Seasonal thermal tolerance in marine Crustacea

Seasonal values of the critical thermal maximum (CTMax) of eight species of adult marine Crustacea from temperate latitudes were measured and found to range between 20 and 34 °C. The extent to which CTMax was dependent on acclimatization varied with species but for most of the species studied, summer-captured animals had significantly higher CTMax values than winter-captured animals. Heat shock resulted in an increase in thermotolerance in most species in winter-captured animals, but a different pattern was found for summer-captured animals. Then, only Cancer pagurus and Pagurus bernhardus showed a positive increment of CTMax on heat shock. Test for Serial Independence analysis indicated no significant phylogenetic autocorrelation between CTMax values in winter or summer-captured animals. Temperature measurements taken by remote data loggers in the intertidal zone of the North-East coast of England are reported. These suggest that several species, whose distribution extends into the intertidal zone, may experience temperatures close to their CTMax in summer.     

Unifying indices of heat tolerance in ectotherms

1.

Researchers commonly rely on indices of heat tolerance to infer the limits of performance in nature. Unfortunately, many methods are used to estimate heat tolerance, creating difficulties when synthesizing or comparing results among studies. Here, we relate several measures of heat tolerance based on the concept of a performance curve.     

Behavioral thermoregulation, temperature tolerance and oxygen consumption in the Mexican bullseye puffer fish, Sphoeroides annulatus Jenyns (1842), acclimated to different temperatures

An inverse and unusual relationship was found between preferred temperature and acclimation temperature in the bullseye puffer, Sphoeroides annulatus. The final preferendum temperature (PT) was 26.8 °C. The critical thermal maxima (CTMax) were 37.7, 38.8, 40.0, 40.8 and 41.3 °C where the temperatures of acclimation were 19, 22, 25, 28 and 31 °C±1 °C, respectively, and the endpoint of CTMax was loss of the righting response. The acclimation response ratio presented an interval of 0.22-0.38; these values are in agreement with results for other subtropical and tropical fishes. The temperature significantly affected the oxygen consumption of bullseye puffer juveniles. The oxygen consumption rate (OCR) increased significantly with an increment in the temperature from 19 to 31 °C. The range of the temperature coefficient Q₁₀ in bullseye puffer individuals was lowest between 25 and 28 °C, at 1.37. The optimal temperature for growth was 26 °C. The results of this study will be useful for optimizing the culture of bullseye puffer juveniles in controlled conditions.     

Thermal biology of bonefish (Albula vulpes) in Bahamian coastal waters and tidal creeks: An integrated laboratory and field study

Little is known about the thermal tolerances of fish that occupy tropical intertidal habitats or how their distribution, physiological condition, and survival are influenced by water temperature. We used a combination of laboratory and field approaches to study the thermal biology of bonefish, Albula vulpes, a fish species that relies on nearshore intertidal habitats throughout the Caribbean. The critical thermal maximum (CTMax) for bonefish was determined to be 36.4±0.5 and 37.9±0.5 °C for fish acclimated to 27.3±1.3 and 30.2±1.4 °C, respectively, and these tolerances are below maximal temperatures recorded in the tropical tidal habitats where bonefish frequently reside (i.e., up to 40.6 °C). In addition, daily temperatures can fluctuate up to 11.4 °C over a 24-h period emphasizing the dramatic range of temperatures that could be experienced by bonefish on a diel basis. Use of an acoustic telemetry array to monitor bonefish movements coupled with hourly temperature data collected within tidal creeks revealed a significant positive relationship between the amount of time bonefish spent in the upper portions of the creeks with the increasing maximal water temperature. This behavior is likely in response to feeding requirements necessary to fuel elevated metabolic demands when water temperatures generally warm, and also to avoid predators. For fish held in the laboratory, reaching CTMax temperatures elicited a secondary stress response that included an increase in blood lactate, glucose, and potassium levels. A field study that involved exposing fish to a standardized handling stressor at temperatures approaching their CTMax generated severe physiological disturbances relative to fish exposed to the same stressor at cooler temperatures. In addition, evaluation of the short-term survival of bonefish after surgical implantation of telemetry tags revealed that there was a positive relationship between water temperature at time of tagging and mortality. Collectively, the data from these laboratory and field studies suggest that bonefish occupy habitats that approach their laboratory-determined CTMax and can apparently do so without significant sub-lethal physiological consequences or mortality, except when exposed to additional stressors.     

Effects of oxygen on responses to heating in two lizard species sampled along an elevational gradient

Thermal tolerance is an important variable in predictive models about the effects of global climate change on species distributions, yet the physiological mechanisms responsible for reduced performance at high temperatures in air-breathing vertebrates are not clear. We conducted an experiment to examine how oxygen affects three variables exhibited by ectotherms as they heat—gaping threshold, panting threshold, and loss of righting response (the latter indicating the critical thermal maximum)—in two lizard species along an elevational (and therefore environmental oxygen partial pressure) gradient. Oxygen partial pressure did not impact these variables in either species. We also exposed lizards at each elevation to severely hypoxic gas to evaluate their responses to hypoxia. Severely low oxygen partial pressure treatments significantly reduced the gaping threshold, panting threshold, and critical thermal maximum. Further, under these extreme hypoxic conditions, these variables were strongly and positively related to partial pressure of oxygen. In an elevation where both species overlapped, the thermal tolerance of the high elevation species was less affected by hypoxia than that of the low elevation species, suggesting the high elevation species may be adapted to lower oxygen partial pressures. In the high elevation species, female lizards had higher thermal tolerance than males. Our data suggest that oxygen impacts the thermal tolerance of lizards, but only under severely hypoxic conditions, possibly as a result of hypoxia-induced anapyrexia.     

中华鳖新孵幼体的热耐受性、体温昼夜变化和运动能力的热依赖性

研究中华鳖新孵幼体的热耐受性、体温及温度对运动能力的影响 .结果表明 ,在干燥和潮湿环境下 ,选择体温分别为 2 8.0℃和 30 .3℃ ;潮湿环境下 ,临界高温和低温分别为 40 .9℃和 7.8℃ .在缺乏温度梯度的热环境中 ,水温对幼鳖体温的影响比气温更直接 ,体温和环境温度的昼夜变化相一致 ,说明幼鳖生理调温能力很弱 .在有温度梯度的热环境中 ,幼鳖能通过行为调温将体温维持到较高且较恒定的水平 ,导致体温昼夜变化不明显 .幼鳖运动能力有显著的热依赖性 ,在一定温度范围内随体温升高而增强 .体温31.5℃时 ,幼鳖的运动表现最好 ,最大续跑距离、单位时间跑动距离和单位时间停顿次数分别为 1.87m、4 92m·min-1和 6 .2次·min-1.体温过高时 ,运动能力下降 .当体温为 33 .0℃时 ,最大续跑距离、单位时间跑动距离和单位时间停顿次数分别为 1.30m、4.2 8m·min-1和 7.7次·min-1.     

Thermal responses of juvenile squaretail mullet (Liza vaigiensis) and juvenile crescent terapon (Terapon jarbua) acclimated at near-lethal temperatures, and the implications for climate change

The negative effects of climate alteration on coral reef fishes receive ever increasing attention; however, implications of rising sea temperatures on fishes inhabiting marine nursery environments are poorly understood. We used critical thermal methodology to quantify critical thermal maxima (CTmaxima) of juvenile squaretail mullet (Liza vaigiensis) and juvenile crescent terapon (Terapon jarbua) captured from shallow seagrass nursery areas around Hoga Island, southeast Sulawesi, Indonesia. We tested the hypothesis that these distantly related fishes, when acclimated to cycling temperatures, would display higher CTmaxima than groups acclimated at constant temperatures. Groups of mullet acclimated to a constant temperature of 37 °C and temperature cycles of 35 to 39 °C or 37 to 41 °C displayed statistically similar mean CTmaxima of 44.7, 44.4 and 44.8 °C, respectively. Likewise, terapon acclimated at temperature cycles of 37 to 40 °C did not display a higher CTmaxima than fish acclimated at a constant temperature of 37 °C, with both acclimation groups' mean CTmaxima equal to 43.8 °C. Acclimation to higher cycling temperatures did not result in significant upper temperature tolerance acquisition for either species; however, mullet values were significantly higher than those seen in terapon (P < 0.0001). These data suggest that mullet and terapon will not suffer direct thermal effects should shallow nursery temperature increases be marginally higher than 1-2 °C above ~ 27 °C, and they provide evidence that the upper thermal tolerance of fishes inhabiting shallow seagrass and mangrove areas can approach the biokinetic limits for vertebrate life. Tropical marine fishes inhabiting fringing nursery environments may have the upper thermal tolerance necessary to endure substantial increases in sea temperatures.     

Heat sensitivity and protein synthesis during heat-shock in the tobacco hornworm,Manduca sexta

Summary Fifth instar larvae of the tobacco hornworm,Manduca sexta, tolerate 1-h exposures to temperatures as high as 42°C. Above 42°C, survival declines rapidly to 18% at 44°C and 0% at 48°C. As in other insects, the heat-shock response ofManduca sexta involves the induction of synthesis of heat-shock proteins very similar in size to theDrosophila heat-shock proteins (84, 73, 71, 27, 25, 23, and 22 kd). In the epidermis, heat-shock protein synthesis peaks at 42°C, correlating with the heat sensitivity of both the tissue itself and the intact larva. Some heat-shock proteins have different isoelectric forms depending on tissue. Also, the heat-shock proteins are synthesized over a wider range of temperatures in the imaginal discs and the fat body as compared to the epidermis. In contrast to dipteran insects,Manduca sexta does not exhibit a strong repression of non-heat-shock protein synthesis under tolerable conditions.Abbreviations TCA trichloroacetic acid - PAGE polyacrylamide gel electrophoresis - AZT arbitrary Zeitgeber time - kd kilodaltons     

Thermal acclimation in a complex life cycle: The effects of larval and adult thermal conditions on metabolic rate and heat resistance in Culex pipiens (Diptera: Culicidae)

It has now been well established that insects can respond to variation in their environment via acclimation, yet the extent of the response varies among populations and environmental characteristics. One under-investigated theme which may contribute to this variation concerns acclimation effects across the life cycle. The present study explores how acclimation in the larval stage of Culex pipiens affects thermal relations in the adult stage. Mosquitoes were reared in a full factorial design at 18 or 26 °C as larvae and adults, then critical thermal maxima (CT_max) and metabolic rate–temperature relationships (MR–T) were determined for all 4 treatments. CT_max was positively affected by both larval and adult acclimation treatments. MR–T slope was significantly affected only by adult treatment: warm acclimated adults had on average shallower slopes and higher y-intercepts than cool acclimated ones. These results demonstrate that larval acclimation effects can alter adult phenotypes in a species whose life cycle includes two drastically different environments, an aquatic and a terrestrial stage. Studying insects with complex life cycles, especially those with aquatic or subterranean larval stages, can provide valuable information on the effects of thermal variability and predictability on phenotypic plasticity.     

Thermal tolerance of Litopenaeus vannamei (Crustacea: Penaeidae) acclimated to four temperatures

Critical thermal minima (CTMin) and maxima (CTMax) values were determined for the Pacific white shrimp Litopenaeus vannamei post-larvae and juveniles at four different acclimation temperatures (15, 20, 25, and 30 °C). The CTMin of shrimp at these acclimation temperatures were 7.82, 8.95, 9.80, and 10.96 °C for post-larvae and 7.50, 8.20, 10.20, and 10.80 °C for juveniles, respectively, at 1 °C h⁻¹ cooling rate. The CTMax values were 35.65, 38.13, 39.91, and 42.00 °C for post-larvae and 35.94, 38.65, 40.30, and 42.20 °C for juveniles at the respective acclimation temperatures. Both acclimation temperature and size of the shrimp affected CTMin values of L. vannamei (P<0.01). Overall, juveniles displayed significantly lower CTMin values than the post-larvae (P<0.0001). However, the CTMax response by post-larvae and juveniles were not significantly different from each other and no interaction was determined between the acclimation temperature and development stage (P>0.01). The area of the thermal tolerance polygon over four acclimation temperatures (15, 20, 25, and 30 °C) for the post-larvae of L. vannamei was calculated to be 434.94 °C². The acclimation response ratio (ARR) values were high ranging from 0.35 to 0.44 for both post-larvae and juveniles. L. vannamei appears to be more sensitive to low temperatures than other penaeid species and its cold tolerance zone ranged from 7.5 to 11 °C. In successful aquaculture temperature must never fall below 12 °C to prevent mortalities. Upper thermal tolerance is less of a problem as in most subtropical regions maximum water temperature rarely exceeds 34 °C, but care should be given if shallow ponds with low water renewal rate are being used.     

Effect of the rate of temperature increase of the dynamic method on the heat tolerance of fishes

Heat tolerance is commonly determined by exposing organisms to increasing temperatures until they show symptoms of thermal stress or death. Here we carried out an experiment on a blenny species (Acantemblemaria hancocki; Pisces: Chaenopsidae) and reviewed the literature to evaluate the extent to which variations in the rate at which temperature is increased in experimental trials affects thermal tolerance of fishes. For the blenny species, we found that thermal tolerance decreases significantly from an intermediate heating rate of ∼1 °C/h towards quicker and slower heating rates. In the literature we found very few comparisons of thermal tolerance among heating rates (i.e. eight fish species) and although such comparisons were done over narrow ranges of heating rates, overall they appear to follow the pattern described for the blenny species. We discuss a variety of factors including variations in the levels of acclimation, energy use and body quality among heating rates as the causes for this pattern. However, available data are still limited and further research will be necessary to determine the generality and causes of the pattern we found here. Nevertheless, our results indicate the need for caution in the extrapolation of thermal tolerance data when assessing the tolerance of organisms to environmental phenomena that vary in their rates of warming.     

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

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

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

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

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

     

Fatty acid composition and extreme temperature tolerance following exposure to fluctuating temperatures in a soil arthropod

Ectotherms commonly adjust their lipid composition to ambient temperature to counteract detrimental thermal effects on lipid fluidity. However, the extent of lipid remodeling and the associated fitness consequences under continuous temperature fluctuations are not well-described. The objective of this study was to investigate the effect of repeated temperature fluctuations on fatty acid composition and thermal tolerance. We exposed the springtail Orchesella cincta to two constant temperatures of 5 and 20 °C, and a continuously fluctuating treatment between 5 and 20 °C every 2 days. Fatty acid composition differed significantly between constant low and high temperatures. As expected, animals were most cold tolerant in the low temperature treatment, while heat tolerance was highest under high temperature. Under fluctuating temperatures, fatty acid composition changed with temperature initially, but later in the experiment fatty acid composition stabilized and closely resembled that found under constant warm temperatures. Consistent with this, heat tolerance in the fluctuating temperature treatment was comparable to the constant warm treatment. Cold tolerance in the fluctuating temperature treatment was intermediate compared to animals acclimated to constant cold or warmth, despite the fact that fatty acid composition was adjusted to warm conditions. This unexpected finding suggests that in animals acclimated to fluctuating temperatures an additional underlying mechanism is involved in the cold shock response. Other aspects of homeoviscous adaptation may protect animals during extreme cold. This paper forms a next step to fully understand the functioning of ectotherms in more thermally variable environments.