Oviposición intrasexual en Belostoma oxyurum. Una nota sobre sus determinantes ecológicos

Intrasexual egg laying was detected in a female giant water bug, Belostoma oxyurum (Dufour) which was capturad carrying six fertilized eggs on its back. The location of the eggs does not belong to the pattern known for incubant males of this species. This finding is attributed to the absolute shortage of a sexual resource constituted by the male back space. Such environmental circuinstance was recorded in the field when this female was captured. The adult population from which it was taken included a hundred percent of both, gravid females and incubant males, and sex ratio was female biased though without statistical significance. The observed phenomenon has also been recorded in the Nearctic species Belostoma flumineum Say. Comparative considerations referred to bothspecies are included.Un caso de oviposición intrasexual fue detectado en una población de Belostoma oxyurum (Dufour) localizada en un limnótopo léntico de Pinamar, Provincia de Buenos Aires. El fenómeno observado es atribuido a la limitación del recurso sexual constituido por el área de postura, es decir, la superficie dorsal de los machos reproductivos. Tal circunstancia ambiental fue registrada en el campo cuando la “hembra incubante” era extraída de su habitat. La población de adultos incluía entonces, el máximo porcentaje de hembras grávidas y machos incubantes, ostentando elevados valores de fecundidad potencial y real, y un predominio, aunque no significativo, de hembras sobre machos

WHY WETLANDS?

Since the creation of Ramsar Convention on Wetlands in 1971, the term wetland has been widely and increasingly mentioned by scientists and environmental managers. During the last decades of the Twentieth Century environmental concerns due to the dramatic loss of aquatic and related habitats have made wetlands target ecosystems for their conservation and restoration. Instead of regarding them as wetlands, they were identified prior to the mid-1970s according to their typology, by numerous denominations, for example bogs, marshes, swamps, oxbow lakes, some of them constituting individual wetlands within larger wetlands like floodplains. So, why wetlands? The arrival of a single catchy term embracing a diverse constellation of aquatic and water related environments was certainly useful to know their importance relative to other kinds of ecosystems, and also to tackle their wise use. Nevertheless, the need to conserve wetland\u27s basic resources according to ecological and human demands frequently led to a misunderstanding of the actual attributes exhibited by these specific ecosystems, being some types of aquatic ecosystems which do not fit the wetland\u27s scientific definition, like rivers, deep lakes, and coral reefs, frequently considered as such. Through this presentation I aspire to analyze the term wetland in such a way to conciliate scientific knowledge, management plans, and natural resources conservation, as well as to contribute to harmonize different conceptual approaches, searching for the achievement of shared viewpoints which would, eventually, overcome the ambiguity going around the term wetland by which the epigraph\u27s question still remains.Desde la creación de la Convención Ramsar sobre Humedales en 1971, la voz humedal ha sido mencionada ampliamente y con incrementada frecuencia, tanto por científicos como por administradores ambientales. Durante las últimas décadas del Siglo XX, las preocupaciones ambientales debidas a la alarmante pérdida de humedales, hizo que muchos esfuerzos se dirigieran a su conservación y restauración. Antes de mediados de la década de 1970, estos ecosistemas no estaban referidos con el término unificador ‘humedal\u27 recibiendo, en consecuencia, numerosas denominaciones de acuerdo con su tipología, tales  como pantanos turbosos, bañados, ciénagas y lagunas semilunares, constituyendo algunos de ellos humedales individuales subsumidos en otros mayores como por ejemplo las planicies de inundación. Entonces: ¿Porqué humedales? El surgimiento de un término simple y atractivo conteniendo una diversa constelación de ambientes acuáticos y otros a ellos relacionados ha sido de utilidad para conocer su importancia, en relación con otros  cosistemas y también para adoptar su uso racional. No obstante, la necesidad de conservar los recursos básicos provistos por los humedales, de acuerdo con las demandas ecológicas y humanas ha llevado con frecuencia a interpretaciones erróneas acerca de sus verdaderos atributos, considerándose frecuentemente como humedales a determinados ambientes acuáticos que no se ajustan a su definición científica (e.g. ríos, lagos profundos y arrecifes de coral). Con esta presentación, aspiro analizar el término humedal de modo que contribuya a conciliar el conocimiento científico, los planes de manejo y conservación de los recursos naturales, y armonizar los diferentes enfoques conceptuales, en la búsqueda de lograr puntos de vista comunes que pudieran ser de utilidad para superar la ambigüedad que acompaña a la voz humedal y por la cual la pregunta del epígrafe aún persiste.  Since the creation of Ramsar Convention on Wetlands in 1971, the term wetland has been widely and increasingly mentioned by scientists and environmental managers. During the last decades of the Twentieth Century environmental concerns due to the dramatic loss of aquatic and related habitats have made wetlands target ecosystems for their conservation and restoration. Instead of regarding them as wetlands, they were identified prior to the mid-1970s according to their typology, by numerous denominations, for example bogs, marshes, swamps, oxbow lakes, some of them constituting individual wetlands within larger wetlands like floodplains. So, why wetlands? The arrival of a single catchy term embracing a diverse constellation of aquatic and water related environments was certainly useful to know their importance relative to other kinds of ecosystems, and also to tackle their wise use. Nevertheless, the need to conserve wetland\u27s basic resources according to ecological and human demands frequently led to a misunderstanding of the actual attributes exhibited by these specific ecosystems, being some types of aquatic ecosystems which do not fit the wetland\u27s scientific definition, like rivers, deep lakes, and coral reefs, frequently considered as such. Through this presentation I aspire to analyze the term wetland in such a way to conciliate scientific knowledge, management plans, and natural resources conservation, as well as to contribute to harmonize different conceptual approaches, searching for the achievement of shared viewpoints which would, eventually, overcome the ambiguity going around the term wetland by which the epigraph\u27s question still remains

The Sarcophagidae (Diptera) of the Coastline of Buenos Aires City, Argentina

Fil: Mariluis, Juan C. ANLIS Dr.C.G.Malbrán. Centro Nacional de Diagnóstico e Investigación en Endemo-Epidemias; Argentina.Fil: Schnack, Juan A. División Entomología, Museo de La Plata, Universidad Nacional de La Plata, La Plata; Argentina.Fil: Mulieri, Pablo R. ANLIS Dr.C.G.Malbrán. Centro Nacional de Diagnóstico e Investigación en Endemo-Epidemias; Argentina.Fil: Torretta, Juan P. Cátedra de Botánica Agrícola, Facultad de Agronomía, Universidad de Buenos Aires, Buenos Aires; Argentina.The flesh fly community was surveyed on the shoreline of Río de la Plata at an ecological reserve whose western border directly abuts downtown eastern Buenos Aires. Samples were taken at monthly intervals from September 2004 to August 2005. To attract the flies, dog faeces and rotten cow liver were used as bait. Overall number, species composition and sex ratio were referred to each chosen bait. Of the thirteen species captured during the sampling period, Helicobia aurescens (Townsend), Oxysarcodexia culmiforceps Dodge, Oxysarcodexia marina (Hall), Oxysarcodexia thornax (Walker), Sarcophaga (Lipoptilocnema) koehleri (Blanchard), S. (L.) lanei (Townsend) and Tricharaea (Sarcophagula) occidua (Fabricius) were recorded for the first time in Buenos Aires city. Regardless of species composition, higher number of flies were obtained on faeces. Tricharaea (S.) occidua, was highly dominant (78,35%) followed in abundance by Oxysarcodexia varia (7,82%), both species showing a strong preference for dog faeces. Microcerella muehni and Oxysarcodexia paulistanensis did not show any preference on either bait. Sex ratio was male biased for O. varia, while females were dominant for O. paulistanensis and T. (S.) occidua, and no differences were found for M. muehni. Bait's preference and sex ratio could not be estimated for the remaining species due to their low abundance

Ecología de una taxocenosis de Calliphoridae del área platense (Provincia de Buenos Aires) (Insecta, Diptera)

This paper constitutes the first approach to the knowledge of the ecology of Calliphoridae from Argentina. The selected stüdied area is a rural one located at 34°55’S and 58° W in the suburbs of Villa Elisa, Province of Buenos Aires. Samples were taken hourly from 10.15 am to 4.15 pm, every month from November 1985 to October 1986. Specimens were captured with entomological net while lying on the bait composed by cow meat. The sampling program included shaded and unshaded sites. Air temperature was recorded every hour. Results showed a remarkable heliophily for some of the recorded species. Chrysomya albiceps, Phaenicia sericata, Phaenicia purpurescens and Cochlipmyia macellaria were codominants during spring and summer, while Calliphora vicina and Calliphora nigribasis were so along the winter months. Chrysomya megacephala, Cochliomyia hominivorax,. Compsomyiops fulvierura, Paralucilia fulvinota, Phaenicia eximia, and Sarconesia chlorogaster were poorly represented for most o f the sampling dates. Sex ratio was female biased for the majority of the studied species.This paper constitutes the first approach to the knowledge of the ecology of Calliphoridae from Argentina. The selected stüdied area is a rural one located at 34°55’S and 58° W in the suburbs of Villa Elisa, Province of Buenos Aires. Samples were taken hourly from 10.15 am to 4.15 pm, every month from November 1985 to October 1986. Specimens were captured with entomological net while lying on the bait composed by cow meat. The sampling program included shaded and unshaded sites. Air temperature was recorded every hour. Results showed a remarkable heliophily for some of the recorded species. Chrysomya albiceps, Phaenicia sericata, Phaenicia purpurescens and Cochlipmyia macellaria were codominants during spring and summer, while Calliphora vicina and Calliphora nigribasis were so along the winter months. Chrysomya megacephala, Cochliomyia hominivorax,. Compsomyiops fulvierura, Paralucilia fulvinota, Phaenicia eximia, and Sarconesia chlorogaster were poorly represented for most o f the sampling dates. Sex ratio was female biased for the majority of the studied species

Estudio del pleuston y bafon de las lagunas de Chascomus y Yalca

Se estudia la mesofauna asociada a la vegetación flotante y sumergida en las lagunas del epígrafe, realizándose un análisis cuali y cuantitativo de la misma y del sustrato, así como también su variación estacional. Se describe el método utilizado en la obtención de las muestras y extracción de la mesofauna, así como también se pone de manifiesto el criterio seguido para la selección de las “asociaciones vegetales” que sirven de sustrato a la fauna en cuestión. Tres asociaciones flotantes fueron seleccionadas y se individualizaron con el nombre de la especie dominante: Ricciocarpus natans; Azolla filiculoides y Salvinia rotundi- folia; siendo dos las sumergidas: Ceratophyllum demersum y Potamogetón striatus. Se describe cada asociación respecto de su extensión, permanencia y fluctuaciones a lo largo de un año calendario, así como también se da a conocer la lista de presencias de las distintas taxias discriminadas por asociación. Se analizan los pleustontes y bafontes de cada asociación, y sus posibles relaciones interespecíficas y con el sustrato, demostrándose la existencia de especies caracterizantes en cada uno de los mismos, siendo algunas exclusivas; se analizan, además, mediante correlaciones, las relaciones predator-presa y animal sustrato en cada asociación. La aplicación del índice de diversidad específica pone de manifiesto la madurez de las distintas asociaciones flotantes consideradas y la mayor o menor influencia del sustrato como elemento morigerador de los agentes externos en relación con el ciclo anual de los componentes de su mesofauna, evidenciándose en dos de ellos un comportamiento estacional similar al del plancton. De las consideraciones de estas poblaciones y sus relaciones con el ambiente acuático se propone dividir al pleuoton en: eupleuston y hemipleuston y un extrapleuston: pseudopleuston.In the Chascomús and Yalca lagoons, the mesofauna associated with floating and submerged vegetation was studied through a cualitative- quantitative analysis which also included the substratum and the seasonal variations. After a description of the sampling technique employed and the method of extraction of mesofauna, there follow-s an explanation of the criterium adopted in selecting the “vegetable associations’’ which act as a subtratum for the analysed fauna. Three floating associations each named after the dominant species, were selected: Ricciocarpus natans, Azolla filiculoides and Salvinia rotundifolia; two submerged associations were also studied: Ceratophillum demersum and Potamogetón stria- tus. Each association is described in relation to extensión, permanency and fluctuation through a whole calender year, and a list of presences of different taxias discriminated by association is presented. In each association an analysis of the “pleustontes” and ‘ bafontes” and of their interespecific relations as well as those related to the substratum, which have shown the existence of species characteristic of each substratum, some of them exclusive. Furthermore, through correlations, each association was determined the relationships predator-prey and animal-substratum. The application of the “Índex of specific diversity” has shown the maturity of the different floating associations and the greater or lesser influence of the substratum as a moderating element of external agents related to annual cycle of the constituents in the meso- fauna. In two of them a seasonal behavior, similar to that of plankton, has been evinced. From a consideration of these populations and their relation-ships to the acqueos environmets, it is proposed to divide pleuston into: eupleuston, hemipleuston and a extrapleuston: pseudopleuston

Estudio ecológico sobre una población domiciliaria de Triatoma infestans klug de la Provincia Biogeográfica Chaqueña

A typical country house located in an endemic chagasic area (La Batea, Córdoba,Argentina), was completely demolished on order lo look primarily upon the numerical level achieved by triatomines population as well as to establish distribution patterns and habitat preference. Furthermore, some emergent population parameters and attributes were studied, such as density, fecundity, age, structure and sex ratio. Triatoma infestans was the only well established resident population species in thedomestic boundary, even though very few individuals belonging to the congeneric T. guasayana were detected in coexistence with the former species. A low degree of egg's parasitism by microhymenoptera was found. Ninety six sample units were taken during demolition in the bedroom’s walls in ordor to count number of eggs per unit and calculation of a dispersión index. Three removal methods for relative estimates were tested before the demolition took place, which were compared with values obtained from direct counting while demolition. Our results show a high degree of crowding and different habitat preference fornymphs, adults and oviposition microhabitats. T. infestaos population seems to be still well below the carrying capacity of the environment. The use of a feeding index, to calculate number of bites per day and person, required to satisfy “vinchucas” feeding needs, alowed us to postulate T. infestaos domestic population haven't yet developed an intensive intraspecific competition. This is so because the studied population would be undergoing an expansión stage of growing.A typical country house located in an endemic chagasic area (La Batea, Córdoba,Argentina), was completely demolished on order lo look primarily upon the numerical level achieved by triatomines population as well as to establish distribution patterns and habitat preference. Furthermore, some emergent population parameters and attributes were studied, such as density, fecundity, age, structure and sex ratio. Triatoma infestans was the only well established resident population species in thedomestic boundary, even though very few individuals belonging to the congeneric T. guasayana were detected in coexistence with the former species. A low degree of egg's parasitism by microhymenoptera was found. Ninety six sample units were taken during demolition in the bedroom’s walls in ordor to count number of eggs per unit and calculation of a dispersión index. Three removal methods for relative estimates were tested before the demolition took place, which were compared with values obtained from direct counting while demolition. Our results show a high degree of crowding and different habitat preference fornymphs, adults and oviposition microhabitats. T. infestaos population seems to be still well below the carrying capacity of the environment. The use of a feeding index, to calculate number of bites per day and person, required to satisfy “vinchucas” feeding needs, alowed us to postulate T. infestaos domestic population haven't yet developed an intensive intraspecific competition. This is so because the studied population would be undergoing an expansión stage of growing

Q-dependence of the inelastic neutron scattering cross section for molecular spin clusters with high molecular symmetry

For powder samples of polynuclear metal complexes the dependence of the inelastic neutron scattering intensity on the momentum transfer Q is known to be described by a combination of so called interference terms. They reflect the interplay between the geometrical structure of the compound and the spatial properties of the wave functions involved in the transition. In this work, it is shown that the Q-dependence is strongly interrelated with the molecular symmetry of molecular nanomagnets, and, if the molecular symmetry is high enough, is actually completely determined by it. A general formalism connecting spatial symmetry and interference terms is developed. The arguments are detailed for cyclic spin clusters, as experimentally realized by e.g. the octanuclear molecular wheel Cr8, and the star like tetranuclear cluster Fe4.Comment: 8 pages, 1 figures, REVTEX

Calculating the energy spectra of magnetic molecules: application of real- and spin-space symmetries

The determination of the energy spectra of small spin systems as for instance given by magnetic molecules is a demanding numerical problem. In this work we review numerical approaches to diagonalize the Heisenberg Hamiltonian that employ symmetries; in particular we focus on the spin-rotational symmetry SU(2) in combination with point-group symmetries. With these methods one is able to block-diagonalize the Hamiltonian and thus to treat spin systems of unprecedented size. In addition it provides a spectroscopic labeling by irreducible representations that is helpful when interpreting transitions induced by Electron Paramagnetic Resonance (EPR), Nuclear Magnetic Resonance (NMR) or Inelastic Neutron Scattering (INS). It is our aim to provide the reader with detailed knowledge on how to set up such a diagonalization scheme.Comment: 29 pages, many figure