1,720,985 research outputs found
The role of horizontally transferred genes in the xenobiotic adaptations of the spider mite Tetranychus urticae
Get PDFPlant feeding arthropods adapt in diverse ways to dietary plant toxins. The genetic basis of these adaptations is not well characterized, especially in non-insect lineages. Using the sequenced genome of the herbivorous spider mite Tetranychus urticae as a starting point, this work aimed at uncovering which genes and mechanisms underpin spider mite resistance to chemical plant defenses. First, the detoxification of the defensive compound produced by cyanogenic plants in spider mites was investigated. This work successfully identified the gene of which the protein product (B-cyanoalanine synthase) detoxifies plant synthesized cyanide and uncovered that this gene was horizontally transferred from a bacterial species. Second, genome-wide gene-expression responses upon various chemical pressures were further analyzed to explore the spider mite’s xenobiotic metabolism in more detail. New gene families, including one which was horizontally transferred from fungi (intradiol ring-cleaving dioxygenases), emerged as potential key components in the mite’s detoxification pathways. Additionally, these transcriptomic comparisons support the theorem that polyphagous herbivores co-opt their pre-evolved phytochemical detoxification pathways to detoxify synthetic pesticides
Genomic regions under selection in crop-wild hybrids of lettuce: implications for crop breeding and environmental risk assessment
Get PDFThe results of this thesis show that the probability of introgression of a putative transgene to wild relatives indeed depends strongly on the insertion location of the transgene. The study of genomic selection patterns can identify crop genomic regions under negative selection in multiple environments and in several cultivar-wild crosses, which could be applicable to TM strategies. For lettuce, a fitness QTL region was identified on LG7 where the crop allele conferred a selective disadvantage through delayed flowering, lower survival, and a lower fitness and possibly through a lower competitive ability. This crop genomic background is likely deleterious in the wild habitat, especially in environments with high density competition and a seasonal flowering period. However, QTL results were also (partly) cultivar specific, so that implementation in ERA will still need to be on a case-by-case basis, which decreases its general applicability. In addition, our results show that it is more informative to identify specific genomic regions under selection than to estimate average hybrid fitness. Fitness distributions indicated there is a high likelihood in lettuce for novel crop-wild hybrids to arise that have a higher fitness than the wild parent even though the average fitness of the hybrid offspring was lower. This provides an avenue for introgression of crop alleles into the wild population. A mitigation strategy based solely on placing a transgene close to a major negatively selected crop gene could have a huge quantitative effect by reducing the chances of introgression, but it would be difficult to design a strategy that would prevent it with certainty. It is commendable to evaluate the remaining risk in the perspective of the potential consequences an escape would have for the recipient environment, as well as the foreseen benefits of the GM crop
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe 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
Get PDF“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
Get PDFWe 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
Get PDFWe 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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