Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “environmental variability”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 811 records · Page 45Linked to original sources
PubMed1983

Annual cycle of body size and blood parameters of the aquatic adult red-spotted newt, Notophthalmus viridescens.

A minimum of 20 aquatic, adult Notophthalmus viridescens were captured approximately every other month during 1980 in order to investigate seasonal changes in body size and blood parameters. Hemoglobin concentration, hematocrit, mean cell hemoglobin, sex, weight, snout-to-tail length, snout-to-vent length, and the presence of trypanosomes on blood smears were determined. Environmental variables measured included temperature (range 5-26 degrees C), oxygen concentration (range 5.7-12.2 mg/L), and pH (range 6.5-7.5) of water at the pond's edge. Three anemic specimens (less than 0.03 gHb/100 ml blood) were found. The only significant (P less than 0.05) seasonal effects were that the mean hematocrit of the July sample was greater than that of the March sample and the incidence of trypanosome infection of the March collected newts was lower than those collected in May, July, and August. Significant (P less than 0.01) linear relationships were found within the body size and blood parameters but not between them. Females had significantly (P = 0.000) higher hematocrits than males. The hemoglobin concentration and hematocrit did not correlate with the assumed seasonal oxygen demands of the newt.

Animals↗
PubMedDate not supplied

Culturing primary brain astrocytes under a fully controlled environment in a novel bioreactor.

We report the first approach for growth and maintenance of primary astrocytes on a fully controlled environment. For this purpose, cells were immobilized in Cytodex microcarriers and grown in a stirred tank bioreactor. The distribution of astrocytes at the microcarrier surface was visualized using confocal microscopy and glial fibrillary acidic protein (GFAP) labeling, a specific glial probe. Crucial bioreaction parameters such as agitation rate, microcarrier type, and concentration, as well as cell inoculum concentration were assessed. Cytodex 3 proved the best microcarrier for astrocyte growth, with the highest cell densities obtained for 6 g/l of Cytodex 3 using an inoculum of approx. 0.15 x 10(6) cells/ml in vessels operated at 60 rpm, using a refeed operational mode consisting of complete medium replacement every 5 days. Using such optimized conditions, cells were maintained in steady-state for approximately 24 days, allowing online monitoring and control of environmental variables such as temperature, pH, and O(2). To test further the advantages of this fully controlled system, astrocytes were also subjected to hypoxic stress for 5 hr; the cell number was not affected by hypoxia but the glycolytic flux was enhanced during the stress imposed. The culture system described is a novel tool to study brain cell metabolism, allowing sampling over time and the monitoring of cellular behavior through stressful conditions and during recovery.

Animals↗
PubMed2001

Transition to home care after stroke: depression, physical health, and adaptive processes in support persons.

A longitudinal design was used to examine adaptation in primary support persons (PSP) of stroke survivors during the transition from hospitalization (T1) to home care (T2). The major purposes of the study were (a) to examine changes in depression, physical health, and contextual and coping factors from hospitalization of the stroke survivor through the first 6-10 weeks of home care; and (b) to identify predictors of depression. Data (N = 136) were collected on depression, physical health, background, survivor illness, and social environmental variables; appraisal of impact; social support resources; and coping skills. Reduction in mean PSP depression was significant at T2, but the change in physical health was not significant. Significant changes occurred in survivor function, family functioning, and three of six coping skills. Hierarchical multiple regression analyses were used to predict depression. T1 variables accounted for 29% of the variance in T1 PSP depression, with gender and appraisal of impact the strongest of seven predictors. T1 depression, T2 health, family functioning, and avoidance coping were the strongest of seven predictors, explaining 50% of the variance in T2 depression. Findings highlight the importance of maintaining caregiver health and preventing depression and identify variables to target for the reduction of PSP depression.

Adaptation, Psychological↗
PubMed2026

Finlay-Wilkinson random regression for yield and yield stability prediction in cereals.

Year-to-year climate variability poses a challenge for agriculture by increasing crop yield variability; therefore, there is a need to identify genotypes that can withstand these fluctuations. With the right selection criteria, genotypes with yield stability across variable environmental conditions can be selected. Methods such as Finlay-Wilkinson random regression (FWRR) may allow us to use sparse datasets-common in plant breeding pipelines-and incorporate genomic data to leverage phenotypic information from related genotypes to predict yield stability. Our objective was to examine how the number of environments and the variance among those environments affect stability predictions. We also integrate FWRR as a genomic prediction tool for characterizing yield stability, comparing it to the traditional genomic prediction models as a reference. We used three datasets: one highly unbalanced dataset for oats (Avena sativa L.) and two completely balanced datasets with different numbers of environments for barley (Hordeum vulgare L.) and wheat (Triticum aestivum L.). We fit standard Finlay-Wilkinson (FW) and FWRR models to estimate grain yield and stability under various scenarios. We found that the estimated stability values obtained were similar using balanced datasets for FW or FWRR. FWRR also achieved moderate predictive ability for stability using unbalanced datasets under 10-fold cross-validation (CV1) with new genotypes. In terms of environmental representation, selecting the right set of environments for inclusion in the model was more important than adding more environments. Our results suggest the possibility of using FWRR to select stable genotypes earlier in line development, as well as to design resource-efficient stability-testing schemes.

Hordeum↗
PubMed2004

What women want: women's preferences of caregiver behavior when prenatal sonography findings are abnormal.

OBJECTIVE: To determine what women value when receiving news of a pregnancy abnormality detected by ultrasound. METHODS: Women who had a pregnancy complication detected sonographically in the year 2000 were asked to complete a survey of 21 questions measuring the importance of various factors related to the receipt of bad news. Of the target sample of 117 women who agreed to participate, 76 (64.9%) returned completed surveys. Cases included serious anomalies (67%) and soft markers/obstetric complications (33%). RESULTS: Responses to questions on 'information quality', 'prompt provision of information', 'information-provider behavior' and 'information provision environment' showed that women attached the most importance to information quality, much more so than to promptness. Speed was even less important than information-provider empathy. Answers concerning use of the terms 'fetus' or 'baby' revealed greater variation in preferences than any other. Privacy was the most important environmental variable, more important than some information quality variables, or any promptness variable. Intervening variables considered included demographic variables and the seriousness of the prognosis. Education was the most useful predictor of preferences, with highly educated women generally placing less value on environment and some information quality variables, and having different preferences concerning the terms 'fetus' and 'baby'. CONCLUSIONS: Our findings shed some light on what is important to women who face bad news. Although more research is needed in this important area, we hope that our findings may assist institutions and caregivers in establishing guidelines for the effective and considerate communication of bad news.

Caregivers↗
PubMed1998

Shift in investment between sexually selected traits: tarnishing of the silver spoon

Studies of resource allocation strategies have concentrated on the influence of natural selection on the evolution of life history traits. To a lesser degree, the effects of trade-offs between natural and sexual selection on the evolution of allocation strategies have also been considered. Trade-offs between sexually selected traits that are important to females but that appear to differ in cost, however, have not been considered. Female green swordtails, Xiphophorus helleri, prefer males with longer swords to males with shorter swords, and in this study they demonstrated a preference for larger males to smaller males. Furthermore, sexually mature males invested differentially in body and sword growth depending on resource availability; males that had an unlimited amount of food invested in both body and sword growth, but males shifted to a food-restricted regime halted investment in body growth and invested only in sword growth. These results suggest that males shift their pattern of investment in two sexually selected traits when food becomes restricted. In general, variable environmental conditions may favour such conditional investment strategies in species in which there is more than one preferred male trait and the costs of the traits differ. Copyright 1998 The Association for the Study of Animal Behaviour Copyright 1998 The Association for the Study of Animal Behaviour.

Journal Article↗
PubMed1998

Females are responsible for ejection of cuckoo eggs in the rufous bush robin.

Rufous bush robin, Cercotrichas galactotes, nests were experimentally parasitized in order to test which sex is responsible for egg ejection. We tested nests belonging to the same individuals (male, female or pair) in 2 consecutive years. Whether the eggs were rejected did not depend on environmental variables such as laying date and clutch size, and did not change between tests, when the two consecutive nests tested belonged to the same pair members, supporting the idea that some individuals reject odd eggs, while others accept them. The expected frequencies for rejection and acceptance, if females were the sex responsible for ejection behaviour, did not differ from the observed frequencies when the same female owned both the nests tested. However, the expected frequencies calculated for males as if they were the sex responsible differed from those observed, when the same male owned both the nests tested. A lower percentage of females than males changed ejection behaviour. These results show that female rufous bush robins are responsible for egg ejection. Copyright 1998 The Association for the Study of Animal Behaviour.

Journal Article↗
PubMed1999

An FT-IR study of the beta-amyloid conformation: standardization of aggregation grade.

The aggregation of beta-amyloid peptides is very important for their neurotoxic effect; standardization of the aggregation grade is necessary for biological experiments. Measurement of aggregation with physicochemical methods is a difficult task. The present work revealed that FT-IR can be used for studying the aggregation properties of beta-amyloid peptides and the effects of environmental variables (solvent, pH, ions, and temperature) on aggregation. In dimethyl sulfoxide or hexafluoroisopropanol, amyloid peptides are in a monomeric state; on dilution with phosphate buffer just before measurement is made, aggregation begins. A detailed two-dimensional FT-IR correlation spectroscopic study was made of the conformational transitions that occur during the aggregation of beta-amyloid peptides. Two processes (random/helix-to-beta-sheet and aggregation of beta-sheets) and multiple conformational states were observed before the most stable form was attained. beta-Amyloid peptides undergo decomposition in basic buffers containing Ca(2+); this process should be avoided during aging experiments.

Amyloid beta-Peptides↗
PubMed2000

Water-column, sediment, and in situ chronic bioassays with cladocerans.

In situ bioassays are becoming very popular for laboratory test validation and field extrapolation. Natural conditions, including environmental variables, affect the "behavior" of contaminants and, consequently, their toxicity. This work aimed to develop protocols for in situ chronic bioassays with cladocerans and to assess the ecological relevance of conventional protocols for laboratory testing (water-column and sediment). An aquatic system impacted with acid mine drainage was chosen for the study. At some stations that were contaminated with heavy metals, water-column bioassays did not reveal any toxicity, while sediment and, especially in situ bioassays, revealed a delay in reproduction and a reduction in fertility. Thus, both laboratory bioassays underestimated the actual toxicity of studied sites: sediment, besides being an important contaminant source, became significantly altered with sampling, transport, storage, and manipulation. Therefore, an extra caution is needed when interpreting laboratory results, since the extrapolation to natural systems could be a very problematic step.

Animals↗
PubMed1997

Spatial Distribution of Chemical Components in Aerosol Particles as Determined from Secondary Electron Yield Measurements: Implications for Mechanisms of Multicomponent Aerosol Crystallization

Secondary electron yield measurements were used to determine the distribution of chemical components in multicomponent aerosol particles formed by crystallization from aqueous solution droplets. Yield measurements were made by measuring the charge acquired by a beam of particles as they passed through an electron beam (100-600 eV energy) inside a high-vacuum apparatus. Yields were sufficiently different for certain compounds that measurements made on two-component particles could be used to obtain information on the spatial distribution of components. Variations in chemical composition as a function of depth beneath the particle surface were ascertained from the energy dependence of the measured yields, since the electron penetration depth, and therefore the probe depth, increases with electron energy. The results for mixed NaCl-NH4Cl particles indicate that the distribution of components within these particles is relatively homogeneous, while measurements made on mixed NaCl-NaNO3 particles are indicative of particles having a heterogeneous core-shell morphology. Results for mixed Na2SO4-(NH4)2SO4 particles are ambiguous, probably because of the complexity of the phase diagram of this system. It appears that the mechanism by which aerosol particles crystallize, and therefore the resulting distribution of chemical components within particles, is strongly dependent on particle composition and environmental variables. Copyright 1997 Academic Press. Copyright 1997Academic Press

Journal Article↗
PubMed1994

A new model for bacterial growth in heterogeneous systems.

A general theory of spatially dependent bacterial growth in heterogeneous systems is developed by combining a structured-cell kinetic model of bacterial metabolism with reaction-diffusion equations describing the transport of nutrients in the growth medium. Rate constants in the theory are determined for Listeria monocytogenes by fitting the viable count batch growth data acquired in homogeneous, shake-flask cultures. The rate constants are then used to calculate the form of bacterial growth when it occurs as localized microcolonies in structured systems. The same theory is used to analyse the effects of transient variations in environmental variables.

Bacteriological Techniques↗
PubMed1994

No strategy is evolutionarily stable in the repeated prisoner's dilemma.

Following the influential work of Axelrod, the repeated Prisoner's Dilemma game has become the theoretical gold standard for understanding the evolution of co-operative behavior among unrelated individuals. Using the game, several authors have found that a reciprocal strategy known as Tit for Tat (TFT) has done quite well in a wide range of environments. TFT strategists start out co-operating and then do what the other player did on the previous move. Despite the success of TFT and similar strategies in experimental studies of the game, Boyd & Lorberbaum (1987, Nature, Lond. 327, 58) have shown that no pure strategy, including TFT, is evolutionarily stable in the sense that each can be invaded by the joint effect of two invading strategies when long-term interaction occurs in the repeated game and future moves are discounted. Farrell & Ware (1989, Theor. Popul. Biol. 36, 161) have since extended these results to include finite mixes of pure strategies as well. Here, it is proven that no strategy is evolutionarily stable when long-term relationships are maintained in the repeated Prisoner's Dilemma and future moves are discounted. Namely, it is shown each completely probabilistic strategy (i.e. one that both co-operates and defects with positive probability after every sequence of behavior) may be invaded by a single deviant strategy. This completes the proof started by Boyd and Lorberbaum and extended by Farrell and Ware. This paper goes on to prove that no reactive strategy with a memory restricted to the opponent's preceding move is evolutionarily stable when there is no discounting of future moves. This is true despite the success of a more forgiving variant of TFT called GTFT in a recent tournament among reactive strategies conducted by Nowak & Sigmund (1992, Nature 355, 250) where future moves were not discounted. GTFT, for example, may be invaded by a pair of reactive mutants. Since no strategy is evolutionarily stable when future moves are discounted in the repeated game, the restriction of strategy types to those actually maintained by mutation and phenotypic and environmental variability in natural populations may be the key to understanding the evolution of co-operation. However, the result presented here that the somewhat realistic reactive strategies are also not evolutionarily stable at least in the non-discounted game suggests something else may be going on. For one, the proof that no reactive strategy is evolutionarily stable ironically shows the robustness of TFT-like strategies.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1995

Learning and evolution: a quantitative genetics approach.

Recent models of the interactions between learning and evolution show that learning increases the rate at which populations find optima in fixed environments. However, learning ability is only advantageous in variable environments. In this study, quantitative genetics models are used to investigate the effects of individual learning on evolution. Two models of populations of learning individuals are constructed and analyzed. In the first model, the effect of learning is represented as an increase in the variance of selection. Dynamical equations and equilibrium conditions are derived for a population of learning individuals under fixed and variable environmental selection. In the second model, the amount of individual learning effort is regulated by a second gene specifying the duration of a critical learning period. The second model includes a model of the learning process to determine the individual fitness costs and benefits accrued during the learning period. Individuals are then selected for the optimal learning investment. The similarities of the results from these two models suggest that the net effects of learning on evolution are relatively independent of the mechanisms underlying the learning process.

Animals↗
PubMed2001

Control mechanisms of diel vertical migration: theoretical assumptions.

We explore control mechanisms underlying the vertical migration of zooplankton in the water column under the predator-avoidance hypothesis. Two groups of assumptions in which the organisms are assumed to migrate vertically in order to minimize realized or effective predation pressure (type-I) and to minimize changes in realized or effective predation pressure (type-II), respectively, are investigated. Realized predation pressure is defined as the product of light intensity and relative predation abundance and the part of realized predation pressure that really affects organisms is termed as effective predation pressure. Although both types of assumptions can lead to the migration of zooplankton to avoid the mortality from predators, only the mechanisms based on type-II assumptions permit zooplankton to undergo a normal diel vertical migration (morning descent and evening ascent). The assumption of minimizing changes in realized predation pressure is based on consideration of DVM induction only by light intensity and predators. The assumption of minimizing changes in effective predation pressure takes into account, apart from light and predators also the effects of food and temperature. The latter assumption results in the same expression of migration velocity as the former one when both food and temperature are constant over water depth. A significant characteristic of the two type-II assumptions is that the relative change in light intensity plays a primary role in determining the migration velocity. The photoresponse is modified by other environmental variables: predation pressure, food and temperature. Both light and predation pressure are necessary for organisms to undertake DVM. We analyse the effect of each single variable. The modification of the phototaxis of migratory organisms depends on the vertical distribution of these variables.

Animals↗
PubMed2000

Characteristics of exercise behavior among college students: application of social cognitive theory to predicting stage of change.

BACKGROUND: Young adulthood is characterized by a steep decline in the level of physical activity, but few theory-based studies have examined characteristics associated with regular exercise in this population. This study applied Social Cognitive Theory (SCT) and the Stages of Change Model (SCM) to determine personal, behavioral, and environmental characteristics associated with exercise behavior and intentions among undergraduate university students. METHODS: A random sample of 937 undergraduate students (mean age 22.0 +/- 5.6 years; 84.7% ages 17-24 years) enrolled at a large Midwestern university completed a mailed questionnaire. Valid and reliable instruments were used to measure personal, behavioral, and environmental variables based on the SCT that were hypothesized to influence stage of exercise behavior change. Multivariate discriminant analysis was used to determine associations among these variables with stage of exercise behavior change. RESULTS: Exercise self-efficacy, physical activity history, and nonexercise estimation of aerobic capacity were significant predictors of the stage of exercise behavior change for both males and females. Among females, exercise self-efficacy (P < 0.001) and family social support (P < 0. 001) for physical activity were the best predictors of stage of exercise behavior change. Friend social support (P < 0.001), physical activity history (P < 0.001), and exercise self-efficacy (P < 0.001) were significant predictors of stage of exercise behavior change among males. CONCLUSIONS: The SCT framework predicted stage of exercise behavior change as defined by the SCM. Exercise self-efficacy was associated with exercise stage, but the source of significant social support (family versus friends) was different for males and females.

Adolescent↗
PubMed1986

Dietary fiber and human cancer: critique of the literature.

The relationship between dietary fiber consumption and risk of gastrointestinal cancer in humans is examined using representative studies of several types: international and intranational correlations, case-control analyses, metabolic investigations, cohort studies, and migrant studies. The strongest statistical association between diet and cancer is found in international studies in which numerous environmental variables differ. Studies on smaller groups within a single culture have not given strong support to the findings of international comparisons. Colon cancer rates within regions of the U.S. and other countries vary with sufficient magnitude that diet is unlikely to account for more than a minor proportion of risk. The evidence that a diet containing fiber-rich foods reduces risk of colon cancer must be considered tentative. Foods high in starch and fiber are statistically associated with a high rate of stomach cancer. Examination of the combined rates of colon and gastric cancer shows that the U.S. risk is low relative to countries in which a diet higher in fiber is consumed. It would be premature to suggest that a high fiber diet will confer protection against gastrointestinal cancer.

Colonic Neoplasms↗
PubMed1991

Orientation in birds. Spatiotemporal programmes and genetics of orientation.

A number of migratory bird species have endogenous annual rhythms that regulate the entire annual cycle, including migration. Moreover, captive migrants display inherited migrational activity; this could theoretically also be used by free-living migrants as a time programme for migration. Finally, this heritable migrational activity is oriented in a seasonally appropriate direction, even in naive birds. These characteristics should enable inexperienced migrants isolated from contact with experienced conspecifics, to utilize a heritable vector-navigation programme to migrate from the breeding grounds to the winter quarters. That is, migrants should reach goal areas they have never experienced by migrating in programmed directions, for as long a period as the genetically fixed time programme for migrational activity induces them to do so. The time course of migration, as established by trapping stations, theoretical influences of environmental variables on migration programmes, and also compensatory behaviour and backup measures, are discussed. The present evidence supports the view that a large number of migrants are essentially brought to their wintering areas by vector-navigation systems.

Animals↗
PubMed1992

NE/DA interactions in prefrontal cortex and their possible roles as neuromodulators in schizophrenia.

The monoaminergic innervation of the rat prefrontal cortex arises from well-defined mesencephalic nuclei, with noradrenergic (NE) neurons located in the locus coeruleus, dopaminergic (DA) neurons located in the ventral tegmental area, and serotonergic (5-HT) neurons originating in the raphe nuclei. Specific destruction of the NE bundle was found to induce morphological (i.e., sprouting) as well as metabolic (i.e., changes in rate of DA utilization) modifications of mesocortical DA neurons, suggesting that these two catecholaminergic systems have functional interactions within the prefrontal cortex. This was substantiated by experiments showing that DA afferents modulate the sensitivity of cortical post-synaptic beta-adrenergic receptors and that, reciprocally, NE neurons control the sensitivity of cortical D1 receptors. Behavioural and pharmacological data have further indicated that the stimulation of cortical alpha-1 adrenergic receptors inhibits cortical DA transmission at D1 receptors. Secondly, we have attempted to analyze how such interactions between neuromodulatory systems may be related to the development of mental diseases such as schizophrenia. On the basis of studies in the literature describing the effects produced by the ingestion of hallucinogenic drugs or data collected regarding REM sleep, it is postulated that two modes of brain functioning exist: analogical and cognitive. Each mode is characterized by differences in the relative activities of NE, DA and 5-HT neurons. At birth, during REM sleep, and following the ingestion of hallucinogens, the mode of brain functioning is essentially analogical; in contrast, both analogic and cognitive modes are postulated to coexist in the awake state. Oscillations between these two modes are under the control of monoaminergic systems on which an increase in cortical DA release favours the cognitive processing mode, whereas intermittent activations of NE neurons would switch the brain into the analogical mode of processing. It is proposed that schizophrenic patients with "positive" symptoms suffer from an abnormal preponderance of the analogical mode while awake, whereas "negative" symptoms are due to the excessive presence of the cognitive mode. Although pure biological deficits cannot be excluded, these dysfunctions could be related to the absence of particular environmental variables early in the development of these patients. This condition is probably required to establish normal regulatory control of monoaminergic neuronal activity.

Dopamine↗