1,720,955 research outputs found
EVOLUTION OF THE MITOCHONDRIAL RIBOSOMAL-RNA IN THE ORIENTAL SPECIES SUBGROUPS OF DROSOPHILA
No full textThe nucleotide sequence of two segments of the mtDNA molecule of
different species of Drosophila containing a portion of the large rRNA
(16S) and a portion of the small rRNA (23S) has been determined.
The polymerase chain reaction (PCR) technique with ''universal'' primers
has been used to amplify the segments for direct sequencing.
The species analysed belong to four different subgroups of the
melanogaster species group.
The phylogenetic relationships of the species have been reconstructed by
using the neighbour-joining algorithm and the significance of the
inferred phylogeny tested by bootstrap method
Evolution of reproductive strategies and male sexual ornaments in poeciliid fishes as inferred by mitochondrial 16S rRNA gene phylogeny.
No full textPoeciliid fishes have been widely used as a model system in the study of
sexual selection mechanisms. In several species belonging to the genera
Xiphophorus and Poecilia males show conspicuous ornaments and use
courtship display to obtain female cooperation during mating. Conversely
most of the remaining poeciliids are drab and achieve copulation mainly
through gonopodial thrusting, a fertilization strategy that bypasses the
female's consent. We sequenced a portion of the large (16S)
mitochondrial ribosomal RNA gene to estimate the phylogenetic
relationships among the Eve tribes of the subfamily Poeciliinae (ROSEN &
BAYLEY 1963) and we used the molecular phylogeny to reconstruct the
origin of male ornaments and the evolutionary history of the
reproductive strategies in this family. Gambusiini were found to be the
basal tribe in the subfamily Poeciliinae. In our phylogeny, Xiphophorus
and Poecilia were not closely related thus suggesting that the tribe
Poeciliini is not a monophyletic group. Gonopodial thrusting was
probably the primitive mating strategy of the poeciliids. Sexual
ornaments and elaborate courtship behaviour apparently evolved more
recently in the genus Xiphophorus and independently in the genus
Poecilia
Large differences in substitutional pattern and evolutionary rate of 12S ribosomal RNA genes
No full textWe demonstrate using Drosophila, periodical cicadas, and hominid
primates, that the molecular clock based on animal mitochondrial
small-subunit (12S) rRNA genes ticks at significantly different relative
rates depending on which taxa and which region of the gene are examined.
Drosophila, which are commonly used as model taxa, are evolving in a
highly peculiar manner with the majority of sites in the 3' half of the
12S gene apparently invariant. The analogous 3' half of the
mitochondrial large-subunit rRNA gene (16S) appears to be similarly
constrained. It is surprising that these regions that are already highly
constrained in all animals should be even more constrained in
Drosophila, especially when the Drosophila mitochondrial genome as a
whole does not display a similar rate slowdown. This extreme 12S rate
slowdown is not apparent in periodical cicadas or hominid primates and
appears to be related to strong structural and functional constraints
rather than a depressed mutation rate. Finally, the slow average rate of
evolution in the third domain of Drosophila does not imply that the few
variable sites lack multiple hits
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
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
koamabayili/VECTRON-author-checklist: VECTRON author checklist
No full textWe have done our best to complete the author checklist relating to the use of animals in the hut study. Note that the objective for the hut study was to evaluate the IRS treatment applications for residual efficacy against Anopheles mosquitoes, including the local An. coluzzii mosquito population. Cows were only used to attract mosquitoes into the huts and no tests were carried out directly on the cows. The author checklist is intended for use with studies where experiments are carried out on animals, which is why we have had such difficulty in completing this for the hut study, as many of the questions do not relate to how the cows were used
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