Tolerances of wild potato species from different altitudes to cold and heat

The ability of wild potatoes (Solanum spp.) to adapt to potentially stressful environmental temperatures was investigated by measuring the cold and heat tolerances of plants grown near sea-level in Lima following collection of tubers from plants growing naturally at altitudes ranging from 450 to 4,200 m. Relative cold tolerance was measured in leaves stored at 0°C by the decrease in the induced rise of chlorophyll fluorescence. Similarly, changes in chlorophyll fluorescence were used to determine the relative heat tolerance of leaves heated at 41°C for 10 min. With increasing altitude, the cold tolerance of different species tended to increase and conversely, heat tolerance decreased. However, these two genotypic adaptations were not closely correlated and appear to vary independently of each other in response to climate.     

Freezing tolerance, cold acclimation and oxidative stress in potato. Paraquat tolerance is related to acclimation but is a poor indicator of freezing tolerance

Potato is a species commonly cultivated in temperate areas where the growing season may be interrupted by frosts, resulting in loss of yield. Cultivated potato, Solanum tuberosum, is freezing sensitive, but it has several freezing-tolerant wild potato relatives, one of which is S. commersonii. Our study was aimed to resolve the relationship between enhanced freezing tolerance, acclimation capacity and capacity to tolerate active oxygen species. To be able to characterize freezing tolerant ideotypes, a potato population (S1), which segregates in freezing tolerance, acclimation capacity and capacity to tolerate superoxide radicals, was produced by selfing a somatic hybrid between a freezing-tolerant Solanum commersonii (LT₅₀=-4.6°C) and -sensitive S. tuberosum (LT₅₀=-3.0°C). The distribution of non-acclimated freezing tolerance (NA-freezing tolerance) of the S1 population varied between the parental lines and we were able to identify genotypes, having significantly high or low NA-freezing tolerance. When a population of 25 genotypes was tested both for NA-freezing and paraquat (PQ) tolerance, no correlation was found between these two traits (R = 0.02). However, the most NA-freezing tolerant genotypes were also among the most PQ tolerant plants. Simultaneously, one of the NA-freezing sensitive genotypes (2022) (LT₅₀=-3.0°C) was observed to be PQ tolerant. These conflicting results may reflect a significant, but not obligatory, role of superoxide scavenging mechanisms in the NA-freezing tolerance of S. commersonii. The freezing tolerance after cold acclimation (CA-freezing tolerance) and the acclimation capacity (AC) was measured after acclimation for 7 days at 4/2°C. Lack of correlation between NA-freezing tolerance and AC (R =-0.05) in the S1 population points to independent genetic control of NA-freezing tolerance and AC in Solanum sp. Increased freezing tolerance after cold acclimation was clearly related to PQ tolerance of all S1 genotypes, especially those having good acclimation capacity. The rapid loss of improved PQ tolerance under deacclimation conditions confirmed the close relationship between the process of cold acclimation and enhanced PQ tolerance. Here, we report an increased PQ tolerance in cold-acclimated plants compared to non-acclimated controls. However, we concluded that high PQ tolerance is not a good indicator of actual freezing tolerance and should not be used as a selectable marker for the identification of a freezing-tolerant genotype.     

Differential stress responses to NaCl salt application in early- and late-maturing diploid potato (Solanum sp.) clones

Cultivated tetraploid potatoes (Solanum tuberosum L.) are moderately salt sensitive but greater stress tolerance exists in diploid wild types. However, little work has been published on salt-tolerance in diploid potato. This study utilized sensitive and tolerant diploid potatoes as well as a commercially cultivated potato to investigate mechanisms of stress tolerance. Stem cuttings from salt-tolerant (T) and sensitive (S) clones of early-maturing (EM) and late-maturing (LM) diploid potato clones were stressed for 5 days at the tuber initiation stage with 150 mmol NaCl in a hydroponic sand culture under greenhouse conditions. The stress responses of the early- and late-maturing potato clones were distinctly different. Under stress, early-maturing clones accumulated Na⁺ in the leaf tissues while late-maturing clones generally excluded Na⁺ from the leaf tissues. Salt tolerant clones of both maturity types were able to tolerate high levels of Na⁺ in the leaf tissues. The lower leaves accumulated more Na⁺ than the upper leaves in both maturity types. The potassium to sodium ratio was significantly greater in the leaves of the late-maturing types, reflecting differences in Na⁺ accumulation rather than alterations in K⁺ levels. Proline levels increased upon salt exposure but were not clearly associated with salinity tolerance. Tolerance was manifested in maintenance of vegetative growth, tuber yield, and reduced leaf necrosis. These responses require efficient uptake of water and source–sink translocation. Maintenance of stomatal conductance under stress was not associated with these responses but tuber yield was related to lower-leaf osmotic potential (OP) in both early- and late-maturity types. Salt tolerant clones of both maturity types also had less negative tuber OP under salt stress than sensitive types. High yielding EMT and LMT clones either minimized tuber yield loss or even increased yield after exposure to salt stress. Mechanistic studies and screening experiments for salt tolerant clones should consider maturity type, leaf position and source–sink relationships enhancing tuber yield.     

Effects of alternating exposure to cold and heat for 14 days on cold tolerance in winter

People are exposed to heat regularly due to their jobs or daily habits in cold winter, but few studies have reported whether parallel heat and cold exposure and diminish cold acclimation. This study was conducted to investigate the effects of alternating exposure to cold and heat on cold tolerance in eight young males. A daily acclimation program to cold and heat, which consisted of 2-h sitting at 10 °C air in the morning and 2-h running and rest at 30 °C air in the afternoon, was conducted for 14 consecutive days. Eight male subjects participated in a cold tolerance test (10 °C [ ± 0.3], 40%RH[ ± 3]) before (PRE) and after (POST) completing the alternating exposure program. During the cold tolerance test, subjects remained sitting upright on a chair for 60 min. Rectal temperature (T_re) was lower in POST than in PRE during the 60-min cold tolerance test (P = 0.027). During the cold tolerance test, systolic, diastolic, and mean arterial blood pressures in POST were lower than those in PRE (P = 0.006, P = 0.005, and P = 0.004). No significant differences in skin temperatures between PRE and POST were found for the cold tolerance test. There were no significant differences in energy expenditure during cold exposure between PRE and POST. Subjects felt less cold in POST than in PRE (P = 0.013) whereas there was no significant difference in overall thermal comfort between PRE and POST. These results suggest that cold adaptation can still occur in the presence of heat stress.     

Cold and heat tolerance of drosophilid flies with reference to their latitudinal distributions

The relation between thermal tolerance and latitudinal distribution was studied with 30 drosophilid species collected from the cool-temperate region (Sapporo), the warm-temperate region (Tokyo and Kyoto) and the subtropical region (Iriomote island) in Japan. In addition, intraspecific variation was examined for five species collected from two localities. The subtropical strains of Scaptodrosophila coracina, Drosophila bizonata and D. daruma were less tolerant to cold than their temperate strains. However, the difference of cold tolerance between these two geographic strains was much smaller than the difference between the species restricted to the subtropical region and those occurring in the temperate region. In D. auraria and D. suzukii, no difference was observed in thermal tolerance between their cool- and warm-temperate strains. Thus, geographic variation in thermal tolerance within species was low or negligible. Interspecific comparisons by phylogenetic independent contrasts revealed that species which had the northern boundaries of their distributions at higher latitudes were generally more tolerant to cold than those which had their boundaries at lower latitudes. However, the data for some species did not agree with this trend. The use of man-protected warm places for overwintering, competition or predation would also affect their distributions. It also appeared that species which had their southern boundaries at higher latitudes were generally more cold-tolerant. The acquisition of cold tolerance may lower a flys capacity to compete, survive or reproduce in warmer climates. On the other hand, no relation was observed between heat tolerance and latitudinal distribution. Heat tolerance was higher in species inhabiting openlands or the forest canopy than in those inhabiting the forest understorey.     

Storage temperature influences desiccation and ultra violet radiation tolerance of entomopathogenic nematodes

1. The effect of cold (5 °C) and warm (35 °C) storage on desiccation tolerance of cold-adapted Steinernema feltiae, intermediate S. carpocapsae and warm-adapted S. riobrave was evaluated at 5 and 35 °C.     

Clonal variation for tolerance to polyethylene glycol-induced water stress in cultured tomato cells

Cell clones were isolated from a population of cultured tomato (Lycopersicon esculentum Mill cv VFNT-cherry) cells and their tolerance to polyethylene glycol (PEG)-induced water stress was measured. Considerable variation for tolerance among the clones was found. Tolerance differences between clones appeared to be spontaneous and were different from tolerance differences between adapted and unadapted cells. Unlike adapted (selected by exposure to PEG) cells, cell clones retained their relative tolerance for many generations in the absence of selection pressure, and tolerance of both relatively tolerant and intolerant clones was very dependent on growth cycle stage and inoculum density. Analysis of subclones isolated from relatively tolerant and intolerant parent clones revealed that each parent clone gives rise to progeny with tolerances near the mean tolerance of both parents. However, progeny populations of both tolerant and intolerant parents are enriched with individuals with phenotypes nearer the mean response of their respective parent populations. When exposed to PEG, relatively tolerant and intolerant clones alike become adapted to the level of PEG to which they are exposed, and have the same phenotypic level of tolerance. Thus, selection by exposure to stress is unable to discriminate (on the basis of growth) between the innately tolerant and intolerant cell types within the population. This is indicated also by the fact that clones isolated from a population of cells adjusted to growth on 25% PEG do not show an enriched frequency of tolerant phenotypes when grown in the absence of PEG compared to the nonselected normal cell population which has never been adjusted to growth on PEG.     

Inter-animal radiation as potential heat stressor in lying animals

A model for predicting inter-animal radiant heat exchange in shaded animals is presented, with emphasis on mature cattle. When a cow’s surface temperature is 35 °C, as is common in warmer climates, it loses ～510 Watt m^?2 as radiant heat. Net radiant heat balance depends on radiation coming from bodies in the vicinity. In the 30 °C radiant temperature shaded environment typical of warm climates, net radiant loss from a lactating cow is ～60 Watt m^?2, i.e., 30 % of its ～173 Watt m^?2 heat production. Cows rest for 8–14 h day^?1. The heat exchange of a lying cow differs from that of a standing one: the body center is low and 20–30 % of its surface contacts a surface of relatively low heat conductance. Lying reduces the impact of the surrounding shaded area on heat exchange but increases that of heat radiating from neighboring cows. When a cow rests adjacent to other cows, with 1.25 m between body centers when in stalls, it occupies about 140° of the horizontal plane of view. Heat emitted from the animal’s surface reduces the net radiant heat loss of a resting cow by ～30 Watt m^?2. In contrast, the presence of cows at 5 and 10 m distance, e.g., cows resting on straw in loose yard housing, reduces the net radiant heat loss of the resting cow by 9 and 5 Watt m^?2, respectively. Radiant heat input increases with animal density, which is beneficial in cooler climates, but acts as a stressor in warm climates.     

Life cycle strategies and genotypic variability in populations of aphids

Populations of the rose aphid (Macrosiphum rosae) from various latitudes show differences in their life cycles. In warm climates they are exclusively parthenogenetic, whereas in cold climates sexual reproduction allows the aphid to overwinter in the egg stage. In temperate zones both holocyclic and anholocyclic clones occur within the same population. It is assumed that the reproductive mode has consequences for the genotypic structure of the populations. Continuous parthenogenesis results in low genogypic variability caused by selection and/or random genetic drift. The greater genotypic variability of holocyclic populations is due to recombination during the sexual phase. This yiew is supported by the study of populations which revealed high genotypic variability and homogeneity between populations in areas with harsh winters (e.g. Norway). In temperate countries (e.g. England) the genotypic variability was lower but the uniformity between populations still high, and in warm climates (e.g. the Canary Isles) the variability was lowest and heterogeneity between populations largest.     

Heat tolerance,temperature acclimation,acute oxidative damage and canalization of haemoglobin expression in <Emphasis Type="Italic">Daphnia</Emphasis>

Daphnia is a widespread freshwater zooplankton species, which is both a classic and emerging new model for research in ecological physiology, ecotoxicology and evolutionary biology of adaptation to novel environments. Heat tolerance in Daphnia is known to depend both upon evolutionary history of a genotype and on individuals’ acclimation to elevated temperature and to correlate with the level of haemoglobin expression. We demonstrate the existence of north–south gradient of heat tolerance in North American D. pulex, which is not associated with any parallel changes in haemoglobin expression. Geographically distinct clones differ in the way their haemoglobin expression changes due to acclimation to a sub-stressful (28°C) temperature, but these changes are not correlated with the latitude of clones’ origin. Likewise, the effect of acclimation to sub-stressful temperature is independent from, and cannot be fully explained by, haemoglobin expression changes during acclimation. The degree of oxidative damage to haemoglobin, measured as the ratio of absorbance at 540:576 nm at the acclimation temperature, is a strong predictor of 28°C-acclimated Daphnia survival during an acute heat exposure. The comparison of haemoglobin expression in resistant and tolerant clones acclimated to different temperatures indicates that tolerant clones exhibit canalization of haemoglobin expression, possessing a high level of haemoglobin even at non-stressful temperatures. We discuss the evolutionary biology of adaptation and acclimation to elevated temperatures in an ecologically important component of freshwater ecosystems in the context of global climate change.     

Indirect selection of thermal tolerance during experimental evolution of Drosophila melanogaster

Natural selection alters the distribution of a trait in a population and indirectly alters the distribution of genetically correlated traits. Long‐standing models of thermal adaptation assume that trade‐offs exist between fitness at different temperatures; however, experimental evolution often fails to reveal such trade‐offs. Here, we show that adaptation to benign temperatures in experimental populations of Drosophila melanogaster resulted in correlated responses at the boundaries of the thermal niche. Specifically, adaptation to fluctuating temperatures (16–25°C) decreased tolerance of extreme heat. Surprisingly, flies adapted to a constant temperature of 25°C had greater cold tolerance than did flies adapted to other thermal conditions, including a constant temperature of 16°C. As our populations were never exposed to extreme temperatures during selection, divergence of thermal tolerance likely reflects indirect selection of standing genetic variation via linkage or pleiotropy. We found no relationship between heat and cold tolerances in these populations. Our results show that the thermal niche evolves by direct and indirect selection, in ways that are more complicated than assumed by theoretical models.     

Assessing the heat tolerance of 17 beef cattle genotypes

Cattle production plays a significant role in terms of world food production. Nearly 82% of the world’s 1.2 billion cattle can be found in developing countries. An increasing demand for meat in developing countries has seen an increase in intensification of animal industries, and a move to cross-bred animals. Heat tolerance is considered to be one of the most important adaptive aspects for cattle, and the lack of thermally-tolerant breeds is a major constraint on cattle production in many countries. There is a need to not only identify heat tolerant breeds, but also heat tolerant animals within a non-tolerant breed. Identification of heat tolerant animals is not easy under field conditions. In this study, panting score (0 to 4.5 scale where 0 = no stress and 4.5 = extreme stress) and the heat load index (HLI) [HLI_BG<25°C = 10.66 + 0.28 × rh + 1.30 × BG – WS; and, HLI _{BG> 25°C} = 8.62 + 0.38 × rh + 1.55 × BG – 0.5 × WS + e^{(2.4 – WS)}, where BG = black globe temperature (^oC), rh = relative humidity (decimal form), WS = wind speed (m/s) and e is the base of the natural logarithm] were used to assess the heat tolerance of 17 genotypes (12,757 steers) within 13 Australian feedlots over three summers. The cattle were assessed under natural climatic conditions in which HLI ranged from thermonuetral (HLI < 70) to extreme (HLI > 96; black globe temperature = 40.2°C, relative humidity = 64%, wind speed = 1.58 m/s). When HLI > 96 a greater number (P < 0.001) of pure bred Bos taurus and crosses of Bos taurus cattle had a panting score ≥ 2 compared to Brahman cattle, and Brahman-cross cattle. The heat tolerance of the assessed breeds was verified using panting scores and the HLI. Heat tolerance of cattle can be assessed under field conditions by using panting score and HLI.     

No trade-off between high and low temperature tolerance in a winter acclimatized Danish Drosophila subobscura population

Coping with cold winter conditions is a major challenge for many insects.In early spring we observed newly emerged Drosophila subobscura, which had overwintered as larvae and pupae. As temperatures increase during spring these flies are faced with higher minimum and maximum temperatures in their natural microhabitat. Thus, there is a potential costly mismatch between winter and early spring acclimatization and the increased ambient temperatures later in adult life.We obtained individuals from a natural Danish population of D. subobscura and acclimated them in the laboratory to 20 °C for one generation, and compared critical thermal maximum (CTmax) and minimum (CTmin) to that of individuals collected directly from their natural microhabitat. The two populations (laboratory and field) were subsequently both held in the laboratory at 20 °C and tested for their CTmax and CTmin every third day for 28 days.At the first day of testing, field acclimatized D. subobscura had both higher heat and cold resistance compared to laboratory flies, and thereby a considerable larger thermal scope. Following transfer to the laboratory, cold and heat resistance of the field flies decreased over time relative to the laboratory flies. Despite the substantial decrease in thermal tolerances the thermal scope remained larger for field acclimatized individuals for the duration of the experiment.We conclude that flies acclimatized to their natural microhabitat had increased cold resistance, without a loss in heat tolerance. Thus while a negative correlation between cold and heat tolerance is typically observed in laboratory studies in Drosophila sp., this was not observed for field acclimatized D. subobscura in this study. We suggest that this is an adaptation to juvenile overwintering in temperate cold environments, where developmental (winter) temperatures can be much lower than temperatures experienced by reproducing adults after emergence (spring). The ability to gain cold tolerance through acclimatization without a parallel loss of heat tolerance affects thermal scope and suggests that high and low thermal tolerance act through mechanisms with different dynamics and reversibility.     

Scale‐dependent thermal tolerance variation in Australian mountain grasshoppers

Physiological variation among and within species is thought to play a key role in determining distribution patterns across environmental gradients. We tested inter‐ and intraspecific variation in cold and heat tolerances for three grasshopper species (genus Kosciuscola) with overlapping elevation distributions, across their respective ranges in the Australian mountains. Of the three cold tolerance traits measured, the critical thermal minimum was the only trait to vary among species, with greater cold tolerance associated with a distribution extending to a higher elevation. Cold tolerance limits were regularly exceeded in exposed microhabitats, suggesting a role for cold adaptation in structuring species distribution patterns. In contrast to cold tolerance, heat tolerance variation was primarily partitioned within species. For two species, populations from treeless alpine habitat were more heat tolerant than their lower‐elevation counterparts, supporting recent models that suggest greater exposure to temperature extremes at higher elevations. These contrasting patterns of physiological variation among and within species emphasise the importance of considering variation within species when attempting to understand how species distributions are affected by thermal extremes.     

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.     

Temperature tolerance of the mosquitofish, Gambmia affinis (Baird and Girard)

The capacity of a warm-adapted population of mosquito fish ( Gambusia affinis ) from the Sonoran Desert and a cold-adapted population from northern Utah to adjust to changing environmental temperatures has been described in terms of four criteria: (1) critical thermal maxima, (2) resistance times at high, lethal temperatures, (3) upper incipient lethal temperatures, and (4) lower lethal temperatures. Non-genetic scope for adaptation as related to changes in the thermal history of the individual and expressed in terms of the tolerance domain was identical for both populations. Genetic differences in adaptive capacity were apparent. The cold-adapted population was less tolerant of heat and more tolerant of cold as would be anticipated.     

Evaluation of the cold tolerance of Saccharum spontaneum L. clones with different ploidy levels on the basis of morphological and physiological indices

• Saccharum spontaneum L. is one of the most important germplasm resources for modern sugarcane breeding. Exploring the cold tolerance of S. spontaneum clones with different ploidy levels and screening for cold‐tolerant material can be helpful in parent selection for breeding cold‐tolerant sugarcane.
• Morphological indices, leaf ultrastructure and physiological indices were used to evaluate the cold tolerance of 36 S. spontaneum clones with different ploidy levels (2n = 40, 48, 54, 60, 64, 78, 80, 88, 92 and 96).
• The morphological indices of S. spontaneum clones with different ploidy levels were positively correlated with ploidy. Under low‐temperature stress, the chloroplast and mitochondrial structures of the clones with high ploidy were more severely damaged than were those of clones with low ploidy. A comprehensive evaluation of the physiological indices showed that the 36 S. spontaneum clones could be divided into four categories: strongly cold tolerant, cold tolerant, moderately cold tolerant and cold sensitive. Correlation analysis of the morphological indices and cold tolerance revealed a significant negative correlation between cold tolerance and ploidy. On the basis of the morphological and physiological indices, optimal stepwise regression equations that can be used for the selection of cold‐tolerant S. spontaneum resources were established.
• The S. spontaneum clones with low ploidy are more cold tolerant than those with high ploidy. Clones 12‐37, 13‐10 and 12‐23 are strongly cold‐tolerant germplasm resources, which suggests these germplasm sources have high potential for use in breeding cold‐tolerant sugarcane.

     

Rain shadow effects predict population differences in thermal tolerance of leaf-cutting ant workers (Atta cephalotes)

Tests of hypotheses for the evolution of thermal physiology often rely on mean temperatures, but mounting evidence suggests geographic variation in temperature extremes is also an important predictor of species’ thermal tolerances. Although the tropics are less thermally variable than higher latitude regions, rain shadows on the leeward sides of mountains can experience greater diel and seasonal variation in temperature than windward sites. Rain shadows provide opportunities to test predictions about the relationships of extreme temperatures with thermal physiology while controlling for latitude. We tested the hypothesis that populations of leaf-cutting ants (Atta cephalotes) in leeward, montane, and windward sites in Costa Rica would differ in upper thermal tolerances (CT_max) of workers. As predicted from rain shadow effects via extreme high temperatures, the leeward rain shadow site yielded the highest mean CT_max (rain shadow site 42.1 ± 0.3°C, Montane site 38.2 ± 0.5°C, and windward site 38.2 ± 0.3°C). This suggests that high-temperature extremes in tropical rain shadow forests can select for higher thermal tolerances. CT_max increased with worker body size within sites, but CT_max increased with body size more gradually at the two lowland sites, as predicted if local high temperatures selected more strongly on the most thermally vulnerable society members (small workers). This suggests that warmer lowland climates selected for colonies with less variation in heat tolerance than cooler high elevation climates.