Resumen Introducción: Describir los patrones de biodiversidad y los mecanismos que los subyacen es indispensable para afrontar las desenfrenadas presiones sobre los ecosistemas de agua dulce en el trópico. Esto es particularmente relevante en regiones escasamente estudiadas como el escudo guayanés colombiano Objetivo: Describir la estructura taxonómica y funcional de las comunidades de macroinvertebrados, y evaluar su variación a lo largo de escalas espaciales y temporales Métodos: Las comunidades de macroinvertebrados de cuatro ríos fueron muestreadas durante la época seca del 2017 y 2018. Adicionalmente, se evaluaron los patrones de diversidad dentro y entre los ríos y entre diferentes meses de muestreo en uno de los cursos hídricos. Los patrones de diversidad fueron evaluados mediante la comparación de los patrones entre y dentro de los ríos de la diversidad alfa (diferencias en la riqueza y abundancia de taxones entre comunidades) y de la diversidad beta (diferencias en la composición de taxones entre comunidades). La diversidad alfa fue estimada usando los números de Hill, mientras que la diversidad beta se estimó usando los índices de Sørensen y Morisita-Horn y comparada usando un análisis de similaridad (ANOSIM). Resultados: La composición de taxones fue distinta dentro (escala de mesohábitat) y entre los ríos (escala regional). Sin embargo, la composición de FFG cambió entre, pero no dentro de los ríos. La comparación de los números de Hill y de la composición de taxones sugiere que el tipo de mesohábitat es un factor determinante de la diversidad taxonómica pero no de la diversidad de FFG en distintas escalas. En la escala temporal, la diversidad alfa fue baja para los meses con altas precipitaciones (febrero-abril) y alta para la temporada seca (enero). La diversidad beta temporal fue alta para los periodos muestreados y los procesos de anidamiento fueron el componente más notable de la diversidad beta a lo largo del año. Conclusión: Los ríos de la Serranía de la Lindosa albergan una alta diversidad de macroinvertebrados acuáticos. La estacionalidad y las diferencias en la heterogeneidad del hábitat dentro de los ríos parecen determinar los patrones de diversidad observados a diferentes escalas temporales y espaciales. Profundizar en su estudio es necesario para entender el funcionamiento de estos ecosistemas y mejorar la habilidad para generar estrategias de manejo y conservación.

Abstract Introduction: Describing biodiversity patterns and the underlying drivers is relevant for tackling the rampant pressures on tropical freshwaters. This is particularly relevant in scarcely studied regions, such as in the Colombian Guiana shield. Objective: To describe the taxonomic and functional structure of macroinvertebrate communities and assess their variability across spatial and temporal scales. Methods: We sampled the invertebrate communities in four streams during the dry seasons of 2017 and 2018. Additionally, we assessed diversity patterns within and among streams and between different sampling months in one stream. To assess diversity patterns, we compared alpha (differences in taxon richness and abundance within communities) and beta (differences in taxon composition among communities) diversity patterns among and within rivers. Alpha diversity was estimated using the numbers of Hill, while beta diversity was estimated using the Sørensen and Morisita-Horn indices and compared using a similarities analysis (ANOSIM). Results: The taxon composition of the communities was different within (mesohabitat scale) and among streams (regional scale). However, the composition of FFGs changed among but not within streams. The comparison of the numbers of Hill and the taxon composition suggested that the mesohabitat type is a determining factor of the taxonomic but not FFG diversity across scales. At the temporal scale, alpha diversity was low for months with high precipitation (February-April) and high for the dry season (January). The temporal beta diversity was high among sampling periods, being nestedness processes driving beta diversity among years and turnover processes driving beta diversity within years. Conclusion: Streams from Serranía de la Lindosa host a high diversity of freshwater macroinvertebrates. Seasonality and differences in the in-stream habitat heterogeneity seem to determine the diversity patterns observed at different temporal and spatial scales. A deeper study is needed to understand the functioning of these ecosystems and improve the ability to generate management and conservation strategies.

Resumen Este texto se propone interpretar la mencionada obra del comediante ateniense a la luz de la múltiple relación entre guerra - eros - paz. La hipótesis que queremos sostener indica que para Aristófanes el hombre se encuentra en un curioso estado paradójico respecto de la guerra, puesto que no puede vivir sin deseo, pero es el deseo el que también conduce a la guerra.

Summary This text intends to interpret the mentioned work of the Athenian comedian focusing on the relationship among war - Eros - peace. The hypothesis that we want to mark off indicates that for Aristophanes the man is in a paradoxical situation state regarding war, since he cannot live without desire, but it is desire that also leads to war

Objetivou-se, com este trabalho, avaliar o efeito de diferentes concentrações de sais na água de irrigação sob a emergência e o crescimento inicial de plântulas de albízia (Albizia lebbeck (L.) Benth.). O experimento foi desenvolvido em casa de vegetação do departamento de Ciências Vegetais da Universidade Federal Rural do Semiárido, Mossoró, RN, usando-se o delineamento inteiramente casualizado, com seis tratamentos e quatro repetições, com 24 sementes em cada parcela. Os tratamentos foram constituídos das concentrações salinas 0,68 (água de abastecimento); 1,5; 3,0; 4,5; 6,0 e 7,5 dS m-1, obtidas através da adição de NaCl em água. As variáveis avaliadas foram: porcentagem de emergência de plântulas, índice de velocidade de emergência, comprimento da parte aérea, comprimento de raiz, número de folíolos, condutividade elétrica acumulada do substrato, índice de conteúdo de clorofila, massa seca da raiz, do caule, das folhas e total. O aumento da salinidade na água de irrigação interfere negativamente na emergência e no crescimento inicial de plântulas de albízia, sendo recomendado água com concentração salina até 1,5 dS m-1, caracterizando esta espécie como glicófita, sensível à salinidade.

In order to evaluate the effect of different concentrations of salts in irrigation water on emergence and growth of albízia seedling (Albizia lebbeck (L.) Benth.) an experiment was conducted in the greenhouse of the Department of Plant Sciences, Federal Rural University of Semi-arid, Mossoró, RN, in a completely randomized design with six treatments and four replications with 24 seeds in each plot. The treatments consisted of saline concentrations (EC) of 0.68 (supply water), 1.5, 3.0, 4.5, 6.0 and 7.5 dS m-1, which were obtained by the addition of NaCl in water. The evaluated variables were: percentage of emergence of seedling, speed of emergence index, shoot length, root length, number of leaves, accumulated electrical conductivity of the substrate index, chlorophyll content, dry mass of root, stem, leaves and total. The salinity negatively interferes in all parameters assessed in proportion to its increase in irrigation water. With major damage at concentrations above 1.5 dS m-1, characterizing this species considered as a glycophyte little tolerant to salinity.

Se midieron, bajo condiciones de laboratorio y a varias profundidades, la fluorescencia mínima (F0), máxima (Fm) y variable (Fv = Fm - F0) y la eficiencia fotosintética (Fv/Fm) del fitoplancton del lago Guatavita (Colombia), en los meses de junio y octubre de 2000. Cuando el lago estuvo estratificado (junio) las algas superficiales estuvieron fotoinhibidas y la eficiencia fotosintética fue muy baja, especialmente en el hipolimnio. En octubre, cuando el lago se mezcló, la eficiencia fue más alta en la columna del agua. Los ensayos del laboratorio exhibieron un descenso gradual en la eficiencia a lo largo del tiempo, pero con valores más altos en octubre. Se observaron diferencias significativas entre las eficiencias de junio y de octubre, tanto en laboratorio como en campo. A excepción de las eficiencias en el hipolimnio de junio, no hubo diferencias significativas entre las observaciones del campo y las mediciones de laboratorio. Cuando el lago estuvo estratificado, la concentración de la clorofila-a fue alta en el hipolimnio, pero la eficiencia fue baja. Durante la mezcla, la concentración de la clorofila-a fue baja pero la eficiencia fue más alta. Los resultados demuestran que la eficiencia fotosintética del fitoplancton es independiente de la biomasa y que además de ésta, otros factores tales como disponibilidad de nutrientes y la luz podrían afectar esta variable funcional.

Minimum (F0), maximum (Fm), and variable (Fv = Fm - F0) fluorescence and photosynthetic efficiency (Fv/Fm) of phytoplankton were measured for several depths and under laboratory conditions during two seasons (June and October of 2000) in Lake Guatavita, Colombia. When the lake was stratified (June) the surface algae were photoinhibited and photosynthetic efficiency was very low, especially in the hypolimnion. In October, when the lake was circulating, efficiency was higher throughout the water column. Laboratory samples exhibited a gradual decline in efficiency over time, but with higher values in October. Significant differences between June and October samples were observed both in the laboratory and the field. Except for hypolimnetic samples for June, there were no significant differences between field observations and laboratory measures. When the lake was stratified, the concentration of chlorophyll-a was high in the hypolimnion, but the efficiency was low. During circulation, the concentration of chlorophyll-a was low but the efficiency was higher. The results demonstrate that the photosynthetic efficiency of the phytoplankton is independent of biomass and that in addition to biomass, other factors, such as availability of nutrients and light could affect photosynthetic efficiency.

Estudos recentes demonstram que defesas químicas de algas que inibem o consumo exercido por peixes ou ouriços não inibem herbívoros com pequena mobilidade. As espécies de algas bentônicas Dictyota menstrualis e Dictyota mertensii foram estudadas tendo por objetivo avaliar a atuação de seus extratos brutos nos processos de quimiotaxia e defesa frente aos herbívoros de pequena mobilidade, o anfípodo Parhyale hawaiensis e o caranguejo Pachygrapsus transversus. Os ensaios de preferência alimentar demonstraram que P. hawaiensis não consomem ambas as espécies de Dictyota. Por outro lado, P. transversus também não consomem D. menstrualis, mas se alimentam de grandes quantidades de D. mertensii. Os extratos brutos de ambas as espécies de Dictyota inbiram a herbívoria por estes herbívoros. Além disso, os ensaios demonstraram que os herbívoros apresentaram reação de quimiotaxia negativa, provavelmente devido à presença de metabólitos complementares presentes no alimento artificial. Considerando que ambas as espécies de Dictyota exibem extratos brutos ativos frente a estes herbívoros de pequena mobilidade, supomos que a não-ocorrência em estreita associação com as algas D. menstrualis e D. mertensii pode explicar os resultados obtidos.

Recent studies have show that small marine herbivores with limited mobility (mesograzers) often feed on macroalgae chemically defended against fishes or sea-urchins. In order to verify the involved mechanisms of chemotaxis or chemical defense into this process in Brazilian littoral, two species of brown alga Dictyota menstrualis and Dictyota mertensii were studied against the limited mobility herbivores, the amphipod Parhyale hawaiensis and the crab Pachygrapsus transversus. These two species were studied in order to verify the action of their crude extracts in the defense and chemotaxis processes related to limited mobility of these herbivores. Feeding preference assays revealed that P. hawaiensis do not eaten these Dictyota species. P. transversus do not eaten D. menstrualis either, but consumed large amounts of D. mertensii. Chemical deterrence assays showed that extracts of these species act as feeding deterrent to both species of herbivores. In addition, chemotaxis assays demonstrated that both herbivores are significantly negative chemotactic probably due to the presence of complementary metabolites into artificial foods. Considering that both Dictyota species exhibit active extracts against these small herbivores, we suppose that the non-occurrence of these herbivore species in close relationship with the seaweeds D. menstrualis and D. mertensii may explain the defense action of both extracts related to these mesograzers.

The Ca2+-modulated, dimeric proteins of the EF-hand (helix-loop-helix) type, S100A1 and S100B, that have been shown to inhibit microtubule (MT) protein assembly and to promote MT disassembly, interact with the type III intermediate filament (IF) subunits, desmin and glial fibrillary acidic protein (GFAP), with a stoichiometry of 2 mol of IF subunit/mol of S100A1 or S100B dimer and an affinity of 0.5-1.0 µM in the presence of a few micromolar concentrations of Ca2+. Binding of S100A1 and S100B results in inhibition of desmin and GFAP assemblies into IFs and stimulation of the disassembly of preformed desmin and GFAP IFs. S100A1 and S100B interact with a stretch of residues in the N-terminal (head) domain of desmin and GFAP, thereby blocking the head-to-tail process of IF elongation. The C-terminal extension of S100A1 (and, likely, S100B) represents a critical part of the site that recognizes desmin and GFAP. S100B is localized to IFs within cells, suggesting that it might have a role in remodeling IFs upon elevation of cytosolic Ca2+ concentration by avoiding excess IF assembly and/or promoting IF disassembly in vivo. S100A1, that is not localized to IFs, might also play a role in the regulation of IF dynamics by binding to and sequestering unassembled IF subunits. Together, these observations suggest that S100A1 and S100B may be regarded as Ca2+-dependent regulators of the state of assembly of two important elements of the cytoskeleton, IFs and MTs, and, potentially, of MT- and IF-based activities.