Effect of the critical thermal maximum on the preferred temperatures of Ictalurus punctatus exposed to constant and fluctuating temperatures

No significant differences were found in the temperature of the onset of behavioural response spasms and equilibrium loss in Ictalurus punctatus maintained in constant and fluctuating temperatures. The preferred temperature was determined in an aquatic gradient to be 29.0°C and the temperatures avoided were 21.7–34.1°C. The temperature that causes the loss of equilibrium of acclimation at constant or fluctuating temperatures changes the organisms final preferendum and the avoided temperatures were significantly different (p<0.05) if compared with the control group. The behavioural response that should be considered as the critical thermal maximum (CTMax) of I. punctatus is the equilibrium loss that reflects a major deep core reaction.     

Giant spiny-frog (<Emphasis Type="Italic">Paa spinosa</Emphasis>) from different populations differ in thermal preference but not in thermal tolerance

To examine whether different thermal environments have induced a change in thermal characteristics, we have conducted a between-population comparison on broad geographic patterns of preferred body temperature and critical thermal maximum in a giant spiny-frog Paa spinosa. We found a bimodal pattern of preferred body temperature during the day, with high preferred body temperature during the inactive diurnal period and low temperature during the active nocturnal period. There were significant differences among six populations of P. spinosa in preferred body temperatures, which decreased along a south to north gradient. Unlike preferred body temperatures, critical thermal maximum did not differ between frogs from the six localities. Although not all characteristics of thermal physiology in P. spinosa underwent parallel changes between the populations, the shift of preferred body temperatures suggests that the features of thermal physiology in the frog may change along a latitudinal gradient in response to different thermal environments.     

Acclimation is beneficial at extreme test temperatures in the Danube crested newt, Triturus dobrogicus (Caudata, Salamandridae)

Despite many studies demonstrating the effect of acclimation on behavioural or physiological traits, considerable debate still exists about the evolutionary significance of this phenomenon. One of the unresolved issues is whether acclimation to warmer temperature is beneficial at treatment or at more extreme test temperatures. To answer this question, we assessed the effect of thermal acclimation on preferred body temperatures ( T _ps), maximum swimming and running speed, and critical thermal maximum ( CT _max) in the Danube crested newt ( Triturus dobrogicus ). Adult newts were kept at 15 °C (control) and 25 °C (treatment) for 8 weeks prior to measurements. We measured T _ps in an aquatic thermal gradient over 24 h, maximum speeds in a linear racetrack at six temperatures (5–33 °C), and CT _max in a continuously heated water bath. T _ps were higher in newts kept at 15 °C than in those kept at 25 °C. The maximum swimming speed did not acclimate. The maximum running speed at 30–33 °C was substantially higher in newts kept at 25 °C than in those kept at 15 °C. CT _max increased with the treatment temperature. Hence, we conclude that the acclimation response to warm temperature is beneficial not at treatment but at more extreme temperatures in newts.  © 2007 The Linnean Society of London, Biological Journal of the Linnean Society , 2007, 90 , 627–636.     

Critical thermal minima and maxima of three freshwater game-fish species acclimated to constant temperatures

A total of 120 critical thermal maxima (CT maxima) and 120 critical thermal minima (CT minima) were determined for channel catfish, largemouth bass and rainbow trout acclimated to three constant temperatures: 20, 25 and 30 °C in catfish and bass, and 10, 15 and 20 °C in trout. Highest mean CT maximum and lowest mean CT minimum measured over these acclimation temperatures were 40.3 and 2.7 °C (catfish), 38.5 and 3.2 °C (bass) and 29.8 and ∼ 0.0 °C (trout). Temperature tolerance data were precise with standard deviations generally less than 0.5 °C. Channel catfish had the largest thermal tolerance scope of the three species while rainbow trout had the lowest tolerance of high temperatures and the highest tolerance of low temperatures. In all species CT minima and CT maxima were highly significantly linearly related to acclimation temperature. Within each species, slopes relating CT maxima to acclimation temperature were approximately half as large as those relating CT minima to acclimation temperature, suggesting that acclimation temperature has a greater influence on tolerance to low rather than high temperatures. Slopes relating both CT minima and CT maxima to acclimation temperature for the two warm-water species were similar and approximately twice those for the rainbow trout. This revised version was published online in July 2006 with corrections to the Cover Date.     

Environmental heterogeneity shapes physiological traits in tropical direct‐developing frogs

1. Tropical ectotherm species tend to have narrower physiological limits than species from temperate areas. As a consequence, tropical species are considered highly vulnerable to climate change since minor temperature increases can push them beyond their physiological thermal tolerance. Differences in physiological tolerances can also be seen at finer evolutionary scales, such as among populations of ectotherm species along elevation gradients, highlighting the physiological sensitivity of such organisms.
2. Here, we analyze the influence of elevation and bioclimatic domains, defined by temperature and precipitation, on thermal sensitivities of a terrestrial direct‐developing frog (Craugastor loki) in a tropical gradient. We address the following questions: (a) Does preferred temperature vary with elevation and among bioclimatic domains? (b) Do thermal tolerance limits, that is, critical thermal maximum and critical thermal minimum vary with elevation and bioclimatic domains? and (c) Are populations from high elevations more vulnerable to climate warming?
3. We found that along an elevation gradient body temperature decreases as environmental temperature increases. The preferred temperature tends to moderately increase with elevation within the sampled bioclimatic domains. Our results indicate that the ideal thermal landscape for this species is located at midelevations, where the thermal accuracy (d_b) and thermal quality of the environment (d_e) are suitable. The critical thermal maximum is variable across elevations and among the bioclimatic domains, decreasing as elevation increases. Conversely, the critical thermal minimum is not as variable as the critical thermal maximum.
4. Populations from the lowlands may be more vulnerable to future increases in temperature. We highlight that the critical thermal maximum is related to high temperatures exhibited across the elevation gradient and within each bioclimatic domain; therefore, it is a response to high environmental temperatures.

     

Too cold is better than too hot: Preferred temperatures and basking behaviour in a tropical freshwater turtle

Thermoregulation is critical to the survival of animals. Tropical environments can be particularly thermally challenging as they reach very high, even lethal, temperatures. The thermoregulatory responses of tropical freshwater turtles to these challenges are poorly known. One common thermoregulatory behaviour is diurnal basking, which, for many species, facilitates heat gain. Recently, however, a north-eastern Australian population of Krefft's river turtles (Emydura macquarii krefftii) has been observed basking nocturnally, possibly to allow cooling. To test this, we determined the thermal preference (central 50% of temperatures selected) of E. m. krefftii in an aquatic thermal gradient in the laboratory. We then conducted a manipulative experiment to test the effects of water temperatures, both lower and higher than preferred temperature, on diurnal and nocturnal basking. The preferred temperature range fell between 25.3°C (±SD: 1.5) and 27.6°C (±1.4) during the day, and 25.3°C (±2.4) and 26.8°C (±2.5) at night. Based on this, we exposed turtles to three 24 h water temperature treatments (‘cool’ [23°C], ‘preferred’ [26°C] and ‘warm’ [29°C]) while air temperature remained constant at 26°C. Turtles basked more frequently and for longer periods during both the day and night when water temperatures were above their preferred range (the ‘warm’ treatment). This population frequently encounters aquatic temperatures above the preferred thermal range, and our results support the hypothesis that nocturnal basking is a mechanism for escaping unfavourably warm water. Targeted field studies would be a valuable next step in understanding the seasonal scope of this behaviour in a natural environment.     

Temporal thermal refugia and seasonal variation in upper thermal limits of two species of riverine invertebrates: the amphipod, <Emphasis Type="Italic">Paramelita nigroculus</Emphasis>, and the mayfly, <Emphasis Type="Italic">Lestagella penicillata</Emphasis>

Understanding the response of aquatic organisms to elevated water temperatures offers insight into the ecological consequences of climate change on riverine species. Upper thermal limits were determined for two riverine invertebrates, the amphipod Paramelita nigroculus (Paramelitidae) and the mayfly Lestagella penicillata (Teloganodidae), in two rivers in the south-western Cape, South Africa. Limits were estimated using the critical thermal method (reflected as the critical thermal maxima—CT_max) and the incipient lethal temperature method (reflected as the incipient lethal upper limit—ILUT). Thermal signatures of these rivers were characterized using hourly water temperatures. CT_max for seasonally acclimatized and laboratory-acclimated P. nigroculus varied significantly amongst months and acclimation temperature. CT_max for seasonally acclimatized L. penicillata varied significantly amongst months, but not with acclimation temperature. 96-h ILUT values for seasonally acclimatized individuals varied significantly amongst months for both species. CT_max values, 96-h ILUT and Maximum Weekly Allowable Temperature thresholds were lower for P. nigroculus compared to L. penicillata. Seven-day moving averages of daily mean and maximum water temperatures were significantly correlated with upper thermal limits for seasonally acclimatized L. penicillata but not P. nigroculus. The proportion of time within a 24-h period that chronic thermal stress thresholds are not exceeded provides a measure of monthly or seasonal chronic thermal stress, and reflects the quantity of temporal thermal refugia for vulnerable organisms. Further testing of these relationships for other species, rivers and regions is recommended, to evaluate the potential for stream temperature averaging statistics to serve as proxies for biological thresholds.     

Effects of increasing temperatures on population dynamics of the zebra mussel <Emphasis Type="Italic">Dreissena polymorpha</Emphasis>: implications from an individual-based model

Zebra mussels (Dreissena polymorpha, Pallas, 1771) have had unprecedented success in colonizing European and North American waters under strongly differing temperature regimes. Thus, the mussel is an excellent model of a species which is able to cope with increasing water temperatures expected under global change. We study three principle scenarios for successful survival of the mussel under rising temperatures: (1) no adaptation to future thermal conditions is needed, existing performance is great enough; (2) a shift (adaptation) towards higher temperatures is required; or (3) a broadening of the range of tolerated temperatures (adaptation) is needed. We developed a stochastic individual-based model which describes the demographic growth of D. polymorpha to determine which of the alternative scenarios might enable future survival. It is a day-degree model which is determined by ambient water temperature. Daily temperatures are generated based on long-term data of the River Rhine. Predictions under temperature conditions as recently observed for this river that are made for the phenology of reproduction, the age distribution and the shell length distribution conform with field observations. Our simulations show that temporal patterns in the life cycle of the mussel will be altered under rising temperatures. In all scenarios spawning started earlier in the year and the total reproductive output of a population was dominated by the events later in the spawning period. For maximum temperatures between 20 and 26°C no thermal adaptation of the mussel is required. No extinctions and stable age distributions over generations were observed in scenario 2 for all maximum temperatures studied. In contrast, no population with a fixed range of tolerated temperatures survived in scenario 3 with high maximum temperatures (28, 30, 32°C). Age distributions showed an excess of 0+ individuals which resulted in an extinction of the population for several thermal ranges investigated. Priority programme of the German Research Foundation—contribution 14.     

Critical temperatures for xylogenesis in conifers of cold climates

Aim To identify temperatures at which cell division and differentiation are active in order to verify the existence of a common critical temperature determining growth in conifers of cold climates. Location Ten European and Canadian sites at different latitudes and altitudes. Methods The periods of cambial activity and cell differentiation were assessed on a weekly time‐scale on histological sections of cambium and wood tissue collected over 2 to 5 years per site from 1998 to 2005 from the stems of seven conifer species. All data were compared with daily air temperatures recorded from weather stations located close to the sites. Logistic regressions were used to calculate the probability of xylogenesis and of cambium being active at a given temperature. Results Xylogenesis lasted from May to October, with a growing period varying from 3 to 5 months depending on location and elevation. Despite the wide geographical range of the monitored sites, temperatures for onset and ending of xylogenesis converged towards narrow ranges with average values around 4–5, 8–9 and 13–14 °C for daily minimum, mean and maximum temperature, respectively. On the contrary, cell division in the cambium stopped in July?August, when temperatures were still high. Main conclusions Wood formation in conifers occurred when specific critical temperatures were reached. Although the timing and duration of xylogenesis varied among species, sites and years, the estimated temperatures were stable for all trees studied. These results provide biologically based evidence that temperature is a critical factor limiting production and differentiation of xylem cells in cold climates. Although daily temperatures below 4?5 °C are still favourable for photosynthesis, thermal conditions below these values could inhibit the allocation of assimilated carbon to structural investment, i.e. xylem growth.     

Regulate or tolerate: Thermal strategy of a coral reef flat resident,the epaulette shark,Hemiscyllium ocellatum

Highly variable thermal environments, such as coral reef flats, are challenging for marine ectotherms and are thought to invoke the use of behavioural strategies to avoid extreme temperatures and seek out thermal environments close to their preferred temperatures. Common to coral reef flats, the epaulette shark (Hemiscyllium ocellatum) possesses physiological adaptations to hypoxic and hypercapnic conditions, such as those experienced on reef flats, but little is known regarding the thermal strategies used by these sharks. We investigated whether H. ocellatum uses behavioural thermoregulation (i.e., movement to occupy thermally favourable microhabitats) or tolerates the broad range of temperatures experienced on the reef flat. Using an automated shuttlebox system, we determined the preferred temperature of H. ocellatum under controlled laboratory conditions and then compared this preferred temperature to 6 months of in situ environmental and body temperatures of individual H. ocellatum across the Heron Island reef flat. The preferred temperature of H. ocellatum under controlled conditions was 20.7 ± 1.5°C, but the body temperatures of individual H. ocellatum on the Heron Island reef flat mirrored environmental temperatures regardless of season or month. Despite substantial temporal variation in temperature on the Heron Island reef flat (15–34°C during 2017), there was a lack of spatial variation in temperature across the reef flat between sites or microhabitats. This limited spatial variation in temperature creates a low-quality thermal habitat limiting the ability of H. ocellatum to behaviourally thermoregulate. Behavioural thermoregulation is assumed in many shark species, but it appears that H. ocellatum may utilize other physiological strategies to cope with extreme temperature fluctuations on coral reef flats. While H. ocellatum appears to be able to tolerate acute exposure to temperatures well outside of their preferred temperature, it is unclear how this, and other, species will cope as temperatures continue to rise and approach their critical thermal limits. Understanding how species will respond to continued warming and the strategies they may use will be key to predicting future populations and assemblages.     

不同经度地区北草蜥的喜好体温和热耐受性

在外温动物热生理特征的进化理论中,“静态”和“易变”是两个持续争论的对立观点。热生理学特征的种内变异是检验此类假设的最有力证据。本研究比较了不同经度地区北草蜥的热环境和热生理特征,以检验“静态”和“易变”假设。东部沿海地区(宁德)的环境温度高于内陆地区(贵阳),与之相适应,沿海地区北草蜥的喜好体温也高于内陆地区。然而,两地区蜥蜴的上临界温度和下临界温度无显著差异。尽管这些热生理学特征的种群间变异趋势并不一致,但是喜好温度随环境温度变化而改变的结果符合“易变”假设的预测。此外,本研究表明蜥蜴的喜好体温存在沿经度方向的地理变异。     

Experimental analysis of the thermal and salinity preferences of glass-eels, Anguilla anguilla (L.), before and during the upstream migration

During their upstream migration European glass-eels, Anguilla anguilla (L.), encounter a series of varying environmental situations. The migration requires a sequence of physiological adaptations determined by the different chemico-physical conditions they meet. Temperature and salinity are two of the most important factors. It is reasonable that glass-eels may utilize them as cues to orientation. Laboratory experiments were designed to elucidate the thermal and salinity preferences of glass-eels. These were assessed by examining the choices of specimens caught either at sea and then kept in salt water (33%), or in the Arno river and then reared in fresh water. Water flows, triggering the rheotactic reaction, prompted glass-eels to choose between two different salinities and/or temperatures. The results confirm the preference of glass-eels for flows whose temperature does not differ from that of acclimation. Specimens tested towards two water flows, both at different temperatures from that of acclimation, preferred the colder. Fresh water was usually preferred to salt water, this preference being not so marked in the case of the glass-eels caught at sea and thus not yet adapted to fresh water. Clear-cut choices were recorded when one of the tested flows presented both the preferred temperature and preferred salinity. When only one of the two parameters reproduced the preferred situation, the choices were differently affected by temperature and salinity at different values of temperature. When the temperature of both flows was below 11–12°C, glass-eels preferred fresh water; at higher temperatures the colder of the two flows was preferred, even if salty.     

EVOLUTION OF SPRINT SPEED IN LACERTID LIZARDS: MORPHOLOGICAL,PHYSIOLOGICAL, AND BEHAVIORAL COVARIATION

Organismal performance abilities occupy a central position in phenotypic evolution; they are determined by suites of interacting lower-level traits (e.g., morphology and physiology) and they are a primary focus of natural selection. The mechanisms by which higher levels of organismal performance are achieved during evolution are therefore fundamentally important for understanding correlated evolution in general and coadaptation in particular. Here we address correlated evolution of morphological, physiological, and behavioral characteristics that influence interspecific variation in sprint speed in a clade of lacertid lizards. Phylogenetic analyses using independent contrasts indicate that the evolution of high maximum sprinting abilities (measured on a photocell-timed racetrack) has occurred via the evolution of (1) longer hind limbs relative to body size, and (2) a higher physiologically optimum temperature for sprinting. For ectotherms, which experience variable body temperatures while active, sprinting abilities in nature depend on both maximum capacities and relative performance levels (i.e., percent of maximum) that can be attained. With respect to temperature effects, relative performance levels are determined by the interaction between thermal physiology and thermoregulatory behavior. Among the 13 species or subspecies of lizards in the present study, differences in the optimal temperature for sprinting (body temperature at which lizards run fastest) closely matched interspecific variation in median preferred body temperature (measured in a laboratory photothermal gradient), indicating correlated evolution of thermal physiology and thermal preferences. Variability of the preferred body temperatures maintained by each species is, across species, negatively correlated with the thermal-performance breadth (range of body temperatures over which lizards can run relatively fast). This pattern leads to interspecific differences in the levels of relative sprint speed that lizards are predicted to attain while active at their preferred temperatures. The highest levels of predicted relative performance are achieved by species that combine a narrow, precise distribution of preferred temperatures with the ability to sprint at near-maximum speeds over a wide range of body temperatures. The observed among-species differences in predicted relative speed were positively correlated with the interspecific variation in maximum sprinting capacities. Thus, species that attain the highest maximum speeds are (1) also able to run at near-maximum levels over a wide range of temperatures and (2) also maintain body temperatures within a narrow zone near the optimal temperature for sprinting. The observed pattern of correlated evolution therefore has involved traits at distinct levels of biological organization, that is, morphology, physiology, and behavior; and trade-offs are not evident. We hypothesize that this particular trait combination has evolved in response to coadaptational selection pressures. We also discuss our results in the context of possible evolutionary responses to global climatic change.     

Critical thermal maximum of Amur sleeper <Emphasis Type="Italic">Perccottus glenii</Emphasis> in different seasons of the year

Seasonal differences in the critical thermal maximum are revealed in Amur sleeper Perccottus glenii at the age of 1+ and 2 years. Maximum values of the critical thermal maximum determined by two criteria (rotation of the body and immobile gill covers) are registered in the summer, and minimum values of this parameter are observed in the winter. Maximum thermal resistance is registered at a low water heating rate (0.2–0.4°C/h), and minimum resistance is reported for a heating rate 5.0–10.5°C/h. The difference between the values of the critical thermal maximum assessed by two criteria reaches 1–2°C. Features of behavior of Amur sleeper are described at different heating rates. Based on the characteristics of thermal adaptation (critical thermal maximum and optimal temperature for growth), Amur sleeper is similar to warm water eurythermal species (goldfish Carassius auratus and carp Cyprinus carpio).     

Temperature tolerance polygon of Poecilia sphenops Valenciennes (Pisces: Poeciliidae)

1. The critical thermal maximum (CTMax) and minimum (CTMin), the upper and lower incipient lethal temperature, and the high and low avoidance temperature of Poecilia sphenops were established.2. The area of thermal tolerance of P. sphenops upon considering the lethal limits was 863.9 (°C)², the estimated area using the critical temperatures, as well as the zone of thermal preference were 959 and 323.4 (°C)², respectively.3. P. sphenops is a species highly eurythermical that possesses a high tolerance, resistance and capacity of adaptation to environmental variations.     

Thermal dependence of enzyme function and inhibition; implications for, herbicide efficacy and tolerance

Environmental temperature is a critical factor in the lives of almost all organisms. Plants experience periods of thermal stress related to seasonal patterns of temperature and periodic water deficits. Within the range of non-lethal temperatures, there are a number of thermal effects on metabolism that are a result of the thermal dependence of enzymes. The thermal dependence of enzyme kinetic parameters was used to predict that the efficacy of the herbicide pyrithiobac on Palmer amaranth would be reduced at temperatures outside a 20–34°C thermal application range. This prediction is validated in a controlled environment study described in this paper. Palmer amaranth was grown for 16 days in growth chambers with 34/18°C day/night temperature regime. Pyrithiobac was applied to plants at 18, 27 or 40°C. After 1 h at the application temperatures the plants were returned to the 34/18°C regime for 14 days and post-application biomass accumulation (efficacy) was determined. Dry weight accumulation, as a percentage of untreated controls, was 25, 2.5 and 70% for 18, 27 and 40°C application temperatures. Pyrithiobac efficacy was highest for the application within the thermal application range and significantly reduced at temperatures above and below. The validation of the earlier prediction suggests that temperature-related kinetic limitations on herbicide efficacy may also occur in plants with bioengineered herbicide resistance based on herbicide metabolism. The theoretical aspects of such thermal limitations on herbicide resistance mechanisms are discussed.     

The lower and upper critical temperatures in male Japanese

Critical temperatures were determined by a new estimating system called the polynomial equation method. Its consists of polynomial regression equations of metabolic rate on ambient and body temperatures and conversion equations enable to convert metabolic rate value into temperature value. Nine young adult males were tested using the system. Metabolic rate was calculated indirectly with a reference to protein metabolism and the critical temperatures were determined as follows; the lower critical air temperature to be 26.2 C, the upper critical air temperature to be 47.0 degrees C, the lower and upper mean skin temperature to be 29.2 degrees C and 36.5 degrees C, and the lower and upper critical rectal temperature to be 35.5 degrees C and 37.9 degrees C, respectively. The polynomial equation method has an advantage over the intersect method since it allows estimation of several kinds of critical temperature.     

Thermal parameters and locomotor performance in juvenile of Pleurodema nebulosum (Anura: Leptodactylidae) from the Monte Desert

We studied a combination of thermal parameters (critical thermal maximum, selected body temperature, and field body temperature) and locomotor performance capacities (laboratory and field conditions) of juveniles of Pleurodema nebulosum. We found that field body temperature was determined largely by the temperature of the micro-environment. Field body temperatures of juveniles of P. nebulosum were below selected body temperature. The locomotor performance curve was maximized and reaches a plateau between 30 and 35 °C, with 35 °C being the temperature at which maximum performance was obtained for analyzed individuals. The plateau values were close to the selected body temperature (T_sel) obtained for the studied frogs. In field conditions the locomotor performance was determinated by the substrate temperature. Apparently, juveniles of P. nebulosum show thermal coadaptation because the selected body temperature and the optimum temperature for locomotion had close values. We believe that the temperatures prevailing during the early hours of activity would allow frogs to explore the micro-environment, covering larger areas in search of food.     

Growth and macromolecular composition of a psychrophile,Micrococcus cryophilus,at elevated temperatures

A psychrophilic bacterium,Micrococcus cryophilus, was found to have a maximum growth temperature of 26 C in glutamate salts minimal medium. Macromolecular composition at various temperatures of incubation is reported. When cultures were transferred to temperatures in excess of maximum for growth, the levels of protein and DNA remained fairly constant, whereas the level of RNA fell drastically. The significance of these findings in relation to thermal injury is discussed.     

Retrogradation of corn starch after thermal treatment at different temperatures

Multi-endotherms of the gelatinization of corn starch, such as G, M1, M2, and Z endotherms, have been detected by DSC. The retrogradation of corn starch after initial thermal treatment at different temperatures was studied by DSC; in particular, the effect of thermal treatment before and after each endotherm of gelatinization on retrogradation was determined as a function of annealing time. The effect of thermal treatment at a certain temperature on the residual gelatinization endotherm at a higher temperature is also discussed. It was found that the higher temperature of thermal treatment always removed all the endotherms below that temperature. However, a certain thermal treatment temperature could affect the residual endotherm above this treatment temperature. The time-dependent retrogradation of corn starch is mainly due to G and M1 endotherms. The temperature and enthalpy of the melting of amylose–lipid complexes M2 and nonlipid complex amylose Z were not affected by aging time. The final enthalpy of retrogradation was found to be lower than that of gelatinization.