1,721,085 research outputs found
Detailed morphological descriptions of the immature stages of the ant parasite Microdon mutabilis (Diptera: Syrphidae: Microdontinae) and a discussion of its functional morphology, behaviour and host specificity
Full text linkThe myrmecophilous immature stages of hover flies of the genus Microdon Meigen, 1803 (Diptera, Syrphidae) are still poorly known and only about 15 species were previously incompletely described and/or illustrated using light microscopy based on occasional findings mainly of pupae and third instar larvae. The exceptional finding of a large number of second and third instar larvae and pupae (159 specimens) of Microdon mutabilis (Linnaeus, 1758) inside the nest of a new host species, Formica cunicularia Latreille,1798, enabled us to rear them and obtain a great number of eggs and first instar larvae. We filmed and described the feeding behaviour and locomotion of these highly derived slug-like larvae. Combining light, fluorescence and scanning electron (SEM) microscopy, we describe in detail and illustrate the external features of all the immature stages of M. mutabilis (eggs, larvae and pupae). Covering the entire chorion of the egg is a peculiar microsculpture composed of volcano-like processes. The three larval instars strongly differ from each other, especially at the level of the shape of the body, the posterior spiracular tubercle and the cephaloskeleton. SEM microscopy was used to describe in detail the microsculpture, sensorial structures, spiracles and cephalic appendages of larvae and pupae. Fluorescence microscopy was used to reveal the exceptional presence of resilin in the external layer of the posterior spiracular tubercle in first instar larvae. The possible functional significance of these structures is discussed
From stress proteins to apoptosis and autophagy in sea urchin embryos
No full textMarine invertebrates inhabit a key position as intermediate consumers in the pelagic as well as in the benthonic food chains, making them suitable model systems for ecotoxicological studies.
Among benthonic organisms, echinoderms represent a simple, though significant, model system to test how specific stress can simultaneously provoke dangerous effects on growth and vitality of organisms. Sea urchins provide an attractive and exceptional model for investigating environmental pollution.
Most studies investigating the effects of Cd stress were conducted on Paracentrotus lividus, one of the most important marine invertebrates used as bioindicator of metal/heavy metal pollution and an important model organism in developmental biology.
It was shown that exposure to different toxics causes the synthesis of heat-shock proteins (HSPs), providing a protective role during stress conditions. The synthesis of a specific set of HSPs was demonstrated in P. lividus embryos continually exposed to 1mM of CdCl2 at the blastula (15 h) and gastrula (24 h) stages. Cd insult induces an alteration of normal development, probably inducing alternative pathways of growth, as demonstrated from the presence of several typologies of embryo morphology. Contextually, embryos activate other molecular defense mechanisms such as apoptosis.
Studies on the apoptotic processes activated in P. lividus were conducted after a long-lasting exposure to low Cd concentrations, similar to those found in moderately or highly polluted seawaters. These exposures caused severe developmental delays and abnormalities in the larvae, suggesting that even very small amounts of Cd, if accumulated in cells, can produce significant cytotoxic effects and apoptosis. Finally, we can assume that in sea urchin embryos/larvae, apoptosis can be considered part of a defense strategy that, by sacrificing a few cells, can safeguard the whole organism and the developmental program, provided that the exposure to Cd is not excessively prolonged or too intense.
Another molecular process studied in sea urchin embryos is autophagy, a mechanism of self-eating described as an important intracellular pathway responsible for degradation and recycling of long-term proteins and cytoplasmic organelles.
Autophagy has been recently observed in eggs and embryos, in response to stress induced by Cd and other stressors. Results of these studies revealed a higher level of autophagosomes in embryos exposed to Cd for 18 h.
Several experiments have been conducted on sea urchin embryos exposed to Cd to study the relationship between autophagy and apoptosis. Results suggest that autophagy may have a key role providing the energy supply necessary for apoptosis, delivering ATP molecules by recycling damaged cellular components.
Recent studies suggest that autophagy is important for the clearance of protein aggregates that are formed in cells following stress, and in this process, the p62/SQSTM1 protein (sequestosome 1) appears to play a key role. p62/SQSTM1 is a multifunctional, multidomain adaptator protein which resides at the autophagosome membranes. It is an autophagosome cargo protein that targets other proteins that bind to it for selective autophagy.
To highlight any protein aggregates concomitantly with the peak of autophagic vacuolation, control P. lividus embryos and embryos exposed to 1 mM CdCl2 for 18 and 24 h were submitted to the immunofluorescence/confocal laser scan microscopy protocol, using the anti-p62/SQSTM1 heterologous antibody.
Qualitative analysis showed a diffuse globular signal that is often referred to as Ibs (inclusion bodies), suggesting that the presence of polyubiquitinated protein aggregates was intended for autophagic degradation.
Taken together, these data indicate that in conjunction with the peak of autophagic vacuolation, there is an intense formation of protein aggregates that would be sent to degradation mediated by the autophagic process.
Reported data about the defense mechanisms induced by Cd in P. lividus suggest a hierarchical choice of defense strategies; strikingly, the temporal choice of activation of different mechanisms depends on the fact that the embryo tries to face the stress conditions using, initially, defense strategies that are less deleterious to preserve the developmental program. If these processes are not sufficient to offset the damage, the autophagic and apoptotic mechanisms are activated
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
BIOGEOGRAPHY OF HYCLEUS (COLEOPTERA: MELOIDAE): SPATIAL AND TEMPORAL DIVERSIFICATION OF A HYPER-DIVERSE GENUS
No full textThe genus Hycleus is a hyper-diverse genus of blister beetles including ~500 species with a wide geographic
distribution in different biogeographic regions in the Old World, and with the highest diversity occurring in
the Afrotropical Region. The phylogenetic relationships among the species and the biogeographic processes
related to their diversification have never been investigated. In this study, to provide a biogeographic
hypothesis that allow explaining the current diversity and the observed distribution patterns of Hycleus, we
built a robust time-calibrated phylogenetic tree using mitochondrial and nuclear DNA obtained from 125
species. Phylogenetic results were subsequently used for biogeographic inference carried out with the R
package BioGeoBEARS. Four main lineages were detected in our tree: A. including only Afrotropical species; B. including only Saharo-Sindian species; C. comprising Afrotropical, Palaearctic and Saharo-Sindian species; and D. comprising Afrotropical and Oriental species. According to our results, the genus Hycleus likely originated in the Afrotropical Region during the Early Miocene (~20 Mya), and subsequently spread in the Saharo-Sindian Transitional Region and in the Palaearctic Region. In the Late Miocene (~7.5 Mya) a second Saharo-Sindian group branched off from the Palaearctic lineage, whereas the Oriental Region was colonized (~7.8 Mya) following a dispersal event through the Arabian Peninsula from the Afrotropical Region
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
MULTIPLE COLONIZATION EVENTS OF ANTARCTIC WATERS FROM THE CILIATE EUPLOTES: EVIDENCE FROM PHYLOGENETIC ANALYSIS OF ANTARCTIC AND NON ANTARCTIC POPULATIONS
No full textThe Antarctic convergence together with the west-to-east circumpolar current provide a powerful barrier to the movement of marine life into, or out of the region. Despite this physical isolation, Antarctic coastal sea waters are extremely rich in biodiversity. Among unicellular eukaryotes, diatoms and dinoflagellates are the dominant autotrophic forms that bloom into huge biomasses in the water column, while filter-feeding ciliates are a dominant heterotrophic group that links the benthic and pelagic food webs by eating bacteria decomposers on the seabed and being, in turn, a relevant food source for sub-adult stages of benthonic and planktonic animals. Through many years of sampling coastal sites of Terra Nova Bay (Ross Sea) for species of the most speciose ciliate, Euplotes, we established a numerous laboratory collection of strains representing five well-distinct morphospecies, E. euryhalinus, E. focardii, E. nobilii, E. petzi and E. rariseta, which manifest sex in the form of conjugation under the genetic control of high-multiple mating-type systems that, by greatly favoring outbreeding, generate an ample intraspecific genetic diversity instrumental to establish reliable inter-population phylogenetic links and phylogeographic patterns. By determining and comparing the small-subunit ribosomal RNA (SSU-rRNA) gene sequences of these strains with homologous gene sequences from strains of non-Antarctic congeneric populations, evidence was obtained that E. euryhalinus, E. focardii, E. nobilii, E. petzi and E. rariseta split into distinct clades of the Euplotes phylogenetic tree. This phylogenetic split implies that the evolutionary history of Euplotes entails multiple, independent events of colonization of the Antarctic waters and suggests, in a general perspective of microbial biogeography, that the ecological barriers to move into, or out of Antarctic waters are largely ineffective to disrupt a bipolar, cosmopolitan dispersal of eukaryotic microorganisms. Which reinforces the concept of “metapopulation” (i.e., a group of populations of the same species separated by space but linked by dispersal and migration) originally applied to protists’ biogeography
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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