Showing papers by "University of Buenos Aires published in 1998"

Ant biodiversity and its relationship to ecosystem functioning: a review

Abstract: Ants are important components of ecosystems not only because they constitute a great part of the animal biomass but also because they act as ecosystem engineers. Ant biodiversity is incredibly high and these organisms are highly responsive to human impact, which obviously reduces its richness. However, it is not clear how such disturbance damages the maintenance of ant services to the ecosystem. Ants are important in below ground processes through the alteration of the physical and chemical environment and through their effects on plants, microorganisms, and other soil organisms. This review summarizes the information available on ant biodiversity patterns, how it can be quantified, and how biodiversity is affected by human impacts such as land use change, pollution, invasions, and climate change. The role of ants in ecosystems is discussed, mainly from the perspective of the effects of ground-dwelling ants on soil processes and function, emphasizing their role as ecosystem engineers. Some lines of research are suggested after demonstrating the gaps in our current information on ant-soil interactions.

Beta-sheet breaker peptides inhibit fibrillogenesis in a rat brain model of amyloidosis: implications for Alzheimer's therapy.

Abstract: Inhibition of cerebral amyloid beta-protein deposition seems to be an important target for Alzheimer's disease therapy. Amyloidogenesis could be inhibited by short synthetic peptides designed as beta-sheet breakers. Here we demonstrate a 5-residue peptide that inhibits amyloid beta-protein fibrillogenesis, disassembles preformed fibrils in vitro and prevents neuronal death induced by fibrils in cell culture. In addition, the beta-sheet breaker peptide significantly reduces amyloid beta-protein deposition in vivo and completely blocks the formation of amyloid fibrils in a rat brain model of amyloidosis. These findings may provide the basis for a new therapeutic approach to prevent amyloidosis in Alzheimer's disease.

G-protein-coupled receptor of Kaposi's sarcoma-associated herpesvirus is a viral oncogene and angiogenesis activator

Abstract: The Kaposi's sarcoma-associated herpesvirus (KSHV/HHV8) is a gamma-2 herpesvirus that is implicated in the pathogenesis of Kaposi's sarcoma and of primary effusion B-cell lymphomas (PELs). KSHV infects malignant and progenitor cells of Kaposi's sarcoma and PEL, it encodes putative oncogenes and genes that may cause Kaposi's sarcoma pathogenesis by stimulating angiogenesis. The G-protein-coupled receptor encoded by an open reading frame (ORF 74) of KSHV is expressed in Kaposi's sarcoma lesions and in PEL and stimulates signalling pathways linked to cell proliferation in a constitutive (agonist-independent) way. Here we show that signalling by this KSHV G-protein-coupled receptor leads to cell transformation and tumorigenicity, and induces a switch to an angiogenic phenotype mediated by vascular endothelial growth factor, an angiogenesis and Kaposi's-spindle-cell growth factor. We find that this receptor can activate two protein kinases, JNK/SAPK and p38MAPK, by triggering signalling cascades like those induced by inflammatory cytokines that are angiogenesis activators and mitogens for Kaposi's sarcoma cells and B cells. We conclude that the KSHV G-protein-coupled receptor is a viral oncogene that can exploit cell signalling pathways to induce transformation and angiogenesis in KSHV-mediated oncogenesis.

The climate of Patagonia: general patterns and controls on biotic processes

Abstract: In this article we review the main characteristics of the Patagonian climate, the spatial and temporal patterns of the most important climatic variables, and the influence of climate on ecosystem processes. The winter distribution of precipitation determines an asynchrony between the wet and the growing season in Patagonia. The amount of water that can be transferred from the wet season to the growing season depends mainly on the physical characteristics of the soil. In the semiarid steppe of Chubut, drainage accounted for 10% of annual precipitation. Winter distribution of precipitation determines also an asynchronic dynamics of evaporation and transpiration fluxes. The ENSO phenomenon have a significant impact on regional precipitation. In central-west Patagonia, spring precipitation (September to November) was lower than normal during La Nina events and greater than normal during El Nino events. From December to February the opposite pattern can be observed: higher than normal precipitation during La Nina events and lower than normal precipitation during El Nino events. The impact of this phenomenon on the seasonal temperature was not as clear as for precipitation. We did not detect any temporal trends in annual precipitation for the period 1961-1996. The phenology of carbon gains is quite homogeneous in Patagonia. Most of the region showed a peak of production in November, when, simultaneously, water availability and temperature are high. Toward the west, production peaked later (December). Deciduous forests showed the peak in January and February.

Clinical Features Associated with Mutations in the Chromosome 1 Open-Angle Glaucoma Gene (GLC1A)

Abstract: Background A substantial proportion of cases of glaucoma have a genetic basis. Mutations causing glaucoma have been identified in the chromosome 1 open-angle glaucoma gene (GLC1A), which encodes a 57-kd protein known as myocilin. The normal role of this protein and the mechanism by which mutations cause glaucoma are not known. Methods We screened 716 patients with primary open-angle glaucoma and 596 control subjects for sequence changes in the GLC1A gene. Results We identified 16 sequence variations that met the criteria for a probable disease-causing mutation because they altered the predicted amino acid sequence and they were found in one or more patients with glaucoma and in less than 1 percent of the control subjects. These 16 mutations were found in 33 patients (4.6 percent). Six of the mutations were found in more than 1 subject (total, 99). Clinical features associated with these six mutations included an age at diagnosis ranging from 8 to 77 years and maximal recorded intraocular pressures ranging...

Grandes unidades de vegetación de la Patagonia extra andina

Abstract: El objetivo de este trabajo fue presentar, a escala regional, una caracterizacion fisonomica floristica integrada de la Patagonia extra andina. Dentro del marco de los trabajos que alcanzaron la mayor sintesis a nivel regional, se analizo la informacion producida en las ultimas decadas, en especial aquella que produjo informacion cartografica. El trabajo de sintesis permitio subdividir distritos fitogeograficos, delimitar ecotones y confirmar o modificar limites. El resultado es un mapa en donde se proponen 16 unidades fisonomico floristicas, 12 incluidas en los seis distritos de la provincia Patagonica, dos en la del Monte y dos de caracter ecotonal. A la descripcion general de cada subunidad se agrega la informacion fitosociologica existente.

Ecosystem consequences of changing biodiversity

Abstract: F. Stuart Chapin (e-mail: fschapin@socrates. berkeley.edu) is a professor and David U. Hooper is a postdoctoral fellow in the Department of Integrative Biology, University of California, Berkeley, CA 94720. Osvaldo E. Sala is a professor at the Faculty of Agronomy, University of Buenos Aires, Av. San Martin 4453, Buenos Aires 1417, Argentina. Ingrid C. Burke is an associate professor in the Department of Forest Sciences, Colorado State University, Ft. Collins, CO 80523. J. Phillip Grime is a professor in the Unit of Comparative Plant Ecology, The University of Sheffield, Sheffield S10 2TN, UK. William K. Lauenroth is a professor in the Rangeland Ecosystem Science Department, Natural Resource Ecology Laboratory, Colorado State University, Ft. Collins, CO 80523. Amanda Lombard is a research scientist at the FitzPatrick Institute, University of Cape Town, Cape Town, 7700 South Africa. Harold A. Mooney is a professor in the Department of Biological Sciences, Stanford University, Stanford, CA 94305. Arvin R. Mosier is a research scientist in the USDA Agricultural Research Service, P. O. Box E, Ft. Collins, CO 80522. Shahid Naeem is an assistant professor and David Tilman is a professor in the Department of Ecology, Evolution, and Behavior, University of Minnesota, St. Paul, MN 55108. Stephen W. Pacala is a professor in the Department of Ecology and Evolutionary Biology, Princeton University, Princeton, NJ 08544. Jacques Roy is director of research at the Centre d'Ecologie Fonctionnelle et Evolutive, CNRS, F-34293 Montpellier Cedex 5, France. William L. Steffen is executive officer of GCTE, CSIRO, Division of Wildlife and Ecology, Lyneham ACT 2602, Australia. Changes in biodiversity can have significant

Plant-Soil interactions in temperate grasslands

Abstract: We present a conceptual model in which plant-soil interactions in grasslands are characterized by the extent to which water is limiting. Plant-soil interactions in dry grasslands, those dominated by water limitation (‘belowground-dominance’), are fundamentally different from plant-soil interactions in subhumid grasslands, where resource limitations vary in time and space among water, nitrogen, and light (‘indeterminate dominance’). In the belowground-dominance grasslands, the strong limitation of soil water leads to complete (though uneven) occupation of the soil by roots, but insufficient resources to support continuous aboveground plant cover. Discontinuous aboveground plant cover leads to strong biological and physical forces that result in the accumulation of soil materials beneath individual plants in resource islands. The degree of accumulation in these resource islands is strongly influenced by plant functional type (lifespan, growth form, root:shoot ratio, photosynthetic pathway), with the largest resource islands accumulating under perennial bunchgrasses. Resource islands develop over decadal time scales, but may be reduced to the level of bare ground following death of an individual plant in as little as 3 years. These resource islands may have a great deal of significance as an index of recovery from disturbance, an indicator of ecosystem stability or harbinger of desertification, or may be significant because of possible feedbacks to plant establishment. In the grasslands in which the dominant resource limiting plant community dynamics is indeterminate, plant cover is relatively continuous, and thus the major force in plant-soil interactions is related to the feedbacks among plant biomass production, litter quality and nutrient availability. With increasing precipitation, the over-riding importance of water as a limiting factor diminishes, and four other factors become important in determining plant community and ecosystem dynamics: soil nitrogen, herbivory, fire, and light. Thus, several different strategies for competing for resources are present in this portion of the gradient. These strategies are represented by different plant traits, for example root:shoot allocation, height and photosynthetic pathway type (C3 vs. C4) and nitrogen fixation, each of which has a different influence on litter quality and thus nutrient availability. Recent work has indicated that there are strong feedbacks between plant community structure, diversity, and soil attributes including nitrogen availability and carbon storage. Across both types of grasslands, there is strong evidence that human forces that alter plant community structure, such as invasions by nonnative annual plants or changes in grazing or fire regime, alters the pattern, quantity, and quality of soil organic matter in grassland ecosystems. The reverse influence of soils on plant communities is also strong; in turn, alterations of soil nutrient supply in grasslands can have major influences on plant species composition, plant diversity, and primary productivity.

Mechanisms for memory types differ.

Abstract: The formation of long-term memory takes several hours1,2,3, during which time memories rely on short-term systems1,2,4,5. For over 100 years1, the main unanswered question of memory research has been whether short-term memory is a necessary step towards long-term memory4,5, or whether they are separate processes1,2. Here we report four treatments that block short-term memory while leaving long-term memory intact, showing that these memory systems are separate to some degree.

Alcohol preference and sensitivity are markedly reduced in mice lacking dopamine D2 receptors.

Abstract: Although dopaminergic transmission has been strongly implicated in alcohol self-administration, the involvement of specific dopamine receptor subtypes has not been well established. We studied the ethanol preference and sensitivity of D2-receptor-deficient mice to directly evaluate whether dopamine D2 receptors contribute to alcohol (ethanol) consumption. We report a marked aversion to ethanol in these mice, relative to the high preference and consumption exhibited by wild-type littermates. Sensitivity to ethanol-induced locomotor impairment was also reduced in these mutant mice, although they showed a normal locomotor depressant response to the dopamine D1 antagonist SCH-23390. These data demonstrate that dopamine signaling via D2 receptors is an essential component of the molecular pathway determining ethanol self-administration and sensitivity.

Functional responses of coyotes and lynx to the snowshoe hare cycle

Abstract: Coyotes and lynx are the two most important mammalian predators of snow- shoe hares throughout much of the boreal forest. Populations of hares cycle in abundance, with peaks in density occurring every 8-11 yr, and experimental results suggest that pre- dation is a necessary factor causing these cycles. We measured the functional responses of coyotes and lynx during a cyclic fluctuation of hare populations in the southwest Yukon, to determine their effect on the cyclic dynamics. We used snow-tracking and radio telemetry to examine changes in the foraging behavior of the predators. Coyotes and lynx both fed mostly on hares during all winters except during cyclic lows, when the main alternative prey of coyotes was voles, and lynx switched to hunting red squirrels. Both predators showed clear functional responses to changes in the densities of hares. Kill rates of hares by coyotes varied from 0.3 to 2.3 hares/d, with the most hares killed one year before the cyclic peak, while those of lynx varied from 0.3 to 1.2 hares/d, with the highest one year after the peak. Maximum kill rates by both predators were greater than their energetic needs. The functional response of coyotes was equally well described by linear and type-2 curves, and that of lynx was well described by a type-2 curve. Kill rates by coyotes were higher during the increase in density of hares than during the cyclic decline, while the reverse was true for lynx. Coyotes killed more hares early in the winter, and cached many of these for later retrieval. Lower densities of hares were associated with longer reactive distances of both predators to hares, but with little apparent change in time spent searching or handling prey. In summary, our data show that the two similarly sized predators differed in their foraging behavior and relative abilities at capturing alternative prey, leading to different patterns in their functional responses to fluctuations in the density of their preferred prey.

Spin asymmetries A1 and structure functions g1 of the proton and the deuteron from polarized high energy muon scattering

Abstract: We present the final results of the spin asymmetries A1 and the spin structure functions g1 of the proton and the deuteron in the kinematic range 0.0008

Surface Properties of Bifidobacterial Strains of Human Origin

Abstract: The adherence of Bifidobacterium strains isolated from infant feces and commercial fermented dairy products to enterocyte-like cells was correlated with the autoagglutination and hemagglutination properties of these organisms. These results allowed us to define two groups: (i) cell-adherent bacteria showing hemagglutination and autoagglutination and (ii) non-cell-adherent, nonhemagglutinating, nonautoagglutinating bacteria. Glass adherence was shown to be nonspecific and was discarded as a criterion for selection of adherent cells. Hydrophobicity appeared to be necessary for adhesion to enterocyte-like cells and autoagglutination. Adhesive strains were highly hydrophobic, and the degree of adherence was slightly dependent on the surface potential. Cells autoagglutinated more when the electrostatic negative charges on the cell surface were shielded by a decrease in the pH from 7 to 2. However, in some strains negative charges at the cell surface were adjuvant to adhesion, thus suggesting that specific chemical interactions occurred. The present results provide a method for preliminary selection of bacteria potentially adherent to epithelial cells by means of autoagglutination.

Phytochromes and seed germination

Abstract: The control of seed germination by red and far-red light is one of the earliest documented phytochrome-mediated processes Phytochrome is now known to be a small family of photoreceptors whose apoproteins are encoded by different genes Phytochrome B (phyB) is present in dry seeds and affects germination of dark imbibed seeds but other phytochromes could also be involved Phytochrome A (phyA) appears after several hours of imbibition and mediates very-low-fluence responses PhyB and other phytochromes different from phyA mediate the classical low-fluence responses The phytochrome involved in high-irradiance responses of seed germination (inhibition of germination under continuous far-red) has not been unequivocally established, although phyA is the most likely candidate Phytochrome can affect embryo growth capacity and/or the constraint imposed by the tissues surrounding the embryo At least in some species, gibberellins participate in the signalling process In the field, phyA has been implicated in the perception of light during soil cultivations, and phyB would be involved in the perception of red/far-red ratios associated with the presence of gaps in the canopy This review describes recent advances in phytochrome research, particularly those derived from the analysis of germination in specific mutants, and their connection with traditional observations on phytochrome control of seed germination

A High-Resolution Radio Study of the W50-SS 433 System and the Surrounding Medium

Abstract: We present VLA images at 327.5 and 1465 MHz of the nebula W50 surrounding the stellar source of relativistic jets SS 433. At 1.4 GHz, we have produced an image of W50 with an angular resolution of 55'' that contains all the spatial structures. The technique consists of a complex combination of 58 separate VLA pointings plus the addition of single-dish data into a single mosaic. For the first time, this high-quality radio image has revealed the puzzling structure of W50, which resembles a seashell. The present data confirm the connection between the subarcsecond relativistic jets from SS 433 and the extended nebula W50 over ~5 orders of magnitude in scale. The central component can be very accurately described by a circle 58' in diameter. The eastern wing exhibits a clear helical pattern that mirrors at larger scales the precession of the jets from SS 433. The western wing, smaller and brighter than its eastern counterpart, has a bright bowed arch at the edge, in the region where the structure appears to interact with a higher density medium. The spectral index of the radio continuum emission exhibits striking asymmetries: the central spherical component has a quite normal spectrum for shell-type supernova remnants, α ~ 0.5 (S ∝ ν-α), while it steepens toward the eastern wing (α ~ 0.8) and flattens toward the western one (α ~ 0.4). A chimney, apparently radiating away from W50, is observed in the eastern wing. The atomic hydrogen emission was surveyed in an area of 4° × 4° around W50 using the NRAO Green Bank 140 foot (43 m) telescope. Based on these observations, unmistakable evidence of an interaction of W50 with the surrounding H I gas at the systemic radial velocity v = 42 km s-1 is found. Clear traces of the interaction of the jets of SS 433 with the surrounding gas are shown. Based on these observations a kinematic distance of 3 kpc is determined for the W50–SS 433 system. An elliptical shell of ~30,000 M⊙, expanding at about 76 km s-1, can be associated with the radio nebula. The kinetic energy transferred into the ambient medium is estimated (~2 × 1051 ergs), thus confirming that the relativistic jets from SS 433 represent an important contribution to the overall energy budget of W50.

Orogenias paleozóicas no domínio sul-ocidental do gondwana e os ciclos de subsidência da bacia do paraná

Abstract: The geological development of the Parana Basin was influenced by the geodynamics of southwestern Gondwana, a domain continuously affected during almost all the Phanerozoic eon by compressional stresses derived from a persistently active convergent motion between the continental block and the oceanic lithosphere of Panthalassa. The Parana Basin was supported by a cratonic basement since its inception, but had in its neighbourhood evolving collisional belts fringed by foreland basins. Some areas were selected representing the history of subsidence along the foreland domain of southwestern Gondwana during Paleozoic times. The subsidence analysis showed that such foreland basins experienced cycles of accelerated subsidence that coincide in time with the major orogenic phases, that were related to the docking of terranes along the margin of the continent. The computation of average subsidence rates revealed the main subsidence cycles for the region as a whole. Subsidence and sediment accumulation in the Parana Basin started during Middle to Late Ordovician times when the Precordillera terrane collided against Gondwana and produced the different contractional phases of the Ocloyic Orogeny. The intraplate response to the compressional stresses related to this orogenic cycle was transtensional reactivation of weakness zones, providing the initial subsidence for the Parana Basin. Repeatedly during the geologic history of the Parana Basin orogenic cycles left their signature as periods of accelerated subsidence. Subsidence plots revealed that Early Devonian times, when the stresses generated by the Precordilleran Orogeny affected Gondwana, and Late Permian times, under the yoke of the Sanrafaelic Orogeny, were periods when intracratonic subsidence rates increased remarkably. An integrated analysis of the sedimentary record of the Parana Basin, considering eustatic variations of the sea level and subsidence cycles of southwestern Gondwana led to the conclusion that the stratigraphic cyclicity observed in the Parand Basin was ultimately influenced by its subsidence history. The presumed global correlation peaks shown in Vail's curve, of Late Silurian, Early Carboniferous and Early Permian ages, are not present in the Parana Basin. Instead, local maximum flooding levels developed in each one of the second order transgressive cycles, during Early Silurian, Early Devonian and Late Permian times, defining the particular subsidence history of this interior basin as an intraplate response to geodynamic processes affecting southwestern Gondwana margin.