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At least 775 records · Page 43Linked to original sources
PubMed2000

Nonrandom mating in Drosophila melanogaster laboratory populations derived from closely adjacent ecologically contrasting slopes at "Evolution Canyon".

Ecological differentiation of natural populations of Drosophila melanogaster, Drosophila simulans, and another drosophilid, Zaprionus tuberculatus, in "Evolution Canyon," Mount Carmel, Israel, is well established. The fitness complex of D. melanogaster includes oviposition temperature preferences, tolerance to high temperature, drought stress and starvation, and different longevity patterns. This remarkable differentiation has evolved despite small interslope distances (only 100-400 m), within easy dispersal distance. The differences between populations are those expected from genetic adaptation to local microclimates. How such differentiation could evolve and be maintained despite the likelihood of genetic exchange between populations is a challenging question. We hypothesized that interslope microclimatic differences caused strong differential selection for stress tolerance, accompanied by behavioral differentiation (habitat choice and reduced migration rate), reinforced by sexual isolation. Here we report highly significant mate choice by flies from different slopes of the canyon, with preference for sexual partners originating from the same slope. No preferences were found when the sexual partners belonged to different isofemale lines from the same slope.

Animals↗
PubMed2003

Modeling current and future potential wintering distributions of eastern North American monarch butterflies.

Monarch butterflies overwinter in restricted areas in montane oyamel fir forests in central Mexico with specific microclimates that allow the butterflies to survive for up to 5 months. We use ecological niche modeling (ENM) to identify areas adequate for overwintering monarch colonies under both current and future climate scenarios. The ENM approach permits testing and validation of model predictivity, and yields quantitative, testable predictions regarding likely future climate change effects. Our models predicted monarch presence with a high degree of accuracy, and indicated that precipitation and diurnal temperature range were key environmental factors in making locations suitable for monarchs. When we projected monarch distribution onto future climate scenarios (Hadley Centre climate models), we found that conditions were likely to be inadequate across the entire current winter range, particularly owing to increased cool-weather precipitation that could cause increased mortality. This study applies ENM to understanding the seasonal dynamics of a migratory species under climate change, and uses ENM to identify key limiting environmental parameters in species' responses to climate change.

Abies↗
PubMed1997

Regulation of intestinal uroguanylin/guanylin receptor-mediated responses by mucosal acidity.

Guanylin and uroguanylin are intestinal peptides that stimulate chloride secretion by activating a common set of receptor-guanylate cyclase signaling molecules located on the mucosal surface of enterocytes. High mucosal acidity, similar to the pH occurring within the fluid microclimate domain at the mucosal surface of the intestine, markedly enhances the cGMP accumulation responses of T84 human intestinal cells to uroguanylin. In contrast, a mucosal acidity of pH 5.0 renders guanylin essentially inactive. T84 cells were used as a model epithelium to further explore the concept that mucosal acidity imposes agonist selectivity for activation of the intestinal receptors for uroguanylin and guanylin, thus providing a rationale for the evolution of these related peptides. At an acidic mucosal pH of 5.0, uroguanylin is 100-fold more potent than guanylin, but at an alkaline pH of 8.0 guanylin is more potent than uroguanylin in stimulating intracellular cGMP accumulation and transepithelial chloride secretion. The relative affinities of uroguanylin and guanylin for binding to receptors on the mucosal surface of T84 cells is influenced dramatically by mucosal acidity, which explains the strong pH dependency of the cGMP and chloride secretion responses to these peptides. The guanylin-binding affinities for peptide-receptor interaction were reduced by 100-fold at pH 5 versus pH 8, whereas the affinities of uroguanylin for these receptors were increased 10-fold by acidic pH conditions. Deletion of the N-terminal acidic amino acids in uroguanylin demonstrated that these residues are responsible for the increase in binding affinities that are observed for uroguanylin at acidic pH. We conclude that guanylin and uroguanylin evolved distinctly different structures, which enables both peptides to regulate, in a pH-dependent fashion, the activity of receptors that control intestinal salt and water transport via cGMP.

Amino Acid Sequence↗
PubMed2003

Photosynthetic flexibility in Pedilanthus tithymaloides poit, a CAM plant.

The induction of CAM in Pedilanthus tithymaloides (Euphorbiaceae) under water-limited conditions was evaluated by following diurnal oscillations of CO2 fixation, titratable acidity and malic acid content in the leaf extracts. CAM induction was assessed by measuring the activities of phosphoenolpyruvate carboxylase (PEPC), NADH-malate dehydrogenase (MDH) and phosphoenolpyruvate caroxykinase (PEPCK) in the leaves as well. Drought resulted in large increases in the nocturnal acid accumulation and rates of CO2 uptake in the leaves of P. tithymaloides. The drought-induced CAM activity tended to be reversible after re-watering. Nevertheless, under well-watered conditions, plants of P. tithymaloides showed day time CO2 uptake patterns with less pronounced diurnal oscillations of organic acids. Our data indicate that although P. tithymaloides is a CAM plant, environmental variables like drought induce photosynthetic flexibility in this species. This type of plasticity in CAM and metabolic versatility in P. tithymaloides should be an adaptation for prolonged survival under natural adverse edaphic and microclimate situations.

Carbon Dioxide↗
PubMed1990

Incidence and diel pattern of oviposition outdoors of the mosquito, Aedes aegypti (L.) (Diptera: Culicidae) in Trinidad, W.I. in relation to solar aspect.

The incidence and diel patterns of oviposition of domestic Aedes aegypti in Trinidad, West Indies during the middle of the wet season (July and August) was compared, using modified ovitraps, in unshaded peridomestic outdoor sites facing east or west. Sites close to each other along a transect differed greatly in the total eggs they received, 18.2% of sites receiving 50.6% of the eggs. Sites receiving most eggs were close to other breeding sites. The incidence of oviposition in sites facing west, as measured by the number of eggs laid (greater than 59%) and by the number of occurrences of eggs (greater than 57%), was greater than in sites facing east. The diel pattern of oviposition was closely similar in sites facing east and west, indicating that the sun's azimuth at the moment of oviposition does not determine whether a female lays in sites facing east or west. The diel pattern of oviposition resembled an earlier study in being bimodal but differed from it in featuring a much larger morning peak (comprising more than 34% of eggs laid v. about 5% in the earlier study). This bimodal pattern closely resembles the diel periodicity of landing on humans described previously by several authors and is probably close to the typical oviposition pattern for Ae. aegypti; an artefact may have modified the oviposition periodicity characterized earlier. In the evening significantly more eggs were laid in sites facing west than in sites facing east. These findings have implications for effective placement of ovitraps for surveillance or suppression of Ae. aegypti, and give rise to an hypothesis which invokes responses to microclimate to account for the form of the bimodal oviposition pattern.

Aedes↗
PubMed2001

Thermal resistance of chicken (Gallus domesticus) plumage: a comparison between broiler and free-range birds.

1. We compared Ross chickens reared under broiler and free-range conditions to see whether there was a difference in thermal resistance of the plumage. 2. There was no difference in resistance to heat loss attributable to rearing environment for plumage from the back and leg but there was a significant difference in the pectoral region. 3. Free-range birds had a thicker plumage and a higher total resistance to heat transfer in the pectoral region, despite showing a lower resistance per unit depth than broiler birds. The pectoral plumage was more heavily soiled in broiler birds, which is the most likely explanation for the higher resistance per unit depth. 4. We suggest that behavioural selection of microclimate is likely to be a more important determinant of heat balance in free-range birds than intrinsic plumage adaptations.

Adaptation, Physiological↗
PubMed1995

Protective clothing and heat stress.

The high level of protection required by protective clothing (PPC) severely impedes heat exchange by sweat evaporation. As a result work associated with wearing PPC, particularly in hot environments, implies considerable physiological strain and may render workers exhausted in a short time. Current methods of describing evaporative heat exchange with PPC are insufficient, will overestimate evaporative heat loss and should not be recommended. More reliable measures of the resistance to evaporative heat transfer by PPC should be developed and standardized. Direct measurements of evaporative resistance of PPC may be carried. However, a more promising method appears to be the definition of evaporative resistance on the basis of the icl-index for the fabric layers. The icl-index is a permeation efficiency ratio, which in combination with clothing insulation determines the evaporative heat transfer. Current methods should be further developed to account for effects of moisture condensation and microclimate ventilation.

Body Temperature Regulation↗
PubMed2005

A serial cross-sectional study of the prevalence of rabbit haemorrhagic disease on three farms in the lower North Island of New Zealand.

AIM: To estimate over a 3-year period following the first release of rabbit haemorrhagic disease virus (RHDV) the prevalence of rabbit haemorrhagic disease (RHD) and the abundance of rabbits (Oryctolagus cuniculus) in an area that historically had low rabbit densities. METHODS: Three farms grazing predominantly sheep and beef cattle, located close together and with low initial rabbit densities, were selected for study. RHDV had been deliberately released on all farms in December 1997. Farms were visited 2-3 times per year between June 1998 and April 2001. At each visit, rabbits were shot with the aid of spotlights at night and blood samples were collected for detection of RHDV antibodies. Rabbit carcasses were necropsied and the age of the animals was determined. Rabbit abundance on each property was measured throughout the study using spotlight night counts. Logistic regression was used to identify factors associated with the risk of carcasses being seropositive for RHDV. RESULTS: Rabbit density differed initially between farms (8.2, 9.9, 2.3 rabbits per spotlight km in June 1998), and declined on all three properties over time (1.2, 2.4, 1.1 rabbits per spotlight km in November 2000). Highest antibody titres to RHDV were initially evident on the farm on which rabbits were most abundant. The average prevalence of seropositive rabbits overall was 21% (95% CI=15-28%). Female rabbits tended to be less likely to be seropositive for RHDV than males (OR=0.47; 95% CI=0.21-1.02). The odds of becoming seropositive were reduced for rabbits born in the breeding season of 1999-2000 (OR=0.17; 95% CI=0.05-0.64). CONCLUSIONS: The temporal pattern of outbreaks measured by peaks of seroprevalence differed between closely-spaced farms when they had different rabbit densities, but were similar when rabbit densities were similar. Microclimate and vegetation influencing abundance of insect vectors for RHDV and intrinsic population-related factors like rabbit breeding behaviour are also likely to be involved in local patterns of spread.

Animals↗
PubMed2005

Use of porous aluminosilicate pellets for drug delivery.

Three pelletized porous aluminosilicate ceramics were obtained commercially and their potential to act as extended release drug delivery systems was assessed. The pellets were drug loaded using a vacuum impregnation technique. Factors such as the concentration of the loading solution and the porosity and bulk density of the ceramic influenced the drug loading. The release of drug from the pellets was extended as the drug was entrapped within their porous interior. The rate of release was influenced by the porous microstructure of the pellets and the physicochemical properties of the drug. Extrusion-spheronization was used to prepare pellets similar to the porous ceramics. The pellet formulations contained an aluminosilicate clay mineral (kaolin or halloysite), ethylcellulose 100 cps, ethanol and varying quantities of sucrose. The latter two components acted as pore forming agents. Diltiazem HCl was loaded into the pellets and its release was extended. The release rate could be modified by changing the quantity of sucrose included in the initial formulation, as this influenced the porous microstructure of the pellets. In halloysite-based products the release was further extended due to entrapment of the drug within the halloysite microtubules. Porous kaolin-based pellets were also prepared by cryopelletization. This involved freezing droplets of an aqueous suspension containing kaolin, sodium silicate solution and sodium lauryl sulphate. The resulting pellets were freeze-dried, which removed ice from them to leave pores behind. The pellets gave extended drug release with the release rate being influenced by the porous microstructure of the pellets and their microclimate pH.

Aluminum Silicates↗
PubMed1998

The Effects of Local Cooling on Thermophysiological Response in Participants Wearing Dust-Free Garments.

This study was designed to find the effects of two kinds of dust-free garments with (A) and without (B) frozen gel strip (FGS), and half-naked clothing (brassiere and shorts; C) on thermophysiological parameters and on temperature and humidity within clothing. The heart rate, rectal, and skin temperatures as well as sweat rate and clothing microclimate were measured during 140 min in 9 healthy females. Inquiries were also made into the subjective rating of thermal, humidity, and comfort sensations. The main findings in our experiments are as follows: (a) Physiological parameters such as rectal and skin temperatures (chest and forehead), heart rate, and sweat rate were clearly lowest in garb C, intermediate in garb A, and highest in garb B throughout the experiment; (b) Temperature and humidity within clothing were lower in garb A than in garb B; (c) More than half of the 9 participants decreased thermal sensation by wearing garb A. These results suggest that the usage of FGS could improve the heat load in lightly working participants wearing dust-free garments.

Journal Article↗
PubMed1998

Risk Assessment in the Working Environment in Estonia.

The first step to chart hazards in the working environment in Estonia (labour force: 0.65 million) was taken by the National Board of Health Protection in the beginning of 1996. The existing chemical, physical, and biological agents in the working environment were investigated with the help of local health inspectors in all counties. An identification of hazards and workers at risk was carried out. The results of the analysis showed that 16% of Estonian industrial workers are exposed to different hazards: 20,000 persons are exposed to noise, 11,000 are working in the conditions of vibration, 10,000 are affected by unsatisfactory microclimate, 6,000 complain about long-lasting work in a compulsory posture, the overexertion of eyes is suffered by 5,500 persons, and physical overload by 3,500 workers. In the group of chemical hazards the greatest numbers of workers are exposed to organic dust (6,500) and welding aerosols (5,400), followed by petroleum products (2,700), and oil-shale dust (4,300). The measurements of working conditions showed that an average of 30.3% of the results are above the standards. Proposals for the improvement of the situation in occupational safety and health are presented.

chemicals↗
PubMed1987

Heat strain and heat stress for workers wearing protective suits at a hazardous waste site.

In order to evaluate the effects of heat stress when full body protective suits are worn, heart rates, oral temperatures and environmental parameters were measured for five unacclimatized male workers (25-33 years of age) who performed sampling activities during hazardous waste clean-up operations. The protective ensembles included laminated PVC-Tyvec chemical resistant hood suits with rubber boots, gloves full facepiece dual cartridge respirators and hard hats. For comparison, measurements also were performed when the men worked at a similar level of activity while they wore ordinary work clothes. A comparison of the heart rates for the men working with and without suits indicated that wearing the suits imposed a heat stress equivalent to adding 6 degrees to 11 degrees C (11 degrees to 20 degrees F) to the ambient WBGT index. A similar result was obtained by calculating the WBGT in the microclimate inside the suits and comparing it to the ambient WBGT. These results indicate the following: 1) there exists a significant risk of heat injury during hazardous waste work when full body protective clothing is worn, and 2) threshold limit values for heat stress established by the ACGIH must be lowered substantially before extending them to cover workers under these conditions.

Adult↗
PubMed1987

The effect of temperature and humidity levels in a protective mask on user acceptability during exercise.

Subjective and physiological responses were obtained from six subjects wearing a ventilated face mask while exercising (3.8 met) for 15 min on a bicycle ergometer. Different combinations of ambient air temperatures (7 degrees, 16 degrees, 25 degrees C) and mask air temperatures (22 degrees, 27 degrees, 33 degrees C) were studied together with two different air humidities inside the mask (61% and 86% RH). Control experiments were performed without the mask at the same ambient temperatures. Skin temperatures, heart rates and skin wettedness were monitored during exercise. The subject's acceptance of the mask and thermal environment, thermal sensation, sensations of discomfort, sweating and skin wettedness, and their judgment of the work of breathing were assessed at the end of the 15 min exercise period. The acceptance of both the ambient thermal environment and of the thermal microclimate in the mask primarily was determined by the ambient air temperature, but it was influenced by the air temperature and humidity inside the mask. At ambient temperatures of 7 degrees C and 25 degrees C, the acceptance of the thermal work conditions decreased. In the warm environment a mask air temperature less than or equal to 27 degrees C was 100% acceptable and increased the acceptance of thermal environment. In the cool environment, a mask air temperature greater than or equal to 27 degrees C was 100% acceptable. The humidity content of the mask air was only important when the mask air was warm. Warm humid air significantly decreased acceptance of the mask conditions.

Adult↗
PubMed1978

Intestinal transport of weak electrolytes: Determinants of influx at the luminal surface.

The determinants of weak electrolyte influx into everted segments of rat small intestine have been studied. Preliminary experiments showed that the observed influxes could be described as unidirectional, diffusional fluxes of the nonionized compound uncomplicated by a parallel ionic component. It is shown that the determinants of weak electrolyte influx in this situation may be described in terms of the resistance of the unstirred layer to movement from the bulk phase to the cell surface, the degree of ionization of the weak electrolyte at the cell surface, and the cellular permeability to the nonionized weak electrolyte. Quantitative considerations indicated that the unstirred layer was totally rate-limiting in the cases of some poorly ionized, or highly permeant compounds, but the unstirred layer was not totally rate limiting for most of the compounds studied. Calculation of cellular permeabilities for the nonionized forms of weak electrolytes required assumptions to be made concerning the pH value in the surface fluid layer. A uniform set of permeability data including both weak acids and weak bases was obtained only when it was assumed that the pH in the surface fluid layer was equal to that in the bulk phase, and it was concluded that these studies do not support the concept of a microclimate of distinctive pH at the epithelial surface as a determinant of weak electrolyte transport.

Animals↗
PubMed1981

The use of infrared radiation to reduce heat loss in burned patients: experiments with a phantom.

Heat losses from patients with severe burns place considerable demands on the body. The metabolic rate, already elevated as a result of the injury, must rise further to maintain thermal equilibrium. To compare different methods of supplying heat to burned patients, a phantom has been constructed in which a free water surface has been used to simulate burned tissue. The effect of environmental temperature, humidity and air velocity, and of radiant energy, on the evaporation rate from the water surface, and on the energy supplied to the water to maintain its temperature, have been measured. Results showed that humidity and air velocity were the main factors determining evaporation. The internal energy required to maintain the temperature of the phantoms could be reduced by use of infrared radiation. This is particularly appropriate in the clinical situation, as energy is supplied to the skin surface, where it can replace directly energy lost through evaporation. Because the effect of radiant energy on the evaporation rate was small, it may be possible to create a microclimate around a patient where air velocity can be set to give a desired rate of evaporation, and the infrared level can be adjusted for patient comfort.

Body Temperature Regulation↗
PubMed1999

The physicochemical environment of the neonatal intestine.

Dietary intake, bacterial metabolites, and the secretion of factors (eg, proteins, electrolytes, lipid-soluble molecules, and water) by the body each contribute to the physicochemical environment of the gastrointestinal tract. Peristalsis regulates the changes along the length of the intestine. However, coordinated peristaltic responses develop as premature infants mature. In addition, the physicochemical environment of the center of the intestinal lumen differs from that of the epithelial surface. The area adjacent to the small intestinal epithelium is more acid than the bulk phase. Na+/H+ exchange antiporters in the epithelial cell apical membrane generate this acidity. Mucus maintains the acid microclimate by preventing free diffusion of hydrogen ions into the bulk phase. Development also affects these mechanisms. Changes in the lumenal environment may alter the synthesis of signaling molecules expressed by the intestinal epithelium. Thus, the epithelium, through changes in gene regulation, may act as an active interface that transmits information about the composition of the intestinal lumen to the mucosal immune system. Premature neonates are at risk of necrotizing enterocolitis, a disease almost exclusively associated with oral feeds. The pathogenesis of this condition may, in part, be due to the immaturity of the interactions between the physicochemical environment of the lumen and intestine.

Cytokines↗
PubMed2002

Measuring and simulating crown respiration of Scots pine with increased temperature and carbon dioxide enrichment.

Acclimation to elevated atmospheric carbon dioxide concentration and temperature of respiration by the foliage in the crown of Scots pine (Pinus sylvestris) trees is measured and modelled. Starting in 1996, individual 20-year-old trees were enclosed in chambers and exposed to either normal ambient conditions (CON), elevated CO2 concentration (EC), elevated temperature (ET) or a combination of EC and ET (ECT). Respiration of individual leaves within the crown was measured in 2000. To extrapolate the response of respiration of individual leaves to the whole crown, a multi-layer model was developed and used to predict daily and annual crown respiration, in which the crown structure and corresponding microclimate data were used as input. Respiration measurements showed that EC led to higher Q10 values (4.6%) relative to CON, but lower basal respiration rates at 20 degrees C [R1.d(20)] (-7.1%) during the main growth season (days 120-240), whereas ET and ECT both reduced Q10 (-12.0 and -9.8%, respectively) throughout the year but increased R1.d(20) (27.2 and 21.6%, respectively) during the period of no-growth, and slightly reduced R1.d(20) (-1.7 and -2.8%, respectively) during the main growth season. Model computations showed that annual crown respiration increased: (1) by 16% in EC, with 92% of this increase attributable to the increase in foliage area; (2) by 35% in ET, with 66% related to the increase in foliage area and 17% to the rise in ambient temperature; and (3) by 27% in the case of ECT, with 43% attributable to the increase in foliage area and 29% to the rise in ambient temperature. Changed respiration parameters for individual leaves, induced by treatments, made only a small contribution to the annual crown respiration compared with the increased foliage area. The effects of changes in crown architecture and nitrogen distribution, caused by treatments, on the daily and annual course of crown respiration are discussed.

Carbon Dioxide↗
PubMed2003

Effects of plant traits on ecosystem and regional processes: a conceptual framework for predicting the consequences of global change.

Human activities are causing widespread changes in the species composition of natural and managed ecosystems, but the consequences of these changes are poorly understood. This paper presents a conceptual framework for predicting the ecosystem and regional consequences of changes in plant species composition. Changes in species composition have greatest ecological effects when they modify the ecological factors that directly control (and respond to) ecosystem processes. These interactive controls include: functional types of organisms present in the ecosystem; soil resources used by organisms to grow and reproduce; modulators such as microclimate that influence the activity of organisms; disturbance regime; and human activities. Plant traits related to size and growth rate are particularly important because they determine the productive capacity of vegetation and the rates of decomposition and nitrogen mineralization. Because the same plant traits affect most key processes in the cycling of carbon and nutrients, changes in plant traits tend to affect most biogeochemical cycling processes in parallel. Plant traits also have landscape and regional effects through their effects on water and energy exchange and disturbance regime.

Biomass↗