Influencia de la Cordillera de los Andes sobre las perturbaciones baroclínicas invernales

La cordillera de los Andes produce importantes modificaciones en la estructura y evolución de las ondas baroclínicas que afectan el sur de Sudamérica que hasta el momento no han sido totalmente explicados. En consecuencia, este trabajo de Tesis reproduce mediante simulaciones numéricas tal evolución de las ondas baroclínicas y se identifica cuáles son las características morfológicas de los Andes que las dominan. Para alcanzar este objetivo general se realizaron simulaciones con un modelo numérico tridimensional en ecuaciones primitivas, hidrostático y seco basado en el sistema anelástico Boussinesq, con geometría esférica y la altura (z) como coordenada vertical. A este modelo se le incluyó una representación realista de los Andes, que retuvo todas las características salientes de los mismos: altura, pendientes y cambio en la orientación. Las condiciones iniciales fueron determinadas de forma de simular las perturbaciones sinópticas que alcanzan latitudes subtropicales de Sudamérica durante el invierno y que crecen embebidas en la Corriente en Chorro subtropical. Las simulaciones muestran que al atravesar los Andes una perturbación ciclón durante el invierno: i) sufre un debilitamiento en niveles bajos mientras se desplaza sobre la orografía alrededor de los 40ºS, ii) luego comienza a reorganizarse a sotavento, en una latitud más al norte respecto de la inicial a barlovento, iii) en niveles altos, el tren de ondas sigue una trayectoria casi zonal mientras se desplaza desde el este, iv) Este diferente comportamiento entre los niveles bajos y altos, produce un desacople de 180° entre la fase de la perturbación en niveles altos y aquella en niveles bajos, debilitando en consecuencia los procesos que favorecen el desarrollo baroclínico, y vi) alrededor de 1000 km hacia el este de los Andes, la perturbación reestablece su estructura baroclínica y el ciclón en niveles bajos se intensifica. Los estudios de sensibilidad muestran que con Andes de altura reducida a la mitad de la observada, la perturbación tiene una velocidad de fase mayor, no se desplaza hacia el Norte y es menos intensa. Por lo tanto se concluye que la altura de los Andes es el factor determinante en la extensión de la vaguada hacia el NO y en la disminución de la velocidad de fase de las ondas. Asimismo, cuando se duplica la extensión lateral, las advecciones de temperatura exhiben una menor extensión meridional. Los resultados de las simulaciones tanto para el invierno como para el verano muestran que la interacción de las ondas baroclínicas y los Andes, producen la intensificación del flujo del norte en niveles bajos al este de los Andes hacia el sur de su posición climatológica sin necesidad de incluir fuentes de calor diabático ni procesos húmedos.The Andes cordillera produces strong modifications in the structure and evolution of the baroclinic waves moving along the southern portion of South America, that have not been explained so far. Therefore, performing numerical simulations this work reproduce such modifications and identify the morphologic features of the Andes have strongest influence. A primitive equation model, hydrostatic, dry and based on the Boussinesq system was used. It includes spherical geometry and the vertical height (z) as vertical coordinate. A realistic representation of the Andes was included that includes the most relevant features of this orography like its steep slopes, its height and its geographical orientation. Initial conditions are based on the features of the observed mean flow in the vicinity of South America that during winter, they are associated with the Subtropical Jet. Simulations show that a cyclonic perturbation evolving across the Andes during winter: i) weakens at low levels while it moves over the orography along the 40°S; ii) it reorganizes on the lee side at a latitude equatorward from the initial one upwind; iii) at upper levels, the perturbation follows a more zonal trajectory while it moves eastward, iv) the different behavior between upper and lower levels, results in a 180° out-of-phase in the vertical structure of the perturbation, reducing the associated baroclinicity; v) once the low-level perturbation is located at around 1000 km eastward from the Andes, intesifies due to and increased baroclinicity. Sensitivy experiments show that in cases with Andes with a half of the observed, the perturbation exhibits a larger phase speed, a more zonal propagation, and lower rates of intensification. It can be then concluded that the Andes height is responsible of the northwestern extension of the trough on the lee and its reduced phase speed. Moreover, experiments with lateral extension of the Andes doubled, show temperature advections less extended meridionally. Finally, simulations not only for winter but also for summer show that the interaction between baroclinic waves and the Andes produce a intensification of the northerly low-level flow on the lee, southward from its climatological maximum, in absence of diabatic heating and moisture processes.Fil:Campetella, Claudia M.. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales; Argentina

Exploring patterns of beta-diversity to test the consistency of biogeographical boundaries: A case study across forest plant communities of Italy

Aim: To date, despite their great potential biogeographical regionalization models have been mostly developed on descriptive and empirical bases. This paper aims at applying the beta-diversity framework on a statistically representative data set to analytically test the consistency of the biogeographical regionalization of Italian forests. Location: Italy. Taxon: Vascular plants. Methods: Forest plant communities were surveyed in 804 plots made in a statistically representative sample of forest communities made by 201 sites of Italian forests across the three biogeographical regions of the country: Alpine, Continental, and Mediterranean. We conducted an ordination analysis and an analysis of beta-diversity, decomposing it into its turnover and nestedness components. Results: Our results provide only partial support to the consistency of the biogeographical regionalization of Italy. While the differences in forest plant communities support the distinction between the Alpine and the other two regions, differences between Continental and Mediterranean regions had lower statistical support. Pairwise beta-diversity and its turnover component are higher between- than within-biogeographical regions. This suggests that different regional species pools contribute to assembly of local communities and that spatial distance between-regions has a stronger effect than that within-regions. Main conclusions: Our findings confirm a biogeographical structure of the species pools that is captured by the biogeographical regionalization. However, nonsignificant differences between the Mediterranean and Continental biogeographical regions suggest that this biogeographical regionalization is not consistent for forest plant communities. Our results demonstrate that an analytical evaluation of species composition differences among regions using beta-diversity analysis is a promising approach for testing the consistency of biogeographical regionalization models. This approach is recommended to provide support to the biogeographical regionalization used in some environmental conservation polices adopted by EU

Plant functional traits are correlated with species persistence in the herb layer of old-growth beech forests

This paper explores which traits are correlated with fine-scale (0.25 m2) species persistence patterns in the herb layer of old-growth forests. Four old-growth beech forests representing different climatic contexts (presence or absence of summer drought period) were selected along a north–south gradient in Italy. Eight surveys were conducted in each of the sites during the period spanning 1999–2011. We found that fine-scale species persistence was correlated with different sets of plant functional traits, depending on local ecological context. Seed mass was found to be as important for the fine-scale species persistence in the northern sites, while clonal and bud-bank traits were markedly correlated with the southern sites characterised by summer drought. Leaf traits appeared to correlate with species persistence in the drier and wetter sites. However, we found that different attributes, i.e. helomorphic vs scleromorphic leaves, were correlated to species persistence in the northernmost and southernmost sites, respectively. These differences appear to be dependent on local trait adaptation rather than plant phylogenetic history. Our findings suggest that the persistent species in the old-growth forests might adopt an acquisitive resource-use strategy (i.e. helomorphic leaves with high SLA) with higher seed mass in sites without summer drought, while under water-stressed conditions persistent species have a conservative resource-use strategy (i.e. scleromorphic leaves with low SLA) with an increased importance of clonal and resprouting ability

First Jurassic brittlestar from Neuquén Basin, Argentina

Articulated fossil ophiuroids from South America were reported for the Devonian, Cretaceous, Eocene, and Miocene. Here we report the first Jurassic record of an articulated ophiuroid from the Sierra Chacaicó Formation (early Pliensbachian– Sinemurian) in Neuquén Basin, Argentina, and discuss the taphonomic processes that allowed its preservation. The Sierra Chacaicó Formation represents the onset of the Early Jurassic extensive marine transgression in the basin. The basal section comprises shoreface and offshore Gilbert-type delta system, which was affected by hyperpycnal discharges. The middle and upper sections are represented by offshore deposits, affected by storms and eroded by hyperpycnal channel-levee systems. The ophiuroid specimen was found in levels of massive, fine, tuffaceous sandstone beds and covered by coarse sandstone containing a large amount of plant debris and organic matter. It was preserved articulated, with a complete disc and almost complete arms. Based on the microstructure of the spine-bearing lateral arm plates, the ophiuroid is assigned to Sinosura, an extinct genus of the family Ophioleucidae, widespread in the Lower Jurassic deposits of Europe but previously unknown from other parts of the world. The posture of the ophiuroid, with one arm curved distally and extended in one direction and the other four arms symmetrically oriented in the opposite direction, suggests a walking or escape movement frozen in time. This implies that the ophiuroid was buried alive by sediment thick enough to prevent successful escape. The taphonomic and sedimentologic evidence indicates that the fossil material was found in hyperpycnal deposits accumulated in offshore positions, which carried a high concentration of sediment in suspension

Can management intensity be more important than environmental factors? A case study along an extreme elevation gradient from central Italian cereal fields

This paper aims to assess the importance of environmental and management factors determining the weed species composition along a strong elevation gradient. A total of 76 cereal fields (39 low input and 37 intensively managed) were sampled along an elevation gradient in central Italy. Explanatory variables were recorded for each field to elucidate the role of large-scale spatial trends, of site-specific abiotic environmental conditions and of field management characters. Redundancy analysis was used to assess the relative importance of each environmental variable in explaining the variation in species composition. Our results indicate that variation in weed species composition is strongly determined by altitude, mean annual precipitation, mean annual temperature and also by soil characteristics. However, the level of intensification proved to be the most influential variable. There was a significant difference in species richness and composition between low-input and intensively managed fields. Intensification leads to considerable species loss at both lower and higher elevations. Low-input fields had 296 species in total, while intensively managed fields had only 196

Contribution of microscopy for understanding the mechanism of action against trypanosomatids

Transmission electron microscopy (TEM) has proved to be a useful tool to study the ultrastructural alterations and the target organelles of new antitrypanosomatid drugs. Thus, it has been observed that sesquiterpene lactones induce diverse ultrastructural alterations in both T. cruzi and Leishmania spp., such as cytoplasmic vacuolization, appearance of multilamellar structures, condensation of nuclear DNA, and, in some cases, an important accumulation of lipid vacuoles. This accumulation could be related to apoptotic events. Some of the sesquiterpene lactones (e.g., psilostachyin) have also been demonstrated to cause an intense mitochondrial swelling accompanied by a visible kinetoplast deformation as well as the appearance of multivesicular bodies. This mitochondrial swelling could be related to the generation of oxidative stress and associated to alterations in the ergosterol metabolism. The appearance of multilamellar structures and multiple kinetoplasts and flagella induced by the sesquiterpene lactone psilostachyin C indicates that this compound would act at the parasite cell cycle level, in an intermediate stage between kinetoplast segregation and nuclear division. In turn, the diterpene lactone icetexane has proved to induce the external membrane budding on T. cruzi together with an apparent disorganization of the pericellar cytoskeleton. Thus, ultrastructural TEM studies allow elucidating the possible mechanisms and the subsequent identification of molecular targets for the action of natural compounds on trypanosomatids.Fil: Lozano, Esteban Sebastián. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mendoza. Instituto de Medicina y Biología Experimental de Cuyo; ArgentinaFil: Spina Zapata, Renata María. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mendoza. Instituto de Histología y Embriología de Mendoza Dr. Mario H. Burgos. Universidad Nacional de Cuyo. Facultad de Ciencias Médicas. Instituto de Histología y Embriología de Mendoza Dr. Mario H. Burgos; ArgentinaFil: Barrera, Patricia Andrea. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mendoza. Instituto de Histología y Embriología de Mendoza Dr. Mario H. Burgos. Universidad Nacional de Cuyo. Facultad de Ciencias Médicas. Instituto de Histología y Embriología de Mendoza Dr. Mario H. Burgos; ArgentinaFil: Tonn, Carlos Eugenio. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - San Luis. Instituto de Investigaciones en Tecnología Química. Universidad Nacional de San Luis. Facultad de Química, Bioquímica y Farmacia. Instituto de Investigaciones en Tecnología Química; ArgentinaFil: Sosa Escudero, Miguel Angel. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mendoza. Instituto de Histología y Embriología de Mendoza Dr. Mario H. Burgos. Universidad Nacional de Cuyo. Facultad de Ciencias Médicas. Instituto de Histología y Embriología de Mendoza Dr. Mario H. Burgos; Argentin

TRY plant trait database - enhanced coverage and open access

Plant traits-the morphological, anatomical, physiological, biochemical and phenological characteristics of plants-determine how plants respond to environmental factors, affect other trophic levels, and influence ecosystem properties and their benefits and detriments to people. Plant trait data thus represent the basis for a vast area of research spanning from evolutionary biology, community and functional ecology, to biodiversity conservation, ecosystem and landscape management, restoration, biogeography and earth system modelling. Since its foundation in 2007, the TRY database of plant traits has grown continuously. It now provides unprecedented data coverage under an open access data policy and is the main plant trait database used by the research community worldwide. Increasingly, the TRY database also supports new frontiers of trait-based plant research, including the identification of data gaps and the subsequent mobilization or measurement of new data. To support this development, in this article we evaluate the extent of the trait data compiled in TRY and analyse emerging patterns of data coverage and representativeness. Best species coverage is achieved for categorical traits-almost complete coverage for 'plant growth form'. However, most traits relevant for ecology and vegetation modelling are characterized by continuous intraspecific variation and trait-environmental relationships. These traits have to be measured on individual plants in their respective environment. Despite unprecedented data coverage, we observe a humbling lack of completeness and representativeness of these continuous traits in many aspects. We, therefore, conclude that reducing data gaps and biases in the TRY database remains a key challenge and requires a coordinated approach to data mobilization and trait measurements. This can only be achieved in collaboration with other initiatives