1,720,962 research outputs found
Behavioural responses of the colonial sea squirt botrylloides violaceus oka to suspended food micro‐ particles in laboratory cultures
Full text linkViolet sea squirts are noteworthy model organisms, because they provide insights into various physiologic processes, including cell senescence, ageing, apoptosis and allorecognition. Consequently, their culture is critical to permit experimental studies. Most papers refer to short periods of rearing using various feeds, both living and conserved, missing a formal justification for their use or indications of their actual nutritional value. Here, we use two behavioural responses— the percentage of open siphons and the frequency of zooid contractions—as compared to the abundance of suspended microparticles during feeding tests, to identify feeds able to promote filter-feeding. The results will enable to formulate compound diets that maximise positive physiological responses. Our tests demonstrated that plant items, such as dry microalgae and cyanobacteria (Arthrospira platensis, commercially known as Spirulina), along with living planktonic Haptophyta (Isochrysis galbana), trigger clear positive reactions, represented by a higher frequency of zooid contractions and larger proportions of open siphons. These responses correspond to decreases in the concentrations of suspended microparticles during the experiment and indicate higher filter-feeding activity. In contrast, feeds commonly administered to colonies, such as milk powder, dried eggs and artificial plankton, triggered negative behavioural responses, and their intake was lower during the feeding trials
Assessing the ecotoxicity of copper and polycyclic aromatic hydrocarbons: Comparison of effects on Paracentrotus lividus and Botryllus schlosseri, as alternative bioassay methods
Full text linkAdult sea urchins and their embryos are ideal targets to investigate the medium- and long-term effects of various toxic agents, such as organic and inorganic pollutants, to forecast and mitigate their environmental effects. Similarly, small colonial tunicates such as Botryllid ascidians may reveal acute toxicity processes and permit quick responses for the management of contaminants impacting coastal waters, to preserve the functional integrity of marine ecosystems. This investigation compares the functional responses of two model invertebrates, the sea urchin Paracentrotus lividus and the sea squirt Botryllus schlosseri, to chronic and acute exposures to organic and inorganic toxic agents. Such heavy metals as copper produce both acute and chronic effects on marine biota, while polycyclic aromatic hydrocarbons (PAHs) mainly produce chronic effects at the concentrations ordinarily measured in marine coastal waters. Both models were tested over a range of concentrations of copper and PAHs. Copper triggered a clear effect in both species, producing a delay in the embryo development of P. lividus and a rapid death of sea squirts. B. schlosseri was less sensitive to PAHs than P. lividus. The results on both species may synergistically contribute to assess the toxicity of organic and inorganic compounds at various concentrations and different physiologic levels
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Single and combined effects of two trace elements (Cd and Cu) on the asexual reproduction of Aurelia sp. polyps
No full textJellyfish blooms are an increasingly common event in our seas. Occurring via polyps’ asexual reproduction induced by human stresses, they represent a hazard for ecosystems equilibrium. The aim of this study is to highlight polyps underrated role during these events by investigating cadmium (Cd) and copper (Cu) exposure on Aurelia sp. polyps under laboratory conditions. Cd treatments seemed to not cause toxic effects on polyps up to 1000 μg/L, while 150 μg/L of Cu resulted above polyps’ tolerance for the metal, leading to a 62% of mortality and inducing the regression-regeneration cycle of polyps. Surprisingly, combined treatments of Cd and Cu had lesser effects, working antagonistically. Our results show how, in natural conditions, the chosen concentrations and combinations could not represent a hazard for polyps, instead, they stimulate the asexual reproduction, supporting the hormesis and, through jellyfish blooms, altering the Good Environmental Status aimed by the Marine Strategy Framework Directive
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
The detection of specific prey cues triggers distinct predatory behaviour in Aurelia coerulea polyps (Cnidaria: scyphozoa)
No full textPredatory behaviour of cnidarian polyps is poorly described, although their tentacles are equipped with thousands of stinging cells to capture preys. The predatory action is elicited by the tactile stimulation of the tentacles due to the physical encounter between the prey and the polyp. Micro-predation involves low-energetic movements of tentacles and fast ingestion of more small prey simultaneously. In contrast, macro-predation includes expensive actions of the whole body, with a duration of up to 15 min to ingest a large prey. When polyps are spatially aggregated, they can engage in a collective predation in which they first cooperate and then compete for the division of the prey. We hypothesized that an additional stimulation represented by specific prey-produced cues could serve as an additional trigger for predation. We provided three diets (1 large prey, 2 small preys) to groups of five polyps and later stimulated them with prey homogenates as prey-produced cues. Behaviours were first observed and categorized and later used to evaluate feeding activity, together with tentacle contractions and rapid movements. Polyps fed with the large prey and later stimulated with its homogenate showed 2.2 to 6.5 times higher number of tentacle contractions and rapid movements and 55.7% higher occurrence of the category "active feeding" in comparison to all the other combinations of prey/prey cue, resembling the predatory action necessary for macro-predation. These outcomes suggest the ability of polyps to discern the prey cues in the water medium and to modify their behaviour accordingly. Cnidarians are metazoans lacking a central nervous system; however, they are able to detect the presence of prey in their surroundings, process this information and adjust their behaviour accordingly, maximizing the benefits of predation
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
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