtii) in a steppe grassland in northern China.
3. We used logistic generalized additive models to quantify the relationship between local disappearance probability of Brandt''s voles and environmental variables. The year following the last observation year was used to estimate the disappearance threshold of Brandt''s voles. We projected the distribution change of Brandt''s voles under future climate warming scenarios.
4. We found climate warming attributed to local disappearance and range contraction for southern populations of Brandt''s voles from 1971 to 2020. Human stressors and high vegetation coverage increased the probability of local disappearance of voles in years of abundant precipitation. The southern boundary retreated northward at a speed of 99.0 km per decade with the temperature rise of 0.36°C. The disappearance threshold of maximum air temperature of Brandt''s voles in the warmest month (27.50 ± 1.61°C) was similar to the lower critical temperature of its thermal neutral zone.
5. Our study suggests that the rapid climate change over the past decades contributed to the range contraction of its southern boundary of this keystone species in the steppe grassland of China. It is necessary to take actions to preserve the isolated populations of Brandt''s voles from the effects of accelerated climate change and human disturbance.

     

Effects of Temperature on Resistance in Phaseolus vulgaris Genotypes and on Development of Meloidogyne Species

Phaseolus vulgaris lines with heat-stable resistance to Meloidogyne spp. may be needed to manage root-knot nematodes in tropical regions. Resistance expression before and during the process of nematode penetration and development in resistant genotypes were studied at pre- and postinoculation temperatures of 24 °C and 24 °C, 24 °C and 28 °C, 28 °C and 24 °C, and 28 °C and 28 °C. Resistance was effective at all temperature regimes examined, with fewer nematodes in roots of a resistant line compared with a susceptible line. Preinoculation temperature did not modify resistance expression to later infections by root-knot nematodes. However, postinoculation temperatures affected development of Meloidogyne spp. in both the resistant and susceptible bean lines tested. The more rapid development of nematodes to adults at the higher postinoculation temperature of 28 °C in both bean lines suggests direct temperature effects on nematode development instead of on resistance expression of either of two gene systems. Also, resistance was stable at 30 °C and 32 °C.     

Leaf physiological and anatomical responses of two sympatric Paphiopedilum species to temperature

Paphiopedilum dianthum and P. micranthum are two endangered orchid species, with high ornamental and conservation values. They are sympatric species, but their leaf anatomical traits and flowering period have significant differences. However, it is unclear whether the differences in leaf structure of the two species will affect their adaptabilities to temperature. Here, we investigated the leaf photosynthetic, anatomical, and flowering traits of these two species at three sites with different temperatures (Kunming, 16.7 ± 0.2 °C; Puer, 17.7 ± 0.2 °C; Menglun, 23.3 ± 0.2 °C) in southwest China. Compared with those at Puer and Kunming, the values of light-saturated photosynthetic rate (P_max), stomatal conductance (g_s), leaf thickness (LT), and stomatal density (SD) in both species were lower at Menglun. The values of P_max, g_s, LT, adaxial cuticle thickness (CT_ad) and SD in P. dianthum were higher than those of P. micranthum at the three sites. Compared with P. dianthum, there were no flowering plants of P. micranthum at Menglun. These results indicated that both species were less resistance to high temperature, and P. dianthum had a stronger adaptability to high-temperature than P. micranthum. Our findings can provide valuable information for the conservation and cultivation of Paphiopedilum species.     

Effect of Incubation Temperature on the Detection of Thermophilic Campylobacter Species from Freshwater Beaches,Nearby Wastewater Effluents,and Bird Fecal Droppings

This large-scale study compared incubation temperatures (37°C versus 42°C) to study the detection of thermophilic Campylobacter species, including Campylobacter jejuni, C. coli, and C. lari, in various surface water samples and bird fecal droppings around Hamilton Harbor, Lake Ontario. The putative culture isolates obtained from incubation temperatures of 37 and 42°C were confirmed by Campylobacter genus- and species-specific triplex PCR assays targeting the 16S rRNA gene and the 16S-23S rRNA gene internal transcribed spacer (ITS) region. A total of 759 water, wastewater, and bird fecal dropping samples were tested. Positive amplification reactions for the genus Campylobacter were found for 454 (60%) samples incubated at 37°C, compared to 258 (34%) samples incubated at 42°C. C. jejuni (16%) and C. lari (12%) were detected significantly more frequently at the 42°C incubation temperature than at 37°C (8% and 5%, respectively). In contrast, significantly higher rates of C. coli (14%) and other Campylobacter spp. (36%) were detected at the 37°C incubation temperature than at 42°C (8% and 7%, respectively). These results were consistent across surface water, wastewater, and bird fecal dropping samples. At times, Campylobacter spp. were recovered and detected at 37°C (3% for C. jejuni, 10% for C. coli, and 3% for C. lari) when the same samples incubated at 42°C were negative. A significantly higher rate of other Campylobacter spp. was detected only at 37°C (32%) than only at 42°C (3%). These results indicate that incubation temperature can significantly influence the culturability and detection of thermophilic and other fastidious Campylobacter spp. and that a comprehensive characterization of the Campylobacter spp. in surface water, wastewaters, or bird fecal droppings will require incubation at both 37 and 42°C.     

EXPERIMENTS ON TOLERATION OF TEMPERATURE BY DROSOPHILA

1. Most wild stocks of Drosophila melanogaster can be bred indefinitely on banana agar at a temperature of 31°C. There is no relation between the geographical origin of these stocks and their ability to tolerate this temperature. 2. A single wild stock has been found which will breed for only one generation at temperatures above 29°C. The offspring hatched at 31°C. will breed normally at 24°C. This difference from other wild stocks is apparently genetic, but its genetic basis has not yet been worked out. 3. The mutant stocks of D. melanogaster tested by us will breed for only one generation at 31°C. and their offspring at this temperature are also fertile at 24°C. This condition is apparently a physiological effect of the presence of any of the mutant genes in a homozygous condition. 4. Similar tests indicate that wild stocks of D. virilis and Chymomyza procnemis will breed at 31°C., while D. simulans, D. immigrans, and D. funebris will not. The last two species are northern forms not commonly found in the tropics. 5. Both male and female flies from mutant stocks hatched at 31°C. produce offspring at this temperature if mated to flies hatched at 24°C. Their germ cells are therefore capable of development, and the cause of their failure to develop at 31°C. when inbred must lie either in the failure of the germ cells to reach each other or in the fertilization process itself.     

Concomitant changes in high temperature tolerance and heat-shock proteins in desert succulents

Raising the day/night air temperatures from 30°C/20°C to 50°C/40°C increases the high temperature tolerated by Agave deserti, Carnegiea gigantea, and Ferocactus acanthodes by 6°C to 8°C; the increase is about half completed in 3 days and fully completed in 10 days. A 25 to 27 kilodalton protein concomitantly accumulates for all three desert succulents upon transfer to 50°C/40°C, while accumulation of other heat “heat-shock” proteins is species specific. Some of the induced proteins are more abundant at 3 days, while others (including the 25-27 kilodalton protein) remain after completion of high temperature acclimation.     

Elevated seawater temperature causes a microbial shift on crustose coralline algae with implications for the recruitment of coral larvae

Crustose coralline algae (CCA) are key reef-building primary producers that are known to induce the metamorphosis and recruitment of many species of coral larvae. Reef biofilms (particularly microorganisms associated with CCA) are also important as settlement cues for a variety of marine invertebrates, including corals. If rising sea surface temperatures (SSTs) affect CCA and/or their associated biofilms, this may in turn affect recruitment on coral reefs. Herein, we report that the CCA Neogoniolithon fosliei, and its associated microbial communities do not tolerate SSTs of 32 °C, only 2–4 °C above the mean maximum annual SST. After 7 days at 32 °C, the CCA exhibited clear signs of stress, including bleaching, a reduction in maximum quantum yield (F_v/F_m) and a large shift in microbial community structure. This shift at 32 °C involved an increase in Bacteroidetes and a reduction in Alphaproteobacteria, including the loss of the primary strain (with high-sequence similarity to a described coral symbiont). A recovery in F_v/F_m was observed in CCA exposed to 31 °C following 7 days of recovery (at 27 °C); however, CCA exposed to 32 °C did not recover during this time as evidenced by the rapid growth of endolithic green algae. A 50% reduction in the ability of N. fosliei to induce coral larval metamorphosis at 32 °C accompanied the changes in microbiology, pigmentation and photophysiology of the CCA. This is the first experimental evidence to demonstrate how thermal stress influences microbial associations on CCA with subsequent downstream impacts on coral recruitment, which is critical for reef regeneration and recovery from climate-related mortality events.     

Subtropical mouse-tailed bats use geothermally heated caves for winter hibernation

We report that two species of mouse-tailed bats (Rhinopoma microphyllum and R. cystops) hibernate for five months during winter in geothermally heated caves with stable high temperature (20°C). While hibernating, these bats do not feed or drink, even on warm nights when other bat species are active. We used thermo-sensitive transmitters to measure the bats’ skin temperature in the natural hibernacula and open flow respirometry to measure torpid metabolic rate at different ambient temperatures (T_a, 16–35°C) and evaporative water loss (EWL) in the laboratory. Bats average skin temperature at the natural hibernacula was 21.7 ± 0.8°C, and no arousals were recorded. Both species reached the lowest metabolic rates around natural hibernacula temperatures (20°C, average of 0.14 ± 0.01 and 0.16 ± 0.04 ml O₂ g⁻¹ h⁻¹ for R. microphyllum and R. cystops, respectively) and aroused from torpor when T_a fell below 16°C. During torpor the bats performed long apnoeas (14 ± 1.6 and 16 ± 1.5 min, respectively) and had a very low EWL. We hypothesize that the particular diet of these bats is an adaptation to hibernation at high temperatures and that caves featuring high temperature and humidity during winter enable these species to survive this season on the northern edge of their world distribution.     

Thermal activation of the bovine Hsc70 molecular chaperone at physiological temperatures: physical evidence of a molecular thermometer

Defferential scanning calorimetry was used to monitor the thermal transitions of the 70 kDa heat shock cognate protein (Hsc70). Hsc70 had endothermic trasitions with midpoints (Tm) at 59°C and 63°C in the absence and presence of ATP, respectively, and a similar increase in Tm was observed using intrinsic fluorescence of tryptophan. Combined with increased exposure at 60°C of non-polar residues of Hsc70 to which the hydrophobic, fluorescent probe ANS bound, these data indicate that the endotherms represent thermal denaturation and that bound nucleotide stabilizes Hsc70. An exothermic transition (Tm=66°C) was detected by calorimetry for Hsc70-apocytochrome c (apo c) complexes. An increase in intrinsic fluorescence with the same Tm and increased turbidity indicated aggregation of the denatured Hsc70-apo c. A novel finding was an exothermic transition of Hsc70 begining at about 30°c (Tm=41°C). No changes in either intrinsic fluorescence or ANS fluorescence attributable to protein transitions were detected in this temperature range. Examination of samples run on native polyacrylamide gels indicated that this exothermic transition was not due to Hsc70 aggregation or multimer formation. However, Hsc70 was protease-resistant at 20°C, sensitive at 40°C and resistant when returned to 20°C, indicating that this exotherm is associated with a reversible conformational change. As an assay for Hsc70 chaperoning function, complex formation was measured as a function of temperature using a variety of substrates including the model unfolded protein apo c a pigeon cytochrome c fragment, a representative hydrophobic-aromatic peptide FYQLALT, and a representative hydrophobic-basic motif NIVRKKK. For all of these substrates, the amount of complex formed increased with increasing termperature over the same range as the 41°C exotherm. It is proposed that a conformational change exposes polar and charged residues in Hsc70 Which subsequently become hydrated, resulting in an active chaperone. Hsc70 may be a thermal sensor that supply of chaperoning activity with demand for it over the physiological temperature range of mammalian cells. Thermal activation of Hsc70 may also have a role in acquired thermotolerance.