Effects Of Temperature Acclimation Research Articles

Combined effects of temperature acclimation and cadmium exposure on mitochondrial function in eastern oystersCrassostrea virginicaGmelin (Bivalvia: Ostreidae)

Cadmium and temperature have strong impacts on the metabolic physiology of aquatic organisms. To analyze the combined impact of these two stressors on aerobic capacity, effects of Cd exposure (50 microg/L) on mitochondrial function were studied in oysters (Crassostrea virginica) acclimated to 12 and 20 degrees C in winter and to 20 and 28 degrees C in fall. Cadmium exposure had different effects on mitochondrial bioenergetics of oysters depending on the acclimation temperature. In oysters acclimated to 12 degrees C, Cd exposure resulted in elevated intrinsic rates of mitochondrial oxidation, whereas at 28 degrees C, a rapid and pronounced decrease of mitochondrial oxidative capacity was found in Cd-exposed oysters. At the intermediate acclimation temperature (20 degrees C), effects of Cd exposure on intrinsic rates of mitochondrial oxidation were negligible. Degree of coupling significantly decreased in mitochondria from 28 degrees C-acclimated oysters but not in that from 12 degrees C- or 20 degrees C-acclimated oysters. Acclimation at elevated temperatures also increased sensitivity of oyster mitochondria to extramitochondrial Cd. Variation in mitochondrial membrane potential explained 41% of the observed variation in mitochondrial adenosine triphosphate synthesis and proton leak between different acclimation groups of oysters. Temperature-dependent sensitivity of metabolic physiology to Cd has significant implications for toxicity testing and for extrapolation of laboratory studies to field populations of aquatic poikilotherms, indicating the importance of taking into account the thermal regime of the environment.

Effects of acclimation temperature and cadmium exposure on cellular energy budgets in the marine molluskCrassostrea virginica: linking cellular and mitochondrial responses

In order to understand the role of metabolic regulation in environmental stress tolerance, a comprehensive analysis of demand-side effects (i.e. changes in energy demands for basal maintenance) and supply-side effects (i.e. metabolic capacity to provide ATP to cover the energy demand) of environmental stressors is required. We have studied the effects of temperature (12, 20 and 28 degrees C) and exposure to a trace metal, cadmium (50 microg l(-1)), on the cellular energy budget of a model marine poikilotherm, Crassostrea virginica (eastern oysters), using oxygen demand for ATP turnover, protein synthesis, mitochondrial proton leak and non-mitochondrial respiration in isolated gill and hepatopancreas cells as demand-side endpoints and mitochondrial oxidation capacity, abundance and fractional volume as supply-side endpoints. Cadmium exposure and high acclimation temperatures resulted in a strong increase of oxygen demand in gill and hepatopancreas cells of oysters. Cd-induced increases in cellular energy demand were significant at 12 and 20 degrees C but not at 28 degrees C, possibly indicating a metabolic capacity limitation at the highest temperature. Elevated cellular demand in cells from Cd-exposed oysters was associated with a 2-6-fold increase in protein synthesis and, at cold acclimation temperatures, with a 1.5-fold elevated mitochondrial proton leak. Cellular aerobic capacity, as indicated by mitochondrial oxidation capacity, abundance and volume, did not increase in parallel to compensate for the elevated energy demand. Mitochondrial oxidation capacity was reduced in 28 degrees C-acclimated oysters, and mitochondrial abundance decreased in Cd-exposed oysters, with a stronger decrease (by 20-24%) in warm-acclimated oysters compared with cold-acclimated ones (by 8-13%). These data provide a mechanistic basis for synergism between temperature and cadmium stress on metabolism of marine poikilotherms. Exposure to combined temperature and cadmium stress may result in a strong energy deficiency due to the elevated energy demand on one hand and a reduced mitochondrial capacity to cover this demand on the other hand, which may have important implications for surviving seasonally and/or globally elevated temperatures in polluted estuaries.

Effect of temperature acclimation on metabolism and hemocyanin binding affinities in two crayfish, Procambarus clarkii and Procambarus zonangulus

Procambarus clarkii and Procambarus zonangulus are two of the most widespread crayfish species in North America. In regions where their ranges overlap species composition can vary greatly. The physiological basis for this variable species composition is unknown. Temperature and oxygen level are two parameters that vary in shallow water habitats. We examined the metabolic rate and hemocyanin binding affinities in relation to thermal history. Temperature acclimation did not have the predicted effect on metabolic rate. Acclimation to high temperature (30 °C) decreased metabolic rate at 35 °C for both species. Low temperature acclimation (10 °C) resulted in 20% mortality in P. clarkii and 100% mortality in P. zonangulus when exposed to 35 °C. The range of P. clarkii is known to extend farther south than that of P. zonangulus, and this response may be a consequence of adaptations to higher temperatures in this range. Hemocyanin binding affinity was directly affected by assay and acclimation temperature. The highest P 50 values were recorded for crayfish of both species acclimated to 10 °C and assayed at 30 °C. There was also a shift in the isoelectric points of hemolymph proteins (possibly due to structural changes) that correlated with and an increase in the hemocyanin binding affinity following acclimation to high temperatures (30 °C) in both species.

Thermal history-dependent expression of the hsp70 gene in purple sea urchins: Biogeographic patterns and the effect of temperature acclimation

Thermal variation associated with large spatial scales is thought to significantly affect the physiology of organisms in marine systems and consequently limit their distribution. To examine this phenomenon, this study compared the heat shock protein ( hsp70) mRNA expression of purple sea urchins ( Strongylocentrotus purpuratus) collected from different geographic locations and those acclimated to different temperatures. Tube feet were removed from S. purpuratus freshly collected from Fogarty Creek, Oregon (FC-OR) and Carpinteria, California (CRP-CA) and from urchins acclimated to 5 °C and 20 °C in the laboratory. Tissue samples were then immediately frozen or incubated at various temperatures between 5 °C and 36 °C for 30 min in vitro. Real-time PCR was used to measure the hsp70 mRNA levels of each sample. The results showed evidence for differential regulation of hsp70 between S. purpuratus in both field and laboratory studies. For example, the incubation temperature that induced maximum hsp70 mRNA expression ( T max) was higher in CRP-CA urchins (26 °C) than those from FC-OR (23 °C). Additionally, although the T max of the two acclimation groups was identical (26 °C), S. purpuratus acclimated to 5 °C failed to induce hsp70 mRNA after incubation at 32 °C, while tube feet of the 20 °C-acclimated urchins remained transcriptionally active. In general, the extent of hsp70 mRNA induction was substantial, exceeding 250-fold in the 5 °C-acclimated urchin tissues after incubation at 26 °C. These data suggest that the thermal variation encountered across S. purpuratus' range is sufficient to effect the regulation of thermally sensitive genes, like hsp70.

The effects of acclimation on thermal tolerance, desiccation resistance and metabolic rate in Chirodica chalcoptera (Coleoptera: Chrysomelidae)

Despite much focus on species responses to environmental variation through space and time, many higher taxa and geographic areas remain poorly studied. We report the effects of temperature acclimation on thermal tolerance, desiccation rate and metabolic rate for adult Chirodica chalcoptera (Coleoptera: Chrysomelidae) collected from Protea nerifolia inflorescences in the Fynbos Biome in South Africa. After 7 days of acclimation at 12, 19 and 25 °C, critical thermal maxima (mean±s.e.: 41.8±0.2 °C in field-fresh beetles) showed less response (<1 °C change) to temperature acclimation than did the onset of the critical thermal minima (0.1±0.2, 1.0±0.2 and 2.3±0.2 °C, respectively). Freezing was lethal in C. chalcoptera (field-fresh SCP −14.6 °C) and these beetles also showed pre-freeze mortality. Survival of 2 h at −10.1 °C increased from 20% to 76% after a 2 h pre-exposure to −2 °C, indicating rapid cold hardening. Metabolic rate, measured at 25 °C and adjusted by ANCOVA for mass variation, did not differ between males and females (2.772±0.471 and 2.517±0.560 ml CO 2 h −1 , respectively), but was higher in 25 °C-acclimated beetles relative to the field-fresh and 12 °C-acclimated beetles. Body water content and desiccation rate did not differ between males and females and did not respond significantly to acclimation. We place these data in the context of measured inflorescence and ambient temperatures, and predict that climate change for the region could have effects on this species, in turn possibly affecting local ecosystem functioning.

Steady-state effects of temperature acclimation on the transcriptome of the rainbow trout heart

Cold-acclimated (CA) phenotype of trout heart was induced by 4-wk acclimation at 4 degrees C and was characterized by 32.7% increase in relative heart mass and 49.8% increase in ventricular myocyte size compared with warm-acclimated (WA; 18 degrees C) fish (P < 0.001). Effect of temperature acclimation on transcriptome of the rainbow trout heart was examined using species-specific microarray chips containing 1,380 genes. After 4 wk of temperature acclimation, 8.8% (122) of the genes were differently expressed in CA and WA hearts, and most of them (82%) were upregulated in the cold (P < 0.01). Transcripts of genes engaged in protein synthesis and intermediary metabolism were most strongly upregulated, whereas genes contributing to the connective tissue matrix were clearly repressed. Extensive upregulation of the genes coding for ribosomal proteins and translation elongation and initiation factors suggest that the protein synthesis machinery of the trout heart is enhanced in the cold and is an essential part of the compensatory mechanism causing and maintaining the hypertrophy of cardiac myocytes. The prominent depression of collagen genes may be indicative of a reduced contribution of extracellular matrix to the remodeling of the CA fish heart. Temperature-related changes in transcripts of metabolic enzymes suggest that at mRNA level, glycolytic energy production from carbohydrates is compensated in the heart of CA rainbow trout, while metabolic compensation is absent in mitochondria. In addition, the analysis revealed three candidate genes: muscle LIM protein, atrial natriuretic peptide B, and myosin light chain 2, which might be central for induction and maintenance of the hypertrophic phenotype of the CA trout heart. These findings indicate that extensive modification of gene expression is needed to maintain the temperature-specific phenotype of the fish heart.

The effect of temperature acclimation on myocardial β-adrenoceptor density and ligand binding affinity in African catfish ( Claris gariepinus)

This study assessed the effects of temperature acclimation on myocardial β-adrenoceptor density ( B max) and binding affinity ( K d) in African catfish ( Claris gariepinus) acclimated to 15, 22 and 32 °C. B max values were not significantly different ( P > 0.05) among the three acclimation groups. Conversely, the K d value of the 32 °C acclimation group ( K d = 0.88) was significantly higher ( P = 0.002) than both the 15 °C ( K d = 0.48) and 22 °C ( K d = 0.46) acclimation groups. In addition, K d of rainbow trout ( Oncorhynchus mykiss) was significantly lower ( P < 0.001) and B max significantly higher ( P < 0.05) than that of African catfish at all three acclimation temperatures. These results contrast with those reported previously for temperate species, in which B max is inversely related to acclimation temperature, and counter a previous suggestion that B max is higher in tropical versus temperate species.

Upper temperature tolerances of exotic brackish-water mussel, Mytilopsis leucophaeata (Conrad): An experimental study

The dark false mussel, Mytilopsis leucophaeata is an important mussel colonising the brackish-water systems of temperate and subtropical regions. Of late it has earned notoriety as a biofouling species in industrial cooling water systems. However, there are no published data on the temperature tolerance of this species. This paper presents data on the upper temperature tolerance of this mussel from the view point of biofouling control using thermal methods. In addition to mortality, response of physiological activities such as oxygen consumption, filtration rate, foot activity and byssus thread production were also studied at temperatures varying from 5 to 35 degrees C. Experiments were also carried out to understand the effect of mussel size, breeding condition, nutritional status and acclimation conditions (temperature and salinity) on the mortality pattern. The physiological activities were significantly reduced at temperatures beyond 27.5 degrees C and ceased at 35 degrees C. In 20 mm size group mussels exposed to 37 degrees C, 50% mortality was observed after 85 min and 100% mortality after 113 min. The effect of mussel size on mortality at different temperatures was significant, with the larger size group mussels showing greater resistance. M. leucophaeata collected during the non-breeding season (December-April) were more tolerant to temperature than those collected during the breeding season (June-October). Nutritional status of the mussel had no significant influence on the thermal tolerance of the mussel: fed and starved (non-fed) mussels succumbed to temperature at comparable rates. The effect of acclimation temperature and acclimation salinity on M. leucophaeata mortality at different temperatures was significant. Survival time increased with increasing acclimation temperature and decreased with increasing salinity. In comparison with other co-occurring species such as Mytilus edulis and Dreissena polymorpha, M. leucophaeata appears to be more tolerant to high temperature stress.

Effects of temperature acclimation and age on movement of Cryptolestes ferrugineus (Coleoptera: Laemophloeidae) adults in response to temperature gradients

AbstractAdult Cryptolestes ferrugineus (Stephens) were reared at 30 °C or acclimated to 15, 25, or 35 °C for different periods (2 days or 1, 2, or 5 weeks). Populations 1 day old, 1, 5, 10, or 20 weeks old, or of mixed age were held in 10 cm × 10 cm × 100 cm wheat columns (14.5% ± 0.2% moisture content) with a temperature gradient (10 °C/m, 25–35 °C) or a constant temperature (25 or 30 °C) for 1, 6, or 12 days; movement and distribution were then determined. Acclimation to 25 °C for a short time (less than 2 days) did not influence adults' response to temperature in the wheat column. Adults acclimated to 15 and 35 °C responded differently to temperature in the wheat column, preferring temperatures above 30 and 35 °C, respectively. Increasing the duration of the acclimation to 15 or 35 °C resulted in higher aggregation. Acclimation temperature might be more important than exposure time for influencing insect behaviour. During their movement in the wheat columns, adults were also acclimated to the tested temperatures, and they did not always stay in a warmer area if the "cold" area was warmer than 25 °C. Adults that were 1 day old had a lower response (i.e., less movement) to temperature gradients than the older insects. Among the older insects, the response to temperature gradients did not decrease with increasing age, even at 20 weeks.

Respiratory response to temperature and hypoxia in the zebra mussel Dreissena polymorpha

The effects of temperature acclimation, acute temperature variation and progressive hypoxia on oxygen consumption rates V ̇ o 2 were determined for the zebra mussel Dreissena polymorpha. In the first experiment, after acclimation to 5, 15 or 25 °C for at least 2 weeks, V ̇ o 2 was determined at 5 °C increments from 5 to 45 °C. V o 2 increased in all three acclimation groups from 5 to 30 °C, corresponding to the normal ambient temperature range for this species. Mussels displayed imperfect temperature compensation at temperatures above 15 °C, but exhibited little acclimatory ability below 15 °C. In the hypoxia experiment, V o 2 was determined over the course of progressive hypoxia, from full saturation (oxygen tension [ P o 2]=160 Torr [21.3 kPa]) to a P o 2 at which oxygen uptake ceased (<10 Torr [1.3 kPa]). Mussels were acclimated to either 5, 15 or 25 °C for at least 2 weeks and their respiratory response to progressive hypoxia was measured at three test temperatures (5, 15 and 25 °C). The degree of oxygen regulation increased with increasing test temperature, particularly from 5 to 15 °C, but decreased with increasing acclimation temperature. The decreased metabolic rate observed for warm-acclimated animals, particularly in the upper portion of the temperature range of the zebra mussel, may allow for conservation of organic energy stores during warm summer months. Compared to other freshwater bivalves, D. polymorpha is a relatively poor oxygen regulator, corresponding with its preference for well-oxygenated aquatic habitats. In addition, a new quantitative method for determining the degree of oxygen regulation is presented.

Effects of temperature acclimation on lactate dehydrogenase of cod(Gadus morhua): genetic, kinetic and thermodynamic aspects

The aim of this study was to determine the effects of seasonal temperature variation on the functional properties of lactate dehydrogenase (LDH) from white muscle and liver of Norwegian coastal cod (Gadus morhua) and the possible relevance of LDH allelic variability for thermal acclimation. Two groups of fishes were acclimated to 4 degrees C or 12 degrees C for one year. Polymorphism was observed in only one (Ldh-B) of the three Ldh loci expressed in cod liver and/or muscle. Isozyme expression remained unchanged regardless of acclimation temperature (T(A)). The products of locus Ldh-B comprise only 14-19% (depending on the tissue) of total LDH activities and, consequently, differences between phenotypes are negligible in terms of their effect on LDH total performance. No kinetic (, V(max)) or thermodynamic (E(a), DeltaG) differences were found among Ldh-B phenotypes. Clear kinetic differences were observed between LDH isoforms in the two tissues. However, the Arrhenius activation energy (E(a)) for pyruvate reduction was the same for both tissues (E(a)=47 kJ mol(-1)) at T(A)=12 degrees C. Factors T(A), tissue and phenotype did not reveal a significant effect on the Gibbs free energy change (DeltaG) of the reaction (55.5 kJ mol(-1)). However, at T(A)=4 degrees C, the E(a) was increased (E(a)=53-56 kJ mol(-1)) and the temperature dependence of the constant of substrate inhibition for pyruvate () decreased in both muscle and liver. In conclusion, the strategies of LDH adjustment to seasonal temperature variations in cod involve changes in LDH concentration (quantitative), adjustment of thermodynamic (E(a)) and kinetic () properties of the LDH (modulative) but not the expression of alternative isoforms (qualitative). We assume that the observed increase in E(a) and the decrease of temperature dependence of at low T(A) is the result of structural changes of the LDH molecule (temperature-driven protein folding). We propose a new mechanism of metabolic compensation of seasonal temperature variations - cold acclimation results in changes in the kinetic and thermodynamic properties of LDH in a way that favours aerobic metabolism through reduction of the competition of LDH for pyruvate in normoxic conditions.

Daily variations in the influence of noradrenaline on preferred ambient temperature of the Siberian hamster

Daily variations in sensitivity to noradrenaline (NA) and the activation of nonshivering thermogenesis (NST) are important for survival under a potentially wide range of environmental conditions. However, little is known regarding the ability of the Siberian hamster and other species to activate NST in the day and night when they may be subjected to marked variations in environmental temperature. In this study, the effects of acclimation temperature and time of day on the behavioral thermoregulatory response to NA injections in Siberian hamsters ( Phodopus sungorus) was investigated. Hamsters were acclimated for 4 weeks to 23 °C and a L:D 12:12 h photoperiod. After acclimation, preferred ambient temperatures ( PT a) in saline- and NA-injected animals were measured continuously in the temperature gradient system. NA (0.6 mg/kg; s.c.) was given every 4 h while PT a was monitored. After NA injections there was a rapid drop in PT a, decreasing to ∼15 °C within 10–20 min after each NA injection. Following 4 weeks of acclimation to 10 °C and a L:D 8:16 h photoperiod, the same hamsters were re-tested in the temperature gradient system. Cold acclimation led to an accentuation in the behavioral response with a decrease in PT a of ∼10 °C. The maximal decrease in preferred ambient temperatures was recorded during the light phase of the day and during the second part of the night. Lowering of PT a after NA allows for rapid dissipation of the heat from NST. Overall, the behavioral response reflects the daily changes in brown adipose tissue sensitivity to NA and thus capacity for NST.

Control of brackish water fouling mussel, Mytilopsis leucophaeata (Conrad), with sodium hypochlorite.

Though the Conrad's false mussel, Mytilopsis leucophaeata, is an important fouling animal in industrial cooling water systems, there are no published reports on the tolerance of this species to chlorination. A series of experiments was conducted to determine the effects of mussel size (2-20 mm shell length), season (breeding versus nonbreeding), nutritional status (fed versus starved) and acclimation temperature (5-30 degrees C) on the mortality pattern of M. leucophaeata under continuous chlorination (0.25-5 mg/L). The effect of mussel size on M. leucophaeata mortality in the presence of chlorine was significant, with 10 mm size group mussels showing greater resistance. At 0.25 mg/L residual chlorine, 2 mm size group mussels took 89 days to reach 100% mortality, whereas 10 mm size group mussels took 109 days. M. leucophaeata collected during nonbreeding season (December-April) was more tolerant to chlorine than those collected during breeding season (June-October). Nutritional status of the mussel had no significant influence on the chlorine tolerance of the mussel: fed and starved mussels succumbed to chlorine at equal rates. The effect of acclimation temperature on M. leucophaeata mortality in the presence of chlorine was significant. At 0.5 mg/L residual chlorine, mussels acclimated at 5 degrees C required 99 days to reach 95% mortality, whereas mussels acclimated at 30 degrees C required 47 days. A comparison of present data with previous reports suggests that resistance of M. leucophaeata to chlorination is higher than other mussel species causing fouling problems in The Netherlands ( Mytilus edulis and Dreissena polymorpha).

Temperature acclimation of upper and lower thermal limits and freeze resistance in the nonindigenous brown mussel, Perna perna (L.), from the Gulf of Mexico

Acute and chronic upper and lower thermal limits and freeze resistance were investigated in the nonindigenous brown mussel, Perna perna, from the Texas Gulf of Mexico coast in order to assess its potential distribution in North American coastal waters. This species' long-term, incipient lower and upper thermal limits were 7.5°C and 30°C, congruent with the seasonal ambient water temperature range of 10–30°C reported for other populations worldwide. Effects of temperature acclimation and individual size on survival time were most pronounced on chronic exposures to lethal temperatures approaching incipient lower or upper thermal limits. When exposed to temperature increasing at 0.1°C min–1, the acute upper lethal limit was 44°C regardless of acclimation temperature or individual size. P. perna had a limited freeze resistance, being intolerant of emersion at –2.5°C. This species' narrow incipient thermal limits, limited capacity for temperature acclimation and poor freeze resistance may account for its restriction to subtidal and lower eulittoral zones of cooler subtropical rocky shores. Near extinction of P. perna from Texas Gulf of Mexico waters occurred in the summer of 1997 when mean surface-water temperatures approached its incipient upper limit of 30°C.

The effect of acclimation temperature on the fusion kinetics of lipid vesicles derived from endoplasmic reticulum membranes of rainbow trout ( Oncorhynchus mykiss) liver

Membrane fusion is an obligatory step in many vital cellular processes. The well-established enrichment of bilayer-destabilizing lipids in membranes of poikilotherms subjected to growth at low temperatures leads to the prediction that such membranes will possess a greater propensity to undergo fusion. This hypothesis was explicitly tested in the present study by determining the kinetics of fusion between small unilamellar vesicles (SUVs) prepared from endoplasmic reticulum (ER) membranes of thermally-acclimated (to 5 and 20°C) rainbow trout ( Oncorhynchus mykiss) liver and bovine brain phosphatidylserine (BBPS). At temperatures above 10°C, ER vesicles from 5°C-acclimated trout, fused more rapidly and to a greater extent with BBPS vesicles (by average factors of 1.25- and 1.45-fold, respectively) than ER vesicles of 20°C-acclimated trout. At temperatures >35°C, apparent fusion rates declined while the extent of fusion increased in both acclimation groups. Fusion kinetics were found to be well correlated with and limited by the physical properties and phase state of the BBPS vesicles. These results indicate that dynamic attributes of biological membranes, such as the propensity to undergo fusion, are of potential regulatory significance and are partially conserved when growth or environmental temperature changes.

Effects of low-level chlorination on zebra mussel, Dreissena polymorpha

Mortality pattern of different size groups (5–20 mm shell lengths) of the zebra mussel Dreissena polymorpha (Pallas), was studied in the laboratory under different chlorine concentrations (0.25–3.0 mg l −1). Results showed that exposure time for 100% mortality of mussels significantly decreased with increasing chlorine concentration. For example, mussels in the 10 mm size group exposed to 0.25 mg l −1 chlorine residual took 1080 h to reach 100% mortality whereas those exposed to 3 mg l −1 chlorine took 252 h. All size groups (between 5 and 20 mm shell length) took identical exposure time to reach 100% mortality at given chlorine concentration (between 1 and 3 mg l −1). The effect of acclimation temperature on D. polymorpha mortality in the presence of chlorine was significant. For example, 1026 h is required to reach 95% mortality using 0.5 mg l −1 residual chlorine at 10°C, compared to 456 h at 0.50 mg l −1 chlorine and 25°C. Resistance of D. polymorpha to chlorine appeared to be lower than that for other mussel species in The Netherlands viz., Mytilus edulis L. and Mytilopsis leucophaeata (Conrad). The present study also suggests that 100% mortality data for European populations of D. polymorpha at different chlorine concentrations are similar to those for the North American populations.

Antibody-producing cells correlated to body weight in juvenile chinook salmon (Oncorhynchus tshawytscha) acclimated to optimal and elevated temperatures

The immune response of juvenile chinook salmon (Oncorhynchus tshawytscha) ranging in weight from approximately 10 to 55g was compared when the fish were acclimated to either 13 or 21°C. A haemolytic plaque assay was conducted to determine differences in the number of antibody-producing cells (APC) among fish of a similar age but different body weights. Regression analyses revealed significant increases in the number of APC with increasing body weight when fish were acclimated to either water temperature. These results emphasise the importance of standardising fish weight in immunological studies of salmonids before exploring the possible effects of acclimation temperatures.

Effects of acclimation temperature on enzymatic capacities and mitochondrial membranes from the body wall of the earthworm Lumbricus terrestris

Many ectotherms respond to low temperature by adjusting capacities of enzymes from energy metabolism, restructuring membrane phospholipids and modulating membrane fluidity. Although much is known about the temperature biology of earthworms, it is not known to what extent earthworms employ compensatory changes in enzymatic capacities and membrane physical properties after exposure to low temperature. We examined activities of enzymes from glycolysis and central oxidative pathways as well as fluidity and phospholipid fatty acid composition of mitochondrial membranes prepared from the body wall of the temperate oligochaete Lumbricus terrestris after a one month acclimation to 5° and 15°C. No compensation occurs in central pathways of oxidative metabolism since activities of cytochrome- c oxidase and citrate synthase, when measured at a common temperature, are similar for 5°C and 15°C-acclimated animals. In contrast, activity of pyruvate kinase is elevated 1.3-fold after acclimation to 5°C. Mitochondrial membranes display inverse compensation with respect to temperature (membranes from 5°C animals are more ordered than membranes from 15°C animals). Our results, in combination with earlier reports, indicate that routine metabolism in L. terrestris may be maintained at reduced temperatures with little or no change in enzymatic capacities and inverse compensation of mitochondrial membranes.

Trout Erythrocyte Membranes. Thermoresistivity and thermally induced structural transitions

Differential scanning microcalorimetry and equilibrium thermohemolysis procedure were used to study the effect of acclimation temperature on thermally induced transitions and thermoresistivity of fish (trout) erythrocyte membranes. Strong correlation has been found between the rates and activation energies of erythrocyte thermohemolysis and acclimation temperature. Transition temperatures of five thermodynamically irreversible and one partially reversible transitions at about 87°C as well as the overall shape of microcalorimetric curves of the erythrocyte ghosts do not vary with acclimation temperature. The results suggest an essential conservation of phospholipid microenvironment of membrane skeleton proteins despite the compensatory response in lipid composition of erythrocyte membrane bilayer.

The effects of temperature and swimming speed on instantaneous fuel use and nitrogenous waste excretion of the Nile tilapia.

The effects of acclimation temperature (30 degrees, 20 degrees, and 15 degrees C) and swimming speed on the aerobic fuel use of the Nile tilapia (Oreochromis niloticus; 8-10 g, 8-9-cm fork length) were investigated using a respirometric approach. As acclimation temperature was decreased from 30 degrees C to 15 degrees C, resting oxygen consumption (Mo2) and carbon dioxide excretion (Mco2) decreased approximately twofold, while nitrogenous waste excretion (ammonia-N plus urea-N) decreased approximately fourfold. Instantaneous aerobic fuel usage was calculated from respiratory gas exchange. At 30 degrees C, resting Mo2 was fueled by 42% lipids, 27% carbohydrates, and 31% protein. At 15 degrees C, lipid use decreased to 21%, carbohydrate use increased greatly to 63%, and protein use decreased to 16%. These patterns at 30 degrees C and 15 degrees C in tilapia paralleled fuel use previously reported in rainbow trout acclimated to 15 degrees C and 5 degrees C, respectively. Temperature also had a pronounced effect on critical swimming speed (UCrit). Tilapia acclimated to 30 degrees C had a UCrit of 5.63+/-0. 06 body lengths/s (BL/s), while, at 20 degrees C, UCrit was significantly lower at 4.21+/-0.14 BL/s. Tilapia acclimated to 15 degrees C were unable or unwilling to swim. As tilapia swam at greater speeds, Mo2 increased exponentially; Mo2min and Mo2max were 5.8+/-0.6 and 21.2+/-1.5 micromol O2/g/h, respectively. Nitrogenous waste excretion increased to a lesser extent with swimming speed. At 30 degrees C, instantaneous protein use while swimming at 15 cm/s ( approximately 1.7 BL/s) was 23%, and at UCrit (5.6 BL/s), protein use dropped slightly to 17%. During a 48-h swim at 25 cm/s (2.7 BL/s, approximately 50% UCrit), Mo2 and urea excretion remained unchanged, while ammonia excretion more than doubled by 24 h and remained elevated 24 h later. These results revealed a shift to greater reliance on protein as an aerobic fuel during prolonged swimming.