bluuebunny/crossref_metadata_2025_split huggingface dataset:
Structural mapping in basin‐and‐range‐like geology by electromagnetic methods: a powerful aid to seismic
Authors: Galibert Pierre‐Yves , Guerin Roger , Andrieux Pierre 
Published: April 2006

AbstractA case history is presented where electromagnetic (EM) methods were applied as a complement to seismic, for structural mapping in basin‐and‐range‐like geology: 366 five‐component magnetotelluric (MT) soundings were carried out together with 331 transient soundings (TDEM) along seismic lines.Due to high structural complexity, seismic shows a number of limitations. For the same reasons, MT is highly perturbed and three specific interpretation techniques were comprehensively applied:1. a classical correction of static effect using TDEM sounding, to determine the high‐frequency nondistorted apparent resistivities and thus the corrected tensor;2. a so‐called regional correction based upon the same concept as the static effect, to transform distorted resistivity curves due to the horst/graben situation into plausible 1D curves, through the use of nomograms built for 2D H‐polarization situations;3. a stripping technique which made it possible to map areas where a deep conductive Mesozoic shale was present below carbonates, at a depth of 3 km.After the best MT interpretation was obtained along each line, it was integrated with seismic and with the results from two boreholes. A crude empirical law relating resistivity and acoustic velocity was established and the MT horizons were plotted on the two‐way traveltime seismic sections.The final integrated cross‐sections obtained are undoubtedly of greater use to the explorationist than the initial seismic sections alone and two wells were accurately predicted.
Advances in the combined interpretation of seismics with magnetotellurics1
Authors: Nagy Zoltán 
Published: April 2006

AbstractFive examples, obtained during exploration for hydrocarbons in the Pannonian Basin of Hungary, are used to show how the interpretation of seismic sections can be usefully complemented by results from MT surveys.Selection of the most appropriate MT quantities, considered to be proper ‘MT attributes’ for the purpose of visualization as well as recognition of the subsurface structures and the different inversions of MT data is essential for practical integration of seismic and MT surveys.A new technique providing a semiquantitive MT‐attribute pseudosection for the purpose of visualization of the subsurface structures is proposed. The procedure utilizes derivative functions of the phase of MT impedance for visualization and derives estimated depths from the Bostick transformation of Cagniard apparent resistivities.On the basis of the MT‐attribute pseudosections, constructed from the phase derivatives and transformed resistivity data, depths are estimated for interfaces between geological formations with significant resistivity contrast. In particular examples, the interface between the Tertiary sediments and the older basement rocks as well as tectonic fracture zones with decreased resistivity can be resolved.
Role of exotic tree stands on the current distribution and social behaviour of Swainson's hawk, Buteo swainsoni in the Argentine Pampas
Authors: Sarasola José Hernán , Negro Juan José 
Published: April 2006

AbstractAim  The Argentine Pampas was extensively and abruptly altered by European colonization. Between 1880 and 1885 the indigenous human inhabitants were completely displaced, and native grasslands were replaced by exotic pasture plants and crops. One of the most important ecological changes in the Pampas landscape, the introduction of tall exotic tree species, has received little attention, and its effect on wildlife has never been assessed. We have made an intensive survey of habitat use of Swainson's hawk, Buteo swainsoni in its most important non‐breeding quarters, the Pampas of Argentina, aiming to characterize the sites used by hawks for communal roosting.Location  Pampas grasslands, Argentina.Methods  We surveyed 30,000 km of roads by car during the austral summer from 2001 to 2004, covering the main non‐breeding area occupied by Swainson's hawks. Their roost sites were located by direct observation of birds roosting in tree stands close to the roads, by surveying potential roost sites around places where groups of pre‐ and post‐roosting hawks were recorded, and by gathering information from local farmers.Results  Swainson's hawks exclusively used stands of exotic tree species for roosting. Eucalyptus viminalis was present in all 34 roosts surveyed, and in 59% of them it was the only species present. The remaining exotic tree species were the Siberian elm, Ulmus pumila, pines (Pinus spp.) and cypress (Cupressus spp.). Flock sizes at roost sites were unusually high for a raptor, with an average of 658 individuals (range 8–5000 hawks, n = 27 flocks).Main conclusions  The introduction of exotic trees may have resulted in the expansion of the suitable habitat for Swainson's hawks, permitting a recent colonization of the Argentine Pampas. Tree stands may have also changed the communal roosting behaviour of this raptor, by virtue of their providing new structural elements in a region that almost completely lacked trees prior to European occupation.
Improving generalized regression analysis for the spatial prediction of forest communities
Authors: Maggini Ramona , Lehmann Anthony , Zimmermann Niklaus E. , Guisan Antoine 
Published: April 2006

AbstractAim This study used data from temperate forest communities to assess: (1) five different stepwise selection methods with generalized additive models, (2) the effect of weighting absences to ensure a prevalence of 0.5, (3) the effect of limiting absences beyond the environmental envelope defined by presences, (4) four different methods for incorporating spatial autocorrelation, and (5) the effect of integrating an interaction factor defined by a regression tree on the residuals of an initial environmental model.Location State of Vaud, western Switzerland.Methods Generalized additive models (GAMs) were fitted using thegrasppackage (generalized regression analysis and spatial predictions,http://www.cscf.ch/grasp).Results Model selection based on cross‐validation appeared to be the best compromise between model stability and performance (parsimony) among the five methods tested. Weighting absences returned models that perform better than models fitted with the original sample prevalence. This appeared to be mainly due to the impact of very low prevalence values on evaluation statistics. Removing zeroes beyond the range of presences on main environmental gradients changed the set of selected predictors, and potentially their response curve shape. Moreover, removing zeroes slightly improved model performance and stability when compared with the baseline model on the same data set. Incorporating a spatial trend predictor improved model performance and stability significantly. Even better models were obtained when including local spatial autocorrelation. A novel approach to include interactions proved to be an efficient way to account for interactions between all predictors at once.Main conclusions Models and spatial predictions of 18 forest communities were significantly improved by using either: (1) cross‐validation as a model selection method, (2) weighted absences, (3) limited absences, (4) predictors accounting for spatial autocorrelation, or (5) a factor variable accounting for interactions between all predictors. The final choice of model strategy should depend on the nature of the available data and the specific study aims. Statistical evaluation is useful in searching for the best modelling practice. However, one should not neglect to consider the shapes and interpretability of response curves, as well as the resulting spatial predictions in the final assessment.
No relationship between microsatellite variation and neonatal fitness in Antarctic fur seals, Arctocephalus gazella
Authors: HOFFMAN J. I. , FORCADA J. , AMOS W. 
Published: April 2006

AbstractPublished studies of wild vertebrate populations have almost universally reported positive associations between genetic variation measured at microsatellite loci and fitness, creating the impression of ubiquity both in terms of the species and the traits involved. However, there is concern that this picture may be misleading because negative results frequently go unpublished. Here, we analyse the relationship between genotypic variation at nine highly variable microsatellite loci and neonatal fitness in 1070 Antarctic fur seal pups born at Bird Island, South Georgia. Despite our relatively large sample size, we find no significant association between three different measures of heterozygosity and two fitness traits, birth weight and survival. Furthermore, increasing genetic resolution by calculating parental relatedness also yields no association between genetic variation and fitness. Our findings are consistent with necropsy data showing that most pups die from starvation or trauma, conditions that are unlikely to be influenced strongly by genetic factors, particularly if the benefits of high heterozygosity are linked to immune‐related genes.
Chloroplast diversity in the genus Malus: new insights into the relationship between the European wild apple (Malus sylvestris (L.) Mill.) and the domesticated apple (Malus domestica Borkh.)
Authors: COART E. , VAN GLABEKE S. , DE LOOSE M. , LARSEN A. S. , ROLDÁN‐RUIZ I. 
Published: April 2006

AbstractTo unravel the relationship between the European wild apple, Malus sylvestris (L.) Mill., and its domesticated relative M. domestica Borkh., we studied chloroplast DNA variation in 634 wild and 422 domesticated accessions originating from different regions. Hybridization between M. sylvestris and M. domestica was checked using 10 nuclear microsatellites and a Bayesian assignment approach. This allowed us to identify hybrids and feral plants escaped from cultivation. Sixty‐eight genotypes belonging to 12 other wild Malus species, including 20 M. sieversii (Ledeb.) Roem. accessions were also included in the analysis of chloroplast diversity. Marker techniques were developed to type a formerly described duplication and a newly detected transversion in the matK gene. Chloroplast DNA variation was further investigated using PCR‐RFLP (Polymerase Chain Reaction‐Random Fragment Length Polymorphism), and haplotypes were constructed based on all mutational combinations. A closer relationship than presently accepted between M. sylvestris and M. domestica was established at the cytoplasmic level, with the detection of eight chloroplast haplotypes shared by both species. Hybridization between M. sylvestris and M. domestica was also apparent at the local level with sharing of rare haplotypes among local cultivars and sympatric wild trees. Indications of the use of wild Malus genotypes in the (local) cultivation process of M. domestica and cytoplasmic introgression of chloroplast haplotypes into M. sylvestris from the domesticated apple were found. Only one of the M. sieversii trees studied displayed one of the three main chloroplast haplotypes shared by M. sylvestris and M. domestica. This is surprising as M. sieversii has formerly been described as the main maternal progenitor of the domesticated apple. This study hereby reopens the exciting discussion on the origin of M. domestica.
MHC class IIB alleles contribute to both additive and nonadditive genetic effects on survival in Chinook salmon
Authors: PITCHER TREVOR E. , NEFF BRYAN D. 
Published: April 2006

AbstractThe genes of the major histocompatibility complex (MHC) are found in all vertebrates and are an important component of individual fitness through their role in disease and pathogen resistance. These genes are among the most polymorphic in genomes and the mechanism that maintains the diversity has been actively debated with arguments for natural selection centering on either additive or nonadditive genetic effects. Here, we use a quantitative genetics breeding design to examine the genetic effects of MHC class IIB alleles on offspring survivorship in Chinook salmon (Oncorhynchus tshawytscha). We develop a novel genetic algorithm that can be used to assign values to specific alleles or genotypes. We use this genetic algorithm to show simultaneous additive and nonadditive effects of specific MHC class IIB alleles and genotypes on offspring survivorship. The additive effect supports the rare‐allele hypothesis as a potential mechanism for maintaining genetic diversity at the MHC. However, contrary to the overdominance hypothesis, the nonadditive effect led to underdominance at one heterozygous genotype, which could instead reduce variability at the MHC. Our algorithm is an advancement over traditional animal models that only partition variance in fitness to additive and nonadditive genetic effects, but do not allocate these effects to specific alleles and genotypes. Additionally, we found evidence of nonrandom segregation during meiosis in females that promotes an MHC allele that is associated with higher survivorship. Such nonrandom segregation could further reduce variability at the MHC and may explain why Chinook salmon has one of the lowest levels of MHC diversity of all vertebrates.
Major histocompatibility complex class II variation in the giant panda (Ailuropoda melanoleuca)
Authors: WAN QIU‐HONG , ZHU LIANG , WU HUA , FANG SHENG‐GUO 
Published: April 2006

AbstractHabitat destruction and human activity have greatly impacted the natural history of the giant panda (Ailuropoda melanoleuca). Although the genetic diversity of neutral markers has been examined in this endangered species, no previous work has examined adaptive molecular polymorphisms in the giant panda. Here, the major histocompatibility complex (MHC) class IIDRBlocus was investigated in the giant panda, using single‐strand conformation polymorphism (SSCP) and sequence analysis. Comparisons of DNA samples extracted from faecal and blood samples from the same individual revealed that the two materials yielded similar quantities and qualities of DNA, as well as identical SSCP patterns and allelic sequences, demonstrating the reliability of DNA isolation from panda faeces. Analysis of faecal samples from 60 giant pandas revealed relatively low number of alleles: seven alleles. However, the alleles were quite divergent, varying from each other by a range of 7–47 nucleotide substitutions (4–25 amino acid substitutions). Construction of a neighbour‐joining tree and comparisons amongDRBalleles from other species revealed that both similar and highly divergent alleles survived in the bottlenecked panda populations. Despite species‐specific primers used and excellent faecal DNA isolated, a lower level of heterozygosity than expected was still observed due to inbreeding. There were three types of evidence supporting the presence of balancing selection in the giant panda: (i) an obvious excess of nonsynonymous substitutions over synonymous at the antigen‐binding positions; (ii)trans‐species evolution of two alleles between the giant panda and other felids; and (iii) a more even distribution of alleles than expected from neutrality.
An apparatus for measuring photosynthetic quantum yields and quanta absorption spectra of intact plants
Authors: ÖQUIST G. , HÄLLGREN J.‐E. , BRUNES L. 
Published: April 2006

Abstract An apparatus is described which consists of an assimilation chamber mounted in the centre of a light‐integrating Ulbricht sphere, irradiated through two fibreoptic light pipes. This arrangement provides totally diffuse radiation in the sphere. The quantum flux density in die sphere is measured by an integrating quantaspectrometer connected to the sphere by eight fibreoptic light pipes. The quantaspectrometer gives the spectral and the total quantum flux density in the sphere. By measuring the quantum flux density in the sphere before and after the insertion of a plant the number of absorbed quanta per unit time and plant area can be determined. In addition, the spectral distribution of the absorbed quantum flux density is obtained.CO2‐assimilation per unit time and plant area is determined in the same apparatus. The totally diffuse radiation within the sphere minimizes mutual shading between branches and leaves. Hence, well‐defined light‐responsecurves of photosynthesis can be obtained by plotting the flux density of C02‐assimilation as a function of the absorbed quantum flux density, and the quantum yields of intact plants can be calculated.Examples of photosynthetic quantum yield determinations and quanta absorption spectra are given for some plant species.
Stomatal mechanics II*: material properties of guard cell walls
Authors: WU HSIN‐I , SHARPE PETER J. H. 
Published: April 2006

Abstract In this revised formulation of guard cell mechanics, the material properties of the walls are re‐examined. The observed elastic anisotropy of guard cell walls can be explained by non‐random orientation of the cellulose micellae in the unstrained state. This micellar network is assumed to be loosely embedded in the wall matrix causing a two phase elongation process. In the first phase, the micellar network is ‘loose’ resulting in the walls behaving as an isotropic polymer when stretched. As the volume of the cell expands beyond some threshold, the network becomes ‘tightened’ and a second phase of elongation is initiated. During this anisotropic phase of cell expansion, wall elasticity reflectes changes in the orientation of the network to reduce its load.Using the above theoretical analysis, a turgor‐pressure versus lumen volume relationship is simulated for Vicia faba. The relationship between aperture and water potential for this species is also established. The simulated results agree with the experimental evidence reported for Vicia faba. The estimated shear modulus of elasticity for guard cell walls is 2 MPa (20 bars) which is well within the limits of reported values for other biological tissues.
Acid‐base regulation during nitrate assimilation in Hydrodictyon africanum
Authors: RAVEN J. A. , DE MICHELIS M. I. 
Published: April 2006

Abstract The acid‐base balance during NO3− assimilation in Hydrodictyon africanum has been investigated during growth from (1) an analysis of the elemental composition of the cells, (2) the alkalinity of the ash and (3) the net H+ changes in the medium during growth. These investigations agree in showing that some 0.25 excess organic negative charges are generated per N assimilation from No3− as N‐source and C02 as C‐source; the excess OH− (0.75 OH− per NO3− assimilated) appears in the medium. Approximately half of the excess organic negative charge is attributable to cell wall uronates; the remainder is intracellular. All of the excess OH− appearing in the medium must have crossed the plasmalemma (as net downhill H+ influx or OH− efflux).Previous work has shown that the value of ψco is more negative than ψK+ during NO3− assimilation, suggesting that the active electrogenic H+ extrusion pump is still operative despite the net downhill H+ influx. The interpretation of this in terms of H+−NO3− symport which causes the entry of more H+ than is consumed in NO3− metabolism, with extrusion of the excess H+via the active, electrogenic H+ pump, was tested by measuring short‐term H+ influx upon addition of NO−3. A net H+ influx occurs before NOa assimilation (as indicated by additional O2 evolution in the light) has commenced, suggesting a mechanistic relation of H+ and NO3− influxes. This is consistent with the interpretation suggested above. Determinations of cytoplasmic pH showed no significant effect of NO3− assimilation, suggesting that cytoplasmic pH changes sufficient to change the ‘pH‐regulating’ H+ fluxes are smaller than the errors in the determination of cytoplasmic pH.
Compartmental modelling of photorespiration and carbon metabolism of water stressed leaves
Authors: LAWLOR D. W. , PEARLMAN J. G. 
Published: April 2006

Abstract Carbon fluxes in photosynthesis and photorespiration of water stressed leaves have been analysed in a steady state model based on the ribulose diphosphate carboxylase (RuDP carboxylase) and RuDP oxygenase enzyme activities and the CO2 and O2 concentrations in the leaf. Agreement between predicted and observed photorespiration (Lawlor & Fock, 1975) and C flux in the glycollate pathway is good over much of the range of water stress, but not at severe stress. An alternative source of respiratory CO2 is suggested to explain the discrepancy. The model suggests that resistance to CO2 fixation is mainly in the carboxylation reactions, not in CO2 transport.Using the steady state model, the kinetics of 14C incorporation into photosynthetic and photorespiratory intermediates are simulated. The predicted rate of 14C incorporation is faster than observed and delay terms in the model are used to simulate the slow rates of mixing and metabolic reactions. Inactive pools of glycine and serine are suggested to explain the observed specific activities of glycine and serine. Three models of carbon flux between the glycollate pathway, the photosynthetic carbon reduction cycle and sucrose synthesis are considered. The most satisfactory simulation is for glycollate pathway carbon feeding into the PCR cycle pool of 3‐phosphoglyceric acid which provides the carbon for sucrose synthesis. Simulation of the specific activity of CO2 released in photorespiration suggests that a source of unlabelled carbon may contribute to photorespiration.
The use of immunological methods to study the activity of cellulase isozymes (B 1:4 glucan 4‐glucan hydrolase) in bean leaf abscission
Authors: DURBIN M. L. , SEXTON R. , LEWIS L. N. 
Published: April 2006

Abstract The changes in the levels of two different isozymes of cellulase (EC 3.2.1.4) have been followed during the abscission of the primary leaves of bean (Phaseolus vulgaris c.v. Red Kidney), using antibodies raised against the 9.5 form of the enzyme. Data from both radioimmune and direct assay show that the 9.5 form of cellulase is undetectable prior to the induction of abscission. After a 12 h lag this isozyme increases in activity, the increase preceding a decrease in integrity of the abscission zone cell walls. The results are consistent not only with the view that this specific isozyme is involved in wall hydrolysis but also with previous data which showed that cellulase is synthesized ‘de novo’.The 4.5 isozyme of cellulase is more widely spread throughout the plant, being most active in young tissues. During abscission the activity of this isozyme in the abscission layer falls and consequently it is not thought to be involved directly in the abscission process.
Charge balance and acidity regulation during growth of sugar‐cane cell suspensions
Authors: KOMOR EWALD , THOM MARGARET , MARETZKI ANDREW 
Published: April 2006

Abstract. An analysis of nutrient uptake by batch cultures of sugar‐cane cells was performed to gain information about the ionic balance during uptake of charged metabolites. Whereas younger cultures (up to 1 week old) have to compensate excess cation influx with proton efflux, older cultures show balanced cation–anion uptake.Younger cells produce a small amount of carboxylic acids to furnish protons for charge compensation at the cytoplasmic membrane. Older cells synthesize organic acids more abundantly to generate protons necessary for the proton demand of nitrate and sulphate assimilation. Despite these assimilation reactions only a small percentage of carbon, which is taken up mainly as hexose, needs to be oxidized to carboxylic acids for that purpose. In contrast, younger cultures preferentially use the amino acids of the medium instead of assimilating nitrate. The use of amino acids as a nitrogen source does not require a significant part of metabolism for biochemical pH‐stability, whereas an efficient proton circulation on the cytoplasmic membrane seems to be of major importance.A balance study of the main metabolized elements, carbon, nitrogen and sulphur was performed to get a quantitative impression of the fate of these nutrients during growth of cell cultures.