Increasing Acclimation Temperature Research Articles

Effect of temperature on exercise metabolism, hypoxia tolerance, and RNA-seq analysis in Sinilabeo rendahli from the Yangtze River, China

Temperature variation affects the growth performance of fish species due to growing constraints and trade-off on physiological functions. Here we experimentally investigated several metabolic and physiological parameters in Sinilabeo rendahli, an endemic fish species found in the Yangtze River in China. After a 14-day acclimation period, we measured routine metabolic rate (RMR), individual metabolic rate (MO2), temperature quotient (Q10), loss of equilibrium (LOE), and critical oxygen tension (Pcrit) at three different temperatures (15, 20, and 25°C). Moreover, we sampled the muscle tissue from juvenile S. rendahli under experimental conditions after 28 days of acclimation and performed transcriptome-RNA sequencing (RNA-seq). The Pcrit of the fish at the above acclimation temperatures were determined to be 1.07, 1.28, and 1.33 mg·L−1, respectively, and corresponded with increasing acclimation temperatures (15–25°C). RMR was positively correlated with Pcrit (r = 0.4711, P = 0.0201), negatively correlated with LOE (r = −0.4284, P = 0.0367), and significantly positively correlated with MRcrit (r = 0.8797, P < 0.001) at temperatures ranging from 15 to 25°C. In addition, a total of 4,710 differentially expressed genes (DEGs) were identified. The results of DEG analysis and KEGG clustering analysis indicated that energy metabolism played a central role in thermal stress in S. rendahli for the major upregulated genes. This was followed by autophagy, mitophagy, cardiac muscle contraction, extracellular matrix (ECM)-receptor interaction, and protein digestion and absorption. This study is significant for understanding the adaptive response of S. rendahli to thermal stress. Even more importantly, this study demonstrates that S. rendahli is more suitable for cold-water life.

There and back again: A meta-analytical approach on the influence of acclimation and altitude in the upper thermal tolerance of amphibians and reptiles

Realistic predictions about the impacts of climate change onbiodiversity requires gathering ecophysiological data and the critical thermal maxima (CTMax) is the most frequently used index to assess the thermal vulnerability of species. In the present study, we performed a systematic review to understand how acclimation and altitude affect CTMax estimates for amphibian and non-avian reptile species. We retrieved CTMax data for anurans, salamanders, lizards, snakes, and turtles/terrapins. Data allowed to perform a multilevel random effects meta-analysis to answer how acclimation temperature affect CTMax of Anura, Caudata, and Squamata and also meta-regressions to assess the influence of altitude on CTMax of frogs and lizards. Acclimation temperature influenced CTMax estimates of tadpoles, adult anurans, salamanders, and lizards, but not of froglets. In general, the increase in acclimation temperature led to higher CTMax values. Altitudinal bioclimatic gradient had an inverse effect for estimating the CTMax of lizards and anuran amphibians. For lizards, CTMax was positively influenced by the mean temperature of the wettest quarter. For anurans, the relationship is inverse; we recover a trend of decreasing CTMax when max temperature of warmest month and precipitation seasonality increase. There is an urgent need for studies to investigate the thermal tolerance of subsampled groups or even for which we do not have any information such as Gymnophiona, Serpentes, Amphisbaena, and Testudines. Broader phylogenetic coverage is mandatory for more accurate analyses of macroecological and evolutionary patterns for thermal tolerance indices as CTMax.

Critical thermal maximum and minimum of juvenile shortnose sturgeon ( Acipenser brevirostrum ) acclimated to 12 and 18°C

Thermal tolerance is crucial to understanding the biology of fishes and their responses to changes in temperatures, such as that produced by climate change. Shortnose sturgeon (Acipenser brevirostrum) is an endangered species (USA) and a species of special concern (Canada) that live on the eastern coast of North America. Although previous studies have focused on the acute critical thermal maximum (CTmax) of shortnose sturgeon, nothing is known with respect to their acute critical thermal minimum (CTmin) and the overall thermal tolerance of this species. This study examined the upper (CTmax) and lower (CTmin) thermal tolerance of shortnose sturgeon acclimated to 12 and 18°C. CTmax increased with increasing acclimation temperature; however, there was no significant relationship between acclimation temperature and CTmin. Taken together, the results of the present study show that shortnose sturgeon are well adapted to tolerate acute exposures to both cold and warm water environments.

Food quality mediates responses ofDaphnia magnalife history traits and heat tolerance to elevated temperature

AbstractSurface waters are warming due to climate change, potentially pushing aquatic organisms closer to their thermal tolerance limits. However, cyanobacterial blooms are expected to occur more often with rising temperature, increasing the likelihood of poor‐quality food available for herbivorous zooplankton. Zooplankton can adapt locally by genetic differentiation or via adaptive phenotypic plasticity to increasing temperatures, but there is limited knowledge on how these processes may be affected by food quality limitation imposed by cyanobacteria.To test the effects of cyanobacteria‐mediated food quality on local temperature adaptation, we measured juvenile somatic growth and reproduction of fiveDaphnia magnaclones from different latitudinal origin grown on three food qualities at 20, 24, and 28°C. Additionally we estimated short‐term heat tolerance, measured as knockout time (time to immobility) at lethally high temperature, of two clones acclimated to the three temperatures and two food quality levels to test for the effects of food quality on adaptive plastic responses.As expected, clones from lower latitudes showed on average better somatic growth and reproduction than clones from higher latitudes at higher temperatures. However, the difference in somatic growth diminished with increasing cyanobacteria abundance in the diet, suggesting constraints on local genetic adaptation under predicted decreases in food quality. As expected, short‐term heat tolerance of the clones generally increased with increasing acclimation temperature. However, heat tolerance of animals acclimated to the highest temperature was larger when grown at medium than at good food quality, whereas the opposite response was observed for animals acclimated to the lowest temperature. This suggests a better adaptive phenotypic response of animals to elevated temperatures under higher cyanobacteria abundance, and thus shows an opposite pattern to the results for somatic growth.Overall, we demonstrate that food quality limitation can mediate responses ofD. magnalife history traits and heat tolerance to increasing temperatures, and that the effects differ depending on the time scale studied, that is, mid‐term (somatic growth) versus short‐term (tolerance to acute heat stress). These aspects will need further attention to accurately predict of how organisms will cope with future global warming by local adaptation and adaptive phenotypic plasticity.

Metabolic plasticity improves lobster\u2019s resilience to ocean warming but not to climate-driven novel species interactions

Marine species not only suffer from direct effects of warming oceans but also indirectly via the emergence of novel species interactions. While metabolic adjustments can be crucial to improve resilience to warming, it is largely unknown if this improves performance relative to novel competitors. We aimed to identify if spiny lobsters—inhabiting a global warming and species re-distribution hotspot—align their metabolic performance to improve resilience to both warming and novel species interactions. We measured metabolic and escape capacity of two Australian spiny lobsters, resident Jasus edwardsii and the range-shifting Sagmariasus verreauxi, acclimated to current average—(14.0 °C), current summer—(17.5 °C) and projected future summer—(21.5 °C) habitat temperatures. We found that both species decreased their standard metabolic rate with increased acclimation temperature, while sustaining their scope for aerobic metabolism. However, the resident lobster showed reduced anaerobic escape performance at warmer temperatures and failed to match the metabolic capacity of the range-shifting lobster. We conclude that although resident spiny lobsters optimise metabolism in response to seasonal and future temperature changes, they may be unable to physiologically outperform their range-shifting competitors. This highlights the critical importance of exploring direct as well as indirect effects of temperature changes to understand climate change impacts.

Genetic variation for upper thermal tolerance diminishes within and between populations with increasing acclimation temperature in Atlantic salmon.

Populations may counteract lasting temperature changes or recurrent extremes through plasticity or adaptation. However, it remains underexplored how outbreeding, either naturally, unintentionally, or facilitated, may modify a local response potential and whether genotype-by-environment interactions or between-trait correlations can restrict this potential. We quantified population differences and outbreeding effects, within-population genetic variation, and plasticity of these, for thermal performance proxy traits using 32 pedigreed wild, domesticated, and wild-domesticated Atlantic salmon families reared under common-garden conditions. Following exposure to ambient cold (11.6 °C) or ~4° and ~8° warmer summer temperatures, populations differed notably for body length and critical thermal maximum (CTmax) and for thermal plasticity of length, condition, and CTmax, but not for haematocrit. Line-cross analysis suggested mostly additive and some dominant outbreeding effects on means and solely additive outbreeding effects on plasticity. Heritability was detected for all traits. However, with increasing acclimation temperature, differences in CTmax between populations and CTmax heritability diminished, and CTmax breeding values re-ranked. Furthermore, CTmax and body size were negatively correlated at the genetic and phenotypic levels, and there was indirect evidence for a positive correlation between growth potential and thermal performance breadth for growth. Thus, population differences (including those between wild and domesticated populations) in thermal performance and plasticity may present a genetic resource in addition to the within-population genetic variance to facilitate, or impede, thermal adaptation. However, unfavourable genotype-by-environment interactions and negative between-trait correlations may generally hamper joint evolution in response to an increase in average temperature and temporary extremes.

Increased acute thermal tolerance and little change to hematology following acclimation to warm water in juvenile Striped Bass, Morone saxatilis

Striped Bass naturally inhabit a wide range of temperatures, yet little is known about the processes that control their acute and chronic temperature limits. The objective of this study was to determine the effect of temperature acclimation on acute thermal maxima and physiology of juvenile Striped Bass. Juvenile fish were acclimated to 15, 25 or 30 °C for 4 weeks, then split into two sampling groups: post-acclimation and post-critical thermal maximum trials. We found that fish survived in all acclimation temperatures with little change to underlying hematology, and that critical thermal maximum (CTmax) increased with increasing acclimation temperature. At CTmax, fish acclimated to 30 °C had elevated plasma cortisol, lactate and potassium levels. These results suggest that, while 30 °C is likely to be outside their thermal optima, Striped Bass can survive at high temperatures. This ability to cope with warm temperatures may provide an advantage with increasing global temperatures.

Thermal tolerance and routine oxygen consumption of convict cichlid, Archocentrus nigrofasciatus, acclimated to constant temperatures (20°C and 30°C) and a daily temperature cycle (20°C → 30°C).

Organismal temperature tolerance and metabolic responses are correlated to recent thermal history, but responses to thermal variability are less frequently assessed. There is great interest in whether organisms that experience greater thermal variability can gain metabolic or tolerance advantages through phenotypic plasticity. We compared thermal tolerance and routine aerobic metabolism of Convict cichlid acclimated for 2weeks to constant 20°C, constant 30°C, or a daily cycle of 20 → 30°C (1.7°C/h). Acute routine mass-specific oxygen consumption ([Formula: see text]O2) and critical thermal maxima/minima (CTMax/CTMin) were compared between groups, with cycle-acclimated fish sampled from the daily minimum (20°C, 0900h) and maximum (30°C, 1600h). Cycle-acclimated fish demonstrated statistically similar CTMax at the daily minimum and maximum (39.0°C, 38.6°C) but distinct CTMin values, with CTMin 2.4°C higher for fish sampled from the daily 30°C maximum (14.8°C) compared to the daily 20°C minimum (12.4°C). Measured acutely at 30°C, [Formula: see text]O2 decreased with increasing acclimation temperature; 20°C acclimated fish had an 85% higher average [Formula: see text]O2 than 30°C acclimated fish. Similarly, acute [Formula: see text]O2 at 20°C was 139% higher in 20°C acclimated fish compared to 30°C acclimated fish. Chronic [Formula: see text]O2 was measured in separate fish continually across the 20 → 30°C daily cycle for all 3 acclimation groups. Chronic [Formula: see text]O2 responses were very similar between groups between average individual hourly values, as temperatures increased or decreased (1.7°C/h). Acute [Formula: see text]O2 and thermal tolerance responses highlight "classic" trends, but dynamic, chronic trials suggest acclimation history has little effect on the relative change in oxygen consumption during a thermal cycle. Our results strongly suggest that the minimum and maximum temperatures experienced more strongly influence fish physiology, rather than the thermal cycle itself. This research highlights the importance of collecting data in both cycling and static (constant) thermal conditions, and further research should seek to understand whether ectotherm metabolism does respond uniquely to fluctuating temperatures.

The thermal acclimation potential of maximum heart rate and cardiac heat tolerance in Arctic char (Salvelinus alpinus), a northern cold-water specialist.

Increasing heart rate (ƒH) is a central, if not primary mechanism used by fishes to support their elevated tissue oxygen consumption during acute warming. Thermal acclimation can adjust this acute response to improve cardiac performance and heat tolerance under the prevailing temperatures. We predict that such acclimation will be particularly important in regions undergoing rapid environmental change such as the Arctic. Therefore, we acclimated Arctic char (Salvelinus alpinus), a high latitude, cold-adapted salmonid, to ecologically relevant temperatures (2, 6, 10, 14 and 18°C) and examined how thermal acclimation influenced their cardiac heat tolerance by measuring the maximum heart rate (ƒHmax) response to acute warming. As expected, acute warming increased ƒHmax in all Arctic char before ƒHmax reached a peak and then became arrhythmic. The peak ƒHmax, and the temperature at which peak ƒHmax (Tpeak) and that at which arrhythmia first occurred (Tarr) all increased progressively (+33%, 49% and 35%, respectively) with acclimation temperature from 2 to 14°C. When compared at the same test temperature ƒHmax also decreased by as much as 29% with increasing acclimation temperature, indicating significant thermal compensation. The upper temperature at which fish first lost their equilibrium (critical thermal maximum: CTmax) also increased with acclimation temperature, albeit to a lesser extent (+11%). Importantly, Arctic char experienced mortality after several weeks of acclimation at 18°C and survivors did not have elevated cardiac thermal tolerance. Collectively, these findings suggest that if wild Arctic char have access to suitable temperatures (<18°C) for a sufficient duration, warm acclimation can potentially mitigate some of the cardiorespiratory impairments previously documented during acute heat exposure.

Thermal Tolerance and Metabolism of Archocentrus nigrofasciatus Acclimated to a Large Daily Temperature Fluctuation Reflect its Success as an Invasive Species

Fish exhibit thermal tolerance and metabolism correlated to recent thermal history, and more studies should examine species’ responses to large fluctuations in daily temperatures. We compared thermal tolerance and metabolic responses between fish acclimated to constant temperatures and a large, daily thermal cycle of 10°C. Black Convict cichlid (Archocentrus nigrofasciatus) is a freshwater teleost native to Central America, with non‐native populations established in numerous locations. Black Convict cichlid were acclimated for two weeks to constant 20°C or 30°C, or a daily cycle of 20–30°C (“cycling group”, ~0900–1500 hrs). Following acclimation, routine metabolism (oxygen consumption, Mo2) and Critical thermal maxima/minima (CTmax/CTmin) were measured. Critical thermal limits were compared via ANOVA, with the cycling group sampled from both the daily minimum at 20°C (0900 hrs) and daily maximum at 30°C (1600 hrs). CTmax (0.3°C per degree of acclimation) and CTmin (0.4 °C per degree of acclimation) increased with acclimation. CTmax for the cycling group were 0.7°C higher when sampled from the maximum 30°C (39.3°C) of the daily cycle compared to 20°C (38.6°C). CTmin values for the cycling group were 2.2°C higher when sampled from the maximum 30°C (14.6°C) of the daily cycle compared to 20°C (12.4°C). Mo2 was measured acutely at 20°C and 30°C for each acclimation group, with the cycling group sampled from the daily minimum at 20°C (0900 hrs) and daily maximum at 30°C (1600 hrs). ANOVA showed that mass‐specific Mo2 decreased with increasing acclimation temperature for fish measured acutely at 30°C, where fish acclimated to 20°C (Mo2 = 0.329 mg/h/g) demonstrated an 84% higher Mo2 than fish acclimated to 30°C (Mo2 = 0.178 mg/h/g). Mass‐specific Mo2 also decreased with increasing acclimation temperature for fish measured acutely at 20°C, where fish acclimated to 20°C (Mo2 = 0.170 mg/h/g) demonstrated a 139% higher Mo2 than fish acclimated to 30°C (Mo2 = 0.071 mg/h/g). Mo2 was measured continually across the 24h daily thermal acclimation cycle of 20 – 30°C for all groups. Total oxygen consumption across the 24h cycle was highest for the constant 30°C group naively exposed to the cycle and lowest for the cycling group. Black Convict cichlid retains more upper thermal tolerance than lower thermal tolerance with altered thermal acclimation, and this hardy species shows metabolic compensation following high temperature acclimation (30°C) and large, daily cycling temperature acclimation (20 – 30°C). These aspects of fish thermal physiology phenotypes are reflective of a successful invasive fish species that may respond more robustly to impacts from anthropogenic climate change.Support or Funding InformationFunding was provided through startup funds to JE from CSUSM.

Short-term thermal acclimation of dark respiration is greater in non-photosynthetic than in photosynthetic tissues.

Thermal acclimation of plant respiration is highly relevant to climate projections; when included in models, it reduces the future rate of atmospheric CO2 rise. Although all living plant tissues respire, few studies have examined differences in acclimation among tissues, and leaf responses have received greater attention than stems and roots. Here, we examine the short-term temperature acclimation of leaf, stem and root respiration within individuals of eight disparate species acclimated to five temperatures, ranging from 15 to 35 °C. To assess acclimation, we measured instantaneous tissue temperature response curves (14–50 °C) on each individual following a 7-day acclimation period. In leaves and photosynthetic stems, the acclimation temperature had little effect on the instantaneous tissue temperature response of respiration, indicating little to no thermal acclimation in these tissues. However, respiration did acclimate in non-photosynthetic tissues; respiratory rates measured at the acclimation temperature were similar across the different acclimation temperatures. Respiratory demand of photosynthetic tissue increased with acclimation temperature as a result of increased photosynthetic demands, resulting in rates measured at the acclimation temperature that increased with increasing acclimation temperature. In non-photosynthetic tissue, the homeostatic response of respiration suggests that acclimation temperature had little influence on respiratory demand. Our results indicate that respiratory temperature acclimation differs by tissue type and that this difference is the consequence of the coupling between photosynthesis and respiration in photosynthetic, but not non-photosynthetic tissue. These insights provide an avenue for improving the representation of respiratory temperature acclimation in large-scale models.

Thermal preference, tolerance, and thermal aerobic scope in clownfish Amphiprion ocellaris (Cuvier, 1830) predict its aquaculture potential across tropical regions

The clownfish Amphiprion ocellaris is widely distributed in the coral reef ecosystems of tropical and subtropical regions of the West Indo Pacific, an area that hosts economically valuable species, and, thus, a suitable candidate for warm water aquaculture. This study determined the preferred temperature, critical threshold limits, represented by critical thermal maximum and critical thermal minimum, thermal window width, and aerobic metabolic scope of A. ocellaris clownfish acclimated to 20, 23, 26, 29, 32, and 35 °C. A positive response (P < 0.05) occurred when the preferred temperature significantly increased with increasing acclimation temperature. The preferred temperature obtained graphically was 30.0 °C. Acclimation temperature significantly affected the thermal tolerance which increased with acclimation temperature. The thermal window calculated for A. ocellaris was 301.5 °C2. The thermal metabolic scope obtained in animals acclimated at the interval from 23 to 32 °C (P > 0.05) had a mean value of 4240.8 mg O2 h−1 kg−1 w.w., revealing that A. ocellaris is a eurythermal species with a range of optimal physiological performance that closely matches the environmental conditions where it can be farmed. Therefore, the highest value of the thermal aerobic scopes corresponded to the intervals of the preferred temperature obtained for A. ocellaris. These results may partially explain their worldwide distribution pattern, as well as their aquaculture potential in tropical regions.

Impact of Changing Temperature on Critical Thermal Maximum and Metabolic Rate of Uca perplexa and Uca crassipes

This study quantifies thermal tolerance and metabolic rates for two fiddler crab species ( Uca perplexa and Uca crassipes ) exposed to increasing temperatures. Uca perplexa prefers sun-exposed mangal zones, while U. crassipes inhabits shaded as well as sun-exposed areas. A total forty crabs (20 crabs from each species) were collected from the Ambeua mangrove on Kaledupa Island, and transported to the Hoga Island Research Laboratory for testing. Fifteen crabs of each species were used for CTmax trials, and five crabs were used in metabolic trials. Crabs were acclimated for 10 days at 26, 28, or 30°C prior to experimentation. Critical Thermal Maximum (CTmax) was measured by increasing the temperature by 0.3°C per minute until loss of righting responses was observed. A Gilson differential respirometer was used to determine oxygen uptake at 26 and 31°C for each species, and the results used to calculate temperature quotient (Q 10 ) values. While both crab species showed an increase in thermal tolerance with increasing acclimation temperature, U. crassipes was more heat tolerant (CTmax = 42.21°C), than U. perplexa (CTmax = 41.95°C). Likewise, U. crassipes was less metabolically sensitive to temperature increase (Q 10 = 1.33) than U. perplexa , (Q 10 = 2.38) suggesting that U. crassipes is better adapted to high environmental temperature conditions.

Effect of temperature on critical oxygen tension (Pcrit) and gill morphology in six cyprinids in the Yangtze River, China

We evaluated the hypoxia tolerance capacities of fish in response to a range of temperatures which they often experience in aquaculture. We selected six cyprinids in the Yangtze River that were closely related in their phylogeny and widely used in the Chinese aquaculture industry as experimental animals: juvenile qing bo Spinibarbus sinensis, Chinese bream Parabramis pekinensis, grass carp Ctenopharyngodon idellus, big head carp Aristichthys nobilis, silver carp Hypophthalmichthys molitrix and common carp Cyprinus carpiovar Jian. We measured individual metabolic rate (ṀO2) and calculated the routine metabolic rate (RMR), Q10 and critical oxygen tension (Pcrit) after two weeks of acclimation at either 10, 15, 20, 25 or 30 °C. Gill morphology was also examined. A variety of Pcrit responses was observed: the Pcrit increased (qing bo), decreased (Chinese bream and grass carp) or was conserved (big head carp, silver carp and common carp) with increasing acclimation temperatures (10 - 30 °C). Apparent thermal-induced gill remodeling was found in three (grass carp, big head carp and silver carp) of the six cyprinids studied, with common carp also exhibiting some degree of gill structure modification. RMR was positively correlated with Pcrit at temperatures ranging from 10 to 30 °C in qing bo and big head carp; however, such significant correlation was not found in the remaining cyprinids, possibly due to their gill remodeling potential during thermal changes and thus an increased lamellar surface area at higher temperatures.

Temperature-induced changes in body lipid composition affect vulnerability to oxidative stress in Daphnia magna.

Optimizing physiological functions at different temperatures includes shifts in the lipid composition of ectothermic animals. These shifts may be associated with changes in lipid peroxidation in response to oxidative stress, because lipids differ in their susceptibility to oxidative damage. Polyunsaturated fatty acids (PUFA) are particular prone to peroxidation. Here, we analyzed changes in the fatty acid composition, cholesterol content and the level of oxidative damage as thiobarbituric reactive substances (TBARS) in Daphnia magna as a function of acclimation temperature. The total fatty acid content was highest in cold-acclimated animals. The relative share of most PUFA decreased with increasing acclimation temperature. In contrast, the contribution of saturated and monounsaturated fatty acids (SFA and MUFA) increased with acclimation temperature, although the latter to a lower extent. Cholesterol content remained unchanged. The level of oxidative damage was lowest in animals reared at warm temperatures, most likely reflecting their lowest content of PUFA. Heat exposure (1 h at 33 °C) caused the highest increase in lipid peroxidation in cold-acclimated animals, containing more PUFA. Our data suggest that cold-induced adjustments in the body lipid composition increase the vulnerability of zooplankton to heat-induced oxidative stress. In particular, animals performing diel vertical migration may be highly susceptible to temperature-induced lipid damage.

The analysis and interpretation of critical temperatures.

Critical temperatures are widely used to quantify the upper and lower thermal limits of organisms. But measured critical temperatures often vary with methodological details, leading to spirited discussions about the potential consequences of stress and acclimation during the experiments. We review a model based on the simple assumption that failure rate increases with increasing temperature, independent of previous temperature exposure, water loss or metabolism during the experiment. The model predicts that mean critical thermal maximal temperature (CTmax) increases non-linearly with starting temperature and ramping rate, a pattern frequently observed in empirical studies. We then develop a statistical model that estimates a failure rate function (the relationship between failure rate and current temperature) using maximum likelihood; the best model accounts for 58% of the variation in CTmax in an exemplary dataset for tsetse flies. We then extend the model to incorporate potential effects of stress and acclimation on the failure rate function; the results show how stress accumulation at low ramping rate may increase the failure rate and reduce observed values of CTmax We also applied the model to an acclimation experiment with hornworm larvae that used a single starting temperature and ramping rate; the analyses show that increasing acclimation temperature significantly reduced the slope of the failure rate function, increasing the temperature at which failure occurred. The model directly applies to critical thermal minima, and can utilize data from both ramping and constant-temperature assays. Our model provides a new approach to analyzing and interpreting critical temperatures.

Scaling from Metabolism to Population Growth Rate to Understand How Acclimation Temperature Alters Thermal Performance.

The mean and variance of environmental temperature are changing as a consequence of human activities. Ectotherms are sensitive to these temperature changes in the short term, typically displaying a unimodal response of most biological rates to temperature (thermal performance curves; TPCs). Many organisms, however, may acclimate or evolve in response to new temperature regimes. In particular, population growth rate TPCs (r TPCs) reflect the ability to maintain positive growth under a range of temperatures, and therefore shifts in r TPCs due to acclimation are fundamental to our understanding of how ectotherms will respond to changes in climate. Here, we derive a model for r TPCs rooted in temperature dependent metabolic rate (through enzyme kinetics and activity). We then use this model to interpret the effects of acclimation to different temperatures on r TPCs of the protist Paramecium bursaria. Intermediate acclimation temperatures generally resulted in higher upper critical thermal limits, thermal optima, maximum population growth rate, and the area under the TPC. Lower critical thermal limits increased linearly with acclimation temperature, causing a decrease in thermal breadth with increased acclimation temperature. Thus, rather than showing improved performance at the acclimation temperature, P. bursaria appeared to pay a price at all temperatures for acclimating to higher temperatures. The fits of our data to our model also suggest that changes in the structure and function of metabolic enzymes may underlie the changes in the TPCs. Specifically, our results suggest that both the delta heat capacity and delta enthalpy of formation of metabolic enzymes may have increased with acclimation. Since these two factors are correlated across acclimation temperatures, our data also suggest potential trade-offs that may constrain changes in TPCs.

Modulation of acetylcholine esterase activity in the brain and muscle of Horabagrus brachysoma acclimated to increasing temperatures

The present study investigated the effect of increasing acclimation temperatures on the acetylcholine esterase (AChE) activity in the brain and muscle of an endemic catfish Horabagrus brachysoma. Fish were acclimated to 26 (ambient), 31, 33 and 36°C for 30 days. The AChE activity significantly decreased (P<0.05) in fish acclimated at 36°C. The results indicated that, a temperature of 36°C was stressful to H. brachysoma, which may lead to behavioural changes in the fish

Oxygen Consumption and Lethal Dissolved Oxygen Level of Hybrids of Siniperca chuatsi♀ × S. scherzeri♂

Oxygen consumption rate (OCR) and lethal dissolved oxygen levels (DO) of the hybrids (225.3 ± 4.6 g) of Siniperca chuatsi ♀ × S. scherzeri ♂, were determined after acclimating the fish to 15, 20, 26 and 30°C for 20 days. The same parameters were measured for hybrids with different body weight (146.8 ± 6.3 g, 234.3 ± 8.4 g, 273.9 ± 3.3 g, 327 ± 5.1 g) at 26 °C. OCR increased significantly (P &lt;0.05) with increasing acclimation temperature between 20-26°C, and decreased with increasing body weight. Final preferred temperature estimated from the Q10 was between 26-30°C. The lethal DO concentration for the hybrids at 30°C was significantly higher (P &lt;0.05) than at other temperatures. OCR over the daily cycle under natural lighting conditions was also determined at 26°C. It showed a circadian rhythm with the lowest point at 0830 and peak rates at 1430. Results show that the hybrid has a higher stress tolerance and higher stocking density than the female parent S. chuatsi and indicate their culture potential in subtropical freshwater regions.

Temperature-dependent physiological and biochemical responses of the marine medaka Oryzias melastigma with consideration of both low and high thermal extremes

This study aimed to investigate temperature effect on physiological and biochemical responses of the marine medaka Oryzias melastigma larvae. The fish were subjected to a stepwise temperature change at a rate of 1°C/h increasing or decreasing from 25°C (the control) to six target temperatures (12, 13, 15, 20, 28 and 32°C) respectively, followed by a 7-day thermal acclimation at each target temperature. The fish were fed ad libitum during the experiment. The results showed that cumulative mortalities were significantly increased at low temperatures (12 and 13°C) and at the highest temperature (32°C). For the survivors, their growth profile closely followed the left-skewed ‘thermal performance curve’. Routine oxygen consumption rates of fish larvae were significantly elevated at 32°C but suppressed at 13 and 15°C (due to a high mortality, larvae from 12°C were not examined). Levels of heat shock proteins and activities of malate dehydrogenase and lactate dehydrogenase were also measured in fish larvae exposed at 15, 25 and 32°C. The activities of both enzymes were significantly increased at both 15 and 32°C, where the fish larvae probably suffered from thermal discomfort and increased anaerobic components so as to compensate the mismatch of energy demand and supply at these thermal extremes. Coincidently, heat shock proteins were also up-regulated at both 15 and 32°C, enabling cellular protection. Moreover, the critical thermal maxima and minima of fish larvae increased significantly with increasing acclimation temperature, implying that the fish could develop some degrees of thermal tolerance through temperature acclimation.