149 research outputs found
Phytoplankton diversity and strategies in regard to physical disturbances in a shallow, oligotrophic, tropical reservoir in Southeast Brazil
The IAG Lake is a small, oligotrophic, and shallow reservoir located in the Parque Estadual das Fontes do Ipiranga Biological Reserve, south of Municipality of Sao Paulo, southeast Brazil. The study of the phytoplankton community dynamics is based on samples collected along the vertical profile of the water column in the pelagic region of the reservoir (Zmax = 4.7 m), 3 times a day (7 h, 13 h, and 19 h) during 7 consecutive days of the dry period (20-26 August 1996) and of the rainy period (22- 28 January 1997), but at 5 depths during the dry period and at 4 depths during the rainy one. The relationships among species richness, diversity, evenness, and dominance were discussed within the Connell's Intermediate Disturbance Hypothesis (IDH). The responses of the descriptive species in the community and C-R-S strategies were studied. The variation of the mixing zone was the main factor responsible for the changes in the community structure as well as for the maintenance of the diversity during both climate periods. The disturbance was considered of high frequency during the dry period and of intermediate frequency during the rainy one. The diversity was higher during the rainy period, confirming the IDH, at least during the present study. Peridinium gatunense Nygaard was dominant in most sample units during the dry period. During the rainy one, Chlamydomonas debaryana Goroschankin and Oocystis lacustris Chodat were the species that contributed the most. Regarding the functional groups, S-strategists dominated the dry period, differing from the rainy one, when the functional diversity was higher. In conclusion, changes in the phytoplankton community structure were well explained by Connell's IDH.El lago IAG es un embalse pequeño, oligotrófico y somero, ubicado en la Reserva Biológica del Parque Estadual das Fontes do Ipiranga, Sur de la Municipalidad de Sao Paulo, sureste del Brasil. El estudio de la dinámica de la comunidad fitoplanctónica está basado en muestras colectadas al largo del perfil vertical de la columna de agua en la región pelágica del embalse (Zmax = 4.7 m), 3 veces al dÃa (7 h, 13 h y 19 h) durante 7 dÃas consecutivos de los perÃodos seco (20-26 Agosto 1996) y húmedo (22-28 Enero 1997), pero en 5 profundidades durante el perÃodo seco y en 4 durante el húmedo. Las relaciones entre riqueza de especies, diversidad, equitabilidad y dominancia fueron discutidos dentro de la Hipótesis de Connell de la Perturbación Intermedia (HPI). Las respuestas de las especies descriptoras de la comunidad y estrategias C-R-S fueron estudiadas. La variación de la zona de mezcla fue el factor más importante en los cambios en la estructura de la comunidad asà como para el mantenimiento de la diversidad durante los dos perÃodos climáticos. La perturbación fue considerada de frecuencia alta durante el perÃodo seco y de frecuencia intermedia durante el húmedo. La diversidad fue más alta durante el perÃodo de lluvias, confirmando la HPI, por lo menos en este estudio. Peridinium gatunense Nygaard fue dominante en la mayorÃa de las unidades de muestreo durante el perÃodo seco. Durante el perÃodo húmedo, Chlamydomonas debaryana Goroschankin y Oocystis lacustris Chodat fueron las especies que más contribuyeron. Considerando los grupos funcionales, los estrategas S dominaron el perÃodo seco, a diferencia del perÃodo húmedo, cuando la diversidad funcional fue más alta. Concluyendo, los cambios en la estructura de la comunidad del fitoplancton fueron bien explicados por la HPI de Connell
The dominance of desmids in tropical monomictic lakes (SE Brazil)
Disturbance is a concept used to explain the structure of communities. This concept emphasizes the effects of disturbance on the "break" of biomass stability in stable environments and the opportunities for the development of other species. The major disturbances in natural warm monomictic lakes include the contrasting effects of seasonal changes and long-term in thermal stability, as well as short-term changes in the mixing layer. This study investigated the effects of disturbance and abiotic environmental factors on the biomass of desmids, based on samples collected monthly from January 2002 through December 2006 in the limnetic region of two natural lakes, Carioca (small and shallow) and Dom Helvécio (large and deep), located in Rio Doce State Park, Minas Gerais State,south east Brazil.At Lake Dom Helvécio,the extensive banks of aquatic macrophytes, the lake's dendritic shape and the period of clear water produced higher richness values and facilitated the occurrence of relatively large (maximum linear dimension >20 µm) desmid species, primarily species belonging to Staurastrum and Staurodesmus. In contrast, less richness and a dominant group of relatively small (maximum linear dimension <20 µm) desmid species, especially species belonging to the genus Cosmarium, were observed at Lake Carioca in conjunction with a sparse macrophyte cover. The lakes showed a seasonal thermal stratification characterized by high temperature (25-32ºC), thermal stability and higher desmid biomass. The stability of the epilimnetic desmid biomass was an indicator of the adaptive flexibility of the desmid species and the capacity of the biomass to recover after the mixing period.La perturbación es un concepto utilizado para explicar la estructura de las comunidades, con énfasis en sus efectos sobre la "ruptura" de la estabilidad de la biomasa en ambientes estables y sobre las oportunidades para el desarrollo de nuevas especies. Entre las perturbaciones más importantes encontradas en lagos naturales monomÃticos destaca el efecto de las variaciones estacionales y de largo plazo en la estabilidad térmica, asà como los cambios a corto plazo en la profundidad de la mezcla. En este trabajo se describe el efecto de la estratificación y mezcla del lago asà como de otros factores abióticos sobre la biomasa de desmidiáceas en lagos tropicales. Los muestreos se realizaron mensualmente entre enero de 2002 y diciembre de 2006 en la región pelágica de dos lagos naturales monomÃticos cálidos, Carioca (pequeño y poco profundo) y Dom Helvécio (grande y bastante profundo) ubicados en el Parque Estadual do Rio Doce (Estado Minas Gerais, SE Brasil). En el lago Dom Helvécio, las grandes acumulaciones de macrófitas acuáticas, la forma dendrÃtica del lago y el perÃodo de aguas transparentes influyeron de forma sinérgica en una mayor riqueza de especies y de tamaños grandes, mayores de 20 µm, siendo principalmente especies de Staurastrum y Staurodesmus. Sin embargo, en el Lago Carioca se observó una menor riqueza y el dominio de desmidiáceas de pequeño tamaño (<20 µm), especialmente Cosmarium. Este último lago presentó también una cobertura escasa de macrófitas. Los lagos mostraron un patrón estacional caracterizado, durante la estratificación térmica, por el aumento de la temperatura (25-32ºC), estabilidad térmica y mayor biomasa de desmidiáce. La estabilidad de la biomasa epilimnética fue indicativo de una flexibilidad adaptiva y recuperación después del perÃodo de mezcla
The Theta+ (1540) as a heptaquark with the overlap of a pion, a kaon and a nucleon
We study the very recently discovered Theta+ (1540) at SPring-8, at ITEP and
at CLAS-Thomas Jefferson Lab. We apply the same RGM techniques that already
explained with success the repulsive hard core of nucleon-nucleon, kaon-nucleon
exotic scattering, and the attractive hard core present in pion-nucleon and
pion-pion non-exotic scattering. We find that the K-N repulsion excludes the
Theta+ as a K-N s-wave pentaquark. We explore the Theta+ as a heptaquark,
equivalent to a N+pi+K borromean bound-state, with positive parity and total
isospin I=0. We find that the kaon-nucleon repulsion is cancelled by the
attraction existing both in the pion-nucleon and pion-kaon channels. Although
we are not yet able to bind the total three body system, we find that the
Theta^+ may still be a heptaquark state. We conclude with predictions that can
be tested experimentally.Comment: 5 pages, 5 figures, 2 tables, submitted to Phys. Rev. D, rapid
communicatio
A New Nucleolar Body Appears in Drosophila saltans Salivary Gland Cells Before Histolysis, in Programmed Cell Death
The salivary glands of Drosophila saltans (saltans group, saltans subgroup) analyzed in an advanced stage of programmed cell death showed the appearance of a single, round, nucleolar corpuscle inside the highly altered nucleus of every gland cell, at a time during which the integrity of the original nucleolus was already lost and the original nucleolar material apparently disappeared. In the same nuclei, which already had also lost the characteristic chromosome structure, some delicate chromosome threads were maintained. In many cells, the new nucleolar corpuscle and these chromosome threads are associated. These findings are novel. However, the hypothesis put forward concerning their meaning remains dependent on other studies
Algas e cianobactérias continentais no estado do Pará, Brasil.
Estudos ficológicos no Pará; Compilação dos dados; Diversidade; Cyanophyceae/Cyanobacteria; Chlamydophyceae; Chlorophyceae; Zygnemaphyceae; Oedogoniophyceae; Charophyceae; Euglenophyceae; Dinophyceae; Chrysophyceae; Xanthophyceae; Cryptophyceae; Rhodophyceae; Classe não definida
Linear square-mass trajectories of radially and orbitally excited hadrons in holographic QCD
We consider a new approach towards constructing approximate holographic duals
of QCD from experimental hadron properties. This framework allows us to derive
a gravity dual which reproduces the empirically found linear square-mass
trajectories of universal slope for radially and orbitally excited hadrons.
Conformal symmetry breaking in the bulk is exclusively due to infrared
deformations of the anti-de Sitter metric and governed by one free mass scale
proportional to Lambda_QCD. The resulting background geometry exhibits dual
signatures of confinement and provides the first examples of holographically
generated linear trajectories in the baryon sector. The predictions for the
light hadron spectrum include new relations between trajectory slopes and
ground state masses and are in good overall agreement with experiment.Comment: 33 pages, 5 figures, updated to the extended version published in
JHEP, vector meson bulk potential and metric corrected, comments and
references added, phenomenology and conclusions unchange
Floraciones de fitoplancton y variación de la estructura comunitaria fitoplanctónica en tres lagos someros eutróficos de Chile Central
The phytoplankton community of three eutrophic shallow lakes located in the same geographical area was compared over a period of three years. Although these lakes are similar in many respects (e.g. location, origin, average depth, high concentration of nutrients, human influence) develop very different phytoplankton communities. Lo Galindo is dominated by Zygnematophyceae, Cyanophyceae and Chlorophyceae, while in Lo Méndez the groups Dinophyceae and Bacillariophyceae and in Las Tres Pascualas the Chlorophyceae, Cryptophyceae and Euglenophyceae. In Lo Mendez and Lo Galindo are frequent blooms of different groups of algae (cyanobacteria, green algae, diatoms and dinoflagellates), which generated wealth increases at different times of the year, even in winter they were presented. In Las Tres Pascualas blooms were rare. The occurrence and frequency of blooms of species representatives of the M, C,Y and Lo functional groups, and VII, VI, IV and V morphological groups, reflect the eutrophic lakes, being indicative of the degree of contamination of these systems that influence their present and future use.La comunidad fitoplanctónica de tres lagos someros eutróficos ubicados en la misma zona geográfica fue comparada durante un periodo de tres años. Aunque estos lagos son similares en muchos aspectos (p.ej. ubicación, origen, profundidad media, alta concentración de nutrientes, influencia humana) desarrollan comunidades de fitoplancton muy diferentes. En Lo Galindo dominan Zygnematophyceae, Cyanophyceae y Chlorophyceae, en Lo Méndez Dinophyceae y Bacillariophyceae y en Las Tres Pascualas Chlorophyceae, Cryptophyceae y Euglenophyceae. En Lo Méndez y Lo Galindo se presentaron frecuentes floraciones de diferentes grupos de microalgas (cianobacterias, algas verdes, diatomeas y dinoflagelados), las que generaron aumentos de abundancia en diferentes épocas del año, incluso en invierno. En Las Tres Pascualas, las floraciones fueron poco frecuentes. La ocurrencia y frecuencia de floraciones de especies representantes de los grupos funcionales M, C, Y y Lo y morfológicos VII, VI, IV y V reflejan las condiciones eutróficas de los lagos, siendo indicadoras del grado de contaminación de estos sistemas que influencia su uso actual y futuro
Distance Decay of Similarity in Neotropical Diatom Communities
Background The regression of similarity against distance unites several ecological phenomena, and thus provides a highly useful approach for illustrating the spatial turnover across sites. Our aim was to test whether the rates of decay in community similarity differ between diatom growth forms suggested to show different dispersal ability. We hypothesized that the diatom group with lower dispersal ability (i.e. periphyton) would show higher distance decay rates than a group with higher dispersal ability (i.e. plankton). Methods/Principal findings Periphyton and phytoplankton samples were gathered at sites distributed over an area of approximately 800 km length in the Negro River, Amazon basin, Brazil, South America (3°08′00″S; 59°54′30″W). Distance decay relationships were then estimated using distance-based regressions, and the coefficients of these regressions were compared among the groups with different dispersal abilities to assess our predictions. We found evidence that different tributaries and reaches of the Negro River harbor different diatom communities. As expected, the rates of distance decay in community similarity were higher for periphyton than for phytoplankton indicating the lower dispersal ability of periphytic taxa. Conclusions/Significance Our study demonstrates that the comparison of distance decay relationships among taxa with similar ecological requirements, but with different growth form and thus dispersal ability provides a sound approach to evaluate the effects of dispersal ability on beta diversity patterns. Our results are also in line with the growing body of evidence indicating that microorganisms exhibit biogeographic patterns. Finally, we underscore that clumbing all microbial taxa into one group may be a flawed approach to test whether microbes exhibit biogeographic patterns.Peer reviewe
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