1,721,016 research outputs found
Reproductive cycle and sex hormones in the feather star Antedon mediterranea
No full textIn the recent decades, the importance of echinoderm endocrinology has increased because of the use of echinoderms as models for aquatic ecotoxicology and due to their evolutionary closeness to chordates. Nonetheless, apart from asteroids and echinoids, there is limited information available on the reproductive physiology of echinoderm groups, particularly crinoids. This investigation focused on the reproductive cycle of Antedon mediterranea and was intended to elucidate the reproductive pattern occurring in this species. We observed spawning throughout the year, though there were preferential months. The sex ratio was biased in favour of females. Possible correlations between steroid level variations and gonad maturity were also evaluated: testosterone and 17β-estradiol mean levels were higher at the beginning of gametogenesis and during vitellogenesis, suggesting their possible involvement in nutrient supply for developing gametes. This study should stimulate further work on steroids and steroid derivatives as ancestral hormones characteristic of the animal kingdom
Potenzialita’ rigenerative nelle larve degli Echinodermi : studio preliminare nel crinoide Antedon mediterranea
No full text
The elusive role of L-glutamate as an echinoderm neurotransmitter: evidence for its involvement in the control of crinoid arm muscles
No full textAlthough l-glutamate is the most widespread excitatory neurotransmitter in vertebrate and invertebrate nervous systems, there is only sparse evidence that it has this role in echinoderms. Following our previous finding that l-glutamate is widely distributed in the arms of the featherstar (crinoid echinoderm) Antedon mediterranea and initiates arm autotomy (defensive detachment), we now provide evidence of glutamatergic involvement in the control of the arm muscles of the same species using immunocytochemical and physiological methods. Immunofluorescence and immunoenzymatic techniques, which employed the same polyclonal antibody against l-glutamate conjugated to glutaraldehyde, revealed a high level of glutamate-like reactivity in the brachial muscles. By recording the mechanical responses of isolated arm pieces, we found that l-glutamate, l-aspartate and elevated [K(+)](o) induced rhythmic muscle contractions, while glycine, γ-aminobutyric acid, adrenaline and acetylcholine had either no, or no consistent, effect. The frequency and duration of the dominant component of the rhythmic contractions indicated that these may be responsible for the rhythmic activity of the arms that occurs during swimming and after autotomy. We conclude that it is highly likely that l-glutamate has at least a neuromodulatory role in the neural pathways controlling the brachial muscles of A. mediterranea
New tools and strategies for biomonitoring marine ecosystems: learning from echinoderms
No full textMarine ecosystems are critically threatened by several anthropogenetic compounds (xenobiotics). In the last decades, among the numerous relevant xenobiotics, specific attention has been given to the Endocrine Disrupter Compounds (EDCs): these chemicals are able to alter the endocrine functions potentially causing serious health problems in humans and wildlife. In spite of the global relevance of these pollutants, most past and recent ecotoxicological research has been addressed only to a selected number of animal models, usually vertebrates, whereas invertebrates (particularly marine invertebrates) have been largely neglected. Among the scarcely considered invertebrate taxa, there are common macroinvertebrates such as echinoderms which actually are regarded as representative animals of the marine ecosystem. This contribution will explore the appropriateness of echinoderm models as test species in marine ecotoxicology. Presence and role of the different echinoderm classes in marine ecosystems will be discussed in terms of their ecological relevance and susceptibility to be targets of EDCs. Moreover, echinoderms can offer a wide range of biological processes appropriate for studies on endocrine dysfunction; although basic knowledge on echinoderm endocrinology is still scarce, several works suggested that many physiological processes of these invertebrates are plausibly regulated by humoral mechanisms, often similar to those found in vertebrates. Here, the sensitivity and responsiveness of different biological processes such as reproduction and regenerative development are discussed in relation to EDCs ecotoxicological tests on two echinoderm species: the sea urchin Paracentrotus lividus and the crinoid (feather star) Antedon mediterranea. The effects of low-dose exposures to several EDCs (triphenyltin, fenarimol, p,p'-DDE, methyltestosterone and cyproterone acetate) were investigated by several parameters including regenerative growth, histological pattern, gamete development and gonad maturation. In most of the exposure experiments, evidences of plausible endocrine disruption were found. These experiments were also considered in terms of modelling the fate of the contaminants in the aquaria. The modelling approach in the evaluation of the exposure can help in the planning phase of ecotoxicological tests, and, later, in the comprehension of the results and in the exportability to the natural environment. Finally, problems and weak points encountered with these animal models will be critically discussed together with considerations and perspectives for future research developments
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
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
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
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