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Results for “Environmental selection”

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PubMed1987

Very slightly deleterious mutations and the molecular clock.

The model of very slightly deleterious mutations was examined from the standpoint of population genetics in relation to the molecular evolutionary clock. The distribution of selection coefficients of mutants (in terms of amino acid changes) with small effect is thought to be continuous around zero, with an average negative value. The variance of selection coefficients depends upon environmental diversity and hence on total population size of a species. By considering various examples of amino acid substitutions, the average and standard error of selection coefficients and the reciprocal of population size are assumed to have similar values. The model predicts negative correlation between evolutionary rate and population size. This effect is expected to be partially cancelled with the generation time effect of intrinsic mutation rate. Implications of this prediction on the molecular evolutionary clock are discussed.

Amino Acids↗

PubMed1998

Evaluating gene flow using selected markers: a case study.

The extent to which an organism is locally adapted in an environmental pocket depends on the selection intensities inside and outside the pocket, on migration, and on the size of the pocket. When two or more loci are involved in this local adaptation, measuring their frequency gradients and their linkage disequilbria allows one to disentangle the forces-migration and selection-acting on the system. We apply this method to the case of a local adaptation to organophosphate insecticides in the mosquito Culex pipiens pipiens in southern France. The study of two different resistance loci allowed us to estimate with support limits gene flow as well as selection pressure on insecticide resistance and the fitness costs associated with each locus. These estimates permit us to pinpoint the conditions for the maintenance of this pocket of adaptation as well as the effect of the interaction between the two resistance loci.

Animals↗

PubMedDate not supplied

Photodegradation of selected herbicides in various natural waters and soils under environmental conditions.

The photochemical degradation of herbicides belonging to different chemical groups has been investigated in different types of natural waters (ground, river, lake, marine) and distilled water as well as in soils with different texture and composition. Studied herbicides and chemical groups included atrazine, propazine, and prometryne (s-triazines); propachlor and propanil (acetanilides); and molinate (thiocarbamate). The degradation kinetics were monitored under natural conditions of sunlight and temperature. Photodegradation experiments were performed in May through July 1998 at low concentrations in water samples (2-10 mg/L) and soil samples (5-20 mg/kg), which are close to usual field dosage. The photodegradation rates of all studied herbicides in different natural waters followed a pseudo-first order kinetics. The half-lives of the selected herbicides varied from 26 to 73 calendar days in waters and from 12 to 40 d in soil surfaces, showing that the degradation process depends on the constitution of the irradiated media. The presence of humic substances in the lake, river, and marine water samples reduces degradation rates in comparison with the distilled and ground water. On the contrary, the degradation in soil is accelerated as the percentage of organic matter increases. Generally, the photodegradation process in soil is faster than in water. The major photodegradation products identified by using gas chromatography-mass spectrometry (GC-MS) techniques were the hydroxy and dealkylated derivatives for s-triazines, the dechlorinated and hydroxy derivative for the anilides, and the keto-derivative for the thiocarbamate, indicating a similar mode of degradation for each chemical category.

Gas Chromatography-Mass Spectrometry↗

PubMed2006

Modularity and intrinsic evolvability of Hsp90-buffered change.

Hsp90 controls dramatic phenotypic transitions in a wide array of morphological features of many organisms. The genetic-background dependence of specific abnormalities and their response to laboratory selection suggested Hsp90 could be an 'evolutionary capacitor', allowing developmental variation to accumulate as neutral alleles under normal conditions and manifest selectable morphological differences during environmental stress. The relevance of Hsp90-buffered variation for evolution has been most often challenged by the idea that large morphological changes controlled by Hsp90 are unconditionally deleterious. To address this issue, we tested an Hsp90-buffered abnormality in Drosophila for unselected pleiotropic effects and correlated fitness costs. Up to 120-fold differences in penetrance among six highly related selection lines, started from an initially small number of flies and rapidly selected for and against a deformed eye trait (dfe), did not translate into measurable differences in any of several tests of viability, lifespan or competitive fitness. Nor were 17 dfe Quantitative Trait Loci (QTL) associated with fitness effects in over 1,400 recombinant lines. Our ability to detect measurable effects of inbreeding, media environment and the white mutation in the selection line backgrounds independent of dfe penetrance suggests that, within the limitations of laboratory tests of fitness, this large morphological change controlled by Hsp90 was selectable independent of strong, correlated and unconditionally deleterious effects--abundant, polygenic variation hidden by Hsp90 allows potentially deleterious alleles to be readily replaced during selection by less deleterious alleles with similar phenotypic effects. Hsp90 links environmental stress with the expression of developmental variation controlling unprecedented morphological plasticity. As outlined here and in the companion paper of this issue, the complex genetic architecture of Hsp90-buffered variation supports a remarkable modularity of Hsp90 effects on quantitative and qualitative phenotypes, consistent with the 'Hsp90 capacitor hypothesis' and standard quantitative genetic models of threshold traits.

Alleles↗

PubMed2006

Selecting soybean meal characteristics preferred for swine nutrition.

As environmental constraints become more important issues for the animal industry, selecting feed ingredients that yield good animal performance but also minimize environmental impact of animal production becomes critical. The objective of this research was to identify which compositional features would be desirable for soybean meal to maximize nutritional value and minimize animal waste. Eight soybean samples were selected from a database of 72, such that maximal variability for CP, NDF, and ADF content was obtained. Samples were subsequently processed into meal using standardized procedures. In Experiment 1, 8 cannulated pigs were used to determine ileal digestibility following a Latin square design. In Experiment 2, 5 of the samples were used in complete feeds and 10 pigs were used in a crossover Latin square design to determine the total tract digestibility, odorants in fresh and 5-d-old manure, and ammonia emission from manure. Differences up to 6% in ileal DM digestibility and 8% in ileal CP digestibility were observed. This difference was reduced to 1.1% for total tract DM digestibility and 4% for total tract CP digestibility. Differences in odorant concentration were 3-fold and for in vitro ammonia emission were 42%. The only compositional variable with a significant effect on digestibility was stachyose, which negatively affected ileal digestibility of DM (r = -0.80, P = 0.02) and energy (r = -0.73, P = 0.04). None of the compositional variables measured affected ileal CP digestibility. Ileal CP digestibility, however, was correlated with estimated CP fermentation in the large intestine (r = -0.86, P = 0.06) and with in vitro ammonia emission after 48 h (r = -0.81, P = 0.09). In conclusion, nutritionally relevant variability exists in soy varieties. Low stachyose content is important for maximizing ileal energy digestibility of soybean meal. Although no compositional variable was identified that explained differences in ileal CP digestibility, maximizing ileal CP digestibility is of interest for maximizing the nutritional value of soybean meal and possibly for reducing ammonia and odor emissions.

Ammonia↗

PubMed1999

Hsp60-induced tolerance in the rotifer Brachionus plicatilis exposed to multiple environmental contaminants.

Hsp60 induction was selected as a sublethal endpoint of toxicity for Brachionus plicatilis exposed to a water accommodated fraction (WAF) of Prudhoe Bay crude oil (PBCO), a PBCO/dispersant (Corexit 9527(R)) fraction and Corexit 9527(R) alone. To examine the effect of multiple stressors, exposures modeled San Francisco Bay, where copper levels are approximately 5 microgram/L, salinity is 22 per thousand, significant oil transport and refining occurs, and petroleum releases have occurred historically. Rotifers were exposed to copper at 5 microgram/L for 24 h, followed by one of the oil/dispersant preparations for 24 h. Batch-cultured rotifers were used in this study to model wild populations instead of cysts. SDS-PAGE with Western Blotting using hsp60-specific antibodies and chemiluminescent detection were used to isolate, identify, and measure induced hsp60 as a percentage of control values. Both PBCO/dispersant and dispersant alone preparations induced significant levels of hsp60. However, hsp60 expression was reduced to that of controls at high WAF concentrations, suggesting interference with protein synthesis. Rotifers that had been preexposed to copper maintained elevated levels of hsp60 upon treatment with WAF at all concentrations. Results suggest that induction of hsp60 by chronic low-level exposure may serve as a protective mechanism against subsequent or multiple stressors and that hsp60 levels are not additive for the toxicants tested in this study, giving no dose-response relationship. The methods employed in this study could be useful for quantifying hsp60 levels in wild rotifer populations.

Animals↗

PubMed2006

Epidemiology of undernutrition in adults in Dhaka slum households, Bangladesh.

OBJECTIVES: To identify socioeconomic, demographic and environmental factors that predict undernutrition in adults in a Dhaka slum population. DESIGN: A panel survey, conducted between 1995 and 1997. A random sample of households was selected. Socioeconomic, demographic and environmental variables were collected monthly by questionnaire and nutritional status was assessed. SETTING: Dhaka slums in Bangladesh. SUBJECTS: A total of 1097 adults surveyed during September-December 1996. MAIN OUTCOME MEASURES: Body mass index (BMI) less than 18.5 kg/m(2). RESULTS: There was a sex difference with female subjects having a significant odds ratio for low BMI compared with male subjects (P<0.03). There was no difference by age for males, but there was a difference by age for female subjects, with women aged 30-39 and 40-49 years having the worst BMI (P<0.04; P<0.04). The Beri Bahd area of residence had the worst BMI (P<0.001). Deficit situation as the self-reported financial situation had the worst BMI (P<0.03). Casual wage workers, unskilled and dependent self-employed individuals had the worst BMI (P<0.005; P<0.003). Not being involved in credit organizations and NGO credit organizations was associated with worst BMI (P<0.008; P<0.03). Those households that had an income of 2000-2499 Taka had the worst BMI (P<0.07). Households with a floor area of 5 m(2) or more per consumption unit had the best BMI (P<0.01). Households without electricity had the worst BMI (P<0.007). Households with tube well water had the worst BMI compared with those with tap water (P<0.001). CONCLUSIONS: Under nutrition was related to demographic, economic, social and environmental factors.

Adult↗

PubMed1995

Selective brain cooling in the horse during exercise and environmental heat stress.

Five horses were exercised on a treadmill [to central blood temperature (Tcore) approximately 42.5 degrees C]. Three of those horses were heated at rest in a climate room (53 degrees C, 90% relative humidity) (to Tcore approximately 41.5 degrees C). Temperatures were measured in the rectum, hypothalamus (Thyp), cerebrum, and cavernous sinus (Tsinus), on the skin of the head and midside, and Tcore. When Tcore increased above 38.5 degrees C, Thyp remained 0.6 +/- 0.1 degree C (SE) lower during heat exposure and 1 +/- 0.2 degrees C lower during exercise. During heat exposure, Tsinus was 2.2 +/- 0.4 degrees C below Tcore, and during exercise, Tsinus was 5 +/- 0.9 degrees C below Tcore. Upper respiratory tract bypass during exercise in one horse resulted in substantial reductions in Tcore-Thyp to 0.4 +/- 0.3 degrees C and Tcore-Tsinus to 0.9 +/- 0.2 degrees C. Thus the horse, a species without a carotid rete, can selectively cool the brain during exercise or heat exposure; this occurs, at least in part, via cool blood within the cavernous sinus, presumably resulting principally from cooling of venous blood within the upper respiratory tract.

Animals↗

PubMed2004

Migration of birds as an indicator of broad-scale environmental condition.

The migration of Neotropical birds may provide a robust measure of changing environmental condition along the migratory route. I review previous work on assessing broad-scale stopover quality in the eastern United States and discuss how future research can aid regional environmental assessment. Scientists can quantify how environmental changes affect the migratory system, and then monitor for those effects on migrant abundance from year to year. The cyclical nature of migration provides a constant re-evaluation of habitat quality and spatial distribution by migrant birds. Avian monitoring programs can detect changes in migrant abundance. Migrating birds may thus provide a living sensor of environmental change, enabling broad-scale environmental assessments to detect and address habitat degradation early on, allowing local managers to prioritize restoration efforts accordingly. Understanding the environmental factors driving stopover selection, and how birds move between stopovers during migration, is an important first step.

Animals↗

PubMed1981

Isolation of Legionella spp. from environmental water samples by low-pH treatment and use of a selective medium.

A selective medium was developed and used successfully to isolate Legionella pneumophila and Legionella-like organisms from environmental specimens previously positive by animal inoculation methods. This medium consists of charcoal-yeast extract agar to which have been added cephalothin (4 micrograms/ml), colistin (16 micrograms/ml), vancomycin (0.5 microgram/ml), and cycloheximide (80 micrograms/ml). Pretreating of the environmental water samples with an acid buffer (pH 2.2), followed by plating on the selective medium, improved the rate of recovery of both Legionella and Legionella-like organisms relative to that with direct plating on selective media.

Cephalothin↗

PubMed1986

Ontogenetic model of ageing and disease formation and mechanisms of natural selection.

It is known that increased mortality due to environmental hazards results, in the course of natural selection, in the shortening of maximum life span and acceleration of sexual maturation in a population subjected to an intensified pressure from external environment. As a consequence, the prereproductive period/maximum life span ratio appears to be approximately the same in each species. Mechanisms responsible for this are not clear yet. Since maximum life span is limited by both ageing and formation of certain diseases (in humans, the so-called main noninfectious diseases), the paper discusses four possible models of development of ageing and age-linked disease--ecological, genetic, degenerative (metabolic) and ontogenetic. It was found that it is the ontogenetic model only that can adequately account for the development of moderate shifts in the duration of both sexual maturation and maximum life span. It also provides the rationale for the pleotropic activity of genes during the development of the organism, its ageing and formation of age-connected diseases.

Aging↗

PubMed2005

Activity of selected oxidizing microbicides against the spores of Clostridium difficile: relevance to environmental control.

BACKGROUND: Clostridium difficile is an increasingly common nosocomial pathogen, and its spores are resistant to common environmental surface disinfectants. Many high-level disinfectants (eg, aldehydes) are unsuitable for environmental decontamination because they need several hours of contact to be sporicidal. This study tested the potential of selected oxidative microbicides to inactivate C. difficile spores on hard surfaces in relatively short contact times at room temperature. METHODS: The spores of a clinical isolate of C. difficile were tested using disks (1 cm diameter) of brushed stainless steel in a quantitative carrier test. The spores of C. sporogenes and Bacillus subtilis, common surrogates for evaluating sporicides, were included for comparison. The clostridia were grown separately in Columbia broth (CB), and B. subtilis was grown in a 1:10 dilution of CB. Each disk received 10 microL test spores with an added soil load, and the inoculum was dried. One disk each was placed in a glass vial and overlaid with 50 microL test formulation; controls received an equivalent volume of normal saline with 0.1% Tween 80. At the end of the contact time the microbicide was neutralized, the inoculum recovered from the disks by vortexing, the eluates were membrane filtered, and the filters placed on plates of recovery medium. The colony-forming units (CFU) on the plates were recorded after 5 days of incubation. The performance criterion was > or = 6 log(10) (> or = 99.9999%) reduction in the viability titer of the spores. The microbicides tested were domestic bleach with free-chlorine (FC) levels of 1000, 3000, and 5000 mg/L; an accelerated hydrogen peroxide (AHP)-based product with 70,000 mg/L H2O2 (Virox STF); chlorine dioxide (600 mg/L FC); and acidified domestic bleach (5000 mg/L FC). RESULTS: Acidified bleach and the highest concentration of regular bleach tested could inactivate all the spores in < or = 10 minutes; Virox STF could do the same in < or = 13 minutes. Regular bleach with 3000 mg/L FC required up to 20 minutes to reduce the viability of the all the spores tested to undetectable levels; chlorine dioxide and the lowest concentration of regular bleach tested needed approximately 30 minutes for the same level of activity. CONCLUSIONS: Acidified bleach, Virox STF, and regular bleach (3000-5000 mg/L FC) could inactivate C. difficile spores on hard environmental surfaces in approximately 10 to 15 minutes under ambient conditions. All of these products are strong oxidizers and should be handled with care for protection of staff, but acidified and regular bleach with high levels of FC also release chlorine gas, which can be hazardous if inhaled by staff or patients.

Chlorine Compounds↗

PubMed1999

Lessons in environmental health in the twentieth century.

Environmental health has evolved rapidly in recent decades, drawing largely on new analytic technologies, advanced data acquisition and modeling, mechanistic studies in toxicology, and the conceptual framework of risk assessment. The latter combines toxicologic and epidemiologic data with improved techniques for quantifying exposure, producing estimates of risks from environmental hazards or conditions to selected target populations. The public and governments have become increasingly concerned with environmental health and quality. The major lessons have been (a) environmental-health scientists must participate in policy debates; (b) environmental health problems are exceedingly complex and require interdisciplinary research; and (c) environmental health is a global issue. The globalization of commerce, the untested impact of international trade agreements, increased migration, and especially increased population, have profound impact on the quality as well as availability of air, water, land, and food. Global atmospheric transport of pollutants and the effect on atmosphere and climate are two examples of globalization of environmental health.

Environmental Health↗

PubMed2006

Understanding environmental influences on nutrition and physical activity behaviors: where should we look and what should we count?

Research interest in the influence of environmental factors on nutrition and physical activity behaviors has surged internationally in recent years. This is evident from a rapidly expanding literature and facilitated by advances in methodological and analytical approaches to assessing multiple levels of influence on health behaviors. However, a number of conceptual challenges complicate research endeavours in this field. The purpose of this paper is to provide a 'state of the science' overview of evidence regarding environmental influences on nutrition and physical activity behaviors. We focus particularly on a number of key conceptual and methodological issues, including: a consideration of how the environment is defined; the selection and operationalization of environmental exposures; and the importance of integrating existing understanding of individual influences on behavior with the emerging data on the role of the environment. We draw on examples from the published literature including our own research studies to illustrate these issues. We conclude by proposing a research agenda to progress understanding of the influences of the environment on population nutrition and physical activity behaviors.

Editorial↗

PubMed1999

Environmental health on the Net.

All living organisms are affected by natural or induced modifications of their surrounding physical environment. A distinct relationship exists between the health of the environment and the health of the individuals living in it. This paper presents a selection of resources about environmental health resources readily accessible on the Internet in October 1998.

Environmental Health↗

PubMed2000

Plasticity versus canalization: population differences in the timing of shade-avoidance responses.

The reliability of environmental cues and costs of a fixed phenotype are two factors determining whether selection favors phenotypic plasticity or environmental specialization. This study examines the relationship between these two factors and the evolution of plant competitive strategies (plastic vs. fixed morphologies). In natural plant populations, shifts in light quality associated with foliar shade reliably indicate the presence of neighbors. These cues mediate plastic stem-elongation responses that often increase competitive ability and access to light. Using experimental light treatments (full sun, neutral shade, and foliar shade), genetic differences among populations of Abutilon theophrasti (velvetleaf) in average elongation and plasticity to foliar-shade cues were examined. Six populations, two from each of three site types (fields in continuous corn cultivation, fields undergoing corn-soy rotation, and weedy sites), were exposed to the light treatments at two stages in their life history. At the seedling stage, populations derived from cornfield sites exhibited higher, average elongation than populations from either rotating corn-soy fields or weedy areas. Because seedling elongation may delay shading of velvetleaf by corn, population differences may reflect adaptive responses to directional selection imposed by competitive conditions. However, the effects of simulated foliar shade on elongation were three times as great as the average population differences, and these comparatively higher levels of elongation were associated with an allocation cost. These results are consistent with the hypothesis that phenotypic plasticity may limit the evolution of specialists; reliable environmental cues enable individuals to facultatively adopt highly elongated, costly phenotypes in crowded patches while avoiding the costs of that phenotype in less crowded microsites. At later life-history stages, populations experiencing competition with corn exhibited lower plasticity to light quality than populations derived from weedy areas. Elongation at later nodes is maladaptive in cornfields because velvetleaf is ultimately incapable of overtopping corn; individuals that elongate therefore experience the cost of allocating to stems but fail to improve leaf exposure. The decreased responsiveness of cornfield populations to light quality is consistent with theoretical predictions in which reduced plasticity is favored when environmental cues fail to mediate an adaptive response.

Biological Evolution↗

PubMed1976

The evolution of the cooperative group.

A simple model, illustrating the transition from a population of free swimming, solitary cells (Chlamydomonas-type) to one consisting of small colonies (Gonium-type) serves as a basis to discuss the evolution of the cooperative group. The transition is the result of a mutation of the dynamics of cell division, delayed cell separation leads to colonies of four cells. With this mutation cooperative features appear, such as synchronised cell divisions within colonies and coordinated flagellar function which enables the colony to swim in definite directions. The selective advantages under given, environmental conditions are defined and the periods necessary for complete allelic replacement in small populations are calculated for asexual and sexual reproduction. The assumption of a steady-state population during allelic substitution is critically considered, particularly under conditions of competition. It is shown that density-dependent population control must operate in the process of selection, Sexual reproduction slows down the rate of selection even though all cells are haploid. This phenomenon can be explained in general terms of "organizational dominance', where individual units coordinate the function of their neighbours which may be of a different allelotype. Cooperativity is pointed out as an a priori systemic feature which resides in the sub-units of systems, group formation and coordination appears thus as an almost inevitable event. A particular type of system described as 'closed cycle of positive fitness interaction' is discussed in more detail. It has the remarkable feature that its members cannot compete with each other; selection takes place between whole cycles (in analogy to Eigen's 1971 model). Gonium has a wide spectrum of 'somatic plasticity' which enables it to assume various colonial configurations depending on physiological and environmental conditions. This feature can be explained as the result of dynamic flexibilities on the macro-molecular level. The particular relationship between the vast, molecular complexity and the relative simple dynamics of the cell cycle must lead eventually to the genetic fixation of an environmentally induced phenotype.

Animals↗

PubMed2003

Do environmental contaminants adversely affect human reproductive physiology?

There is increasing concern among Canadian women that unwitting and unwanted exposures to environmental contaminants are adversely affecting their health, particularly their ability to become pregnant and have a healthy baby. Evidence of adverse reproductive outcomes among populations exposed to environmental contaminants in the workplace via accidental poisoning, together with detection of environmental contaminant residues in serum and ovarian follicular fluid, has led to the hypothesis that chemical contaminants may be contributing to adverse reproductive outcomes such as infertility, endometriosis, polycystic ovary syndrome, spontaneous abortion, preterm labour, intrauterine growth restriction, and pregnancy-induced hypertension in the general population. The lack of clear evidence concerning the association between exposure to environmental contaminants and adverse reproductive outcomes hampers the clinician's ability to counsel women who are trying to conceive or who have concerns about their pregnancy. This review summarizes the evidence linking environmental contaminant exposure to selected adverse health outcomes by examining the changes in health-outcome trends, the consistency of the epidemiological evidence of an association between the health outcome of concern and exposure to environmental contaminants, and the biological plausibility for environmental contaminant mediated effects on human reproductive health. At best, only a moderate association can be found linking exposure to environmental contaminants with evidence of deleterious reproductive effects in women. Lack of disease trend data, weak exposure assessments, and limited mechanistic data supporting the biological plausibility of potential effects are the primary limitations to the hypothesis that exposure to environmental contaminants adversely affects human reproductive physiology.

Animals↗