Proximate and ultimate causes of signal diversity in the electric fish Gymnotus

A complete understanding of animal signal evolution necessitates analyses of both the proximate (e. g. anatomical and physiological) mechanisms of signal generation and reception, and the ultimate (i.e. evolutionary) mechanisms underlying adaptation and diversification. Here we summarize the results of a synthetic study of electric diversity in the species-rich neotropical electric fish genus Gymnotus. Our study integrates two research directions. The first examines the proximate causes of diversity in the electric organ discharge (EOD) - which is the carrier of both the communication and electrolocation signal of electric fishes - via descriptions of the intrinsic properties of electrocytes, electrocyte innervation, electric organ anatomy and the neural coordination of the discharge (among other parameters). The second seeks to understand the ultimate causes of signal diversity -via a continent-wide survey of species diversity, species-level phylogenetic reconstructions and field-recorded head-to-tail EOD (ht-EOD) waveforms (a common procedure for characterizing the communication component of electric fish EODs). At the proximate level, a comparative morpho-functional survey of electric organ anatomy and the electromotive force pattern of the EOD for 11 species (representing most major clades) revealed four distinct groups of species, each corresponding to a discrete area of the phylogeny of the genus and to a distinct type of ht-EOD waveform. At the ultimate level, our analyses (which emphasize the ht-EOD) allowed us to conclude that selective forces from the abiotic environment have had minimal impact on the communication component of the EOD. In contrast, selective forces of a biotic nature - imposed by electroreceptive predators, reproductive interference from heterospecific congeners, and sexual selection - may be important sources of diversifying selection on Gymnotus signals

Electric organ discharge diversity in the genus Gymnotus: anatomo-functional groups and electrogenic mechanisms

Previous studies describe six factors accounting for interspecific diversity of electric organ discharge (EOD) waveforms in Gymnotus. At the cellular level, three factors determine the locally generated waveforms: (1) electrocyte geometry and channel repertoire; (2) the localization of synaptic contacts on electrocyte surfaces; and (3) electric activity of electromotor axons preceding the discharge of electrocytes. At the organismic level, three factors determine the integration of the EOD as a behavioral unit: (4) the distribution of different types of electrocytes and specialized passive tissue forming the electric organ (EO); (5) the neural mechanisms of electrocyte discharge coordination; and (6) post-effector mechanisms. Here, we reconfirm the importance of the first five of these factors based on comparative studies of a wider diversity of Gymnotus than previously investigated. Additionally, we report a hitherto unseen aspect of EOD diversity in Gymnotus. The central region of the EO (which has the largest weight on the conspecific-received field) usually exhibits a negative-positive-negative pattern where the delay between the early negative and positive peaks (determined by neural coordination mechanisms) matches the delay between the positive and late negative peaks (determined by electrocyte responsiveness). Because delays between peaks typically determine the peak power frequency, this matching implies a co-evolution of neural and myogenic coordination mechanisms in determining the spectral specificity of the intraspecific communication channel. Finally, we define four functional species groups based on EO/EOD structure. The first three exhibit a heterogeneous EO in which doubly innervated electrocytes are responsible for a main triphasic complex. Group I species exhibit a characteristic cephalic extension of the EO. Group II species exhibit an early positive component of putative neural origin, and strong EO auto-excitability. Group III species exhibit an early, slow, negative wave of abdominal origin, and variation in EO auto-excitability. Representatives of Group IV generate a unique waveform comprising a main positive peak followed by a small, load-dependent negative component

Una estrategia integradora en la enseñanza de las ciencias naturales: aprendiendo sobre un producto regional

En este trabajo presentamos una estrategia basada en el modelo integrativo, el marco Ciencia–Tecnología–Sociedad (CTS) y los intereses de los alumnos. El bajo interés mostrado por las ciencias nos lleva a indagar sobre una propuesta que logre motivar lo suficiente para alcanzar un aprendizaje significativo, integrando contenidos conceptuales correspondientes a distintos espacios curriculares. El tema que trabajamos para llegar a integrar y relacionar Ciencia, Tecnología y Sociedad fue los productos regionales y a partir de un diagnóstico realizado a los alumnos seleccionamos la elaboración de vino y contenidos vinculados con éste. Realizamos una aplicación piloto con una muestra de estudiantes de segundo año de polimodal (16 a 18 años) y los resultados logrados fueron satisfactorios.Palabras claves: enseñanza; intereses; Ciencia-Tecnología-Sociedad; modelo integrativo.An integration strategy in the education of the natural sciences: learning on a regional productIn this work we present a strategy based on an integrated model, the framework Science-Technology- Society (CTS) and the students’ interests. The low interest shown by students towards the sciences leads us to search for a proposal which motivates enough so as to learn meaningfully, integrating conceptual contents corresponding to different syllabuses. The topic we worked with in order to integrate Science, Technology and Society was regional products and from a diagnostic test made by students we selected the elaboration of wine and the contents related to it. We made a pilot application with a sample of students attending second year of Polimodal level (16 to 18 years old) and the results obtained were satisfactory.Keywords: teaching; interests; Science-Technology-Society; integrated model

Los indios vienen marchando : Experiencias en talleres infantiles de arqueología

El programa de difusión científica "De vacaciones con los dinosaurios" se inició en febrero de 1990, con la finalidad de integrar el Museo de Ciencias Naturales de La Plata con su comunidad. A través de la iniciativa de la Secretaria de Extensión Universitaria de la Facultad de Cs. Naturales y Museo se nos dió la oportunidad de crear los Talleres Infantiles de Arqueología cuyos objetivos giraron en torno de dos aspectos fundamentales: -introducir al niño en el estudio y comprensión del desarrollo cultural del pasado a través de sus restos materiales, que constituyen el patrimonio de su comunidad. -fomentar su interés y lograr su participación activa en la valorización y preservación del patrimonio arqueológico.Facultad de Ciencias Naturales y Muse

21 de setiembre: día de la ciencia y la técnica

Con motivo del 3O aniversario de la instauración del 21 de setiembre como día de la Ciencia y la Técnica en la Provincia de Buenos Aires, la CIC le ha solicitado a un grupo selecto de científicos, su opinión sobre aspectos esenciales del quehacer científico y tecnológico. El presente texto contiene los siguientes trabajos: - Consideraciones acerca de la investigacion técnico-científica sobre materiales, por Eduardo R. Abril. - Ciencia y tecnología de alimentos, por Pedro Cattáneo - Ciencia y tecnología en química orgánica por Venancio Deulofeu. - Ciencia y tecnología - recursos humanos por Ernesto E. Galloni. - Discurso de apertura de la reunion sobre ciencia y tecnologia realizada en Mar del Plata del 6 al 8 de julio de 1978 por Luis F. Leloir. - Incidencia de la investigación en el desarrollo de la metalurgia por Roberto F. Recoder. - Importancia de la investigación matemática en la sociedad contemporánea por Luis A. Santaló. - La investigación en fisicoquímica y su proyección en el desarrollo científico y tecnológico por Hans J. Schumacher

Outbreak of dermatofilosis in calves

La Dermatofilosis es una enfermedad aguda o crónica de la epidermis, caracterizada por lesiones inflamatorias, exudativas, sangrantes con formación de costras, causada por una bacteria, Dermathophilus congolensis. Afecta a bovinos, ovinos, equinos, caprinos, animales salvajes y al hombre considerandose una zoonosis menor. El presente trabajo comunica un brote causado por Dermathophilus congolensis en terneros de tambo. Los animales afectados presentaban lesiones en piel, no pruriginosas, estas eran al comienzo sangrantes y dolorosas, terminando en costras las cuales se desprendían junto a los pelos quedando una superficie lisa alopécica. Las lesiones comenzaron en la cara y continuaron por el lomo y miembros posteriores. Se remitieron al laboratorio costras y exudados. Las muestras se procesaron para diagnóstico de dermatofitos y dermatofilosis. Los resultados dieron negativos para dermatofitos y positivos para Dermatophilus congolensis. En base a la sintomatología clínica y a los hallazgos de laboratorio se llegó al diagnóstico de Dermatophilus congolensis.Dermatophylosis is an acute or chronic epidermal disease, characterized by inflammation, exudation, bleeding injuries with scab formation, caused by a bacterium: Dermathophilus congolensis. The disease it causes is consider a minor zoonosis which affects bovines, ovines, equines, goats, wild animals and human beings. This work informs a bud, in a bull calves inn, caused by Dermathophilus congolensis. The affected animals displayed skin non itching injuries which were firstly bleeding and painful, and then scabby, the scabs were given off with hairs to render alopecia. The injuries began in the face and continued in the back and limbs. Scabs and exudates were sent to the laboratory. The samples were processed for diagnosis of dermatophytes and dermatophylosis. The results were negative for dermatophytes and positve for Dermatophilus congolensis. On the basis of the clinical sintomatology and the laboratory findings the diagnosis of Dermatophilus congoliensis came up.Facultad de Ciencias Veterinaria

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Summary A complete understanding of animal signal evolution necessitates analyses of both the proximate (e.g. anatomical and physiological) mechanisms of signal generation and reception, and the ultimate (i.e. evolutionary) mechanisms underlying adaptation and diversification. Here we summarize the results of a synthetic study of electric diversity in the species-rich neotropical electric fish genus Gymnotus. Our study integrates two research directions. The first examines the proximate causes of diversity in the electric organ discharge (EOD) -which is the carrier of both the communication and electrolocation signal of electric fishes -via descriptions of the intrinsic properties of electrocytes, electrocyte innervation, electric organ anatomy and the neural coordination of the discharge (among other parameters). The second seeks to understand the ultimate causes of signal diversity -via a continent-wide survey of species diversity, species-level phylogenetic reconstructions and field-recorded headto-tail EOD (ht-EOD) waveforms (a common procedure for characterizing the communication component of electric fish EODs). At the proximate level, a comparative morpho-functional survey of electric organ anatomy and the electromotive force pattern of the EOD for 11 species (representing most major clades) revealed four distinct groups of species, each corresponding to a discrete area of the phylogeny of the genus and to a distinct type of ht-EOD waveform. At the ultimate level, our analyses (which emphasize the ht-EOD) allowed us to conclude that selective forces from the abiotic environment have had minimal impact on the communication component of the EOD. In contrast, selective forces of a biotic nature -imposed by electroreceptive predators, reproductive interference from heterospecific congeners, and sexual selection -may be important sources of diversifying selection on Gymnotus signals