Greater Temperature Fluctuations Research Articles

Contrasting responses of Thermocyclops crassus and T. oithonoides (Crustacea, Copepoda) to thermal stress.

Thermal tolerance is a critical factor influencing the survival of living organisms. This study focuses on the thermal resistance of copepod species, Thermocyclops crassus (Fischer, 1853) and T. oithonoides (Sars G.O., 1863), with overlapping distribution ranges in Europe. Short-term heat shock experiments were conducted to assess the thermal resistance of these copepods, considering various temperature increments and exposure durations. Additionally, the study explored the influence of heat shock on egg sac shedding, a vital indicator of population dynamics. Results indicate that widely distributed T. crassus exhibits higher thermal tolerance compared to narrowly distributed T. oithonoides, with survival rates varying under different heat shock conditions. Furthermore, T. crassus demonstrated a quicker response in dropping egg sacs in response to thermal stress, suggesting a potential adaptive mechanism for the survival of adults. However, rapid egg sac droppings pose high risks for eggs facing unfavorable conditions. T. crassus, inhabiting environments with greater temperature fluctuations such as the littoral and pelagial zones, exhibited better survival mechanisms compared to T. oithonoides, which predominantly resides in the pelagic zone. The findings have implications for understanding copepod responses to global warming and thermal pollution. This research contributes insights into the adaptive strategies of thermophilic copepod species and their ecological consequences.

Assessing Seasonal Changes in Physicochemical Traits and Biochemical Profiles of Key Carp Species in Masani Barrage Lake and JLN Canal

Our thorough seasonal analysis of Masani Barrage Lake and JLN Canal in Rewari reveals the profound impact of seasonal changes on aquatic ecosystems. Both water bodies display distinct patterns in temperature, pH, salinity, and other parameters. The unique characteristics of lakes, with greater temperature fluctuations and nutrient cycling, contribute to differences in phytozooplankton and ecological dynamics compared to more regulated canals. Additionally, our study on common carp tissues shows clear seasonal variations in moisture, ash, protein, lipid, and fatty acid levels, indicating specific metabolic responses to environmental conditions. Understanding these nuances is crucial for grasping the diverse influences of these habitats on fish physiology, with lakes experiencing more significant variations than canals due to their larger and more open systems.

Symbiont shuffling dynamics associated with photodamage during temperature stress in coral symbiosis

Reef-building corals usually form a symbiotic relationship with various photosynthetic dinoflagellates, which may determine the physiology and stress tolerance of their hosts. The mechanisms governing symbiont dynamics are still poorly understood, but may be driven by temperature. Therefore, we performed indoor experiments to examine the photochemical efficiency and symbiont dynamics in the coral Pocillopora damicornis with thermo-sensitive Cladocopium (PdC) or thermo-tolerant Durusdinium (PdD) under 6-day temperature stress and after 90-day post-stress recovery. Regardless of the symbiont type, photochemical damage was induced by both heat and cold stress. We observed PdC with greater photodamage had a faster increase in the proportion of Durusdinium when exposed to heat or cold stress, whereas an inverse shuffling to Cladocopium in both PdC and PdD after the recovery period. This is the first record of symbiont shuffling from the originally dominant Durusdinium to Cladocopium in adult corals under laboratory conditions and the degree of symbiont shuffling was highly correlated with the photodamage. Overall, our findings suggest that symbiont shuffling can act as a critical mechanism allowing corals to rapidly adjust to environmental changes, which has implications for the capacity of corals to prevail in oceans with greater temperature fluctuations in the future.

Measurement Method of Thermal Diffusivity of the Building Wall for Summer and Winter Seasons in Poland

The thermal diffusivity of building materials is an extremely important parameter influencing the subsequent thermal comfort of building users. By definition, thermal diffusivity describes how quickly heat from a hot source can flow through a material. Therefore, this parameter includes both the thermal conductivity and the heat capacity of the material. This parameter is often neglected in heat-related calculations which, in the case of dynamic problems, leads to unreliable results. It should be taken into account that heat flows through all materials at a finite speed. On the other hand, knowing the correct thermal diffusivity value of building materials, it is possible to accurately determine the internal parameters in rooms over time. There are several methods for determining thermal diffusivity, most of which are destined to determine this property in laboratories. The aim of the present research is to show how the thermal diffusivity of materials can be determined in existing buildings. The presented method can be used to determine more real thermal parameters used for thermal calculations in buildings, for example, during energy audits or when calculating the demand for cooling for air conditioning or heat for space heating. This research presents the results for a 60 cm brick wall. Thermal diffusivity was determined for specific summer and winter days—most representative of the whole year. This research has shown that the applied method should be used in the summer period, due to the fact that the wall has greater temperature fluctuations. The obtained results are comparable with the previously mentioned laboratory methods. However, due to the fact that the materials analyzed on the spot, the results are more reliable, and also take into account changes in the value of thermal diffusivity resulting from the use of binders, inaccuracies in joining and external layers made of other materials.

Significant advancement in agricultural biotech in the era of climate change

Tropical areas, especially impoverished countries, are more impacted than temperate ones by greater temperature fluctuations and regime changes. When it rains, the demand for water rises. In addition, while mild warming benefits crops in mid and high latitudes, even moderate warming decreases the yields in the low latitudes in the seasonally dry regions. This has an effect not only on everyone in the globe, but also on the rest of the ecosystem. There are so many issues that remain a tough issue with how to prevent and combat climate change. In developing nations which are highly populated and prone to droughts, food insecurity may be especially prevalent. Total worldwide food production capacity is expected to grow if the average region's temperature rises from 1 to 3°C, however the world's food safety is under danger from severe weather and socioeconomic problems. It is notable that comprehensive national research and does not take possible adaptation methods into account the Intergovernmental Panel on Climate Change's gloomy predictions of low latitude agricultural output. On the other hand, the effect on food safety is significant. Food safety in all four dimensions is impacted. Climate change will raise and aggravate the burden for poor nations already dealing with acute food shortages.

River modification reduces climate resilience of brown trout (Salmo trutta) populations in Ireland

AbstractThis study investigated interactions between eco‐hydromorphological state, riparian vegetation cover, water temperature and fish community composition in lowland rivers in Ireland. Physical habitat modification of study sites corresponded with degraded eco‐hydromorphological state (degree of ecological and physical modification) and reduced thermal buffering capacity (greater temperature fluctuation and increased frequency of extreme temperature events). This impact was reflected in the fish community, with a shift from a brown trout‐dominated (Salmo trutta L.) fish assemblage to predominance of the more thermally plastic minnow, Phoxinus phoxinus (L.), and stone loach, Barbatula barbatula (L.). Eco‐hydromorphological state may be a central factor affecting the ability of temperate rivers to resist temperature change in a warming climate and to maintain suitable conditions for salmonids and other cold‐water biota. Strategies aimed at climate change proofing of temperate rivers should focus on preserving or re‐establishing the eco‐hydromorphological processes that create habitat complexity and buffer stream temperature.

Not so free range? Oviposition microhabitat and egg clustering affects Eretmoptera murphyi (Diptera: Chironomidae) reproductive success

Understanding the physiology of non-native species in Antarctica is key to elucidating their ability to colonise an area, and how they may respond to changes in climate. Eretmoptera murphyi is a chironomid midge introduced to Signy Island (Maritime Antarctic) from South Georgia (Sub-Antarctic) where it is endemic. Here, we explore the tolerance of this species’ egg masses to heat and desiccation stress encountered within two different oviposition microhabitats (ground surface vegetation and underlying soil layer). Our data show that, whilst oviposition takes place in both substrates, egg sacs laid individually in soil are at the greatest risk of failing to hatch, whilst those aggregated in the surface vegetation have the lowest risk. The two microhabitats are characterised by significantly different environmental conditions, with greater temperature fluctuations in the surface vegetation, but lower humidity (%RH) and available water content in the soil. Egg sacs were not desiccation resistant and lost water rapidly, with prolonged exposure to 75% RH affecting survival for eggs in singly oviposited egg sacs. In contrast, aggregated egg sacs (n = 10) experienced much lower desiccation rates and survival of eggs remained above 50% in all treatments. Eggs had high heat tolerance in the context of the current microhabitat conditions on Signy. We suggest that the atypical (for this family) use of egg sac aggregation in E. murphyi has developed as a response to environmental stress. Current temperature patterns and extremes on Signy Island are unlikely to affect egg survival, but changes in the frequency and duration of extreme events could be a greater challenge.

Global spatial analysis of Arabidopsis natural variants implicates 5'UTR splicing of LATE ELONGATED HYPOCOTYL in responses to temperature.

How plants perceive and respond to temperature remains an important question in the plant sciences. Temperature perception and signal transduction may occur through temperature‐sensitive intramolecular folding of primary mRNA transcripts. Recent studies suggested a role for retention of the first intron in the 5′UTR of the clock component LATE ELONGATED HYPOCOTYL (LHY) in response to changes in temperature. Here, we identified a set of haplotypes in the LHY 5′UTR, examined their global spatial distribution, and obtained evidence that haplotype can affect temperature‐dependent splicing of LHY transcripts. Correlations of haplotype spatial distributions with global bioclimatic variables and altitude point to associations with annual mean temperature and temperature fluctuation. Relatively rare relict type accessions correlate with lower mean temperature and greater temperature fluctuation and the spatial distribution of other haplotypes may be informative of evolutionary processes driving colonization of ecosystems. We propose that haplotypes may possess distinct 5′UTR pre‐mRNA folding thermodynamics and/or specific biological stabilities based around the binding of trans‐acting RNA splicing factors, a consequence of which is scalable splicing sensitivity of a central clock component that is likely tuned to specific temperature environments.

Zero Energy Overwinter Storage of Apple Nursery Plants in trans-Himalayan Ladakh, India

<p>Studies were conducted during 2015 and 2016 to assess the effects of storage conditions on survival of nursery plants in trans-Himalayan Ladakh region. Apple nursery plants raised under warm climatic conditions of Solan (Himachal) were lifted from nurseries in first week of January and stored upto March in cold Ladakh region. Underground cellar-stored plants showed significantly higher plant survival (92 to 94%) than greenhouse-stored plants (37 to 56% survival). Low and constant temperature (-1.5±4.1 to 10.0±1.4ºC) and absence of light inside the cellar were favorable factors for storage of nursery plants. Lower survival rates of greenhouse-stored plants could be attributed to lower and greater fluctuations in temperature (-9.3±1.7to 25.1±1.9ºC) inside the greenhouse. Cellar-stored plants were less subjected to freezing injury as reflected from shoot electrolyte leakage studies. The underground cellar was found effective for overwinter storage of apple nursery plants for 3 to 4 months. The method described is easy and cost-effective, and can be a satisfactory alternative to refrigerated cold storage in trans-Himalayan region with severe winters.<strong></strong></p><p> </p>

The Impact of Temperature on Activity Patterns of Two Vertiginid Micro-Molluscs (Mollusca: Gastropoda) in Conditions of High, Constant Humidity

Abstract: The goal of this study was to check the activity pattern of two hygrophilous land snails: Vertigo moulinsiana Dupuy, 1849 and Vertigo angustior (Jeffreys, 1830) at 11 °C and 21 °C, in conditions of high, constant humidity. The activity of snails was investigated for two weeks and checked two times a day: at 7AM and 7 PM. One-way ANOVA has shown statistically significant differences in the activity patterns of the studied snails. Both species were more active at 11 °C than 21 °C however, V. moulinsiana was more active than V. angustior in both temperatures. The higher activity of both species at 11 °C may be due to the fact that these vertiginids lose more water under hot conditions than under cold even at the same saturation deficits. On the other hand, higher activity of the climbing species — V. moulinsiana which in nature is exposed to the greater temperature fluctuations than the litter dwelling V. angustior, may cause a quicker response to changes of the temperature, and protect from overhe...

Finite Element Study on Thermal Fatigue Depth of Aluminum Alloy Die Casting Die

A three-dimensional finite element model of the front cover die casting made of aluminum alloy was established by PRO/E and PROCAST software. Thermal balance formation of die casting die and temperature curves of the die cavity surface at different locations were analyzed. The results showed that the nearer the distance from die cavity surface, the greater temperature fluctuation. The thermal fatigue depth of the front cover die casting die was only 0.9mm.

The thermal environment of the nest affects body and cell size in the solitary red mason bee (Osmia bicornis L.)

Many ectotherms grow larger at lower temperatures than at higher temperatures. This pattern, known as the temperature-size rule, is often accompanied by plastic changes in cell size, which can mechanistically explain the thermal dependence of body size. However, the theory predicts that thermal plasticity in cell size has adaptive value for ectotherms because there are different optimal cell-membrane-to-cell-volume ratios at different temperatures. At high temperatures, the demand for oxygen is high; therefore, a large membrane surface of small cells is beneficial because it allows high rates of oxygen transport into the cell. The metabolic costs of maintaining membranes become more important at low temperatures than at high temperatures, which favours large cells. In a field experiment, we manipulated the thermal conditions inside nests of the red mason bee, a solitary bee that does not regulate the temperature in its nests and whose larvae develop under ambient conditions. We assessed the effect of temperature on body mass and ommatidia size (our proxy of cell size). The body and cell sizes decreased in response to a higher mean temperature and greater temperature fluctuations. This finding is in accordance with predictions of the temperature-size rule and optimal cell size theory and suggests that both the mean temperature and the magnitude of temperature fluctuations are important for determining body and cell sizes. Additionally, we observed that males of the red mason bee tend to have larger ommatidia in relation to their body mass than females, which might play an important role during mating flight.

Cooling methodology: to influence or to control the temperature?

The 2010 Guidelines on cardiopulmonary resuscitation and post-resuscitation care, based on the landmark studies on therapeutic hypothermia, state that hypothermia can be induced and maintained with inexpensive means such as simple ice packs and/or wet towels [1]. Indeed there is no method that has proven superior for survival or good neurological outcome. However, this approach comes at the price of an increased burden on nursing staff and greater temperature fluctuations. Also such means do not allow active gradual and controlled rewarming. While effective in contributing to rapid cooling, simple and inexpensive means may result in greater temperature fluctuations and corresponding modifications in heart rate and electrolyte plasma concentrations. Notably this strategy requires close and constant supervision of nursing staff, a distraction from other important aspects of patient care. Several studies demonstrate that influencing patient temperature will not allow a steady maintenance phase, controlled rewarming and, most importantly, ensuring strict normothermia once rewarming is concluded in patients with evidence of persisting neurological injury [2,3]. In essence, rather than speed it is control that is most desirable. This one of the lessons learned from the recent Target Temperature Management Trial [4]. In this study a less selected population than previous trials was treated at either 33 or 36°C followed by strict normothermia with an automatic feedback device for temperature management. The study demonstrated an extremely high survival rate (approximately 50%) and good neurological outcome regardless of the temperature regimen. Managing temperature at 36°C may overcome many of the contraindications of therapeutic hypothermia at 33°C, but is at the same time more challenging and hardly feasible without automatic feedback devices. Post-rewarming fever is also difficult to manage. Fever is associated with poor outcome. Even if causation has not been proven, normothermia is currently a therapeutic objective of modern post-resuscitation care. Influencing temperature is not enough to ensure strict normothermia. In the Target Temperature Management trial, active temperature management was maintained for a minimum of 72 hours in unconscious patients. In other fields of application of hypothermia, such as traumatic brain injury treatment and research, protocols dictate prolonged temperature management and extremely slow controlled rewarming based on intracranial pressure. In conclusion, modern treatment protocols advocate management of temperature, and thus control rather than influence, just like strict management of other vital parameters, is considered a standard of care for the critically ill.

Effects of environmental and farm stress on abalone physiology: perspectives for abalone aquaculture in the face of global climate change

AbstractMany abalone farms are reliant on coastal water inputs which are subject to fluctuations in environmental variables such as temperature, oxygen, CO2 and salinity. Near future climate change scenarios predict that there will be more frequent extreme weather events which can exacerbate these fluctuations and potentially be deleterious to farmed abalone where these variables remain largely uncontrolled. In this review, we have taken an in depth examination of current literature on the effects of environmental stress on abalone physiology and metabolism and how this affects their health and growth. In conjunction, we have also reviewed the effects of farm‐specific stressors such as ammonia, stocking density, handling, nutrition and disease and the synergistic effects of these and environmental stressors on abalone physiology. We have identified currents gaps in our knowledge of this under‐studied species and have made predictions on the effects of climate change on future abalone production with suggestions for future research. In summary, it is expected that abalone will show reduced growth rates as more energy is invested in combating stresses rather than growth. Furthermore, disease outbreaks may become more frequent with greater fluctuations in temperature and salinity, both of which have large‐scale effects on immunity. The current body of knowledge is mainly on whole animal effects of stresses, but we know very little of their mechanistic foundation. Research in this area as well as investments in infrastructure will be pivotal in identifying and implementing strategic interventions to maintain a sustainable abalone industry in Australia.

Bacterial Growth at -15 C

Microbiology Life as a bacterium in the permafrost is not easy. Not only are subzero temperatures the norm, but the liquid water that is available is quite salty. Therefore, for bacteria to survive in these conditions, they need to be well adapted to cold and high-salinity environments. Isolated from Arctic permafrost, the aerobic heterotroph Planococcus halocryophilus is an example of one such species that is up to the task. Through a series of batch and microcosm growth experiments, Mykytczuk et al. show that P. halocryophilus grew—albeit at the slow generation time of 50 days—and had an active carbon metabolism at −15°C. Genomic analyses suggest that this organism has a diverse set of traits to help it survive in addition to those related to cold and osmotic adaptation, including several modifications to the cell envelope and increased tolerance to oxidative stress. Indeed, transcriptomic profiles from cells grown at a range of temperatures and salinities down to −15°C and 18% NaCl show specific parallel responses to mitigate cold and salty conditions. Because a large portion of the world's soil is in permafrost regions, increased activity of these microbial communities may result from warmer temperatures or greater temperature fluctuations. ![Figure][1] CREDIT: N. C. S. MYKYTCZUK ET AL., THE ISME JOURNAL (7 FEBRUARY 2013) © NATURE PUBLISHING GROUP ISME J. 10.1038/ismej.2013.8 (2013). [1]: pending:yes

Reconstructing patterns of temperature, phenology, and frost damage over 124 years: Spring damage risk is increasing

Climate change, with both warmer spring temperatures and greater temperature fluctuations, has altered phenologies, possibly leading to greater risk of spring frost damage to temperate deciduous woody plants. Phenological observations of 20 woody species from 1993 to 2012 in Trelease Woods, Champaign County, Illinois, USA, were used to identify years with frost damage to vegetative and reproductive phases. Local temperature records were used in combination with the phenological observations to determine what combinations of the two were associated with damage. Finally, a long-term temperature record (1889-1992) was evaluated to determine if the frequency of frost damage has risen in recent decades. Frost < or = -1.7 degrees C occurred after bud-break in 14 of the 20 years of observation. Frost damage occurred in five years in the interior and in three additional years at only the forest edge. The degree of damage varied with species, life stage, tissue (vegetative or reproductive), and phenological phase. Common features associated with the occurrence of damage to interior plants were (1) a period of unusual warm temperatures in March, followed by (2) a frost event in April with a minimum temperature < or = -6.1 degrees C with (3) a period of 16-33 days between the extremes. In the long-term record, 10 of 124 years met these conditions, but the yearly probability of frost damage increased significantly, from 0.03 during 1889-1979 to 0.21 during 1980-2012. When the criteria were "softened" to < or = -1.7 degrees C in April and an interval of 16-37 days, 31 of 124 years met the conditions, and the yearly damage probability increased significantly to 0.19 for 1889-1979 and 0.42 for 1980-2012. In this forest, the combination of warming trends and temperature variability (extremes) associated with climate change is having ecologically important effects, making previously rare frost damage events more common.

Ecotypic differentiation and phenotypic plasticity in reproductive traits of Armadillidium vulgare (Isopoda: Oniscidea)

Armadillidium vulgare differed in growth and survivorship on two field sites. Growth rates were higher at a site with consistently higher quality food than at the other site where less high-quality food was produced and which was less predictably accessible. Survivorship was higher at the second site where temperature fluctuations were consistently smaller. Individuals from the two populations were kept for 6 months under the same food and temperature conditions and patterns of resource allocation to reproductive traits analysed. Members of the population from the site with good growth conditions had significantly higher reproductive allocation, by 13.5%, and larger broods, by 9.1%, than those from the site with poor growth conditions. Contrary to theoretical predictions, they also had significantly larger offspring, by 7.5% dry mass. Larger offspring survived better than small ones. This differential survivorship, by 20% for a 3.4% difference in live mass, was much more pronounced under conditions of moisture stress and under fluctuating temperature regimes. Larger offspring would therefore be at a selective advantage on the site with more severe temperature fluctuations. Phenotypic plasticity in reproductive traits in response to experimental changes in food quality, temperature and crowding were monitored. Reproductive allocation was increased by 20.8% under conditions of higher food quality, by 14.7% at higher temperatures, and by 12.5% under less crowded conditions. Brood size, but not offspring dry mass, increased when food quality increased. When crowding increased by 25.0%, the size of broods remained the same but the dry mass of individual offspring decreased by 11.2%. Members of the population from the site with more variable access to high-quality food showed more plasticity in reproductive traits in response to changes in food supply than members of the population from the site with the more predictable food supply. Members of the population from the site with more stable temperatures showed less plasticity to temperature changes than members of the population from the site with greater temperature fluctuations. It is concluded that the observed microevolutionary processes and phenotypic plasticity have adaptative value as responses to spatial and temporal heterogeneity in environmental conditions.

Artificial and natural seed banks differ in seedling emergence patterns

Artificial weed seed banks are practical for studying seed bank depletion and weed seedling emergence because the number, depth, and species composition of seed banks can be managed. However, no studies have determined whether artificial seed banks are representative of natural seed banks. We compared the emergence of velvetleaf, giant foxtail, and common waterhemp in a natural seed bank, an artificial seed bank with stratified seeds, and an artificial seed bank with nonstratified seeds. Velvetleaf seedling emergence was higher in the nonstratified seed bank in 2001, but no differences were observed in 2002. The number of viable velvetleaf seeds at the end of the experiment was lower in the natural seed bank than in the artificial seed banks in 2002. Velvetleaf emergence occurred earlier in the natural seed bank than in the artificial seed banks. Giant foxtail emergence was higher in the artificial seed banks (58 to 82%) than in the natural seed bank (5 to 23%). Common waterhemp emergence ranged from 7 to 65% in the artificial seed banks and from 1 to 5% in the natural seed bank. In general, the distribution of emergence with time differed in the natural seed bank compared with the artificial seed banks. These differences were attributed to differences in soil temperature and soil bulk density between the natural and artificial seed banks. Artificial seed banks showed lower soil bulk density and greater temperature fluctuation than the natural seed bank. However, there was no consistent relationship between growing degree days and emergence timing in the three treatments for any of the species studied.

The hydrochemistry of the headwaters of the River Severn, Plynlimon

Abstract. Water quality data spanning 13 years and covering an extensive range of major, minor and trace elements in rain and stream waters at Plynlimon in mid Wales, are presented. Rainfall water chemistry is highly variable due to varying proportions of marine and pollutant derived constituents associated with patterns of atmospheric circulation. Stream waters, being composed of different proportions of waters from three chemically distinct sources at any one time (atmospheric deposition, the soil system and deeper groundwaters), are also chemically highly variable. For example, components predominantly derived from deposition such as chloride change only in response to sea-salt deposition episodes. Solutes associated with bedrock weathering such as calcium, magnesium, and alkalinity decrease with increasing flow, those associated with the upper soil layers such as aluminium, many transition metals, dissolved organic carbon and hydrogen ions increase with increasing flow. The nutrients (e.g. nitrate, boron, bromide and iodine) exhibit strong seasonal cycles associated with cycles of vegetation growth and decay. The changes in stream water chemistry resulting from tree harvesting in the Afon Hore catchment are shown to have run their course within a period of eight years. Nutrient increases in the first few years following the commencement of felling have returned to or fallen below pre-felling values. Aluminium changes are shown to be complicated by changes in nitrate and calcium. Aluminium concentrations initially increased and have fallen below their pre-felling value. Data for chloride suggest a reduction in capture of dry and mist deposition; this indicates the importance of understanding reduced deposition as a result of felling. Felling has also affected the soil micro-climate which experiences greater fluctuations in temperature and an increase in the concentration of constituents associated with organic matter. Input-output mass balance estimates show that atmospheric inputs of many constituents are retained strongly by the catchment (e.g. ammonium, phosphate, barium, boron, lead and iodine). In contrast, many of the transition elements as well as divalent base cations, aluminium and alkalinity show a net release from the catchment. Conservative constituents such as chloride and sodium show a net input-output balance.

Lethal temperatures of a Neotropical fish relic in Patagonia, the scale-less characinid Gymnocharacinus bergi

Southern South America has a rather low fish species diversity. Gymnocharacinus bergi, the southernmost characid fish of the world, is the only member of Characoidei in the Argentine Patagonia. The isolation of this species in an endorheic stream has been linked to the thermal conditions of its habitat, the head-waters of the Valcheta Stream, which is the only site where this species occurs. We provide information on the distribution and thermal habitat of this species and other fishes in the Valcheta Stream. The responses of G. bergi to high and low temperatures were assessed in the laboratory under different temperatures and heating and cooling rates. Our results suggest that G. bergi is unable to extend its distribution to the colder waters nearby, as well as to waters with greater temperature fluctuations. We discuss the implications of our experimental data, the habitat of G. bergi, and the known responses of a few other paranensean fishes to temperature, within the framework of the thermal ecology of freshwater fishes.