Phylogeography of the mallard Anas platyrhynchos from Eurasia inferred from sequencing of the mtDNA control region

Phylogenetic relationships, demographic history, and geographic distribution of the mtDNA haplotypes of the mallard Anas platyrhynchos were examined in three populations, Indian, Northern European, and Far Eastern. Two divergent halotype groups, A and B, were found in the Far Eastern population, while haplotypes identified in Northern European and Far Eastern populations were exclusively of the A group. The presence of B group haplotypes in the Far Eastern population can be explained either in terms of hybridization of the mallard with spot-billed duck Anas zonorhyncha at the south of the Russian Far East, or by the mtDNA paraphyly in mallards. In general, mallards from Eurasia were characterized by low genetic population differentiation along with slightly expressed phylogeographic structure. The most differentiated was the population from India (??_st = 0.076?0.077), while the difference between Northern European and Far Eastern populations was extremely low (??_st = 0.0029). Differentiation of Anas platyrhynchos Indian population was determined by the fact that a part of the population, inhabiting southern and eastern coasts of the Hindustan Peninsula, was resident.     

Thermal properties of NADP:ferredoxin oxidoreductase and ferredoxin isolated from a thermophilic blue-green alga

NADP:ferredoxin oxidoreductase (EC. 1.6.7.1.) isolated from a thermophilic blue-green alga, Synechococcus sp., was stable at temperatures up to 65°C. The diaphorase and cytochrome c reductase activities of the enzyme were low at 25°C but increased with elevated temperature to reach a maximum at about 60°C. The pH-profile of the diaphorase activity showed a peak at pH 9.0 at 55°C, whereas the activity was largely independent of pH at 25°C. High concentrations of NaCl suppressed activity at both high and low temperatures. In the cytochrome c reductase activity catalyzed by the enzyme, ferredoxin served as an electron carrier in a temperature-insensitive manner over a wide range of temperature. The results support the view that the optimum and the upper limiting temperatures for photosynthesis in this alga are related to thermal properties of proteins.     

Effects of cold stress on metabolic regulation in the overwintering larvae of the Chinese white pine beetle,Dendroctonus armandi

The Chinese white pine beetle, Dendroctonus armandi Tsai & Li (Coleoptera: Curculionidae, Scolytinae), is considered the most destructive forest pest in the Qinling and Bashan Mountains of China. In recent years, winter temperature has dropped in these regions, and extremely low temperatures are hard to survive for insects. Cold hardiness becomes a crucial strategy because temperature change often leads to fluctuations in insect abundance, and the metabolism rate is a key index of resistance to cold in overwintering insects. Therefore, we investigated the relationship between the change in respiratory rate and the activity of metabolism-related mitochondrial enzymes in D. armandi larvae under cold conditions. We found that the respiratory rate decreased, and it was matched with the activity of glutamate dehydrogenase, aconitase, and lipase during overwintering. Among the various test times under cold conditions, the respiratory rate also decreased with decreasing temperature and increased under very low temperatures. At all cold stress periods, glutamate dehydrogenase and lipase showed increased activity at higher temperatures and decreased activity under lower temperatures, but the activity of NAD-malic enzyme, NADP-malic enzyme, mitochondrial isocitrate dehydrogenase, and aconitase were contrary. Under all low temperatures, the activity of enzymes – except for NADP-malic enzyme, glutamate dehydrogenase, and lipase – increased in short-term cold stress and decreased in long-term cold stress at 4, 0, −4, −6, −8, and −10 °C. However, at −2 °C, the activity of enzymes showed a decreasing trend in short-term treatments and an increasing trend in long-term treatments, except for mitochondrial isocitrate dehydrogenase. The results not only improve our understanding of the metabolic mechanism of cold adaptation in D. armandi, but also provide an important experimental basis for further study and biological pest control.     

Geographic variation in thermal and photoperiodic effects on development of zoophytophagous plant bug Nesidiocoris tenuis

The zoophytophagous plant bug Nesidiocoris tenuis (Reuter) is increasingly used for biological control of various agricultural pests. Its native range includes Southern Europe, North Africa, Southern and South‐Eastern Asia, although only the Mediterranean strains have been studied experimentally. We investigated effects of temperature and photoperiod on nymphal survival and development, rate of female maturation and egg load in two strains of N. tenuis originating from temperate and subtropical regions of South‐Eastern Asia: the ‘Temperate strain’ (from Suwon, Republic of Korea, yearly average air temperature is 13.3°C) and the ‘Subtropical strain’ (from Miyazaki, Japan, yearly average air temperature is 18.2°C). Nymphs and adults were reared on tomato leaflets and fed with eggs of the grain moth Sitotroga cerealella under four temperatures (15, 20, 25 and 30°C) and three photoperiods (10, 12 and 14 h of light per day). In spite of long‐term (40–50 generations) rearing under constant laboratory conditions, the studied strains still show a correlation between thermotolerance indices and climate at origin. In particular, at the low temperature of 15°C, survival of nymphs of the Temperate strain was double that of the Subtropical strain, whereas at the higher tested temperatures, survival of the Subtropical strain was not significantly different or even was higher than that of the Temperate strain. The duration of nymphal development in the Temperate strain was significantly shorter than that in the Subtropical strain at 15–25°C, but not at 30°C. In both strains, nymphal survival, duration of nymphal development and rate of female maturation were not significantly dependent on photoperiod, and diapause was not observed under any conditions tested. We conclude that the Subtropical strain of N. tenuis is better adapted to high temperatures, whereas the Temperate strain is more promising for application in greenhouses at medium and low temperatures.     

Are Tropical Highland Frog Calls Cold–adapted? The Case of the Andean Frog Hyla labialis1

Across a wide range of temperatures established in the laboratory, we tape–recorded the advertisement calls of 76 freshly caught Hyla labialis males from three elevationally separated populations in the Eastern Andes of Colombia. Each male was tested once at a single temperature and returned to his capture site after measurement of his snout–vent length. We measured and averaged three characteristics of five to ten successive calls for each individual: number of pulses per call, pulse repetition rate, and call duration. We found that calling activity occurred within temperature ranges that overlapped among frogs from different elevations, but widened and shifted downward with increasing altitude of origin. Males from all sites called at temperatures higher, but not lower, than those naturally occurring during their nightly activity period. No decline in vocal performance was apparent when frogs extended their calling activity into the range of high temperatures selected for basking. Both snout–vent length and temperature affected pulse repetition rate and call duration, while the number of pulses per call was temperature–independent. Compared to the smaller males from lower elevations, the larger, high–mountain males had calls with significandy more pulses, a lower pulse repetition rate, and longer duration. Within each population, rising temperatures caused pulse repetition rate to increase and call duration to decrease significantly, whereas the number of pulses per call remained unchanged. Pulse repetition rate of highland males was the factor least affected by temperature, and it was less sensitive to night temperatures than to day temperatures. This, together with their capacity to call at low temperatures, suggests that highland frog calls are cold adapted.     

A comparison of low temperature tolerance traits between closely related aphids from the tropics, temperate zone, and Arctic

The survival of aphids exposed to low temperatures is strongly influenced by their ability to move within and between plants and to survive exposure to potentially lethal low temperatures. Little is known about the physiological and behavioural limitations on aphid movement at low temperatures or how they may relate to lethal temperature thresholds. These questions are addressed here through an analysis of the thermal ecology of three closely related aphid species: Myzus persicae, a ubiquitous temperate zone pest, Myzus polaris, an arctic species, and Myzus ornatus, a sub-tropical species. Lower lethal temperatures (LLT₅₀) of aphids reared at 15 °C were similar for M. persicae and M. polaris (range: −12.7 to −13.9 °C), but significantly higher for M. ornatus (−6.6 °C). The temperature thresholds for activity and chill coma increased with rearing temperature (10, 15, 20, and 25 °C) for all clones. For M. polaris and M. ornatus the slopes of these relationships were approximately parallel; by contrast, for M. persicae the difference in slopes meant that the difference between the temperatures at which aphids cease walking and enter coma increased by approximately 0.5 °C per 1 °C increase in rearing temperature. The data suggest that all three species have the potential to increase population sizes and expand their ranges if low temperature limitation is relaxed.     

Biochemical and phylogenetic analyses of a cold-active beta-galactosidase from the lactic acid bacterium Carnobacterium piscicola BA

We are investigating glycosyl hydrolases from new psychrophilic isolates to examine the adaptations of enzymes to low temperatures. A beta-galactosidase from isolate BA, which we have classified as a strain of the lactic acid bacterium Carnobacterium piscicola, was capable of hydrolyzing the chromogen 5-bromo-4-chloro-3-indolyl beta-D-galactopyranoside (X-Gal) at 4 degrees C and possessed higher activity in crude cell lysates at 25 than at 37 degrees C. Sequence analysis of a cloned DNA fragment encoding this activity revealed a gene cluster containing three glycosyl hydrolases with homology to an alpha-galactosidase and two beta-galactosidases. The larger of the two beta-galactosidase genes, bgaB, encoded the 76.8-kDa cold-active enzyme. This gene was homologous to family 42 glycosyl hydrolases, a group which contains several thermophilic enzymes but none from lactic acid bacteria. The bgaB gene from isolate BA was subcloned in Escherichia coli, and its enzyme, BgaB, was purified. The purified enzyme was highly unstable and required 10% glycerol to maintain activity. Its optimal temperature for activity was 30 degrees C, and it was inactivated at 40 degrees C in 10 min. The K(m) of freshly purified enzyme at 30 degrees C was 1.7 mM, and the V(max) was 450 micromol. min(-1). mg(-1) with o-nitrophenyl beta-D-galactopyranoside. This cold-active enzyme is interesting because it is homologous to a thermophilic enzyme from Bacillus stearothermophilus, and comparisons could provide information about structural features important for activity at low temperatures.     

Competitive ability of the antagonists Ulocladium atrum and Gliocladium roseum at temperatures favourable for Botrytis spp. development

Ulocladium atrum and Gliocladium roseum are fungal antagonists capable of suppressing sporulation of Botrytis spp. on dead plant parts. The effect of temperature (3 to 36 °C) on antagonist conidial germination and mycelial growth was assessed on agar. In addition conidial germination of U. atrum was measured on dead lily leaves. The optimum temperature of both antagonists for both conidial germination and mycelial growth was between 27 and 30 °C. U. atrum was less affected by lower temperatures than G. roseum. At optimum temperature, 50% of conidia of U. atrum and G. roseum germinated within 2.6 and 10.0 hrs, respectively. At low sub-optimal temperatures (6 °C), 50% of conidia germinated within 18 and 96 hours, respectively.In bioassays on dead onion leaves, U. atrum suppressed sporulation of B. cinerea and B. aclada at all temperatures tested (6 to 24 °C) by more than 85%. On dead cyclamen leaves, G. roseum was more efficient than U. atrum at 21 and 24 °C but, in contrast to U. atrum, showed no antagonistic activity at temperatures below 21 °C. On dead hydrangea leaves, U. atrum significantly reduced sporulation of B. cinerea at temperatures as low as 3 and 1 °C. Under Dutch growing conditions, the mean air temperature during leaf wetness periods in onion and lily fields was 15 °C with temperatures only occasionally above 20 °C. In greenhouse crops of cyclamen, the mean temperature during high humidity periods was 17 °C. It is therefore concluded that U. atrum is better adapted than G. roseum to temperatures which occur in the field, in greenhouse crops such as cyclamen, or during cold storage of plant stocks.     

Effects of low temperature on the development of the microsporidan Glugea stephani in English sole (Parophrys vetulus)

Glugea stephani requires temperatures above 15 C for development in juvenile pleuronectid flatfishes in Yaquina Bay, Oregon. The effect of low temperature (10 C) on the development of recently established parasites was tested experimentally in juvenile English sole (Parophrys vetulus). Low temperature arrested parasite development, but did not kill the protozoan which resumed development on return to 19-20 C after as long as 42 days at 10 C. No parasites detectable with the light microscope were found in fish examined after 70 days at 10 C. Although most juvenile English sole move permanently from the estuary to cooler ocean waters in fall and do not contribute to the continuation of the parasite life cycle, the cycle may be maintained by low numbers of English sole that overwinter in the estuary.     

Effect of Ambient Temperature on the Body Temperature Rhythm of Male Gray Mouse Lemurs (Microcebus murinus)

In order to cope with the seasonal variations in ambient temperature and food availability in the natural habitat, gray mouse lemurs (Microcebus murinus) exhibit adaptive energy-saving mechanisms similar to those in hibernating species with seasonal and daily heterothermia. To determine thermoregulatory responses, via telemetry we recorded body temperature and locomotor activity variations during the breeding season in three captive male mouse lemurs kept at ambient temperatures (T_a) ranging from 18° to 34°C. Rhythms in body temperature and locomotor activity were clearly exhibited regardless of ambient temperature. As _a increased, mean body temperature increased from 36.5 ± 0.1°C to 37.6 ± 0.3°C, with significant change in the amplitude of the body temperature rhythm when _a rose above 28°C. Effects of _a were mostly due to changes in the fall in body temperature occurring daily at the beginning of the light phase when the subjects entered diurnal sleep. The daily decrease in body temperature was not modified by exposure to ambient temperatures from 18°C to 28°C whereas it disappeared under warmer condition. Changes in locomotor activity levels only delayed the occurrence of thermoregulatory modulation. These results strongly suggest that, during the breeding season, the thermoneutral zone of mouse lemurs is close to 28°C and that the diurnal fall in body temperature could be considered as an important adaptive energy-saving mechanism adjusted to ecological constraints.     

Evaluation of manometric temperature measurement, a process analytical technology tool for freeze-drying: Part I, product temperature measurement

This study examines the factors that may cause systematic errors in the manometric temperature measurement (MTM) procedure used to evaluate product temperature during primary drying. MTM was conducted during primary drying using different vial loads, and the MTM product temperatures were compared with temperatures directly measured by thermocouples. To clarify the impact of freeze-drying load on MTM product temperatures, simulation of the MTM vapor pressure rise was performed, and the results were compared with the experimental results. The effect of product temperature heterogeneity in MTM product temperature determination was investigated by comparing the MTM product temperatures with directly measured thermocouple product temperatures in systems differing in temperature heterogeneity. Both the simulated and experimental results showed that at least 50 vials (5 mL) were needed to give sufficiently rapid pressure rise during the MTM data collection period (25 seconds) in the freeze dryer, to allow accurate determination of the product temperature. The product temperature is location dependent, with higher temperature for vials on the edge of the array and lower temperature for the vials in the center of the array. The product temperature heterogeneity is also dependent upon the freeze-drying conditions. In product temperature heterogeneous systems, MTM measures a temperature close to the coldest product temperature, even, if only a small fraction of the samples have the coldest product temperature. The MTM method is valid even at very low product temperature (−45°C). Published: February 10, 2006     

Thermal relations of dwarf caiman, Paleosuchus palpebrosus, in a hillside stream: Evidence for an unusual thermal niche among crocodilians

Body temperatures of 13 Paleosuchus palpebrosus, 7 males and 6 females, were monitored by radio-telemetry during cold periods (dry season) and warm periods (wet and dry seasons) in a stream draining into the Brazilian Pantanal. The mass of the caimans varied from 2.5 to 20.0 kg, and snout–vent length from 47.5 to 95.0 cm. Mean monthly body temperature was 21.6 °C, and varied from 20.1 to 25.6 °C throughout the year. Body temperature was correlated with air and water temperature but did not differ between males and females. Unlike all other crocodilians investigated in detail to date, the caimans did not show evidence of attempts to obtain higher body temperatures when ambient temperatures were low, and had low and generally constant temperatures in relation to the surrounding air and water throughout the year. The caimans remained in burrows during cold periods in the dry season, which may explain why they did not seek higher temperatures. Tolerance of relatively low and constant body temperatures may be a key adaptation of species of Paleosuchus, allowing them to occupy environments inhospitable to other crocodilians.     

Conserving the gene pool of Far Eastern plants by means of seed cryopreservation

Cryotolerance of seeds has been studied in 103 plant species of 33 families from five regions of the Russian Far East. In 89.1% of these species, seed viability has not decreased in the course of cryogenic storage. Six species have shown interpopulation variation in the seed response to extremely low temperature (?196°C). Freezing in liquid nitrogen, which results in deep anabiosis, can be used as a means for long-term seed storage. A preliminary assessment of genetic diversity at the population level provides for the maximum possible mobilization of the species gene pool. The results of this study contribute to the development of a scientific basis for creating a seed bank of the Far Eastern flora with the purpose to conserve and restore biological resources of the region.     

Temperature dependence of courtship behabiour in the male guppy,

We measured frequency and duration of different courtship activities of male guppies (especially the simoid display) at different temperatures, by means of direct observations, and video-recorder. We observed that the animals undergoing long-term temperature adaptation show nearly an independence of courtship frequency to the influence of temperature within the range of 20° to 30°C. After transfer to higher or lower temperatures, the frequency of the sigmoid behaviour was diminished. Afterwords, temperature compensation took place. The duration of the sigmoid display was temperature dependent. We concluded that certain fin movements during the sigmoid display were directly temperature dependent, and that lowering the temperature acted as a stressor on sexual motivation. After adaptation to the new temperature (which lasted 4–5 days) the fish were able to show a complete cycle of 5.5 dorsal fin movements per sigmoid display in temperatures between 20° and 30° C.     

Low temperature perception in plants: effects of cold on protein phosphorylation in cell-free extracts

Activities of prevalent protein phosphatases decreased by nearly 95% and those of individual protein kinases were differentially reduced at low temperature. Inhibition of phosphatase activity at temperatures below 12°C resulted in marked hyperphosphorylation of a 58-kDa protein (PP58). The temperature threshold for hyperphosphorylation of PP58 coincided with the known threshold for cold-induced calcium influx. Since calcium influx is triggered by several environmental stresses, we propose that the observed direct effects of cold on the phosphorylation of specific proteins enable cells to couple a shared calcium signal to a cold-specific transduction pathway.     

Kinetic and thermodynamic characterization of the cold activity acquired upon single amino-acid substitution near the active site of a thermostable α-glucosidase

The α-glucosidase of Bacillus sp. SAM1606, a thermophilic bacterium, is a thermostable enzyme that has maximal activity at an apparent optimal temperature between 65 and 70 °C and only very low activity at low temperatures (0–25 °C). In this study, we identified Thr272, which is located adjacent to Glu271 (a catalytic residue) and Gly273 (a determinant of specificity), as a determinant of the optimal temperature, as substitution of Thr272 with other residues significantly altered the temperature–activity profile of the enzyme. Substitution of Thr272 with other amino acids, in particular bulky hydrophobic residues such as valine, methionine and phenylalanine, resulted in a significant downward shift (by 30 °C) of the apparent optimal temperature with an increase in catalytic activity at low temperatures. The observed downward shift of the apparent optimal temperature was not due to instability of the mutants at 40–65 °C, as the mutants were stable at temperatures up to 65 °C. Among the mutants examined, T272V displayed the highest k_cat values at 10–25 °C, which was at least 11-fold greater than the k_cat value observed for the wild-type enzyme. The thermodynamic characteristics of reactions catalyzed by T272V, T272M, T272F, and wild type at 25 °C were examined in greater detail. The T272V, T272M and T272F mutants displayed large K_s (or K_m) values and reduced and values at 25 °C, consistent with the general features of cold adaptation. The observed cold activities of T272V, T272M and T272F most likely arose from local flexibility of the active site at low temperatures due to loss of a Thr272-mediated hydrogen bond. However, this hydrogen-bond loss likely permits reversible conformational changes of the active site to less active forms at elevated temperatures (e.g., 60 °C). This may explain why catalytic activities for T272V, T272M and T272F at high temperatures (e.g., 60 °C) were lower than those at low temperature (e.g., 25 °C), even though the mutant enzymes appeared stable at 60 °C.     

Influence of rearing temperature on triacylglycerol storage in the pea aphid,Acyrthosiphon pisum

Total fatty acids in the pea aphid reared at low temperatures increased significantly compared to that at high rearing temperatures. This change is reflected in a large increase of myristic acid, which occurs exclusively in triacylglycerols. When aphids were moved from 25°C to a lower rearing temperature at 10°C, saturated fatty acids accumulated over time, reaching a maximum at 16th day. When aphids were moved to 4°C, a temperature below the developmental threshold, those aphids did not accumulate saturated fatty acids. Similar results were observed when aphids were exposed to sequential decrease in rearing temperature. However, both total fatty acids and myristic acid in the aphids from the treatments of sequential decreasing rearing temperature were significantly higher compared to those in the aphids from the treatments of sudden decreasing rearing temperature. This result, therefore, supports the hypothesis that cold‐adapted aphids can survive under threshold temperature for a longer period of time than noncold‐adapted aphids. Acetyl‐CoA carboxylase activity in the aphids at 25°C was twofold higher than that in the aphids at 10°C, whereas fatty acid synthase activities in the aphids reared at 25 and 10°C are similar. Aphids reared at 10°C showed a threefold reduction in reproduction rates. This reduced production of new nymphs reduces energy demand and would allow for accumulation of energy in the form of triacylglycerols. Therefore, the increased level of saturated fatty acids in aphids reared at low temperature is probably related to lower utilization of fatty acids rather than increased rates of biosynthesis.     

Multigenerational exposure to increased temperature reduces metabolic rate but increases boldness in Gambusia affinis

Acute exposure to warming temperatures increases minimum energetic requirements in ectotherms. However, over and within multiple generations, increased temperatures may cause plastic and evolved changes that modify the temperature sensitivity of energy demand and alter individual behaviors. Here, we aimed to test whether populations recently exposed to geothermally elevated temperatures express an altered temperature sensitivity of metabolism and behavior. We expected that long‐term exposure to warming would moderate metabolic rate, reducing the temperature sensitivity of metabolism, with concomitant reductions in boldness and activity. We compared the temperature sensitivity of metabolic rate (acclimation at 20 vs. 30°C) and allometric slopes of routine, standard, and maximum metabolic rates, in addition to boldness and activity behaviors, across eight recently divergent populations of a widespread fish species (Gambusia affinis). Our data reveal that warm‐source populations express a reduced temperature sensitivity of metabolism, with relatively high metabolic rates at cool acclimation temperatures and relatively low metabolic rates at warm acclimation temperatures compared to ambient‐source populations. Allometric scaling of metabolism did not differ with thermal history. Across individuals from all populations combined, higher metabolic rates were associated with higher activity rates at 20°C and bolder behavior at 30°C. However, warm‐source populations displayed relatively bolder behavior at both acclimation temperatures compared to ambient‐source populations, despite their relatively low metabolic rates at warm acclimation temperatures. Overall, our data suggest that in response to warming, multigenerational exposure (e.g., plasticity, adaptation) may not result in trait change directed along a simple “pace‐of‐life syndrome” axis, instead causing relative decreases in metabolism and increases in boldness. Ultimately, our data suggest that multigenerational warming may produce a novel combination of physiological and behavioral traits, with consequences for animal performance in a warming world.     

Effect of maturation conditions on light and temperature requirements during seed germination of Citrullus colocynthis from the Arabian Desert

• Seed germination of Citrullus colocynthis, as in many other species of Cucurbitaceae, is inhibited by light, particularly at low temperatures. Germination response to light and temperature has been attributed to day length and temperature during seed maturation. This study assessed the effects of these factors on the germination response of C. colocynthis to temperature and light quality.
• Ripe fruits were collected from natural habitats during December and February and germinated at three temperatures (15/25, 20/30 and 25/35 °C) in five light treatments (dark, white light and Red:Far Red (R:FR) ratios of 0.30, 0.87 and 1.19). Additionally, unripe fruits were also collected from natural habitats and completed their maturation in growth chambers under different day lengths (6, 16 and 24 h of darkness) at 10/20 °C, and in darkness at both 10/20 °C and 25/35 °C. Mature seeds of the different treatments were germinated in the same five light treatments at 15/25 °C.
• Germination was significantly higher in the dark than that in any light treatment. Seeds matured at higher temperatures (i.e. seeds from the December collection and those matured at 25/35 °C) had significantly higher germination than those matured at lower temperatures (i.e. seeds from the February collection and those matured at 10/20 °C). Dark germination was significantly higher for the December collection than for the February collection. Seeds of the two collections germinated in the dark only at 15/25 °C. However, seeds matured in a growth chamber at 10/20 °C in darkness germinated at 15/25 °C in all light treatments, except for the R:FR ratio 0.30. Seeds of the different treatments failed to germinate in FR‐rich light.
• This study demonstrates that both temperature and day length during seed maturation play significant roles in the germination response of C. colocynthis. Additionally, the dark requirement for germination is likely beneficial for species with the larger seeds, such as C. colocynthis, which produce bigger seedlings that are able to emerge from deep soils and are competitively superior under dense vegetation and resource‐limited conditions.

     

Water temperature behaviour in the River Danube during the twentieth century

Monthly mean water temperatures in the River Danube at Linz, Austria during the period 1901–1990 have been investigated in relation to equivalent information on air temperature and river discharge. Statistical analysis revealed a significant increase in monthly mean water temperatures of 0.8 °C and showed strongest rises in mean values for autumn and early winter months. No statistically significant trends were evident for air temperature or river discharge, and rising water temperatures are likely to reflect increasing human modification of the river system. A strong overall correlation between monthly mean water and air temperatures at Linz was made up of a series of more scattered and less steep water/air temperature relationships for individual months, while the influence of snowmelt runoff depressed average water temperatures in the spring and early summer period by 1.5 °C. Multiple regression relationships developed for individual months from data on air temperature, river discharge and time trend during the study period were able to predict monthly mean water temperatures in 1991 and 1992 with a root mean square error of 0.5 °C. These regression equations, when combined with scenarios of future changes in air temperature and river flow as a consequence of global warming, suggest that only modest rises in monthly mean water temperature will be experienced in the River Danube by the end of the present century, but that increases of > 1 °C for all months, and > 2 °C for the autumn period of low flows, can be anticipated by the year 2030.