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At least 793 records · Page 44Linked to original sources
PubMed1982

The effect of environmental temperature on sebum composition of tropical and temperate breeds of cattle.

This study compared to effect of environmental temperature on sebum composition in 2 breeds of cattle, British (SH) and Brahman (GB), which differ in their abilities to tolerate heat. By long-term exposure of both breeds to environmental temperatures of 24 C and 32 C and the more heat-tolerant GB breed to 38 C, it was possible to make breed comparisons at (a) different body temperatures, i.e., when all animals were exposed to the same environmental temperature, and (b), at the same body temperature, i.e., when the 2 breeds were exposed to different ambient temperatures. The composition of sebum excreted to saturation level on the skin surface was determined. At the same body temperatures, the amounts of fatty acids in each lipid class were higher in GB than in SH animals except during hyperthermia when the amounts of triglyceride fatty acids were similar in both breeds. The total amounts of individual fatty acids except 14:1, 16:1, 20:0 and 14:OH were higher in both breeds at 32 C than at 24 C. The GB cattle excreted more essential fatty acids (EFA) than the SH cattle at 24 C and at 32 C. There was a significant genotype by environment interaction in the amount of EFA excreted in triglyceride decreased whereas the amount excreted in wax esters increased with rising body temperature.

Animals↗
PubMed2006

Phenotypic plasticity of body size in a temperate population of Drosophila melanogaster: when the temperature-size rule does not apply.

A natural population of Drosophila melanogaster in southern France was sampled in three different years and 10 isofemale lines were investigated from each sample. Two size-related traits, wing and thorax length, were measured and the wing/thorax ratio was also calculated. Phenotypic plasticity was analysed after development at seven different constant temperatures, ranging from 12 degrees C to 31 degrees C. The three year samples exhibited similar reaction norms, suggesting a stable genetic architecture in the natural population. The whole sample (30 lines) was used to determine precisely the shape of each reaction norm, using a derivative analysis. The practical conclusion was that polynomial adjustments could be used in all cases, but with different degrees: linear for the wing/thorax ratio, quadratic for thorax length, and cubic for wing length. Both wing and thorax length exhibited concave reaction norms, with a maximum within the viable thermal range. The temperatures of the maxima were, however, quite different, around 15 degrees C for the wing and 19.5 degrees C for the thorax. Assuming that thorax length is a better estimate of body size, it is not possible to state that increasing the temperature results in monotonically decreasing size (the temperature-size rule), although this is often seen to be the case for genetic variations in latitudinal clines. The variability of the traits was investigated at two levels-within and between lines-and expressed as a coefficient of variation. The within-line (environmental) variability revealed a regular, quadratic convex reaction norm for the three traits, with a minimum around 21 degrees C. This temperature of minimum variability may be considered as a physiological optimum, while extreme temperatures are stressful. The between-line (genetic) variability could also be adjusted to quadratic polynomials, but the curvature parameters were not significant. Our results show that the mean values of the traits and their variance are both plastic, but react in different ways along a temperature gradient. Extreme low or high temperatures decrease the size but increase the variability. These effects may be considered as a functional response to environmental stress.

Analysis of Variance↗
PubMed2005

Dual role of endogenous nitric oxide in tumor necrosis factor shock: induced NO tempers oxidative stress.

Tumor necrosis factor (TNF) is involved in pathologies like septic shock, inflammatory bowel disease and rheumatoid arthritis. TNF and lipopolysaccharide can incite lethal shock, in which cardiovascular collapse is centrally orchestrated by the vasodilating free radical nitric oxide (NO). However, NO synthase (NOS) inhibition causes increased morbidity and/or mortality, suggesting a dual role for NO. To investigate the potential protective role of NO during TNF shock, we treated mice with TNF with or without NOS inhibition. Experiments in endothelial- NOS- and inducible NOS-deficient mice identified inducible NOS as the source of protective NO. Distinctive TNF-induced lipid peroxidation, especially in liver and kidney, was aggravated by NOS inhibition. In addition, various antioxidant treatments and a phospholipase A2 (PLA2) inhibitor prevented sensitization by NOS inhibition. Together, these in vivo results indicate that induced NO not only causes hemodynamic collapse, but is also essential for curbing TNF-induced oxidative stress, which appears to hinge on PLA2-dependent mechanisms.

Aldehydes↗
PubMed1997

PCR amplification and cloning of metallothionein complementary DNAs in temperate and Antarctic sea urchin characterized by a large difference in egg metallothionein content.

Metallothionein levels were determined in the eggs of two sea urchin species, the Mediterranean Sphaerechinus granularis and the Antarctic Sterechinus neumayeri. While appreciable levels of metallothionein were found in S. granularis eggs, a negligible amount was detected in S. neumayeri. Two metallothionein isoforms were purified from S. granularis, and metallothionein cDNAs were obtained by means of reverse transcriptase-polymerase chain reaction (RT-PCR). Two distinct cDNA species were cloned and sequenced. The translated amino acid sequences of these two forms consisted of 67 residues and differed in two amino acid substitutions. Despite the lack of metallothionein in S. neumayeri eggs, a metallothionein cDNA was obtained by RT-PCR amplification and a single amino acid sequence coding for a 63 residues MT was deduced. A comparative analysis of the primary structure of S. granularis and S. neumayeri metallothioneins with those of the other sea urchin metallothioneins has been performed. Sea urchin metallothioneins appear to be less similar to each other than metallothioneins of closely related vertebrates.

Amino Acid Sequence↗
PubMed2002

Bacterial community dynamics across a floristic gradient in a temperate upland grassland ecosystem.

Alterations in soil bacterial communities across a transect between a semi natural upland grassland and an agriculturally improved enclosure were assessed using culture-based methods and a nucleic-acid-based method, terminal restriction fragment length polymorphism (TRFLP). While plant diversity decreased across the transect towards the improved area, numbers of 16S rDNA terminal restriction fragments increased, indicating an increase in numbers of bacterial ribotypes. Bacterial numbers, microbial activity, and potential functional diversity also followed a similar trend, increasing with decreasing plant diversity. Alterations in bacterial community structure were coincident with changes in soil physicochemical properties which also changed across the transect. Increases in soil pH, nitrate, phosphorus, potassium, and calcium occurred toward the improved grassland, while organic matter and ammonium declined. The inverse relationship between floristic diversity and bacterial ribotype numbers suggests that soil physicochemical factors may be as influential in determining bacterial diversity in soils of upland grassland communities as floristic diversity.

Bacteria↗
PubMed2003

Swimming ability and behaviour of post-larvae of a temperate marine fish re-entrained in the pelagic environment.

The degree to which behaviour, vertical movement and horizontal transport, in relation to local hydrodynamics, may facilitate secondary dispersal in the water column was studied in post-larval Sillaginodes punctata in Port Phillip Bay, Australia. S. punctata were captured in shallow seagrass beds and released at the surface in three depth zones (1.5, 3 and 7 m) off-shore at each of two sites to mimic the re-entrainment of fish. The behaviour, depth and position of S. punctata were recorded through time. The direction and speed of local currents were described using an S4 current meter and the movement of drogues. Regardless of site, fish immediately oriented toward the bottom, and into the current after release. In shallow water (1.5 m), 86% of fish swam to the bottom within 2 min of release. At one site, the net horizontal displacement of fish was largely unrelated to the speed and direction of local currents; at a second site, fish could not maintain their position against the current, and the net horizontal displacement was related to the speed and direction of currents. In the intermediate depth zone, wide variability in depths of individual fish through time led to an average depth reached by fish that was between the shallow and deep zones. Based on daily increments in the otoliths, however, this variability was not related significantly to the time since entry of fish into Port Phillip Bay. In the deepest depth zone, 81% of fish remained within 1 m of the surface and their horizontal displacement was significantly related to the direction and speed of currents. Secondary dispersal of post-larval fish in the water column may be facilitated by the behaviour and vertical movements of fish, but only if fish reach deeper water, where their displacement (direction and distance) closely resembles local hydrodynamic regimes. In shallow water, fish behaviour and vertical migration actually reduce the potential for secondary dispersal.

Adaptation, Physiological↗
PubMed2003

Soil community composition and the regulation of grazed temperate grassland.

The effect of the community composition of soil microbes on ecosystem processes has received relatively little attention. Here we examined the variation in soil microbial composition in a Yellowstone National Park grassland and the effect of that variation on the growth, in a greenhouse, of the dominant grass in the community. Plants and their rhizospheric soil were collected from paired, Poa pratensis-dominated grassland plots located inside and outside a 40-year-old exclosure. P. pratensis aboveground, belowground, and whole plant growth were greater in pots with soil communities from grazed grassland compared to fenced grassland, indicating (1) soil microbial communities differed, and (2) this difference influenced the growth of the plant that dominated both grasslands. Treating pots with fungicide (benomyl) suppressed the soil community influence, indicating that different fungal communities caused the soil microbe effect. In addition, two lines of evidence are consistent with the hypothesis that arbuscular mycorrhizal fungal (AMF) species composition affected P. pratensis: (1) a divergence in AMF spore communities in the two field soils, and (2) little evidence of pathogenic fungi. These findings emphasize the need to examine the role that the composition of the soil microbial community plays in controlling terrestrial ecosystems.

Climate↗
PubMed2003

Carbon dioxide and water vapor exchange in a warm temperate grassland.

Grasslands cover about 40% of the ice-free global terrestrial surface, but their contribution to local and regional water and carbon fluxes and sensitivity to climatic perturbations such as drought remains uncertain. Here, we assess the direction and magnitude of net ecosystem carbon exchange (NEE) and its components, ecosystem carbon assimilation ( A(c)) and ecosystem respiration ( R(E)), in a southeastern United States grassland ecosystem subject to periodic drought and harvest using a combination of eddy-covariance measurements and model calculations. We modeled A(c) and evapotranspiration (ET) using a big-leaf canopy scheme in conjunction with ecophysiological and radiative transfer principles, and applied the model to assess the sensitivity of NEE and ET to soil moisture dynamics and rapid excursions in leaf area index (LAI) following grass harvesting. Model results closely match eddy-covariance flux estimations on daily, and longer, time steps. Both model calculations and eddy-covariance estimates suggest that the grassland became a net source of carbon to the atmosphere immediately following the harvest, but a rapid recovery in LAI maintained a marginal carbon sink during summer. However, when integrated over the year, this grassland ecosystem was a net C source (97 g C m(-2) a(-1)) due to a minor imbalance between large A(c) (-1,202 g C m(-2) a(-1)) and R(E) (1,299 g C m(-2) a(-1)) fluxes. Mild drought conditions during the measurement period resulted in many instances of low soil moisture (theta<0.2 m(3)m(-3)), which influenced A(c) and thereby NEE by decreasing stomatal conductance. For this experiment, low theta had minor impact on R(E). Thus, stomatal limitations to A(c) were the primary reason that this grassland was a net C source. In the absence of soil moisture limitations, model calculations suggest a net C sink of -65 g C m(-2) a(-1) assuming the LAI dynamics and physiological properties are unaltered. These results, and the results of other studies, suggest that perturbations to the hydrologic cycle are key determinants of C cycling in grassland ecosystems.

Carbon Dioxide↗
PubMed2004

Carbon fluxes to the soil in a mature temperate forest assessed by 13C isotope tracing.

Photosynthetic carbon uptake and respiratory C release from soil are major components of the global carbon balance. The use of 13C depleted CO2)(delta13C = -30 per thousand) in a free air CO2 enrichment experiment in a mature deciduous forest permitted us to trace the carbon transfer from tree crowns to the rhizosphere of 100-120 years old trees. During the first season of CO2 enrichment the CO2 released from soil originated substantially from concurrent assimilation. The small contribution of recent carbon in fine roots suggests a much slower fine root turnover than is often assumed. 13C abundance in soil air correlated best with temperature data taken from 4 to 10 days before air sampling time and is thus rapidly available for root and rhizosphere respiration. The spatial variability of delta13C in soil air showed relationships to above ground tree types such as conifers versus broad-leaved trees. Considering the complexity and strong overlap of roots from different individuals in a forest, this finding opens an exciting new possibility of associating respiration with different species. What might be seen as signal noise does in fact contain valuable information on the spatial heterogeneity of tree-soil interaction.

Carbon Isotopes↗
PubMed2005

Relationships between species' floral traits and pollinator visitation in a temperate grassland.

Knowledge about plant-plant interactions for pollinator service at the plant community level is still scarce, although such interactions may be important to seed production and hence the population dynamics of individual plant species and the species compositions of communities. An important step towards a better understanding of pollination interactions at the community level is to assess if the variation in floral traits among plant species explain the variation in flower visitation frequency among those species. We investigated the relative importance of various floral traits for the visitation frequency of all insects, and bumblebees and flies separately, to plant species by measuring the visitation frequency to all insect-pollinated species in a community during an entire flowering season. Visitation frequency was identified to be strongly positive related to the visual display area and the date of peak flowering of plant species. Categorical variables, such as flower form and symmetry, were important to the visitation frequency of flies only. We constructed floral similarity measures based on the species' floral traits and found that the floral similarity for all species' traits combined and the continuous traits separately were positively related to individual visitation frequency. On the other hand, plant species with similar categorical floral traits did not have similar visitation frequencies. In conclusion, our results show that continuous traits, such as flower size and/or density, are more important for the variation in visitation frequency among plant species than thought earlier. Furthermore, differences in visitation frequency among pollinator groups give a poor support to the expectations derived from the classical pollination syndromes.

Animals↗
PubMed2005

Do carbon-based defences reduce foliar damage? Habitat-related effects on tree seedling performance in a temperate rainforest of Chiloé Island, Chile.

Carbon-based secondary compounds (CBSCs), such as phenols or tannins, have been considered as one of the most important and general chemical barriers of woody plants against a diverse array of herbivores. Herbivory has been described as a critical factor affecting the growth and survival of newly established tree seedlings or juveniles then, the presence of secondary metabolites as defences against herbivores should be a primary strategy to reduce foliar damage. We examined whether light-induced changes in leaf phenolic chemistry affected insect herbivory on seedlings of two rainforest tree species, Drimys winteri (Winteraceae) and Gevuina avellana (Proteaceae). Seedlings of both species were planted under closed canopy and in a canopy gap within a large remnant forest patch. Half of the seedlings in each habitat were disinfected with a wide-spectrum systemic insecticide and the other half were used as controls. Seedling growth, survival, and foliar damage (estimated by an herbivory index) due to insect herbivores were monitored over a period of 16 months (December 2001-April 2003). The total leaf content of phenols and condensed tannins were assessed in seedlings from both habitats. As expected, access to light induced a greater production of CBSCs in seedlings of both tree species, but these compounds did not seem to play a significant defensive role, as seedlings grown in gaps suffered greater leaf damage than those planted in forest interior. In addition, in both habitats, seedlings without insecticide treatment suffered a greater foliar damage than those with insecticide, especially 16 months after the beginning of the experiment. Canopy openness and herbivory had positive and negative effects, respectively, on seedling growth and survival in both tree species. In conclusion, despite the higher levels of defence in tree-fall gap, the higher densities of herbivore override this and lead to higher damage levels.

Animals↗
PubMed2005

Carbon dioxide fluxes in a spatially and temporally heterogeneous temperate grassland.

Landscape position, grazing, and seasonal variation in precipitation and temperature create spatial and temporal variability in soil processes, and plant biomass and composition in grasslands. However, it is unclear how this variation in plant and soil properties affects carbon dioxide (CO2) fluxes. The aim of this study is to explore the effect of grazing, topographic position, and seasonal variation in soil moisture and temperature on plant assimilation, shoot and soil respiration, and net ecosystem CO2 exchange (NEE). Carbon dioxide fluxes, vegetation, and environmental variables were measured once a month inside and outside long-term ungulate exclosures in hilltop (dry) to slope bottom (mesic) grassland throughout the 2004 growing season in Yellowstone National Park. There was no difference in vegetation properties and CO2 fluxes between the grazed and the ungrazed sites. The spatial and temporal variability in CO2 fluxes were related to differences in aboveground biomass and total shoot nitrogen content, which were both related to variability in soil moisture. All sites were CO2 sinks (NEE>0) for all our measurements taken throughout the growing season; but CO2 fluxes were four- to fivefold higher at sites supporting the most aboveground biomass located at slope bottoms, compared to the sites with low biomass located at hilltops or slopes. The dry sites assimilated more CO2 per gram aboveground biomass and stored proportionally more of the gross-assimilated CO2 in the soil, compared to wet sites. These results indicate large spatio-temporal variability of CO2 fluxes and suggest factors that control the variability in Yellowstone National Park.

Carbon Dioxide↗