Physiological stress and the maintenance of adaptive genetic variation in a livebearing fish

The importance of genetic variation in evolution is well established. Yet, the mechanisms by which genetic variation—particularly variation in traits under selection—is maintained in natural populations has long been an evolutionary puzzle. Understanding individual variables driving selection and their functional mechanisms is increasingly important in the context of global change and its potential consequences for biodiversity. Here we examined intra-population performance among allelic variants of a pleiotropic locus in response to thermal stress in the variable platyfish, Xiphophorus variatus. The wild-type tailspot allele exhibited significantly lower heat tolerance than all three pattern alleles found in the population, conforming to predictions based on previously observed correlations between temperature and pattern frequencies in the wild. Furthermore, differences between tailspot pattern frequencies in adults and juveniles were broadly consistent with this trend. Thus, it appears that physiological stress and reduced performance of the wild-type allele at higher relative temperatures is a mechanism balancing its frequency in natural populations. Temperature variation and not dissolved oxygen alone, as previously reported, is likely a important abiotic variable contributing to the maintenance of adaptive polymorphism. Furthermore, our findings underscore the potential implications of rising temperatures and physiological stress for levels of genetic variation in natural populations.     

Physiological costs of combating chemical toxicants: ecological implications.

1. Evidence is presented that combating the poisoning effects of toxic chemicals is metabolically costly. 2. This has implications for relating physiological stress responses observed at the level of individual organisms to population effects, and needs to be incorporated explicitly into models making this link. 3. The cost hypothesis also has implication for the evolution of stress resistance either as a fixed or facultative (inducible) response. Optimization models incorporating these ideas are reviewed and discussed.     

Cardiovascular alterations and autonomic imbalance in an experimental model of depression

Depressed patients with and without a history of cardiovascular pathology display signs, such as elevated heart rate, decreased heart rate variability, and increased physiological reactivity to environmental stressors, which may indicate a predisposition to cardiovascular disease. The specific physiological mechanisms associating depression with such altered cardiovascular parameters are presently unclear. The current study investigated cardiovascular regulation in the chronic mild stress rodent model of depression and examined the specific autonomic nervous system mechanisms underlying the responses. Sprague-Dawley rats exposed to a series of mild, unpredictable stressors over 4 wk displayed anhedonia (an essential feature of human depression), along with elevated resting heart rate, decreased heart rate variability, and exaggerated pressor and heart rate responses to air jet stress. Results obtained from experiments studying autonomic blockade suggest that cardiovascular alterations in the chronic mild stress model are mediated by elevated sympathetic tone to the heart. The present findings have implications for the study of pathophysiological links between affective disorders and cardiovascular disease.     

A comparison of health assessment approaches for evaluating the effects of contaminant-related stress on fish populations

Various methods are available for investigating the effects of environmental conditions or stress on fish ranging from assessments at the individual level to the population and community level. Each method, however, has limitations and advantages, and the type of method used influences the interpretation of stressor effects on fish health. We compared and evaluated three methods for investigating the effects of contaminants on fish health for populations in a stream receiving a variety of industrial effluents including PCBs, heavy metals (primarily mercury), and chlorine. These methods are: (1) individual bioindicator variables including measurements of biochemical, physiological, histopathological, and organismal-level responses, (2) statistically based integrative indices based on multivariate responses, and (3) integrative ecologically relevant measurements such as population and community-level responses. Many of the individual-level measurements reflect biochemical and physiological conditions and are therefore short-term response indicators of stress. Use of several individual variables in multivariate discriminant analysis allows a more integrative approach for evaluating response of fish to stressors. Community- and population-level measurements integrate the responses to a variety of environmental conditions and therefore may be less reflective of contaminant-induced stress. The three methods used together provide the best strategy for evaluating fish health in order that environmentally sound decisions can be made regarding the implications of contaminant-related stress on aquatic ecosystems.Managed by Martin Marietta Energy Systems, Inc., under contract DE-AC05-840R21400 with the U.S. Department of Energy.     

植物光合系统对高温胁迫的响应机制

温度变化是影响植物生长和发育的一个非常重要的因素,而光合作用是植物对温度变化最为敏感的生理过程.高温胁迫给植物光合器官造成了严重的危害,但在高温胁迫下,植物并不是消极被动的,并且能够在生理生化及分子水平上发生各种变化来渡过逆境.本文结合当今国内外研究进展,从光合系统热量耗散与光合修复的相关因素,如类囊体膜上相关蛋白,热激蛋白,水杨酸,抗过氧化物酶及抗坏血酸等几个方面展开分析,阐述了植物光合系统对高温胁迫的防御机制,并对今后的研究方向进行了探讨和展望.     

Satellite solar-induced chlorophyll fluorescence tracks physiological drought stress development during 2020 southwest US drought

Monitoring and estimating drought impact on plant physiological processes over large regions remains a major challenge for remote sensing and land surface modeling, with important implications for understanding plant mortality mechanisms and predicting the climate change impact on terrestrial carbon and water cycles. The Orbiting Carbon Observatory 3 (OCO-3), with its unique diurnal observing capability, offers a new opportunity to track drought stress on plant physiology. Using radiative transfer and machine learning modeling, we derive a metric of afternoon photosynthetic depression from OCO-3 solar-induced chlorophyll fluorescence (SIF) as an indicator of plant physiological drought stress. This unique diurnal signal enables a spatially explicit mapping of plants' physiological response to drought. Using OCO-3 observations, we detect a widespread increasing drought stress during the 2020 southwest US drought. Although the physiological drought stress is largely related to the vapor pressure deficit (VPD), our results suggest that plants' sensitivity to VPD increases as the drought intensifies and VPD sensitivity develops differently for shrublands and grasslands. Our findings highlight the potential of using diurnal satellite SIF observations to advance the mechanistic understanding of drought impact on terrestrial ecosystems and to improve land surface modeling.     

Targeted sorting of single virus-infected cells of the coccolithophore Emiliania huxleyi

Discriminating infected from healthy cells is the first step to understanding the mechanisms and ecological implications of viral infection. We have developed a method for detecting, sorting, and performing molecular analysis of individual, infected cells of the important microalga Emiliania huxleyi, based on known physiological responses to viral infection. Of three fluorescent dyes tested, FM 1-43 (for detecting membrane blebbing) gave the most unequivocal and earliest separation of cells. Furthermore, we were able to amplify the genomes of single infected cells using Multiple Displacement Amplification. This novel method to reliably discriminate infected from healthy cells in cultures will allow researchers to answer numerous questions regarding the mechanisms and implications of viral infection of E. huxleyi. The method may be transferable to other virus-host systems.     

Direct Measurements of Torque During Holliday Junction Migration

DNA experiences torsional stress resulting from the activities of motor enzymes and bound proteins. The mechanisms by which this torsional stress is dissipated to maintain DNA structural integrity are not fully known. Here, we show that a Holliday junction can limit torsion by coupling rotation to translocation and torque to force. The torque required to mechanically migrate through individual junctions was found to be an order of magnitude smaller than that required to melt DNA. We also directly show that substantially more torque was required to migrate through even a single-base sequence heterology, which has important implications for the activity of junction-migrating enzymes.     

Nitric oxide signalling in plants: interplays with Ca2+ and protein kinases

Much attention has been paid to nitric oxide (NO) research since its discovery as a physiological mediator of plant defence responses. In recent years, newer roles have been attributed to NO, ranging from root development to stomatal closure. The molecular mechanisms underlying NO action in plants are just begun to emerge. The currently available data illustrate that NO can directly influence the activity of target proteins through nitrosylation and has the capacity to act as a Ca2+-mobilizing intracellular messenger. The interplay between NO and Ca2+ has important functional implications, expanding and enriching the possibilities for modulating transduction processes. Furthermore, protein kinases regulated through NO-dependent mechanisms are being discovered, offering fresh perspective on processes such as stress tolerance.     

Getting the better of ER stress

Research over the past few years has highlighted the ability of the unfolded protein response (UPR) to minimize the deleterious effects of accumulated misfolded proteins under both physiological and pathological conditions. The endoplasmic reticulum (ER) adapts to endogenous and exogenous stressors by expanding its protein-folding capacity and by stimulating protective processes such as autophagy and antioxidant responses. Although it is clear that severe ER stress can elicit cell death, several recent studies have shown that low levels of ER stress may actually be beneficial to cells by eliciting an adaptive UPR that ‘preconditions’ the cell to a subsequent lethal insult; this process is called ER hormesis. The findings have important implications for the treatment of a wide variety of diseases associated with defective proteostasis, including neurodegenerative diseases, diabetes, and cancer. Here, we review the physiological and pathological functions of the ER, with a particular focus on the molecular mechanisms that lead to ER hormesis and cellular protection, and discuss the implications for disease treatment.     

Physiological costs of combating chemical toxicants: Ecological implications

• 1.1. Evidence is presented that combating the poisoning effects of toxic chemicals is metabotically costly.
• 2.2. This has implications for relating physiological stress responses observed at the level of individual organisms to population effects, and needs to be incorporated explicitly into models making this link.
• 3.3. The cost hypothesis also has implication for the evolution of stress resistance either as a fixed or facultative (inducible) response. Optimization models incorporating these ideas are reviewed and discussed.

     

Determinants of Physiological and Perceived Physiological Stress Reactivity in Children and Adolescents

Aims

Abnormal physiological stress reactivity is increasingly investigated as a vulnerability marker for various physical and psychological health problems. However, studies are inconsistent in taking into account potential covariates that may influence the developing stress system. We systematically tested determinants (individual, developmental, environmental and substance use-related) of physiological and perceived physiological stress reactivity. We also examined the relation between physiological and perceived physiological stress reactivity.

Method

In a stratified sample of 363 children (7–12 years) and 344 adolescents (13–20 years) from the general population, we examined cortisol, heart rate, respiratory sinus arrhythmia and perceived physiological stress reactivity to a psychosocial stress procedure.

Results

Using multivariate linear regression models, we found that individual, developmental, environmental and substance use-related factors were related to each of the stress response indices. These determinant factors were different for each of the stress reactivity indices, and different in children versus adolescents. Perceived physiological stress reactivity predicted cortisol reactivity in adolescents only. All other relations between perceived physiological and physiological stress reactivity were not significant.

Conclusions

As physiological stress variables are often examined as vulnerability markers for the development of health problems, we maintain that it is essential that future studies take into consideration factors that may account for found relations. Our study provides an overview and indication of which variables should be considered in the investigation of the relation between physiological stress indices and illness.     

HSP70 heat shock proteins and environmental stress in Antarctic marine organisms: A mini-review

The ability to understand and predict the effects of environmental stress on biodiversity is becoming increasingly important in our changing environment. Antarctic marine species are some of the most stenothermal on the planet and many inhabit the waters off the Antarctic Peninsula which is one of the areas where there is rapid regional climate change. Therefore these animals are highly vulnerable to changing environmental temperatures and clearly we need to understand the complexities of their response, not just at the individual species level, but also the implications for the ecosystem as a whole. Heat shock proteins have a long history of use in studies of organism stress responses and have frequently been proposed as potential universal molecular biomarkers, especially for non-model species. In this mini-review, the heat shock response and heat shock proteins (specifically the HSP70 family) are examined in Antarctic marine species alongside their physiological capabilities and limits to answer a series of questions: do these animals have a heat shock response which includes the expression of HSP70 genes? What is the relationship between their heat shock response and physiological capabilities? Can HSP70 genes be used as molecular biomarkers for these species?     

The ecology of individuals: incidence and implications of individual specialization

Most empirical and theoretical studies of resource use and population dynamics treat conspecific individuals as ecologically equivalent. This simplification is only justified if interindividual niche variation is rare, weak, or has a trivial effect on ecological processes. This article reviews the incidence, degree, causes, and implications of individual-level niche variation to challenge these simplifications. Evidence for individual specialization is available for 93 species distributed across a broad range of taxonomic groups. Although few studies have quantified the degree to which individuals are specialized relative to their population, between-individual variation can sometimes comprise the majority of the population's niche width. The degree of individual specialization varies widely among species and among populations, reflecting a diverse array of physiological, behavioral, and ecological mechanisms that can generate intrapopulation variation. Finally, individual specialization has potentially important ecological, evolutionary, and conservation implications. Theory suggests that niche variation facilitates frequency-dependent interactions that can profoundly affect the population's stability, the amount of intraspecific competition, fitness-function shapes, and the population's capacity to diversify and speciate rapidly. Our collection of case studies suggests that individual specialization is a widespread but underappreciated phenomenon that poses many important but unanswered questions.     

Plasticity and cross‐tolerance to heterogeneous environments: divergent stress responses co‐evolved in an African fruit fly

Plastic adjustments of physiological tolerance to a particular stressor can result in fitness benefits for resistance that might manifest not only in that same environment but also be advantageous when faced with alternative environmental stressors, a phenomenon termed ‘cross‐tolerance’. The nature and magnitude of cross‐tolerance responses can provide important insights into the underlying genetic architecture, potential constraints on or versatility of an organism's stress responses. In this study, we tested for cross‐tolerance to a suite of abiotic factors that likely contribute to setting insect population dynamics and geographic range limits: heat, cold, desiccation and starvation resistance in adult Ceratitis rosa following acclimation to all these isolated individual conditions prior to stress assays. Traits of stress resistance scored included critical thermal (activity) limits, chill coma recovery time (CCRT), heat knockdown time (HKDT), desiccation and starvation resistance. In agreement with other studies, we found that acclimation to one stress typically increased resistance for that same stress experienced later in life. A more novel outcome, however, is that here we also found substantial evidence for cross‐tolerance. For example, we found an improvement in heat tolerance (critical thermal maxima, CT_max) following starvation or desiccation hardening and improved desiccation resistance following cold acclimation, indicating pronounced cross‐tolerance to these environmental stressors for the traits examined. We also found that two different traits of the same stress resistance differed in their responsiveness to the same stress conditions (e.g. HKDT was less cross‐resistant than CT_max). The results of this study have two major implications that are of broader importance: (i) that these traits likely co‐evolved to cope with diverse or simultaneous stressors, and (ii) that a set of common underlying physiological mechanisms might exist between apparently divergent stress responses in this species. This species may prove to be a valuable model for future work on the evolutionary and mechanistic basis of cross‐tolerance.     

A 3-D constrained mixture model for mechanically mediated vascular growth and remodeling

In contrast to the widely applied approach to model soft tissue remodeling employing the concept of volumetric growth, microstructurally motivated models are capable of capturing many of the underlying mechanisms of growth and remodeling; i.e., the production, removal, and remodeling of individual constituents at different rates and to different extents. A 3-dimensional constrained mixture computational framework has been developed for vascular growth and remodeling, considering new, microstructurally motivated kinematics and constitutive equations and new stress and muscle activation mediated evolution equations. Our computational results for alterations in flow and pressure, using reasonable physiological values for rates of constituent growth and turnover, concur with findings in the literature. For example, for flow-induced remodeling, our simulations predict that, although the wall shear stress is restored completely, the circumferential stress is not restored employing realistic physiological rate parameters. Also, our simulations predict different levels of thickening on inner versus outer wall locations, as shown in numerous reports of pressure-induced remodeling. Whereas the simulations are meant to be illustrative, they serve to highlight the experimental data currently lacking to fully quantify mechanically mediated adaptations in the vasculature.     

A nervous tumor microenvironment: the impact of adrenergic stress on cancer cells,immunosuppression, and immunotherapeutic response

Long conserved mechanisms maintain homeostasis in living creatures in response to a variety of stresses. However, continuous exposure to stress can result in unabated production of stress hormones, especially catecholamines, which can have detrimental health effects. While the long-term effects of chronic stress have well-known physiological consequences, recent discoveries have revealed that stress may affect therapeutic efficacy in cancer. Growing epidemiological evidence reveals strong correlations between progression-free and long-term survival and β-blocker usage in cancer patients. In this review, we summarize the current understanding of how the catecholamines, epinephrine and norepinephrine, affect cancer cell survival and tumor progression. We also highlight new data exploring the potential contributions of stress to immunosuppression in the tumor microenvironment and the implications of these findings for the efficacy of immunotherapies.