Southwestern Argentina Research Articles

Genetic Identification of a New Hantavirus Causing Severe Pulmonary Syndrome in Argentina

A fatal case of serologically confirmed hantavirus pulmonary syndrome (HPS) was recently reported in southwestern Argentina. Nucleotide sequence analysis of PCR fragments from conserved regions of the S and M genomic segments of the virus, amplified from RNA extracted from autopsy lung and liver tissues, showed the virus (referred as Andes virus) to be novel. Comparisons between Andes virus genome sequences with the corresponding sequences of the more closely related hantaviruses revealed differences at the amino acid level from 13.6 to 23.9% for G2 protein regions and from 8.5 to 12.5% for the amino terminal region of the nucleocapsid protein. Phylogenetic analysis using the maximum parsimony and maximum likelihood methods showed that Andes virus maps within the clade containing the HPS-associated viruses from North America. Within this group, Andes virus represents a unique lineage. This is, to our knowledge, the first report on the genetic characterization of a hantavirus from South America.

Ecological Impacts of Introduced Animals in Nahuel Huapi National Park, Argentina

Abstract: In Nahuel Huapi National Park in southwestern Argentina, livestock and exotic deer pose important management problems. Due to the economic and social benefits of sport hunting and production of livestock, it is politically impractical to completely eradicate these animals from the park. Instead, park managers attempt to minimize the effects of these introduced animals by preventing their spread into more pristine parts of the park and by trying to diminish their population densities. Managers are also promoting the relocation of livestock production to appropriate sites in the National Reserve part of the park where livestock raising is permitted. Detailed information on the ecological impacts of introduced herbivores is needed both to guide management of the different vegetation types of the park and to support the park managers' public relations campaign justifying exotic animal control.We examined the ecological effects of introduced animals along the vegetation gradient from Andean rain forests through xeric woodlands to the Patagonian steppe. We sampled 30 stands for floristic composition and structure, assessed browse intensity, and compared stands of similar abiotic habitat but of different browsing regimes. Deer and livestock have significantly altered floristic composition and stand structure along this gradient. They impair tree regeneration and pose a long‐term threat to the continued existence of a forest cover.

Carboniferous glaciation in Gondwana. Evidence for grounded marine ice and continental glaciation in southwestern Argentina

Upper Paleozoic sedimentary rocks in western Argentina accumulated in retro-arc foreland basins in the Gondwana continental margin. A glacial component in these rocks was recognized early in this century but reconstructions of the nature of the glaciation differ markedly. The dominant proposal sustains that glaciation in this region was of alpine-type, with glaciers descending from mountain ranges both inland and along the edge of the continent, and that the numerous intercalated diamictites were mostly deposited as subaquatic debris flows only indirectly connected with the presence of glacier ice. A stratigraphic and sedimentologic study of Middle Carboniferous glacigenic deposits of the Tepuel Group in central western Patagonia, southwestern Argentina, shows that two major diamictite facies are present: (a) massive diamictite, the more abundant, forms regionally extensive and thick (<60 m) pebbly bodies with boundaries transitional to non-glacial open shelf deposits; these are interpreted as rain-out till; and (b) chaotic diamictite, yielding thin (< 10 m) laterally discontinuous bouldery bodies showing erosive bases, strong substratal deformation, and upward transition to massive diamictite; these are interpreted as subglacial till. A third type of glacial deposit consists of interbedded current-deposited and wave-worked conglomerates and sandstones, in strata that downlap onto non-glacial shelf mudstones; these are interpreted as submarine outwash fan deposits. The position of subglacial till and outwash fans relative to the paleoshoreline indicate deep regional incursions of grounded ice onto the shelf. In addition, deepening of the shelf coincident with initial glacial marine sedimentation in the early Middle Carboniferous, at a time of global lowstand, argues for glacio-isostatic depression of the shelf and suggests a considerable ice thickness. Paleotopographic considerations indicate that the centres of ice dispersal were located on moderately high intracratonic highlands. A regional erosion surface across these highlands is attributed to subglacial scour under a Patagonian ice cap that expanded onto the adjacent shelf during glacial maxima. Published information concerning ice distribution in Middle Carboniferous Gondwana supports the existence of an ice cover similar in lateral extent to that in modern Antarctica. The Patagonian ice cap would have been peripheral to this continental-sized ice mass.

Models of geomagnetic secular variations on recent times for South America

Palaeosecular variations of the geomagnetic field obtained from palaeomagnetic and radiometric studies carried out on the bottom sediments from three lakes in southwestern Argentina (records extend back to about 6000 years by 14 C dating) were compared with results from different theoretical models, which suggested the possible sources of the field. Attempts were then made to simulate long period secular variations using modified Alldredge and Hurwitz's models. The Alldredge and Hurwitz model uses a central dipole and eight radial dipoles, all at the same distance from the centre of the Earth, as a first approximation to the sources of the geomagnetic field. The modified models, which have been used to describe the northern hemisphere data, comprise eight radial dipoles, which oscillate sinusoidally and/or drift. The different parameters of the models were fitted to the palaeomagnetic data from southwestern Argentina. The best fit was obtained with a mixed model; between 6000 and 3000 years BP all radial dipoles oscillate and some of them drift as well. Later the drift rates become lower and, finally, between 1700 years BP and present times, all radial dipoles only oscillate.

New evidence for an allochthonous plate in central southwestern Argentina?

Preliminary paleomagnetic data for rocks from the Choiyoi Formation, exposed at the Cerro Chachil and Sierra de Catan-Lil (39.1°S, 70.5°W, Cordillera Principal, Argentina), assigned sensu lato to the Permo-Triassic, are discussed. The directions of the stable remanent magnetization (SRM) for these rocks have been submitted to the fold test. This analysis indicates that most of the Choiyoi Formation rocks are carriers of a prefolding SRM. The mean prefolding SRM for samples of normal and reversed polarity (within 40° of the mean; 277°, +54°, A95 = 8°, N = 21, K = 15.2, R = 19.683) yields a mean pole at 18°S, 126°W, 95 = 10°. The paleomagnetic data indicate two preliminary interpretations. One interpretation suggests that the sampling site rotated 90° clockwise around a vertical axis since Permian times. The other interpretation suggests that the sampling site integrates the allochthonous microplate suggested by Vilas and Valencio (1982) and Valencio and Vilas (1985). This microplate was situated in the Pacific at tropical latitudes in the late Paleozoic.

Beech (Nothofagus) Forests in the Andes of Southwestern Argentina

The subantarctic forest of Argentina extends along the Andes from about 350 S to Tierra del Fuego. The present phytosocio- logical study was concerned with the forest vegetation from 400 S to 430 S. In this region three of the six species of beech (Nothofagus) in Argentina are present. Nothofagus dombeyi, an evergreen Angiosperm, is the dominant tree over much of the mesic and wet-mesic lowland and low- er slope areas. Nothofagus pumilio, a deciduous tree, dominates the upper slope and timberline forests, while N. antarctica (also deciduous) occurs at timberline and also in the lowland areas. In areas of very heavy precipitation ( 150-200 inches/year) a rain forest dominated by Fitz- roya cupressoides, N. dombeyi, and several other tree species develops. A bamboo (Chusquea) forms moderately dense to very dense under- story growth in much of the forested area. A pronounced rain-shadow effect exists in this region so that 50 miles east of the rain forest the precipitation may be only one-tenth as much. Here Libocedrus chilensis, which occurs also in much moister areas, is the dominant tree in the forest-steppe transition.

ARTIFICIAL AND NATURAL HYBRIDS IN THE GRAMINEAE, TRIBE HORDEAE. VIII. FOUR HYBRIDS OF ELYMUS AND AGROPYRON

CERTAIN North American representatives of Agrapyron, Elymus, Hordeum and Sitanion (tribe Hordeae, Gramineae) have been studied previously (Stebbins et al., 1946a, 1946b; Stebbins and Walters, 1949; Stebbins and Singh, 1950; Stebbins and Pun, 1953). Snyder (1950, 1951) made a detailed study of the morphological variability of Elymus glaucus and of the isolation barriers within this species. The present study deals with the morphology and cytogenetics of some North and South American entities of Agrop,yron and Elymus. These entities are: Agropyron spicatum var. inerme (Scribn. et Smith) Heller and Elymus glaucus Buckl., both from North America; and at the diploid (2n 14) and the tetraploid level (2n 28), respectively: Agropyron agroelymoides (Hicken) Hunz. from the center of Argentina (Buenos Aires, San Luis, Rio Negro), an unidentified species of Agropyron from western Argentina (Calmuco, Mendoza) which will be referred to as Agropyron sp. Calmuco and Elymus patagonicus Speg. from Southwestern Argentina (Neuquen to Santa Cruz), all hexaploids (2n 42). MATERIALS. The parental strains as well as the hybrids were grown in the experimental plots of the Department of Genetics, University of California, Berkeley. Herbarium specimens of the parental strains and hvbrids have been deposited in the University of California Herbarium (UC): and at the Instituto de Botinica, Ministerio de Agricultura y Ganaderia, Buenos Aires, Argentina (BAB). Parents.-The parental strains used in the experiments were: Agropyron spicatum var. inerme, U. S. Soil Conservation Service P-7413, collected at Lind, Washington. This is Stebbins' strain 544 (Stebbins and Singh, 1950; Stebbins and Pun, 1953). A. agroelymoides (981) , collected at Balcarce, Provincia de Buenos Aires,' Argentina. A. sp. Calmuco (983), collected by G. Covas, near Calmuco, Provincia de Mendoza, Argentina. Elymus glaucus, U. S. Soil Conservation Service P-10128, collected at Sebastopol, Sonoma County, California. E. patagonicus (982), collected by G. Covas, 56

Observations on the Occurrence and Origin of Petroleum in Argentina and Bolivia

This paper, based on observations in 1917, outlines the geographic and geologic range of petroleum indications in Argentina and the Atlantic watershed of Bolivia, and discusses the probable mother-rocks. Besides the Comodoro Rivadavia field on the Atlantic coast of Patagonia, where petroleum is produced in quantity, seepages and other evidences of oil are scattered along a sub-Andine belt over fifteen hundred miles long from southwestern Argentina to north central Bolivia, and range through many thousands of feet of the sedimentary series. The original sources appear to be sediments containing organic remains in formations of widely different ages, ranging from Devonian to Cretaceous. The chief source beds are here postulated as being the marine Devonian and Cretaceous in the northern Argentine-Bolivian belt; fresh or brackish water Upper Triassic near Mendoza; marine Upper Jurassic-Lower Cretaceous in southwestern Argentina; and marine Cretaceous or older beds on the Atlantic Coast.