			Home About us Contact

Joint Effects (joint + effects)

Distribution by Scientific Domains

Life Sciences	51%
Medical Sciences	20%
Humanities and Social Sciences	5%
Earth and Environmental Science	5%
Business, Economics, Finance and Accounting	5%
3 Other Domains	14%

Distribution within Life Sciences

Human Genetics	27%
Ecology & Organismal Biology	15%
Evolution	9%

Selected Abstracts

Population growth of Daphnia magna under multiple stress conditions: Joint effects of temperature, food, and cadmium

ENVIRONMENTAL TOXICOLOGY & CHEMISTRY, Issue 5 2006
Evelyn H. W. Heugens
Abstract Aquatic organisms in the field often are exposed to combinations of stress factors of variousorigins. Little is known of the interaction between different types of stressors; hence, the predictability of their joint effects is low. Therefore, the present study analyzed the joint effects of temperature, food, and cadmium on the population growth rate of the water flea Daphnia magna. The results revealed that temperature, food, and cadmium, as well as their interactions, were important factors that influenced life-history parameters and, as a consequence, the population growth rate of D. magna. In general, population growth rate increased at high temperature and food level but decreased when cadmium was present. The positive effect of temperature on population growth rate was smallest at limiting food levels. Negative effects of cadmium on the growth rate were enhanced at elevated temperatures, whereas high food levels protected the daphnids from adverse effects of cadmium. To avoid over- or underestimation regarding the toxicity of substances to field populations, results of standard toxicity tests should be applied in a location-specific way. [source]

Assessing the joint effects of chlorinated dioxins, some pesticides and polychlorinated biphenyls on thyroid hormone status in Japanese breast-fed infants

ENVIRONMETRICS, Issue 2 2003
Takashi Yanagawa
Abstract Joint effects of dioxin related chemicals (DXNs), hexachlorocyclohexanes (HCHs), DDT, dieldrin, heptachlor-epoxide (HCE), chlordane and polychlorinated biphenyls (PCB) on the levels of triirodothyronine (T3), thyroxine (T4), thyroid stimulating hormones (TSH) and thyroid binding globulin (TBG) in the peripheral blood of 101 breast-fed infants are studied. The statistical issue involved is how to estimate the effects based on data from volunteer subjects with possible measurement errors. A chain independent graph is applied for modeling the associations among factors, and dicotomizations of selected factors are performed for estimating the effects. Use of nonparametric methods with careful consideration of over-adjustment is suggested. It is shown that the estimated odds ratios of DXNs,DDT, the first principal component of DXNs and DDT, relative to TSH are 3.02 (p -value=0.03) and 7.15 (p -value=0.02), respectively, when PCB is not adjusted and adjusted for, respectively. Copyright © 2003 John Wiley & Sons, Ltd. [source]

Do woodlice and earthworms interact synergistically in leaf litter decomposition?

FUNCTIONAL ECOLOGY, Issue 1 2005
MARTIN ZIMMER
Summary 1In laboratory microcosms, we investigated the influence of diversity of both leaf litter and detritivores on decomposition processes. Either woodlice or earthworms, or a combination of woodlice and earthworms, fed on leaf litter of either oak or alder, or oak and alder for 8 weeks. Mass loss of leaf litter, soil microbial respiration and soil nutrient concentrations were determined every 2 weeks. 2For four out of seven decomposition parameters, the joint effects of woodlice and earthworms were stronger than the sum of single-species effects when they had fed on alder litter. When feeding on oak litter, however, woodlice and earthworms together revealed lower decomposition rates than predicted from their single effects. Joint effects of detritivores on decomposition of mixed litter were always lower than predicted from the sum of their effects. 3In mixed-litter assays, we obtained intermediate values of decomposition parameters, indicating that doubling the species richness of leaf litter from one to two species did not promote decomposition processes. Effects of mixing litter were, thus, mostly additive; essentially only when earthworms fed on mixed litter we observed, mostly positive, non-additive effects of diverse litter. 4Our findings provide evidence for a potential effect on ecosystem functioning through joint action of detritivores even at low species diversity, while litter diversity seems to be less significant. On high-quality litter, isopods and earthworms are not functionally redundant but act synergistically on litter decomposition. The effects of detritivore diversity on ecosystem processes, however, are context-specific and depend on the quality and diversity of the available food sources, and on species-specific characteristics of the detritivores. [source]

Joint effects of coffee consumption and serum gamma-glutamyltransferase on the risk of liver cancer,

HEPATOLOGY, Issue 1 2008
Gang Hu
Only three Japanese prospective studies have suggested an inverse association between coffee drinking and liver cancer risk. No prospective studies on the association between serum gamma-glutamyltransferase (GGT) and liver cancer risk have been reported. We aimed to determine the single and joint associations of coffee consumption and serum GGT with the risk of primary liver cancer. Study cohorts included 60,323 Finnish participants who were 25-74 years of age and free of any cancer at baseline. During a median follow-up period of 19.3 years (interquartile range: 9.3-29.2 years), 128 participants were diagnosed with an incident liver cancer. The multivariable-adjusted (age, sex, alcohol consumption, education, smoking, diabetes and chronic liver disease at baseline and during follow-up, and body mass index) hazards ratios of liver cancer in participants who drank 0-1, 2-3, 4-5, 6-7, and ,8 cups of coffee daily were 1.00, 0.66, 0.44, 0.38, and 0.32 (P for trend = 0.003), respectively. Further adjustment for serum GGT in subgroup analysis affected the results only slightly. The multivariable-adjusted and coffee-adjusted hazard ratio of liver cancer for the highest versus the lowest quartile of serum GGT was 3.13 (95% confidence interval = 1.22-8.07). The multivariable-adjusted inverse association between coffee consumption and liver cancer risk persisted when stratified by baseline factors: age more/less than 50 years, current smoker/never smoked/ever smoked, alcohol drinker/never drinker, obese/nonobese, and the highest/lowest three quartiles of serum GGT. A combination of very low coffee consumption and high level of serum GGT was associated with nearly nine-fold increased risk. Conclusion: Coffee drinking has an inverse and graded association with the risk of liver cancer. High serum GGT is associated with an increased risk of liver cancer. (HEPATOLOGY 2008.) [source]

Synergistic association between alcohol intake and body mass index with serum alanine and aspartate aminotransferase levels in older adults: the Rancho Bernardo Study

ALIMENTARY PHARMACOLOGY & THERAPEUTICS, Issue 11-12 2009
R. LOOMBA
Summary Background The association between body-mass-index (BMI), alcohol consumption and their joint effect in increasing the risk of elevated serum alanine (ALT) and aspartate (AST) is unclear in older community-dwelling adults. Aim To determine the association between alcohol, BMI, and their combined effect with serum ALT and AST in older community-dwelling adults in the United States. Methods A cross-sectional, population-based study in participants (n = 2364) from the Rancho Bernardo Study (54% women; mean age: 70 years, BMI: 25 kg/m2, alcohol users: 63%) who attended a research visit in 1984,87. BMI was recorded by a trained nurse and alcohol use ascertained by a validated questionnaire. Odds-ratio (OR) and 95% confidence intervals (CI) of elevated serum ALT and AST (defined as ,30 U/L in men and ,19 U/L in women) were calculated for alcohol and BMI separately and their joint exposure using logistic regression models. Results In multivariate logistic regression models adjusted for age, alcohol use, total cholesterol, serum triglycerides, fasting plasma glucose, systolic blood pressure, and diabetes mellitus, obesity independently increased the odds of elevated ALT in this cohort of older men and women by 3.0 (95% CI, 1.7,5.3) and 1.8 (95% CI, 1.1,2.7) respectively. Joint effects of consuming >3 alcoholic drinks/day and obesity raised the odds of elevated ALT by 8.9 (95% CI, 2.4,33.1) and AST by 21-fold (95% CI, 2.6,170.1), demonstrating synergism. Obese participants had higher odds of elevated ALT even at 0 , 1 drink/day. Conclusions In older men and women, the combination of obesity with alcohol is synergistic in increasing the risk of liver injury. [source]

Independent predictive roles of eotaxin Ala23Thr, paraoxonase 2 Ser311Cys and ,3 -adrenergic receptor Trp64Arg polymorphisms on cardiac disease in Type 2 Diabetes,an 8-year prospective cohort analysis of 1297 patients

DIABETIC MEDICINE, Issue 4 2010
Y. Wang
Diabet. Med. 27, 376,383 (2010) Abstract Aims, To examine the independent and joint effects of multiple genetic variants on a cardiac end-point in an 8-year prospective study of a Chinese diabetic cohort. Methods, Seventy-seven single nucleotide polymorphisms (SNPs) of 53 candidate genes for inflammation, thrombosis, vascular tone regulation and lipid metabolism were genotyped in 1297 Chinese patients with no prior history of coronary heart disease (CHD) or heart failure at baseline. Cardiac end-point was defined by the occurrence of CHD and/or heart failure. Results, In Cox regression model, after adjustment for baseline confounding variables including age, sex, smoking status, duration of diabetes, glycaemic control, lipid levels, waist circumference, blood pressure, albuminuria and estimated glomerular filtration rate, genetic variants, including Ala/Ala of SCYA11 (eotaxin) Ala23Thr, Cys/Cys or Cys/Ser of PON2 (paraoxonase 2) Ser311Cys and Arg/Arg of ADRB3 (,3 -adrenergic receptor) Trp64Arg, were independently associated with incident cardiac end-point, with respective hazard ratios (95% confidence interval) of 1.70 (1.10,2.61, P = 0.037), 1.42 (1.08,1.88, P = 0.013) and 3.84 (1.18,12.50, P = 0.025). Analysis of the joint effect of the risk alleles showed significant increased risk of the cardiac end-point with increasing number of risk alleles (P < 0.001). The adjusted risk for the cardiac end-point was 4.11 (P = 0.002) for patients carrying four risk alleles compared with those carrying one or no risk allele. Conclusions, The independent risk conferred by genetic variants encoding pathways such as inflammation and lipid metabolism, not adequately reflected by conventional biomarkers, may identify high-risk individuals for intensified control of modifiable risk factors. [source]

Population growth of Daphnia magna under multiple stress conditions: Joint effects of temperature, food, and cadmium

Responses of biofilms to combined nutrient and metal exposure

ENVIRONMENTAL TOXICOLOGY & CHEMISTRY, Issue 3 2002
Núria Ivorra
Abstract Numerous studies have reported marked sensitivities of diatom species to phosphate and organic pollution but have ignored interactions with other common contaminants. The aim of the present study was to investigate the single and joint effects of increased phosphate and metal (cadmium, zinc) concentrations on benthic diatom communities. Microalgal biofilms from a relatively unpolluted stream were exposed in the laboratory to Zn, Cd, and P, separately and in combination, in concentrations found at a polluted stream in the same catchment. The Zn concentration reduced algal growth in biofilms more than the Cd concentration. Phosphate compensated for the single effect of each metal but not for their combined effects. Diatom community changes were evaluated using water quality indices based on the empirical sensitivities of taxa to nutrients (TDI) and organic pollution (%PTV). Phosphate exposure resulted in an increase of the eutrophy rank and presumed pollution-tolerant taxa. In contrast, exposure to Zn, Zn + Cd, and Zn + Cd + P caused a marked reduction of the TDI and %PTV community values. The successional trends in the laboratory matched the observed differences in microphyte communities in the reference and polluted river stations. However, the autoecology of the species present also revealed that the resulting composition of diatom communities cannot be attributed solely to the direct toxic effects of metal and nutrients and their interaction. Observed changes in the relative abundance of species are also determined by their growth form and microdistribution in biofilms. [source]

Assessing the joint effects of chlorinated dioxins, some pesticides and polychlorinated biphenyls on thyroid hormone status in Japanese breast-fed infants

Evidence for canalization of Distal-less function in the leg of Drosophila melanogaster

EVOLUTION AND DEVELOPMENT, Issue 2 2005
Ian Dworkin
Summary A considerable body of theory pertaining to the evolution of canalization has emerged recently, yet there have been few empirical investigations of their predictions. To address this, patterns of canalization and trait correlation were investigated under the individual and joint effects of the introgression of a loss-of-function allele of the Distal-less gene and high-temperature stress on a panel of iso-female lines. Variation was examined for number of sex comb teeth and the length of the basi-tarsus on the pro-thoracic leg of male Drosophila melanogaster. I demonstrate that whereas there is evidence for trait canalization, there is no evidence to support the hypothesis of the evolution of genetic canalization as a response to microenvironmental canalization. Furthermore, I demonstrate that although there are genetic correlations between these traits, there is no association between their measures of canalization. I discuss the prospects of the evolutionary lability of the Distal-less gene within the context of changes in genetic variation and covariation. [source]

Do woodlice and earthworms interact synergistically in leaf litter decomposition?

A novel method to identify gene,gene effects in nuclear families: the MDR-PDT

GENETIC EPIDEMIOLOGY, Issue 2 2006
E.R. Martin
Abstract It is now well recognized that gene,gene and gene,environment interactions are important in complex diseases, and statistical methods to detect interactions are becoming widespread. Traditional parametric approaches are limited in their ability to detect high-order interactions and handle sparse data, and standard stepwise procedures may miss interactions that occur in the absence of detectable main effects. To address these limitations, the multifactor dimensionality reduction (MDR) method [Ritchie et al., 2001: Am J Hum Genet 69:138,147] was developed. The MDR is wellsuited for examining high-order interactions and detecting interactions without main effects. The MDR was originally designed to analyze balanced case-control data. The analysis can use family data, but requires a single matched pair be selected from each family. This may be a discordant sib pair, or may be constructed from triad data when parents are available. To take advantage of additional affected and unaffected siblings requires a test statistic that measures the association of genotype with disease in general nuclear families. We have developed a novel test, the MDR-PDT, by merging the MDR method with the genotype-Pedigree Disequilibrium Test (geno-PDT)[Martin et al., 2003: Genet Epidemiol 25:203,213]. MDR-PDT allows identification of single-locus effects or joint effects of multiple loci in families of diverse structure. We present simulations to demonstrate the validity of the test and evaluate its power. To examine its applicability to real data, we applied the MDR-PDT to data from candidate genes for Alzheimer disease (AD) in a large family dataset. These results show the utility of the MDR-PDT for understanding the genetics of complex diseases. Genet. Epidemiol. 2006. © 2005 Wiley-Liss, Inc. [source]

A mixture of seven antiandrogens induces reproductive malformations in rats

INTERNATIONAL JOURNAL OF ANDROLOGY, Issue 2 2008
Cynthia V. Rider
Summary To date, regulatory agencies have not considered conducting cumulative risk assessments for mixtures of chemicals with diverse mechanisms of toxicity because it is assumed that the chemicals will act independently and the individual chemical doses are not additive. However, this assumption is not supported by new research addressing the joint effects of chemicals that disrupt reproductive tract development in the male rat by disrupting the androgen signalling pathway via diverse mechanisms of toxicity [i.e. androgen receptor (AR) antagonism in the reproductive tract vs. inhibition of androgen synthesis in the foetal testis]. In this study, pregnant rats were exposed to four dilutions of a mixture containing vinclozolin, procymidone, linuron, prochloraz, benzyl butyl phthalate, dibutyl phthalate and diethylhexyl phthalate during the period of sexual differentiation and male offspring were assessed for effects on hormone sensitive endpoints including: anogenital distance, infant areolae retention and reproductive tract tissue weights and malformations. The ratio of the chemicals in the mixture was based upon each chemical's ED50 for inducing reproductive tract malformations (hypospadias or epididymal agenesis). The observed responses from the mixture were compared with predicted responses generated with a toxic equivalency approach and models of dose addition, response addition or integrated addition. As hypothesized, we found that the mixture of chemicals that alter the androgen signalling pathway via diverse mechanisms disrupted male rat reproductive tract differentiation and induced malformations in a cumulative, dose-additive manner. The toxic equivalency and dose addition models provided the best fit to observed responses even though the chemicals do not act via a common cellular mechanism of action. The current regulatory framework for conducting cumulative risk assessments needs to consider the results, including those presented herein, which indicate that chemicals that disrupt foetal tissues during sexual differentiation act in a cumulative, dose-additive manner irrespective of the specific cellular mechanism of toxicity. [source]

Interactive effects of environmental stress and inbreeding on reproductive traits in a wild bird population

JOURNAL OF ANIMAL ECOLOGY, Issue 6 2006
A. B. MARR
Summary 1Conservation biologists are concerned about the interactive effects of environmental stress and inbreeding because such interactions could affect the dynamics and extinction risk of small and isolated populations, but few studies have tested for these interactions in nature. 2We used data from the long-term population study of song sparrows Melospiza melodia on Mandarte Island to examine the joint effects of inbreeding and environmental stress on four fitness traits that are known to be affected by the inbreeding level of adult birds: hatching success, laying date, male mating success and fledgling survival. 3We found that inbreeding depression interacted with environmental stress to reduce hatching success in the nests of inbred females during periods of rain. 4For laying date, we found equivocal support for an interaction between parental inbreeding and environmental stress. In this case, however, inbred females experienced less inbreeding depression in more stressful, cooler years. 5For two other traits, we found no evidence that the strength of inbreeding depression varied with environmental stress. First, mated males fathered fewer nests per season if inbred or if the ratio of males to females in the population was high, but inbreeding depression did not depend on sex ratio. Second, fledglings survived poorly during rainy periods and if their father was inbred, but the effects of paternal inbreeding and rain did not interact. 6Thus, even for a single species, interactions between the inbreeding level and environmental stress may not occur in all traits affected by inbreeding depression, and interactions that do occur will not always act synergistically to further decrease fitness. [source]

Synergistic, antagonistic and additive effects of multiple stressors: predation threat, parasitism and pesticide exposure in Daphnia magna

JOURNAL OF APPLIED ECOLOGY, Issue 6 2008
Anja Coors
Summary 1Predation and parasitism are important factors in the ecology and evolution of natural populations and may, along with other environmental factors, interact with the impact of anthropogenic pollutants. 2Our study aimed at identifying potential interactions between three stressors (predation threat, parasitism and pesticide exposure) and at exploring the predictability of their joint effects by using the model of independent action. We assessed in a full-factorial design the impacts of these stressors on key life-history traits and population growth rate of the water flea Daphnia magna. 3When applied as single stressors, predation threat and parasite challenge induced varying stressor-specific adaptive responses. The pesticide carbaryl was applied at a generally sublethal concentration, which caused low mortality only in first-brood offspring. 4Pesticide exposure interacted synergistically with parasite challenge regarding survival, which suggests immunomodulatory activity of the pesticide. Predation threat by phantom midge larvae showed antagonistic interactions for amount of first-brood offspring with both parasite challenge and carbaryl exposure. All stressors additively affected age and size at maturity, which added up to a considerable delay in the onset of reproduction in the three-stressor combination. The intrinsic rate of natural increase, r, reflected the non-additive and additive effects on single endpoints and showed significant synergistic interactions for all two-stressor combinations. The combination of all stressors resulted in a dramatic reduction of r compared to the stressor-free control. 5The model of independent action proved useful in quantitatively predicting effects of additively acting stressors, and in visualizing the occurrence and magnitude of non-additive effects in accordance with results of analysis of variances. 6Synthesis and applications. Cumulative additive effects and non-additive interactions of natural antagonists and pollutants are shown to result in considerable impacts on ecologically relevant parameters. As a starting point for an environmentally more realistic risk assessment of chemicals, it may be a valuable strategy to screen for non-additive effects among many stress factors simultaneously in simplified experimental designs by using the model of independent action. [source]

The joint effects of larval density and 14C-cypermethrin on the life history and population growth rate of the midge Chironomus riparius

JOURNAL OF APPLIED ECOLOGY, Issue 6 2003
Helen L. Hooper
Summary 1Chemical effects on organisms are typically assessed using individual-level endpoints or sometimes population growth rate (PGR), but such measurements are generally made at low population densities. In contrast most natural populations are subject to density dependence and fluctuate around the environmental carrying capacity as a result of individual competition for resources. As ecotoxicology aims to make reliable population projections of chemical impacts in the field, an understanding of how high-density or resource-limited populations respond to environmental chemicals is essential. 2Our objective was to determine the joint effects of population density and chemical stress on the life history and PGR of an important ecotoxicological indicator species, Chironomus riparius, under controlled laboratory conditions. Populations were fed the same ration but initiated at different densities and exposed to a solvent control and three concentrations of 14C-cypermethrin in a sediment,water test system for 67 days at 20 ± 1 °C. 3Density had a negative effect on all the measured life-history traits, and PGR declined with increasing density in the controls. Exposure to 14C-cypermethrin had a direct negative effect on juvenile survival, presumably within the first 24 h because the chemical rapidly dissipated from the water column. Reductions in the initial larval densities resulted in an increase in the available resources for the survivors. Subsequently, exposed populations emerged sooner and started producing offspring earlier than the controls. 14C-cypermethrin had no effect on estimated fecundity and adult body weight but interacted with density to reduce the time to first emergence and first reproduction. As a result, PGR increased with cypermethrin concentration when populations were initiated at high densities. 4Synthesis and applications. The results showed that the effects of 14C-cypermethrin were buffered at high density, so that the joint effects of density and chemical stress on PGR were less than additive. Low levels of chemical stressors may increase carrying capacity by reducing juvenile competition for resources. More and perhaps fitter adults may be produced, similar to the effects of predators and culling; however, toxicant exposure may result in survivors that are less tolerant to changing conditions. If less than additive effects are typical in the field, standard regulatory tests carried out at low density may overestimate the effects of environmental chemicals. Further studies over a wide range of chemical stressors and organisms with contrasting life histories are needed to make general recommendations. [source]

Refuge habitats modify impact of insecticide disturbance on carabid beetle communities

JOURNAL OF APPLIED ECOLOGY, Issue 2 2001
Jana C. Lee
Summary 1Carabid beetles are polyphagous predators that can act as biological control agents of insect pests and weeds. While current agricultural practices often create a harsh environment, habitat management such as the establishment of within-field refuges has been proposed to enhance carabid beetle abundance and impact. We examined the joint effects of refuge habitats and insecticide application on carabid activity density (parameter of population density and relative activity) and species composition in a cornfield. 2Our 2-year study comprised four treatments: (i) ,refuge/,insecticide; (ii) +refuge/,insecticide; (iii) ,refuge/+insecticide; (iv) +refuge/+insecticide. Refuge strips consisted of grasses, legumes and perennial flowering plants. ,,Refuge' strips were planted with corn and not treated with insecticide. 3Before planting and insecticide application, carabid activity density in the crop areas was similar across all treatments. Insecticide application immediately reduced carabid activity density and altered community composition in the crop area. 4Refuge strips had significantly higher activity density of beetles than ,refuge strips before planting and during the summer. 5During summer, as new carabids emerged and insecticide toxicity declined, the presence of refuge strips influenced carabids in the adjacent crop area. Carabid activity density within crop areas previously treated with insecticide was significantly higher when adjacent to refuge strips. Also, carabid communities within insecticide-treated crop areas were affected by the presence or absence of a refuge strip. 6The presence of refuge strips did not consistently augment carabid numbers in crop areas where insecticide was not applied. One explanation may be that insecticides decreased the quality of crop habitat to carabids by depletion of prey and direct mortality. However, subsequent rebounds in prey density and the absence of competing predators may make these areas relatively more attractive than unperturbed crop habitats to carabid colonization from refuges. 7This study demonstrates that refuges may buffer the negative consequences of insecticide application on carabids in adjacent fields. Diversifying agro-ecosystems with refuge habitats may be a viable strategy for maintaining carabid populations in disturbed agricultural landscapes to keep pests below outbreak levels. [source]

How environmental stress affects density dependence and carrying capacity in a marine copepod

JOURNAL OF APPLIED ECOLOGY, Issue 3 2000
Richard M. Sibly
Summary 1.,Management of the effects of stress on populations , for instance in ecotoxicology , requires understanding of the effects of stressors on populations and communities. Attention to date has too rarely been directed to relevant ecological endpoints, such as carrying capacity and density dependence. Established procedures are instead based on measuring the Life Tables of individual organisms exposed to differing concentrations of a pollutant at low population density, but this approach does not take into account population effects that may occur through interactions between individuals. Here we introduce an approach that allows direct measurement of the effects of stressors on carrying capacity and density dependence. 2.,Using the marine copepod Tisbe battagliai Volkmann-Rocco, we report replicated experiments establishing the effects of 100 µg L,1 pentachlorophenol (PCP) in combination with varying diet and food concentrations. Population density was measured as population biomass in 10 mL volumes. Diet was either the alga Isochrysis galbana Parke (here designated ,poor diet') or a mix of two algal species (I. galbana and Rhodomonas reticulata Novarino: ,good diet'). Each was given at three food concentrations (520, 1300 and 3250 µgC L,1), selected on the basis that at low population density these cover the range between limited and maximal population growth. 3.,Carrying capacity increased linearly with food concentration. On the poor diet the increase was 1·2 ,g L,1 for each ,gC L,1 increase in food concentration. On the good diet the increase was 2·3 ,g L,1/,gC L,1 in the absence of PCP, and 1·9 ,g L,1/,gC L,1 with PCP. Maximum carrying capacity was in the region of 60,80 ,g per 10 mL volume. Population growth rate (pgr) decreased linearly with population biomass when the latter was plotted on a logarithmic scale. Increasing biomass reduced pgr by 1·70 week,1 for each unit increase in log10 biomass. Increasing food concentration and improving diet both increased pgr, but did not affect the slope of the density-dependent relationship. Presence or absence of PCP had no effect except that at some higher food concentrations non-PCP populations initially increased faster than PCP populations, and at high concentration on the good diet the effect of density-dependence was decreased in PCP populations. 4.,The results show that a stressor's effects at high population density may differ from its effects at low density, and emphasizes the importance of finding new protocols, such as those introduced here, with which to study the joint effects of a stressor and population density. Managers and researchers of threatened species, harvested species and pest species need to know the joint effects of stressors and population density, in order to be able to predict the effects of stressors on carrying capacity and on the course of recovery from environmental perturbations. [source]

The evolution of self-fertilization and inbreeding depression under pollen discounting and pollen limitation

JOURNAL OF EVOLUTIONARY BIOLOGY, Issue 3 2005
E. PORCHER
Abstract We model the evolution of plant mating systems under the joint effects of pollen discounting and pollen limitation, using a dynamic model of inbreeding depression, allowing for partial purging of recessive lethal mutations by selfing. Stable mixed mating systems occur for a wide range of parameter values with pollen discounting alone. However, when typical levels of pollen limitation are combined with pollen discounting, stable selfing rates are always high but less than 1 (0.9 < s < 1 in most cases); in this situation, complete selfing does not evolve because pollen discounting becomes very large at high selfing rates, so that the automatic advantage of selfing changes to a disadvantage. These results suggest that mixed mating systems with high selfing rates can be maintained by selection, whereas mixed mating systems with low to moderate selfing rates are more likely attributable to unavoidable geitonogamous selfing. [source]

Impact of Collaborative Management and Early Admission in Labor on Method of Delivery

JOURNAL OF OBSTETRIC, GYNECOLOGIC & NEONATAL NURSING, Issue 2 2003
Debra J. Jackson senior researcher
Objective: This study compared the effects of early admission in labor and perinatal care provider on delivery method. Higher spontaneous vaginal delivery rates for certified nurse midwives as compared with physicians have been reported in observational studies and randomized clinical trials. Certified nurse midwives, with their more expectant approach to labor management, would be expected to admit women later in labor than obstetricians. Methods: Prospective cohort study of 2,196 low-risk pregnancies, with singleton, vertex infants admitted in spontaneous labor. Independent and joint effects of perinatal care provider and cervical dilation at admission on delivery method were evaluated. Confounding was addressed using restriction and multiple regression. Results: Fewer (23.4%) women in collaborative care were admitted in early labor (< 4 cm cervical dilation) than women managed by obstetricians (95% CI =,27.6 to ,19.2). Obstetrician care had 9% to 30% fewer spontaneous vaginal deliveries. Women admitted early in labor also had 6% to 34% fewer spontaneous vaginal deliveries. Evaluation of joint effects suggested that interaction between obstetrician provider and earlier admission increased the risk of operative delivery. Conclusion: Later admission in labor (at 4 cm or greater cervical dilation) and management of perinatal care by certified nurse midwives in collaboration with obstetricians increased the rate of spontaneous vaginal delivery in low-risk women. [source]

Pharmacodynamic interaction of recombinant human interleukin-10 and prednisolone using in vitro whole blood lymphocyte proliferation

JOURNAL OF PHARMACEUTICAL SCIENCES, Issue 5 2002
Abhijit Chakraborty
Abstract Prednisolone, a commonly used synthetic corticosteroid, and IL-10, a cytokine under investigation for strong antiinflammatory properties, are being contemplated as a potential joint therapeutic regimen in immune disorders. Their pharmacodynamic interactions were examined in blood from healthy adult male and female volunteers using an in vitro phytohemagglutinin (PHA)-stimulated whole,blood lymphocyte proliferation technique. Isobolograms along with parametric competitive and noncompetitive interaction models were used to determine the nature and intensity of interactions. Single drug effects show prednisolone more efficacious in inhibiting lymphocyte proliferation with an IC50 of 3.3 ng/mL and Imax value of 1, signifying complete suppression. Analogous parameters for IL-10 were 16.2 ng/mL for IC50 and 0.89 for Imax. There were no significant differences in the single drug immunosuppressive effects among genders. Their joint effects showed additive interaction based on isobolographic analysis. Parametric analysis using the competitive interaction model described their interaction as slightly synergistic, while the noncompetitive interaction modeling indicate a small degree of antagonism. Also, the joint effects in females tend to be more antagonistic than males. Concomitant use of prednisolone and IL-10 should thus reflect the net additive responses to concentrations of each agent. © 2002 Wiley-Liss, Inc. and the American Pharmaceutical Association J Pharm Sci 91:1334,1342, 2002 [source]

Multilevel governance and organizational performance: Investigating the political-bureaucratic labyrinth

JOURNAL OF POLICY ANALYSIS AND MANAGEMENT, Issue 1 2004
Kenneth J. Meier
Research on governance has extensively explored the complex interactions of governmental, nongovernmental, and for-profit entities in the execution of public policy. It has consistently failed, however, to model empirically the joint effects of political and bureaucratic actors in governance systems. To address this issue, a theory of multilevel governance built upon the foundation of representative bureaucracy was developed and tested. Results from an analysis of Texas school districts suggest that Latinos at all levels of the governance system, political and managerial, influence representation at other levels. Findings also indicate that Latinos at each level of governance have positive effects, directly and indirectly, on outcomes for Latino students. The influence of both political and managerial actors at times extends beyond the immediately adjoining level; the effects of such actors cascade through the governance system. The results show that a priority for systematic research should be the identification of approaches and settings for examining the multilevel aspect of governance. © 2004 by the Association for Public Policy Analysis and Management. [source]

Effects of disturbance intensity and frequency on early old-field succession

JOURNAL OF VEGETATION SCIENCE, Issue 5 2001
B. Collins
Radford et al. (1968) Abstract. Early old-field succession provides a model system for examining vegetation response to disturbance frequency and intensity within a manageable time scale. Disturbance frequency and intensity can interact with colonization and competition to influence relative abundance of earlier and later successional species and determine, respectively, how often and how far succession can be reset. We tested the joint effects of disturbance frequency and intensity on vegetation response (species richness, abundance, canopy structure) during the first six years of succession by clipping the dominant species (D) or all species (T) in spring and fall of each year (S), once per year in summer (Y1), each two years in summer (Y2), or each four years in summer (Y4). Vegetation response reflected disturbance effects on expansion of a later monospecific dominant perennial herb, Solidago altissima, and persistence of the early, richer flora of annuals. A more abundant and taller top Solidago canopy developed on plots clipped each 2 yr or less frequently. Plots clipped yearly or seasonally were richer, but had less abundant, shorter, and differently stratified canopy. Disturbance mediated the relative abundance of early and later successional species; however, frequency and intensity effects were not completely congruent. Persistence of a richer early successional flora increased through the most frequent disturbance (S), and was magnified by disturbance intensity. Disturbance as extreme as clipping all vegetation twice yearly did not cause a drop in species richness, but maintained the early successional community over the first six years of succession. We conclude that clipping disturbance influenced the rate of succession, but the early community could rebound through the range of disturbance frequency and intensity tested. [source]

RIGHT ACT, VIRTUOUS MOTIVE

METAPHILOSOPHY, Issue 1-2 2010
THOMAS HURKA
Abstract: The concepts of virtue and right action are closely connected, in that we expect people with virtuous motives to at least often act rightly. Two well-known views explain this connection by defining one of the concepts in terms of the other. Instrumentalists about virtue identify virtuous motives as those that lead to right acts; virtue-ethicists identify right acts as those that are or would be done from virtuous motives. This essay outlines a rival explanation, based on the "higher-level" account of virtue defended in the author's Virtue, Vice, and Value. On this account rightness and virtue go together because each is defined by a (different) relation to some other, more basic moral concept. Their frequent coincidence is therefore like a correlation between A and B based not on either's causing the other but on their being joint effects of a single common cause. [source]

Sibling relationships and best friendships in young adulthood: Warmth, conflict, and well-being

PERSONAL RELATIONSHIPS, Issue 2 2006
AURORA M. SHERMAN
Although much work addresses the importance of siblings and friendships in separate investigations, few studies simultaneously examine both relationships. Young adults (N= 102, M age = 18.7) were surveyed about their friendships, their sibling relationships, and their psychological well-being (assessed by self-esteem and loneliness). Participants with harmonious (high warmth, low conflict) sibling relations and same-gender friends had the highest well-being. Participants with affect-intense (high warmth, high conflict) sibling relationships had low well-being. However, participants who had low-involved (low warmth, low conflict) and affect-intense same-gender friendships did not differ in well-being. When examining joint effects, having a harmonious same-gender friendship compensated for having a low-involved sibling relationship, but having harmonious sibling relations did not compensate for having low-involved friendships. Overall, the results underscore the importance of positive and negative relationship properties and the joint effects of multiple relationships. [source]

Values-based Political Messages and Persuasion: Relationships among Speaker, Recipient, and Evoked Values

POLITICAL PSYCHOLOGY, Issue 4 2005
Thomas E. Nelson
The persuasive power of values-based political messages may depend on recipients having (1) shared values with the speaker (a type of personal identity match); (2) shared political party identifications with the speaker (a type of social identity match); and/or (3) expectations about values traditionally associated with different political parties (an expectancy violation/confirmation). The independent and joint effects of these factors on the success of a persuasive message were examined, using the theoretical framework of dual-process models of persuasion. Participants (N = 301), classified according to their party identifications and primary value orientations, read a political speech that varied by argument quality, speaker party, and values evoked. Results indicated that value matching promotes close attention to the message, while party mismatching increases message rejection. These effects depend to some extent, however, on expectancies about values traditionally associated with different parties. Participants especially rejected messages from rival party members when the speaker evoked unexpected values. Results are discussed in terms of their implications for the efficacy of values-based political communication. [source]

Association between asbestos exposure, cigarette smoking, myeloperoxidase (MPO) genotypes, and lung cancer risk

AMERICAN JOURNAL OF INDUSTRIAL MEDICINE, Issue 1 2002
Matthew B. Schabath MS
Abstract Background As observed in tobacco-associated carcinogenesis, genetic factors such as the polymorphic metabolic/oxidative enzyme myeloperoxidase (MPO) could modulate individual susceptibility to asbestos-associated carcinogenesis. Methods RFLP-PCR analysis identified the MPO genotypes in 375 Caucasian lung cancer cases and 378 matched controls. An epidemiological interview elicited detailed information regarding smoking history and occupational history and exposures. Results Asbestos exposure was associated with a significantly elevated risk estimate (OR,=,1.45; 95% CI 1.04,2.02). On stratified analysis, we found the MPO genotypes modified the effect of asbestos exposure on lung cancer risk. Specifically, G/G carriers who were exposed to asbestos had an odds ratio (OR) of 1.72 (95% CI; 1.09,2.66), while A-allele carriers (G/A,+,A/A) exposed to asbestos exhibited a reduced OR of 0.89 (95% CI; 0.56,1.44). The OR was further reduced to 0.73 (0.49,1.06) for A-allele carriers not exposed to asbestos. A similar trend was observed for the joint effects between the MPO genotypes and pack-years smoking. Next, all three risk factors (MPO genotypes, asbestos exposure, and smoking) were analyzed simultaneously for joint effects. Heavy smokers with the G/G genotype and a history of asbestos exposure demonstrated a statistically significant elevated risk estimate (OR,=,2.19; 95% CI 1.16,4.11), while the A-allele carriers with the same exposure profile were at a lower risk for lung cancer (OR,=,1.18; 95% CI 0.58,2.38). The A-allele genotypes demonstrated similar protective effects for the other three exposure profiles. Conclusions For a similar level of exposure to established carcinogens, individuals with the MPO A-allele genotypes appear to have a reduced risk of lung cancer. Am. J. Ind. Med. 42:29,37, 2002. © 2002 Wiley-Liss, Inc. [source]

Information transmission in electronic versus open-outcry trading systems: An analysis of U.S. equity index futures markets

THE JOURNAL OF FUTURES MARKETS, Issue 7 2005
Aysegul Ates
In this article the intraday price discovery process between regular index futures (floor trading) and E-mini index futures (electronic trading) in the S&P 500 and Nasdaq 100 index futures markets is examined, using intraday data from the introduction of the E-mini index futures to 2001. Using both information shares (Hasbrouck, J., 1995) and common long-memory factor weights (Gonzalo, J., & Granger, C. W. J., 1995) techniques, we find that both E-mini index futures and regular index futures contribute to the price discovery process. However, since September 1998, the contribution made by E-mini index futures has been greater than that provided by regular index futures. Based on regression analysis, we have also found direct empirical evidence to support the hypothesis that the joint effects of operational efficiency and relative liquidity determine the greater contribution made towards price discovery by electronic trading relative to open-outcry trading over time. © 2005 Wiley Periodicals, Inc. Jrl Fut Mark 25: 679,715, 2005 [source]

Identification of Interacting Genes in Genome-Wide Association Studies Using a Model-Based Two-Stage Approach

ANNALS OF HUMAN GENETICS, Issue 5 2010
Zhaogong Zhang
Summary In this paper, we propose a two-stage approach based on 17 biologically plausible models to search for two-locus combinations that have significant joint effects on the disease status in genome-wide association (GWA) studies. In the two-stage analyses, we only test two-locus joint effects of SNPs that show modest marginal effects. We use simulation studies to compare the power of our two-stage analysis with a single-marker analysis and a two-stage analysis by using a full model. We find that for most plausible interaction effects, our two-stage analysis can dramatically increase the power to identify two-locus joint effects compared to a single-marker analysis and a two-stage analysis based on the full model. We also compare two-stage methods with one-stage methods. Our simulation results indicate that two-stage methods are more powerful than one-stage methods. We applied our two-stage approach to a GWA study for identifying genetic factors that might be relevant in the pathogenesis of sporadic Amyotrophic Lateral Sclerosis (ALS). Our proposed two-stage approach found that two SNPs have significant joint effect on sporadic ALS while the single-marker analysis and the two-stage analysis based on the full model did not find any significant results. [source]

Joint Identification of Multiple Genetic Variants via Elastic-Net Variable Selection in a Genome-Wide Association Analysis

ANNALS OF HUMAN GENETICS, Issue 5 2010
Seoae Cho
Summary Unraveling the genetic background of common complex traits is a major goal in modern genetics. In recent years, genome-wide association (GWA) studies have been conducted with large-scale data sets of genetic variants. Most of those studies have relied on single-marker approaches that identify single genetic factors individually and can be limited in considering fully the joint effects of multiple genetic factors on complex traits. Joint identification of multiple genetic factors would be more powerful and would provide better prediction on complex traits since it utilizes combined information across variants. Here we propose a multi-stage approach for GWA analysis: (1) prescreening, (2) joint identification of putative SNPs based on elastic-net variable selection, and (3) empirical replication using bootstrap samples. Our approach enables an efficient joint search for genetic associations in GWA analysis. The suggested empirical replication method can be beneficial in GWA studies because one can avoid a costly, independent replication study while eliminating false-positive associations and focusing on a smaller number of replicable variants. We applied the proposed approach to a GWA analysis, and jointly identified 129 genetic variants having an association with adult height in a Korean population. [source]