Showing papers by "National University of Comahue published in 1995"

A new giant carnivorous dinosaur from the Cretaceous of Patagonia

Abstract: LARGE carnivorous animals, the top members of the trophic chain, are rare, and flesh-eating dinosaurs were rarer still. For years the only known giant theropods were Tyrannosaums rex1 and the poorly known Deinocheirus mirificus2, both from the Northern Hemisphere, but many important new dinosaurs have been dis-covered in the Southern Hemisphere during the past decade, con-siderably increasing our knowledge of ancient ecosystems. Here we report a new giant carnivorous dinosaur from the Upper Creta-ceous of northwestern Patagonia (Argentina). This new taxon, Giganotosaums carolinii gen. et. sp. nov., is characterized by aproportionally low skull, a reduced shoulder girdle, and robust vertebrae and hind limbs. It represents a primitive evolutionary iteration of large theropods, and provides an opportunity to exam-ine the Gondwanan dinosaur palaeocommunities and their relation-ships to those from Laurasia. Several characters place G. carolinii within the Tetanurae3, and closer to Neotetanurae4 than to Torvosauroidea4. G. carolinii is the largest theropod ever recorded from the Southern Hemisphere, and is probably the world's biggest predatory dinosaur, having a body 12.5 metres long and an estima-ted weight of 6 to 8 tonnes.

Leaf phenology and herbivory along a temperature gradient: a spatial test of the phenological window hypothesis

Abstract: In this study, we documented patterns of variation in leaf phenology and leaf herbivory in scrub oak (Quercus ilicifolia Wang) along the slope of a closed topographical depression, 15 m deep and 400 m wide, in the pine barrens of eastern Massachusetts. Minimum temperatures over the grow- ing season averaged 6.5 ?C lower at the bottom of the depres- sion than at the top. Bud break at the bottom of the depression was 2-3 weeks delayed compared with the top. In both years of this study, 1988 and 1989, leaf damage by thrips increased down slope producing differences of about 10 % in the pro- portion of leaf area damaged between the top and the bottom of the depression. Because thrips fed exclusively on the young- est leaves, this pattern could be attributed to a closer synchrony between the timing of leaf flushing and the period of insect feeding activity towards the bottom of the depression. Aver- age differences in leaf damage between years could also be accounted for by variation in leaf phenology. These patterns support the hypothesis that the degree of temporal overlap between availability of high quality foliage and the period of insect feeding activity may greatly determine spatial and tem- poral variation in leaf damage by insect herbivores.

Elemental composition of lichens at Nahuel Huapi National Park, Patagonia, Argentina

Abstract: Five species of epiphytic lichens were sampled from urban and periurban areas of Bariloche, a non industrial city located on the East side of the Nahuel Huapi National Park, North-Western Patagonia, Argentina, and from pristine areas of the Park. Each individual lichen was analyzed using Instrumental Neutron Activation Analysis. The results of the analysis showed high concentrations of lithophile elements, with very good correlations among them. The relative concentration of these elements in all lichen species is in good agreement with the elemental composition of sediments collected in the Park. Elemental concentrations which are not related to detritical inputs are also presented.

Morphology and defensive structures in the predator-prey interaction: an experimental study of Parabroteas sarsi (Copepoda, Calanoida) with different cladoceran prey

Abstract: Parabroteas sarsi is a predaceous calanoid copepod commonly found in South Andes lakes. Feeding experiments were carried out in order to estimate the predation rates and attack patterns on different cladoceran prey. Predation rates were related with prey sizes. The smallest prey, Bosmina longirostris, was ingested up to 5 prey pred−1 h−1 while the largest, Daphnia middendorffiana, only at 0.12 prey pred−1 h−1. The functional response of P. sarsi differed when confronted with different prey although in all cases, the number of kills increased with prey density. A saturation of ingestion rates at high prey densities was only observed for B. longirostris and Ceriodaphnia dubia juveniles. Remains seldom appeared at the end of the experiments, implying that the predator consumed prey totally. Yet, in all experiments carried out with Daphnia ambigua and D. middendorffiana, remains, including soft parts, were found. Direct observations of attack and of number and types of remains showed interference of handling by tail, helmet, and size of the prey.

Asociación de espículas de poríferos cámbricos de la Formación Empozada, precordillera de Mendoza

Abstract: Cambrian spicules assemblages are reported from San Martin olistoliths, Lower Mernber of Empozada Formation (Llanvim), from San Isidro area, Mendoza Precordillera. Variety of disassociated spicules includes stauractines, hexactines and pentactines of the Class Hexactinellida. These spicules were transported and buried in carbonate periplatform deposits by slow currents.

Erysiphaceous species from Nahuel Huapi National Park, Argentina. Part I

Abstract: The vegetation of the Nahuel Huapi National Park is characterised by typical Andean patagonic forests with a majority of autochthonous trees like Austrocedrus chilensis, Nothofagus antarctica, N. dombeyi, and N. pumilio. The natural flora is mixed with numerous introduced species. There is a great diversity of parasitic fungi. In this work the powdery mildews which infect both the autochthonous and introduced hosts were studied. Collections were made in summer and autumn in order to obtain the teleomorphic and the anamorphic stages. As a preliminary result fourteen species can be reported: Erysiphe aquilegiae, E. pisi, E. ulmariae var. acaenae, Microsphaera alphitoides, M. baeumleri, M. myoschili, M. oehrensii, M. ovidiae, M. ribicola, Sphaerotheca pannosa, Phyllactinia antarctica, Uncinula magellanica, U. nothofagi, and Oidium mutisiae. Note: was published in the 6th International Congress of Plant Pathology. July 28–August 6, 1993, Montreal (Quebec), Canada.

A new species of Claussenomyces (Helotiales) from southern South America

Abstract: Claussenomyces pleomorphicus is proposed as a new species, characterised within the genus by lack of an ionomidotic reaction, ascospore size, and the production of anamorph conidiomata in nature, with a microstructure different from all known species belonging to the genus.

Evaluación de algunas propiedades de suelos derivados de cenizas volcánicas asociadas con forestaciones de coníferas exóticas (S.O. de la provincia de Neuquén-R. Argentina)*

Abstract: SUMMARY Soils derived from volcanic ash and pumice have unique and common properties. Afforestation with conifers is an important part of the current management on such soils. Its consequences on soil pH and bulk density are considered in this study. Sustained and enhanced forest soil productivity requires a better understanding of soil properties and behavior under various management regimes.

El crecimiento de Pinus ponderosa Dougl. y Pseudotsuga menziesii (Mirb.) Dougl. en diferentes condiciones de sitio (Prov. NQN-R.A.)

Abstract: Pinus ponderosa Dougl. and Pseudotsuga menziesii (Mirb.) Dougl. are two species used in afforestation in the province of Neuquen (R. Argentina). They are distributed in very different site conditions, from wet forest to ecotones. They have different growth curves and yields, which are associated with different soil conditions. To compare their growth in different site conditions, as a first characterization, we developed height-age curves from stem analysis obtained from the dominant trees, using Site Index at 14 and 21 years. The best sites contain soils classified as Thaptic Hapludands; Thaptic Udivitrands; deep, Humic Vitrixerands; and deep, Vitrandic Argixerolls.

[Larval stages of digenetic trematodes in Chilina sp. (Mollusca, Pulmonata) of some water bodies of Patagonia, Argentina].

Abstract: Chilina sp., found abundantly in Patagonian fresh water bodies, is an intermediate host in the biological cycles of several digenetic trematodes. Larvae at different developmental stages were found in the visceral mass of snails collected from several places, and were determinated to family level. This work shows these findings, with presence and prevalence data, and so attempts to contribute to increase the parasitological knowledge about studied water bodies.

Una nueva especie de Senecio (Asteraceae) del noroeste de la Patagonia Argentina

Abstract: A new species of Senecio (asteraceae) from northwestern Patagonia, Argentina. A new species, Senecio carbonensis Ezcurra, Ferreyra et Clayton sp. nov., from the mountains of Parque Nacional Nahuel Huapi, Prov. Rio Negro, is described and illustrated. Differences with related Senecio julietii Phil. and S. peteroanus Phil. of section Suffrutecius Cabrera subsect. Caespitosi Hoffmann are discussed. En las exploraciones efectuadas en cerros del Parque Nacional Nahuel Huapi (provincias de Neuquen y Rio Negro) durante los veranos de 1993, 1994 y 1995, con el objeto de completar un inventario de la flora de la region altoandina de esta reserva, se colecciono una especie de Senecio aparentemente diferente de las conocidas hasta el momento para Chile y la Patagonia argentina (Cabrera 1939, 1949, 1971, 1980). Aunque la region del Nahuel Huapi ha sido una de las mas exploradas de los Andes australes, el marcado gradiente de precipitacion Este-Oeste, la compleja historia geologica y climatica de la region, y la diversidad de ambientes que producen sus sistemas montanosos, han resultado en que su flora altoandina sea especialmente rica y diversa. Las colecciones realizadas hasta el momento muetran que esta compuesta por mas de 200 especies de las que se conocen ya varios endemismos (e.g. Abrotanella diemii Cabrera, Menonvillea hirsuta Rollins, Nassauvia pulcherrima Cabrera) La nueva especie de Senecio que a continuacion se describe tambien parece ser endemica de este Parque Nascional. Senecio carbonensis Ezcurra, Ferreyra et Clayton Spec. nov. Suffrutex pygmaeus, basi ramosus, ramulis inferne dense foliosis, superne subnudis scapiformibus, circa 10 cm altis. Folia spathulata vel oblanceolata, apice rotundata, basi attenuata, ciliato-dentata, 0,8-1,2 cm longa, 2-3 mm lata, ciliis robustis, 11,5 mm longis. Capitula apice ramulorum solitaria, discoidea. Involucrum campanulatum, 9-10 mm altum, 9-11 mm crassum, longiuscule calyculatum. Bracteolae calyculi 4-5 mm longis. Bracteae involucralis circa 20, lineares, apice attenuatae, dorso glabrae. Flores isomorphi, hermaphroditi, corolla tubulosa 7-8 mm longa, apice breviter pentadentata. Achaenium cylindraceum, costatum glabrum, ca. 4 mm longum. Pappus albus, ca. 6 mm longus. Typus speciei: ARGENTINA. Prov. Rio Negro: Dpto Bariloche, Parque Nacional Nahuel Huapi, Cerro Estratos, 1650-1780 m s.n.m., 25-II-1995, Marcela Ferreyra et Sonia Clayton 352 (Holotypus BCRU, isotypus SI) Sufrutice pigmeo, con rizoma grueso del que nacen ramitas decumbentes o ascendentes, inferiomente densamente hojosas, en la parte superior casi desnudas y escapiformes, de ca. 10 cm de altura. Hojas espatuladas a oblanceoladas, sesiles, de 0,8-1,2 cm long. por 2-3 mm lat., obtusas o redondeadas en el apice y atenuadas en la base, profusamente ciliado-dentadas en el margen, con las cilias gruesas, de 1-1,5 mm long., blancas. Capitulos discoideos, solitarios en el apice de escapos subafilos. Involucro acampanado, caliculado, de 9-10 mm alt. por 9-11 mm diametro. Bracteolas del caliculo lineales, de 4-5 mm long., agudas. Bracteas del involucro alrededor de 20, lineales, atenuadas y puberulas en el apice, glabras en el dorso. Flores numerosas, ca. 40, isomorfas, hermafroditas, con corola tubulosa de 7-8 mm long., cortamente pentadentada en el apice. Aquenios cilindricos, costados, glabros, de unos 4 mm longitud. Papus blanco, de ca. 6 mm longitud. (Fig. 1). Material adicional examinado: ARGENTINA. Prov. Rio Negro: Dpto Bariloche, Parque Nacional Nahuel Huapi, Cerro Carbon, filo, 17-II-1986, M. Naumann s.n. (BCRU). Observaciones: 1) Senecio carbonensis parece ser endemico de las montanas de la region oriental mas arida del Parque Nacional Nahuel Huapi, donde ha sido coleccionado en el cordon formado por los cerros Carbon y Estratos, entre los 1.550 y 1.750 m s.n.m., sobre suelo rocoso. 2) Es una especie muy llamativa por la gran densidad de cilias blancas, muy largas y robustas, en los bordes de sus hojas, que le dan un aspecto erizado a las pequenas matas. Parece ser afin a Senecio julietii y Senecio peteroanus Phil. de la seccion Suffrutecius Cabrera subsect. Caespitosi Hoffman, de los que se diferencia principalmente por la presencia y profusion de estas cilias en los dientes de sus hojas y por el tamano intermedio de sus capitulos (involucro de 9-10 mm de alto y 9-11 mm de diametro) 3) En las citas de material se utiliza la sigla BCRU para el herbario del Departamento de Botanica del Centro Regional Universitario Bariloche, que no figura en la ultima edicion del Index Herbariorum (Holmgren, Holmgren & Barnett, 1990) por haberse iniciado recientemente. Agradecimientos: Agradecemos al Dr. Angel Cabrera por sus valiosas opiniones y la revision de la diagnosis latina, a la Delegacion Tecnica Regional Patagonica de Parques Nacionales el permiso para coleccionar en este Parque, y a la Universidad Nacional del Comahue el subsidio al proyecto de investigacion B025.

Reemplazos y coincidencias en el poblamiento de Neuquén. La integración de un espacio criollo.

Abstract: El presente trabajo tiene por objeto analizar el fenomeno de despoblamiento que se produjo en el noreste neuquino hacia fines del siglo XIX, el reemplazo de las comunidades aborigenes por pobladores criollos y el surgimento de un nuevo modelo campesino de ocupacion del espacio.

Recordando los muertos. La seguridad social, el pleno empleo y las instituciones democráticas en Lord William Beveridge.

Abstract: Razones para recordad William Beveridge, se funda en la necesidad historica de referir al conjunto de las ideas de quien junto con Bismark y Keynes confroman la triada inescindible que explica la entera historia del Estado de Bienestar.

Short-term effects of removing the most abundant species on plant species co-occurrence at a spatial microscale

Abstract: The effect of removing the above ground parts of the most abundant species (1uncus bufonius L.) in an inundated mountain meadow known as "malltn" in Patagonia was analyzed. It was hypothesized that the removal of this species should cause changes in the pattern of plant species co-occurrence in a spatial microscale (i.e., within cells of a few cm 2 ). Two predictions were tested: (I) the removal of the most abundant species would modify the frequency distribution of the pre-existing types of co-occurrences; (2) the open space created by the removal of 1. bufonius could be occupied by other species, resulting in cooccurrences different from the pre-existing ones. A grid composed of 625 cells of 2 x 2 em was overlaid on I 0 random plots of 50 x 50 em. 1. bufonius was removed from five plots and the other five were used as controls. Presence/absence of each species in each one of the 6250 cells were recorded before and after removal of the dominant species. One hundred and twenty eight types of species co-occurrences were coded, with those composed of two species being the most frequent ones. We did not find a change in the frequency distribution pattern of co-occurrences, or replacement of 1. bufonius by the subdominant species due to removal effect at the 2 x 2 em microscale. The restoration of the original species assemblage was observed at the beginning of the following growing season, and 1. bufonius regained its dominance within the community, probably because its early vegetative growth. The number of rare types of co-occurrences was also maintained, although the number of cells occupied by them decreased. The latter indicated a change in the frequency of encounter between rare and abundant species. Both predictions were not supported by the data and, thus, the removal of the most abundant species represents a small disturbance to the mallin community, in terms of the patterns of species co-occurrence at a small scale. This could be a common feature of plant communities dominated by species with active vegetative reproduction.

Especies nuevas de Rutstroemia, (Ascomycotina, Sclerotiniaceae) de Tierra del Fuego, Argentina

Abstract: Gamundi, I. J. & Giaiotti, A. L. 1995. New species of Rutstroemia (Ascomycotina, Sclerotiniaceae), from Tierra del Fuego, Argentina. Darwiniana 33: 115-121. Species of Rutstroemia Karst, recorded for the Andean-Patagonian and Fuegian forests (Argen tina) are: R. megalospora, R. microsperma, R. beaglensis nov. sp. and R. nothofagi nov. sp. The concept of the genus here accepted includes species with a complex excipulum and an evident substratal stroma, but the gelatinization of the excipulum is not stressed, due to the variability observed in collections of the same species in identical habitat and localities. The new species are described and illustrated.

Los inmigrantes italianos en la colonia La Lucinda.

Abstract: Al comienzo del siglo, la inmigracion, masiva de origen europeo llegada a la Argentina fue considerada por los sectores dominantes, un instrumento escencial en la conformacion de una sociedad moderna.

Los propietarios de la nueva frontera: tendencia de la tierra y estructuras del poder en el área andina de Neuquén. Primeros avances.

Abstract: El espacio que nos ocupa es parte del territorio patagonico incorporado al dominio del gobierno central luego de la ofensiva militar del ano 1879, que logro la disolucion definitiva del orden antiguo de las sociedades indigenas en el momento en que los sectores hegemonicos del pais, y el recientemente consolidado Estado Nacional, perseguian en conjunto metas orientadoas a la plena insercion de Argentina en el sistema capitalista internacional.

Is aging related to cell signalling alterations in amphibian oocytes

Abstract: The storage of Bufo arenarum oocytes decreased their ability to become fertilized "in vitro". The stimulation with carbachol of "young oocytes" showed a persistent hydrolysis with phosphatidylinositol 4,5 diphosphate (PIP2) while in "aged oocytes" both phosphatidylinositol 4 phosphate (PIP) and PIP2 were hydrolyzed at a non-significant level. These results and the lower 32P-phosphoinositide levels found in "aged oocytes" at time of stimulation agree with diminished phosphoinositide kinase and phospholipase C activities, as the consequence of a non-specific phosphoinositide hydrolysis probably occurring during storage.