Predation on cephalopods by Pygoscelis papua and Arctocephalus gazelle at south Orkney Islands

The cephalopod diet of the gentoo penguin, Pygoscelis papua and the Ant− arctic fur seal, Arctocephalus gazella was comparatively analyzed at Laurie Island, South Orkney Islands. A total of 125 stomach samples were collected by the water off−loading method from gentoo penguins during the autumns of 1993, 1995 and 1996, and 39 fur seal scats were collected from mid March to April 1988. Cephalopods preyed upon by gentoo penguins were represented by 1974 beaks (1628 lower, 346 upper) which occurred in 50.4% of the samples. Lower beaks identified belonged exclusively to the squid Psychroteuthis glacialis. The mean lower rostral length (LRL) of these beaks was 1.1 mm (range 0.4– 1.8 mm). From the Antarctic fur seal scats 103 beaks (41 lower, 62 upper) were removed from 60.6% of scats which contained prey remains. The cephalopod species identified were Slosarczykovia circumantarctica and P. glacialis which constituted 78.8% and 21.1% in terms of numbers, respectively. The mean lower rostral length for S. circumantarctica was 2.7 mm (range 2.0–3.5 mm), while that of P. glacialis was 1.6 mm (range 1.0–2.5 mm). The foraging behaviour of the two top predators was analyzed and discussed according to the composition and size of their cephalopod prey

Bloqueo y ensombrecimiento en un grupo de vertebrados filogenéticamente antiguo: los anfibios

En este artículo se describe el estudio de los fenómenos de bloqueo y ensombrecimiento en una tarea de aprendizaje espacial en un anfibio, el sapo terrestre Rhinella arenarum. Ambos fenómenos de aprendizaje, ampliamente observados en otras clases de vertebrados, se describen por primera vez en un grupo con un cerebro filogenéticamente antiguo, como es el caso de los anfibios. Específicamente, se observó durante el aprendizaje espacial: (1) bloqueo entre claves visuales asociadas a una meta, y (2) ensombrecimiento de una clave visual lejana por la presencia de una clave cercana. Este hecho permite sentar un precedente para estudiar posteriormente los mecanismos biológicos que rigen el aprendizaje espacial, en búsqueda de patrones funcionales comunes con otras clases de vertebrados, potencialmente presentes en un ancestro común.DOI: http://dx.doi.org/10.14349/rlp.v45i2.113

The Measurement Process in Local Quantum Theory and the EPR Paradox

We describe in a qualitative way a possible picture of the Measurement Process in Quantum Mechanics, which takes into account: 1. the finite and non zero time duration T of the interaction between the observed system and the microscopic part of the measurement apparatus; 2. the finite space size R of that apparatus; 3. the fact that the macroscopic part of the measurement apparatus, having the role of amplifying the effect of that interaction to a macroscopic scale, is composed by a very large but finite number N of particles. The conventional picture of the measurement, as an instantaneous action turning a pure state into a mixture, arises only in the limit in which N and R tend to infinity, and T tends to 0. We sketch here a proposed scheme, which still ought to be made mathematically precise in order to analyse its implications and to test it in specific models, where we argue that in Quantum Field Theory this picture should apply to the unique time evolution expressing the dynamics of a given theory, and should comply with the Principle of Locality. We comment on the Einstein Podolski Rosen thought experiment (partly modifying the discussion on this point in an earlier version of this note), reformulated here only in terms of local observables (rather than global ones, as one particle or polarisation observables). The local picture of the measurement process helps to make it clear that there is no conflict with the Principle of Locality.Comment: 18 page

Quantum measurement as driven phase transition: An exactly solvable model

A model of quantum measurement is proposed, which aims to describe statistical mechanical aspects of this phenomenon, starting from a purely Hamiltonian formulation. The macroscopic measurement apparatus is modeled as an ideal Bose gas, the order parameter of which, that is, the amplitude of the condensate, is the pointer variable. It is shown that properties of irreversibility and ergodicity breaking, which are inherent in the model apparatus, ensure the appearance of definite results of the measurement, and provide a dynamical realization of wave-function reduction or collapse. The measurement process takes place in two steps: First, the reduction of the state of the tested system occurs over a time of order $\hbar/(TN^{1/4})$, where $T$ is the temperature of the apparatus, and $N$ is the number of its degrees of freedom. This decoherence process is governed by the apparatus-system interaction. During the second step classical correlations are established between the apparatus and the tested system over the much longer time-scale of equilibration of the apparatus. The influence of the parameters of the model on non-ideality of the measurement is discussed. Schr\"{o}dinger kittens, EPR setups and information transfer are analyzed.Comment: 35 pages revte

The effects of related experiments

The effects of the experiment itself upon the obtained results and, especially, the influence of a large number of experiments are extensively discussed in the literature. We show that the important factor that stands at the basis of these effects is that the involved experiments are related and not independent and detached from each other. This relationship takes, as shown here, different forms for different situations and is found in entirely different physical regimes such as the quantum and classical ones.Comment: 27 pages, 6 figures, 1 table. One figure removed. Some former text has been rewritten in compact and clearer way. Also the title change

Trichinella spiralis natural infection in Otaria flasvecens from Patagonia, Argentina

Fil: Pasqualetti, Mariana I. Universidad de Buenos Aires, Facultad de Ciencias Veterinarias, Cátedra de Parasitología y Enfermedades Parasitarias; ArgentinaFil: Pasqualetti, Mariana I. Instituto de Investigaciones en Producción Animal (INPA); ArgentinaFil: Pasqualetti, Mariana I. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Fariña, Fernando A. Universidad de Buenos Aires, Facultad de Ciencias Veterinarias, Cátedra de Parasitología y Enfermedades Parasitarias; ArgentinaFil: Fariña, Fernando A. Instituto de Investigaciones en Producción Animal (INPA); ArgentinaFil: Fariña, Fernando A. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Krivokapich, Silvio J. Administración Nacional de Laboratorios e Institutos de Salud "Dr. Carlos G. Malbrán"; ArgentinaFil: Gatti, Genoveva M. Administración Nacional de Laboratorios e Institutos de Salud "Dr. Carlos G. Malbrán"; ArgentinaFil: Daneri, Gustavo A. Laboratorio de Sistemática, Anatomía y Bioecología de Mamíferos Marinos, Division Mastozoología, Museo Argentino de CienciasNaturales,“Bernardino Rivadavia”; ArgentinaFil: Varela, Esperanza A. Laboratorio de Sistemática, Anatomía y Bioecología de Mamíferos Marinos, Division Mastozoología, Museo Argentino de CienciasNaturales,“Bernardino Rivadavia”; ArgentinaFil: Lucero, Sergio. Laboratorio de Sistemática, Anatomía y Bioecología de Mamíferos Marinos, Division Mastozoología, Museo Argentino de CienciasNaturales,“Bernardino Rivadavia”; ArgentinaFil: Ercole, Mariano E. Universidad de Buenos Aires, Facultad de Ciencias Veterinarias,Cátedra de Parasitología y Enfermedades Parasitarias; ArgentinaFil: Bessi, Clara. Universidad de Buenos Aires, Facultad de Ciencias Veterinarias,Cátedra de Parasitología y Enfermedades Parasitarias; ArgentinaFil: Bessi, Clara. Instituto de Investigaciones en Producción Animal (INPA); ArgentinaFil: Bessi, Clara. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Winter, Marina. Universidad Nacional de Río Negro. Sede Atlántica; ArgentinaFil: Winter, Marina. Centro de Investigación y Transferencia Río Negro; ArgentinaFil: Ribicich, Mabel M. Instituto de Investigaciones en Producción Animal (INPA); ArgentinaFil: Ribicich, Mabel M. Universidad de Buenos Aires. Facultad de Ciencias Veterinarias. Cátedra de Parasitología y Enfermedades Parasitarias; ArgentinaFil: Ribicich, Mabel M. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaIn Argentina trichinellosis is an endemic disease representing an important risk for human health due to its high rates of morbidity, mainly transmitted by the consumption of raw or undercooked pork. Nevertheless, the discovery of new Trichinella species have led to a change in the study of the epidemiology of the disease with the addition of new sources of infection. Moreover, Trichinella infection has been detected in a wide range of marine mammals around the world. Until the present time, Trichinella spp. infection has not been detected in marine mammals of South America. Four South American sea lions were found dead in the rookeries of Caleta de los Loros (Lat. 41° 00′ S; 64° 12′ W; n = 1), Promontorio Belén (Lat. 41° 09′ S; Long. 63° 48′ O; n = 1) and Punta Bermeja (Lat. 41° 09′ S; Long. 63° 09′ O; n = 2) in Rio Negro, Argentina. Muscle samples were taken from the tongue and diaphragm and were stored at 4 °C until examination at the Parasitology Laboratory of the Facultad de Ciencias Veterinarias, Universidad de Buenos Aires. The total muscle samples from each animal were analyzed by artificial digestión. Identification at the species level was made by nested multiplex chain reaction (nested multiplex PCR) based on nuclear ribosomal DNA sequences, using six pair of primers. Trichinella spp. larvae were found in one of the four South American sea lions. Based on their morphology, the recovered larvae were suggestive of Trichinella spp. Trichinella larvae generated a fragment of 173 bp corresponding to T. spiralis expansion segment V (ESV) region of the ribosomal DNA. This is the first report of a Trichinella species infecting marine mammals from South America. The inclusion of Otaria flavescens in the wide range of Trichinella hosts adds new questions to the epidemiology of Trichinella in marine animals. We thank the Secretaría de Medio Ambiente y Desarrollo Sustentable (SAyDS) of Río Negro Province for giving us permission to get sample from the rookeries. This work was supported by Universidad de Buenos Aires, Secretaria de Ciencia y Técnica Subsidio UBACyT20020130100336BA and Ministerio de Ciencia y Tecnología, FONCyT Subsidio PICT-2015-235

Updated revision of the marine mammals collection housed at the Museo Argentino de Ciencias Naturales "Bernardino Rivadavia" (Buenos Aires, Argentina)

Se realizó una revisión de los ejemplares de la Colección de Mamíferos Marinos del Museo Argentino de Ciencias Naturales "Bernardino Rivadavia". La misma indicó que del total de ejemplares catalogados (n=378), el 56.9% corresponde a Cetacea mientras que el 43.1% restante corresponde a Pinnipedia. Dentro de Cetacea la familia más representada es Delphinidae y el género con más ejemplares, Pontoporia (Pontoporidae); se reportan además, en forma complementaria, tres ejemplares tipo que no fueron listados en un trabajo previo. Dentro de los Pinnipedia, la familia mejor representada es Otariidae y el género con mayor número de ejemplares, Otaria.A thorough revision of the specimens housed at the Marine Mammals collection of the Museo Argentino de Ciencias Naturales "Bernardino Rivadavia" indicated that 56.9% (n=378), of the total number of specimens catalogued, belongs to Cetacea and the remainder (43.1%) to Pinnipedia. Among Cetacea, Delphinidae is the best represented family, whereas Pontoporia (Pontoporidae) is the genus which comprises the major number of specimens. Furthermore, we report three type specimens which were not cited in a previous work. As regards to Pinnipedia, the best represented family corresponds to Otariidae, being Otaria the genus with the highest number of specimens.Fil: Varela, Esperanza Amalia. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Museo Argentino de Ciencias Naturales; ArgentinaFil: Daneri, Gustavo Adolfo. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Museo Argentino de Ciencias Naturales; ArgentinaFil: Viola, M. Natalia Paso . Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Museo Argentino de Ciencias Naturales; ArgentinaFil: Negri, Maria Fernanda. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Museo Argentino de Ciencias Naturales; ArgentinaFil: Di Martino, Cecilia C.. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Museo Argentino de Ciencias Naturales; ArgentinaFil: Harrington, Ana. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Museo Argentino de Ciencias Naturales; ArgentinaFil: Montiel, Ricardo Alberto. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Museo Argentino de Ciencias Naturales; ArgentinaFil: Zambrana, Mercedes M.. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Museo Argentino de Ciencias Naturales; ArgentinaFil: Bustos, Raimundo Lucas. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Museo Argentino de Ciencias Naturales; ArgentinaFil: Vaccaro, Olga Beatriz. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Museo Argentino de Ciencias Naturales; Argentin

Fish prey of Weddell seals, <i>Leptonychotes weddellii</i>, at Hope Bay, Antarctic Peninsula, during the late summer

The study of the feeding habits of Weddell seals, Leptonychotes weddellii, in the area of west Antarctic Peninsula is essential to understand the role they play in the marine food webs, especially considering that this is one of the regions most affected by climate change. With the aim of detecting temporal changes in the fish predation pattern of seals, a total of 217 scats were collected at Hope Bay, during three consecutive summers (2003, 2004 and 2005). The family Nototheniidae comprised over 80% in numbers of fish preyed by seals. The Antarctic silverfish, Pleuragramma antarctica, was, by far, the most frequent and abundant prey species with a mean percentage frequency of occurrence of 48.7% and representing in average 52.1% in numbers of the fish consumed by seals. Other fish species of lesser importance were the nototheniids Trematomus newnesi, Lepidonotothen larseni, Gobionotothen gibberifrons and the channichthyid Chionodraco rastrospinosus. Temporal variation was observed not only in the relative proportions of the different fish prey taxa but also in the sizes of the dominant prey, P. antarctica. Given the high trophic vulnerability of this species to changes in abiotic factors and food web structure and dynamics, a possible influence of El Nino Southern Oscillation events of 2002–2003 and 2004–2005 should not be discarded. Moreover, special attention should be addressed to its population status, distribution and spatial/temporal availability as prey resource of upper trophic level consumers such as L. weddellii which largely depend on P. antarctica.Facultad de Ciencias Naturales y Muse

Turbulence and hypoxia contribute to dense biological scattering layers in a Patagonian fjord system

The aggregation of plankton species along fjords can be linked to physical properties and processes such as stratification, turbulence and oxygen concentration. The goal of this study is to determine how water column properties and turbulent mixing affect the horizontal and vertical distributions of macrozooplankton along the only northern Patagonian fjord known to date, where hypoxic conditions occur in the water column. Acoustic Doppler current profiler moorings, scientific echo-sounder transects and in situ plankton abundance measurements were used to study macrozooplankton assemblages and migration patterns along Puyuhuapi Fjord and Jacaf Channel in Chilean Patagonia. The dissipation of turbulent kinetic energy was quantified through vertical microstructure profiles collected throughout time in areas with high macrozooplankton concentrations. The acoustic records and in situ macrozooplankton data revealed diel vertical migrations (DVM) of siphonophores, chaetognaths and euphausiids. In particular, a dense biological backscattering layer was observed along Puyuhuapi Fjord between the surface and the top of the hypoxic boundary layer ( ∼ 100&thinsp;m), which limited the vertical distribution of most macrozooplankton and their DVM, generating a significant reduction of habitat. Aggregations of macrozooplankton and fishes were most abundant around a submarine sill in Jacaf Channel. In this location macrozooplankton were distributed throughout the water column (0 to  ∼ 200&thinsp;m), with no evidence of a hypoxic boundary due to the intense mixing near the sill. In particular, turbulence measurements taken near the sill indicated high dissipation rates of turbulent kinetic energy (ε ∼ 10−5&thinsp;W&thinsp;kg−1) and vertical diapycnal eddy diffusivity (Kρ ∼ 10−3&thinsp;m2&thinsp;s−1). The elevated vertical mixing ensures that the water column is well oxygenated (3–6&thinsp;mL&thinsp;L−1, 60&thinsp;%–80&thinsp;% saturation), creating a suitable environment for macrozooplankton and fish aggregations. Turbulence induced by tidal flow over the sill apparently enhances the interchange of nutrients and oxygen concentrations with the surface layer, creating a productive environment for many marine species, where the prey–predator relationship might be favored.</p