Variation In Stress Resistance Research Articles

Germination responses of two key mountain tree species to single and combined fire-related stresses: does elevational origin matter?

Since climate change is expected to increase fire activity and drought stress in forests across the globe, studying seed resistance to heat stress and drought is imperative to predict future mountain forest regeneration scenarios. Here, stress co-occurrence and among population variation in stress resistance are key elements to consider. We hypothesized that i) increasing heat/osmotic stress intensity decreases germination performance; ii) seeds from higher elevations (i.e. cooler and wetter climatic conditions) exhibit lower resistance to heat/osmotic stress showing a stronger decline in germination performance as compared to seeds from lower elevations (i.e. warmer and drier climatic conditions); and that iii) elevational differences in seed stress resistance vary depending on whether stresses are applied alone or in combination. We exposed seeds from Polylepis australis and Escallonia cordobensis from low (1200 – 1400 m), mid (1650 – 1800 m) and high (2000 – 2200 m) elevational origins to different heat (control, 75, 105 °C) and osmotic (0, -0.3, -0.6 MPa polyethylene glycol) stress intensities. Germination performance decreased with increasing heat/osmotic stress intensity and clear differences among elevational origins were observed. In both species low-mid elevation seeds showed lowest performances but exhibited slightly higher stress resistance than high elevation seeds; yet the nature of these responses was species-specific. Our results demonstrate that germination response to a combination of heat stress and drought is different from the response to each of these stresses applied individually. Therefore, understanding how interactions of climate change with fire events can influence germination timing and success in mountain trees requires considering the effect of multiple stressors on seed physiology. Our findings also highlight the potential population-specific and species-specific responses, which could be used as guidance for ongoing restoration plans.

Variation in adult stress resistance does not explain vulnerability to climate change in copper butterflies.

Ongoing climate change is a major threat to biodiversity. However, although many species clearly suffer from ongoing climate change, others benefit from it, for example, by showing range expansions. However, which specific features determine a species' vulnerability to climate change? Phenotypic plasticity, which has been described as the first line of defence against environmental change, may be of utmost importance here. Against this background, we here compare plasticity in stress tolerance in 3 copper butterfly species, which differ arguably in their vulnerability to climate change. Specifically, we investigated heat, cold and desiccation resistance after acclimatization to different temperatures in the adult stage. We demonstrate that acclimation at a higher temperature increased heat but decreased cold tolerance and desiccation resistance. Contrary to our predictions, species did not show pronounced variation in stress resistance, though plastic capacities in temperature stress resistance did vary across species. Overall, our results seemed to reflect population-rather than species-specific patterns. We conclude that the geographical origin of the populations used should be considered even in comparative studies. However, our results suggest that, in the 3 species studied here, vulnerability to climate change is not in the first place determined by stress resistance in the adult stage. As entomological studies focus all too often on adults only, we argue that more research effort should be dedicated to other developmental stages when trying to understand insect responses to environmental change.

Resistance to environmental stress in Drosophila ananassae: latitudinal variation and adaptation among populations

Geographical variation in traits related to fitness is often the result of adaptive evolution. Stress resistance traits in Drosophila often show clinal variation, suggesting that selection affects resistance traits either directly or indirectly. Multiple stress resistance traits were investigated in 45 natural populations of Drosophila ananassae collected from all over India. There was significant positive correlation between starvation resistance and lipid content. Significant negative correlations between desiccation and lipid content and between desiccation and heat resistance were also found. Flies from lower latitudes had higher starvation resistance, heat resistance and lipid content but the pattern was reversed for desiccation resistance. These results suggest that flies from different localities varied in their susceptibility to starvation because of difference in their propensity to store body lipid. Multiple regression analysis provided evidence of climatic selection driven by latitudinal variation in the seasonal amplitude of temperature and humidity changes within the Indian. Finally, our results suggest a high degree of variation in stress resistance at the population level in D. ananassae.

Glutathione and Gts1p drive beneficial variability in the cadmium resistances of individual yeast cells

Phenotypic heterogeneity among individual cells within isogenic populations is widely documented, but its consequences are not well understood. Here, cell-to-cell variation in the stress resistance of Saccharomyces cerevisiae, particularly to cadmium, was revealed to depend on the antioxidant glutathione. Heterogeneity was decreased strikingly in gsh1 mutants. Furthermore, cells sorted according to differing reduced-glutathione (GSH) contents exhibited differing stress resistances. The vacuolar GSH-conjugate pathway of detoxification was implicated in heterogeneous Cd resistance. Metabolic oscillations (ultradian rhythms) in yeast are known to modulate single-cell redox and GSH status. Gts1p stabilizes these oscillations and was found to be required for heterogeneous Cd and hydrogen-peroxide resistance, through the same pathway as Gsh1p. Expression of GTS1 from a constitutive tet-regulated promoter suppressed oscillations and heterogeneity in GSH content, and resulted in decreased variation in stress resistance. This enabled manipulation of the degree of gene expression noise in cultures. It was shown that cells expressing Gts1p heterogeneously had a competitive advantage over more-homogeneous cell populations (with the same mean Gts1p expression), under continuous and fluctuating stress conditions. The results establish a novel molecular mechanism for single-cell heterogeneity, and demonstrate experimentally fitness advantages that depend on deterministic variation in gene expression within cell populations.

Geographic variation for climatic stress resistance traits in the springtail Orchesella cincta

Multiple traits of stress resistance were investigated in the epedaphic springtail Orchesella cincta. Second generation adults from five laboratory populations were compared with respect to resistance to extreme temperatures and desiccation, and traits relevant to climatic adaptation. Populations were collected along a 2000-km latitudinal gradient ranging from Denmark to southern Italy and reared under the same standard laboratory conditions. Traits investigated were resistance to high and low temperature, desiccation resistance, body size and water loss rate (WLR). Results showed genetically based differences in resistance to high and low temperature, desiccation, WLR, water pool and body size between populations. Individuals from the most northern population had the highest desiccation—and cold shock resistance, and the lowest heat shock resistance. Females were significantly more desiccation resistant than males. The results of cold shock resistance showed a positive increase with lowest environmental temperature recorded at the sites of population origin, whereas heat shock resistance showed a positive increase with highest recorded temperature at the sites of population origin. Desiccation resistance increased towards the most southern and northern population, suggesting that both low and high temperature extremes affect desiccation resistance. Body mass, water pool and WLR showed interpopulation as well as sex specific variation. This provides evidence for geographical variation in stress resistance of springtails related to climatic conditions.

Correlations between measures of thermal stress resistance within and between species

Resistance to an environmental stress such as elevated temperature can almost always be measured in several different ways. A number of recent studies in Drosophila show that lethal and non-lethal measures of resistance to heat stress are genetically independent. In contrast, data reported here suggest that there are interspecific correlations between measures of thermal stress resistance. Together, these results show that studies of intraspecific variation in stress resistance must demonstrate the ecological relevance of the measures of stress resistance chosen for study. In contrast, interspecific comparisons could be based on any of several measures of resistance. It would be interesting to determine if this pattern holds for resistance to other major environmental stresses.

Desiccation and starvation resistance in Drosophila: patterns of variation at the species, population and intrapopulation levels.

A substantial number of Drosophila studies have investigated variation in desiccation and starvation resistance, providing an opportunity to test for consistent patterns of direct and correlated responses across studies and across the species and population levels. In general, responses to laboratory selection for these traits in D. melanogaster are rapid and indicate abundant genetic variation in populations. However, slower responses to selection for desiccation resistance occur in other species including D. simulans. Clines suggest adaptive divergence although specific selection pressures have not been documented empirically. Drosophila species differ markedly in desiccation and starvation resistance and there is also marked variation within species for desiccation resistance that may be linked to local climatic conditions. Laboratory selection experiments on starvation resistance in D. melanogaster suggest that changes in lipid content are largely responsible for resistance variation but this factor may be less important in explaining variation among species. For desiccation, lines with increased resistance show reduced rates of water loss but no changes in the minimum water content that flies can tolerate. Changes in life history traits are sometimes associated with altered levels of stress resistance. Increased starvation resistance is associated with longer development time and reduced early age reproduction in different studies. However, other associations are inconsistent between studies as in the case of stress resistance changing following selection for longevity. Multiple mechanisms may underlie genetic variation in stress resistance and future studies should address the evolutionary importance of the different mechanisms at the population and species levels.

Desiccation and starvation resistance in Drosophila: patterns of variation at the species, population and intrapopulation levels

A substantial number of Drosophila studies have investigated variation in desiccation and starvation resistance, providing an opportunity to test for consistent patterns of direct and correlated responses across studies and across the species and population levels. In general, responses to laboratory selection for these traits in D. melanogaster are rapid and indicate abundant genetic variation in populations. However, slower responses to selection for desiccation resistance occur in other species including D. simulans. Clines suggest adaptive divergence although specific selection pressures have not been documented empirically. Drosophila species differ markedly in desiccation and starvation resistance and there is also marked variation within species for desiccation resistance that may be linked to local climatic conditions. Laboratory selection experiments on starvation resistance in D. melanogaster suggest that changes in lipid content are largely responsible for resistance variation but this factor may be less important in explaining variation among species. For desiccation, lines with increased resistance show reduced rates of water loss but no changes in the minimum water content that flies can tolerate. Changes in life history traits are sometimes associated with altered levels of stress resistance. Increased starvation resistance is associated with longer development time and reduced early age reproduction in different studies. However, other associations are inconsistent between studies as in the case of stress resistance changing following selection for longevity. Multiple mechanisms may underlie genetic variation in stress resistance and future studies should address the evolutionary importance of the different mechanisms at the population and species levels.

Stress Response and Survival Time in Three Wildlife Species

The need for studies on the ability of various wildlife species to survive and the factors affecting their survival has become increasingly important in wildlife management research. Such information is not only essential for an understanding of population behavior but also for planning habitat improvement programs designed to meet specific requirements. One approach toward obtaining physiological information of this type is by subjecting an animal to an applied stress and measuring its resistance and survival time. Kabat, Meyer, Flakas, and Hine (1956) in Wisconsin carried out a series of experiments throughout the year on hen pheasants (Phasianus colchicus torquatus) in which they subjected the birds to the artificial stress of caging and starvation and measured the birds' resistance in terms of body-weight loss and body-temperature decline. The design of their studies was based on Selye's (1949) hypothesis that adaptation to a specific stress (such natural stresses as egg laying, molting, etc.) lowers the body's resistance to different stress to which the animal is not adapted. The applied stress, therefore, was used as a means of demonstrating whether there was seasonal variation in adaptation energy, and which of the naturally occurring physiological stresses caused the greatest decrease in resistance. These studies showed that the use of this technique appeared to produce reliable trends in stress resistance and survival time. There was variation in the hen pheasant's ability to survive the applied stress at different times of the year; this variation in stress resistance and survival time, furthermore, was related to the physiological condition of the hen. The hen pheasant studies opened the door to much more investigation along these lines. During the course of the Wisconsin pheasant experiments in January to March 1951, single tests were run on Hungarian partridge (Perdix perdix), chukar partridge (Alectoris graeca chukar), and cottontail rabbits (Sylvilagus floridanus). The purpose of this report is to present the results of these tests in order to document the data and provide background information for other investigators contemplating similar studies.