How to measure the thermal death of Daphnia? A comparison of different heat tests and effects of heat injury

1. 1. The thermal death point of the water flea Daphnia magna (age < 24 h, cultured at 20°C) varied considerably depending on the method used. The median lethal dose (LD₅₀), induced by an acute 24 h heat exposure was 34.8°C. It was 37.8°C following a thermal shock for 15 min, and it was 39.4°C when a continuous temperature increase (0.2°C/min) was used.

2. 2. Heat death temperature of daphnids was related to the acute heating rate.

3. 3. The logarithm of median lethal time (Lt₅₀) of daphnids, kept at a constant high temperature, had a linear relationship to temperature (°C) within the range of 28.0–38.5°C.

4. 4. The mortality after heat exposure increased with recovery time at 20°C for up to 3 days.

5. 5. The animals which survived the heat exposure produced eggs and offspring. Furthermore, no time lag in development between the control and heat exposure group was observed.

6. 6. The comparison of the results made by different heat tests categorized to Methods 1 and 2 by Precht (1973), for use in the determination of lethal limits of ectotherms, has been discussed.

     

Behavioral thermoregulation of Bulla gouldiana (Gastropoda: Opisthobranchia: Cephalaspidea)

1. 1. The preferred temperature of Bulla gouldiana is 26.7–28.7°C.

2. 2. In constant scotophase, photophase, and light and dark photoperiod the organisms do not have a diel cycle of thermoregulation.

3. 3. It takes the animal 6–16 h to reach the preferred temperature.

4. 4. The lowest and highest temperatures visited were 11 and 33°C.

5. 5. Spawning of the species occurred in the thermal gradient between 27 and 28.5°C.

     

Anergy or cell death induced by low physiological temperature in mitogen-stimulated human T lymphocytes

1. 1. Human T cell proliferation is suppressed at 27°C, and is both diminished and delayed at 32°C.

2. 2. Temperature shift-up and viability assays indicated that concanavalin A stimulation at 27°C induced cell death in contrast to a transient unresponsiveness (anergy) induced by monoclonal anti-CD3 antibody (CD3) and the superantigen, staphylococcal exterotoxin B.

3. 3. Phytohemagglutinin also induced cell death at 27°C; however, some cells remained viable and proliferation occurred when such cultures were subsequently moved to 37°C.

4. 4. Low temperature suppression of T cell activation was not overcome by a mixture of phorbol ester and calcium ionophore indicating a probable block post-protein kinase C activation. This was confirmed in temperature shift-down assays where incubation for 18–24 h at 37°C was required to bypass the block at 27°C.

5. 5. With the exception of CD3, stimulation at 27°C with the mitogens resulted in interleukin-2 secretion, indicating that the low temperature block(s) is a relatively late event in cell activation.

     

Dehydration and food deprivation exacerbate mouse cerebral microvascular responses to local hyperthermia

1. 1. Effects of 1-day deprivation from water, food or both on responses of mice pial microvessels to local cerebral hyperthermia were compared to fed mice and with access to water.

2. 2. A set of protocol for all groups was followed, which involved microsurgery and utilized intravital videomicroscopy. Core body temperature was kept at 37°C and hyperthermic exposure was applied locally by heating the artificial cerebrospinal fluid irrigating the brain surface, at 45°C for 25 min.

3. 3. Monitored responses included intravascular thrombo-embolic events and changes in microvascular diameter. Dehydration and food deprivation shortened the time for appearance of passing emboli and lowered the thermal threshold at which thrombo-embolic processes occur.

4. 4. Arteriolar constriction was observed in all groups, coupled with full occlusion.

5. 5. Data of this study revealed that dehydration and food deprivation exacerbate pial microcirculatory responses to local hyperthermia.

     

Thermoregulatory responses to manipulations of photoperiod in wood mice Apodemus sylvaticus from high latitudes (57°N)

1. 1. The thermoregulatory responses to manipulations of photoperiod in wood mice (Apodemus sylvaticus), which were drawn from a population living at a high latitude (57°N) were studied.

2. 2. Mice captured in spring were acclimated to two different photoperiod regimes 16L:8D and 8L:16D at a constant ambient temperature of 24°C, for 3 weeks.

3. 3. Daily rhythms of body temperature, oxygen consumption and body temperature at various ambient temperatures, nonshivering thermogenesis (the response to a noradrenaline injection) and body mass were measured. Minimal overall thermal conductance was calculated for both groups.

4. 4. Acclimation to long photophase increased the thermoregulatory abilities at relatively high ambient temperatures while that of long-scotophase increased thermoregulatory abilities at low ambient temperatures.

5. 5. Changes in photoperiod may therefore be used as cues for seasonal acclimatization of thermoregulatory mechanisms in this population of wood mice.

     

Changes in lipid peroxidation, superoxide dismutase activity, ascorbic acid and phospholipid content in liver of freshwater catfish Heteropneustes fossilis exposed to elevated temperature

1. 1. Lipid peroxidation, superoxide dismutase (SOD) activity, ascorbic acid (AsA) and individual phospholipid contents in liver of fresh water cat fish Heteropneustes fossilis were measured after exposure to different temperatures (25, 27, 32, 37°C) at various times (1–4 h).

2. 2. Lipid peroxidation and superoxide dismutase activity were significantly increased with increases in temperature at various times.

3. 3. Ascorbic acid content was depleted when temperature was increased.

4. 4. After temperature exposure, phosphatidyl inositol was increased while phosphatidyl choline, phosphatidyl serine and phosphatidyl ethanolamine were depleted. Phosphatidic acid level did not change.

5. 5. The findings indicated an increased oxidative stress in liver following increases in temperature at various times. Concurrent with the increase in lipid peroxidation, superoxide dismutase activity and ascorbic acid from the liver of fish varied. It is suggested that depletion of major individual phospholipids following temperature exposure could be due to superoxide created oxidative stress in the liver.

     

Thermoregulatory behavior and critical thermal limits of the angelfish Pterophyllum scalare (Lichtenstein) (Pisces: Cichlidae)

(1)Final temperature preferendum of juvenile (0.9–1.9 g) and adult (5.2–12.5 g) angelfish Pterophyllum scalare were determined with acute and gravitation methods. The final preferenda were similar, independent of the method and development stage (29.0–31.1°C).

(2)The critical thermal maxima (CTMax) for juveniles were 36.9°C, 37.6°C, 40.6°C, 40.8°C and for adults 38.4°C, 38.6°C, 41.0°C, 42.1°C. Adult angelfish CTMax was slightly higher than in juveniles (1°C; P<0.05); the endpoint of CTMax was the onset of spasms.

(3)The acclimation response ratio for both stages had an interval of 0.33–0.44; these values are in agreement with results for subtropical and tropical fishes.

(4)Therefore it is recommended that angelfish cultivation should be consistent with temperatures that do not change abruptly throughout the year and temperature maximum does not exceed 30°C.

     

Carp expresses fast skeletal myosin isoforms with altered motor functions and structural stabilities to compensate for changes in environmental temperature

1. 1. Myosin and its subfragment-1 (Sl) from carp acclimated to 10°C showed higher actin-activated Mg²⁺-ATPase activity and lower thermostability than their counterparts from carp acclimated to 30°C. Accordingly, filament velocity for the 10°C-acclimated carp myosin was higher at any measuring temperatures from 3 to 23°C than that for the 30°C-acclimated carp myosin.

2. 2. Three types of cDNA clones encoding myosin heavy chains were isolated from thermally acclimated carp. The 10 and 30°C types were predominating in carp acclimated to 10 and 30°C, respectively, whereas the intermediate type was found as a minor component in the 10°C-acclimated carp with an intermediate feature in both DNA nucleotide and deduced amino acid sequences between those of the 10 and 30°C types.

3. 3. The three types of myosin rod all showed a typical coiled-coil structure of -helices. DSC scans demonstrated that myosin rod prepared from carp acclimated to 10°C had a lower thermostability than that from carp acclimated to 30°C, showing that low thermostability in cold-acclimated carp myosin prevails over the entire molecule.

4. 4. cDNA clones encoding myosin alkali light chains were isolated from thermally acclimated carp. Northern blot analysis showed that the ratios of LC3/LC1 mRNAs were significantly higher (3.92) in the 30°C- than 10°C-acclimated (3.10) carp.

     

Temperature and the life-history strategies of sea turtles

1. 1. Sea turtles have a high fecundity, high mortality, great longevity life history strategy.

2. 2. With the exception of the leatherback, turtle distribution is constrained by the 20°C surface isotherm.

3. 3. All sea turtles exhibit temperature-dependent sex determination (TSD) with pivotal temperatures close to 29°C.

4. 4. It is suggested that hatchling sex ratio will vary chaotically because of TSD.

5. 5. Because of TSD and natal homing, sea turtles are likely to be adversely affected by global warming.

6. 6. TSD and global warming have implications for conservation/management of sea turtles.

     

Regulation of particle transport within the ventral groove of the mussel (Mytilus edulis) gill in response to environmental conditions

To thoroughly understand the feeding processes of the blue mussel, Mytilus edulis, under the variable environmental conditions it experiences in nature, it is important to examine individually the different components of its feeding system. The ciliated ventral food groove represents one of these components, within which the majority of food particles trapped by the gill are transported to the labial palps and mouth. Any ability of the mussel to adjust food transport rates within this groove could serve as an important feeding regulatory mechanism in response to variations in the environment.

Mucous strand velocities in the ventral groove of the mussel, M. edulis, were determined by video endoscopy over different time periods and during short- and long-term manipulations of ambient particle concentration and temperature. Mucous strand velocity decreased with increasing ambient particle concentration at 14°C, but a similar relationship was not observed at 5°C. The data support the hypothesis that M. edulis possesses compensatory mechanisms to control particle transport at the level of the ventral groove cilia in response to changes in the environment. Furthermore, mucous strand velocity in the ventral groove increased when the ambient temperature of mussels acclimated to 5°C was increased to 15°C during acute and long-term acclimation temperature experiments. This response is consistent with standard physiological responses of ciliary systems to changes in temperature.     

A test of the accuracy of operative temperature thermometers for studies of small ectotherms

1. 1. Various devices have been used to estimate the equilibrium body temperature of ectotherms occupying natural environments. We tested the accuracy of such devices under a range of conditions.

2. 2. We measured body temperatures of lizards (Sceloporus magister) exposed to short-wave radiation under varying convective conditions and compared these to temperatures of hollow metal casts duplicating the animal's shape and reflectivity, as well as to the temperatures of cylinders similar to those used by other workers.

3. 3. Casts equilibrated within 2–3°C of live animals, yielding errors of 14–37% of the radiation-produced elevation of body temperature.

4. 4. Various cylinders differed from animal body temperature more than lizard casts did, producing errors equally 33–53% of the radiation-produced elevation.

5. 5. It is imperative that workers using operative-temperature thermometers experimentally confirm the adequacy of the devices they use for the range of conditions encountered within a specific analysis.

     

Effects of constant and cycling hot environments on mitogen-stimulated proliferation of peripheral blood lymphocytes from sows and litters

1. 1. Lymphocytes from sows maintained in a constant hot environment (32°C) showed reduced proliferative responses to mitogens PHA (P < 0.02) and PWM (P < 0.01) in comparison to sown maintained in a constant cool environment (21°C). In the piglets the hot constant temperature slightly reduced (P < 0.05) proliferative responses of lymphocytes to PHA.

2. 2. No significant effects of a cycling hot environment (27–32°C) were found for any proliferative responses of lymphocytes from sows and litters.

3. 3. In the constant hot environment, serum cortisol concentrations were significantly reduced in the sows (P < 0.0001) while no differences in serum cortisol concentrations were found in the litters.

     

The influence of hypothermia on the restoration of neural activity of brain slices from hibernating ground squirrels

1. 1. Neural activity was recorded in hippocampal slices from deep hibernating Yakut ground squirrels and in hippocampal and septal slices from non-hibernating animals.

2. 2. Slices were placed immediately after preparation in hypothermic conditions (3–4°C). Their activity was tested under standard conditions at 31°C in the incubation chamber. Some of the prepared slices were tested after maintenance in hypothermia for 2 or 24 h.

3. 3. In the hippocampal slices of hibernating ground squirrels, neural activity was present, irrespective of the period in hypothermia.

4. 4. Slices from guinea-pigs and hamsters did not possess neural activity after either 2 or 24 h of hypothermic treatment.

     

The effect of acclimation temperature and the removal of peripheral temperature receptors on body temperature preference in the cockroach, Periplaneta americana

1. 1.|Body temperature preferences were compared between cockroaches acclimated to different ambient temperatures and between 25°C acclimated cockroaches and cockroaches deprived of their peripheral temperature receptors.

2. 2.|Acclimation to 35°C resulted in a significantly higher mean body temperature and low body temperature selected compared with 25°C acclimated cockroaches.

3. 3.|Cockroaches deprived of their peripheral temperature receptors showed a significantly higher mean high body temperature selected when compared to normal 25°C acclimated cockroaches.

4. 4.|It is concluded that cockroach temperature regulation is more precise than expected and that central temperature receptors are the primary sensing elements for cockroach thermoregulation.

Factors influencing the upper temperature tolerances of three mussel species in a brackish water canal: size, season and laboratory protocols

Mussels are the most problematic organisms encountered in the water intake systems of electrical power plants. Various fouling control measures are adopted, among which heat treatment is considered the relatively more attractive from economic and ecological points of view. Thermal tolerance experiments were carried out to determine the effects of mussel size (2-20 mm shell length), season (breeding vs non-breeding), nutritional status (fed vs non-fed), acclimation temperature (5-25 degrees C) and acclimation salinity (1-35%o) on the mortality pattern of three important mussel species, viz. a freshwater mussel Dreissena polymorpha, a brackish water mussel Mytilopsis leucophaeata and a marine mussel Mytilus edulis under different temperatures (36-41 degrees C). The mussels in the 10 mm size group exposed to 36 degrees C showed 100% mortality after 38 min (D. polymorpha), 84 min (M. edulis) and 213 min (M. leucophaeata). The effect of mussel size on M. edulis and M. leucophaeata mortality at different temperatures was significant, with the largest size group of mussels showing greater resistance, while no significant size-dependence was observed in the case of D. polymorpha. All the three mussel species collected during the non-breeding season (June-October). Nutritional status had no significant influence on the thermal tolerance of the three mussels; fed and non-fed mussels showed 100% mortality at comparable rates. Acclimation temperature had a significant effect on the mortality of all three species. Survival time at any given target temperature increased with increasing acclimation temperature. The acclimation salinity showed no significant effect on the thermal tolerance of the three mussel species. In comparison, M. leucophaeata was more tolerant to high temperature stress than the other two species. The present studies clearly show that various factors can influence the mortality of D. polymorpha, M. edulis and M. leucophaeata to elevated temperatures. The results, therefore, suggest that if heat treatment were to be used as a control measure for these mussels, it has to be employed judiciously, depending on the mussel species, mussel size, breeding season, water temperature and salinity.     

The effect of temperature on caecal fermentation processes in a poikilothermic mammal, Heterocephalus glaber

1. 1.|The effect of temperature on caecal function was examined in the naked mole-rat Heterocephalus glaber, a poikilothermic mammal, which consumes a high proportion of fibre in its natural diet.

2. 2.|The temperature of optimal caecal function was determined from fermentation data measure at three specifically chosen temperatures (28, 33 and 40°C).

3. 3.|There was no significant difference between gas production at 33 and 40°C, however, gas production was significantly lower at 28°C.

4. 4.|The relative proportions of the gases produced were markedly different at 33 and 40°C (P ≤ 0.01). More methane and hydrogen were produced at 33°C than at 40°C.

5. 5.|These data suggest that microbial organisms within the caecum were active and functioning more effectively at 33°C (the preferred body temperature of the naked mole-rat) than at the other two temperatures.

The effect of incubation temperatuer on oxygen consumption and organ growth in domestic-fowl embryos

1. 1.|Oxygen consumption and organ growth were measured in domestic-fowl embryos incubated at different temperatures (36, 38 and 40°C).

2. 2.|Embryonic oxygen consumption was highest at an incubation temperature of 40°C and lowest at 36°C. These differences were ascribed largely to variations in embryo size at different incubation temperatures.

3. 3.|At incubation temperatuers of 40 and 38°C, there was a plateau in oxygen consumption late in incubation, but this was not apparent at 36°C.

4. 4.|At 36°C, some tissues (e.g. eyeballs) were “spared” the repression of growth that characterized the embryo as a whole, while other tissues (e.g. stomach) incurred a much greater growth reduction. Similarly, at 40°C, stomach growth exceeded that of the embryo as a whole, while the eyeballs were largely spared the enhanced growth.

5. 5.|A simple index of tissue age revealed that, in general, there were consensual changes in tissue maturity and growth at different temperatures but that there were some disparities between growth and maturity in individual organs.

Alteration of heat sensitivity by treatment with nonpermissive temperature or cycloheximide in temperature-sensitive CHO mutant tsH1 cell

1. 1.|The temperature-sensitive mutant CHO-tsH1 and wild type (CHO-SC) cells became thermal resistant when cells were treated for either 2 h at 39.5°C before heating at 43°C or 2 h with 10 μg/ml cycloheximide (CHM) before and during heating at 43°C.

2. 2.|There was a 2000-fold increase in survival after 2.5 h at 43°C by preincubation at 39.5°C in both cell types. There was also a 200- or 700-fold increase in survival after 2.5 h at 43°C by treatment with CHM in tsH1 or SC cell type respectively.

3. 3.|In contrast to the effects at 43°C, at 41.8°C these protective effects were not evident in tsH1 cells. In wild type, however, there was an 800- or 1800-fold increase in survival after 8 h at 41.8°C by preincubation at the temperature of 39.5°C or treatment with CHM, respectively.

4. 4.|Therefore, these results suggest that killing of tsH1 at low temperature hyperthermia (41.8°C) is probably due to denaturation of thermolabile leucyl-tRNA synthetase.

5. 5.|The denaturation of this enzyme may not be protected by inhibition of protein synthesis by preincubation at the nonpermissive temperature of 39.5°C or by CHM.

Acclimation to temperature and death at changing lethal temperatures in the freshwater fish Chalcalburnues chalcoides

1. 1.|In the freshwater fish Chalcalburnus chalcoides, an increase in the body (standard) size caused decreases in the upper LT-50 from 36.6° to 36.0°C and lower LT-50 from 6.3° to 5.3°C

2. 2.|The fish acclimated to constant temperatures between 10°C and 30°C showed reasonable heat acclimation and also reasonable cold acclimation. Thus, an increase in the acclimation temperature from 10°C to 30°C caused increases in the upper LT-50 from 34° to 36.2°C and the lower LT-50 from 1.25 to 6.5°C.

3. 3|The mean survival time — temperature curves of 10°, 20° and 30°C acclimated fish at various constant temperatures showed decreased in the survival tim ewith increasing lethal temperatures. Furthermore, an increase in the acclimation temperature causes a shift in the survival duration-temperature curve to the right, i.e., the fish become more heat resistant. Thus, the mean survival duration of 10°, 20° and 30°C acclimated fish at 35°C were 7.5, 79.6 and 530 minutes, respectively.

4. 4.|The effect of the thermal experience to changing lethal temperatures depends on the first lethal temperature to which the fish were exposed as well as the sequence of temperature changes. In the experiments in which the first lethal temperatures were between 32° and 34°C and the temperature was varied in an ascending order, their thermal resistance was increased and the fish required 114 to 174% of the expected lethal doses to die while in the experiments in which the starting temperature were between 38° and 40°C and the temperature varied in descending order, the fish become more sensitive to the upper lethal temperature and they died after receiving only 62 to 81% of the expected lethal doses. Thus, with a gradual increase in the lethal temperature, the fish show additional acclimation in the zone of resistance which in turn causes an increase in the thermal resistance. This may have ecological significance in nature.

Skin temperatures, thermosensory and pleasantness estimates in case of heterogeneity in the thermal environment

1. 1. Seven thermal conditions were imposed on male sitting subjects (slightly clothed: 0.6 clo).

2. 2. A thermal mannikin was also used to determine the exact operative temperature, T₀.

3. 3. Conditions were: uniform (UN: all parameters at 24.5°C, air velocity at 0.15 ms⁻¹), heated ceiling (HC at 45°C), heated floor (HF at 34°C), cold floor (CF at 14°C), two conditions of one cold wall at 6°C (CW1 and CW2 respectively with and without air temperature compensation) and increased air velocity (AV at 0.4 ms⁻¹).

4. 4. Local skin temperatures and answers to questionnaires were obtained.

5. 5. Skin temperature variations were affected by conditions and slight T₀ changes.

6. 6. Comfort judgments were fairly well related to T₀, especially when expressed as differences between actual non-uniform environment and the uniform one.

7. 7. It is concluded that, in case of non-uniform environments close to thermoneutral zone, thermal comfort or discomfort reflects the climate alterations better than the thermal sensation does.