1,721,028 research outputs found
Arthropod biology and evolution. Molecules, development, morphology
No full textThe Arthropoda is by far the largest living phylum, comprising over 1.2 million living species, and its unique evolutionary success is the primary focus for this up-to-date and comprehensive overview of the biology of the group. This astonishing species richness is matched by a spectacular diversity in body forms and adaptations. To counter the largely unavoidable trend towards increased specialization within a particular group, this volume adopts a comparative viewpoint across the entire phylum, encompassing both extant and fossil forms. The phylum-wide perspective allows us to appreciate the wave of recent advances in knowledge of arthropod biology and evolution and to identify emerging themes and priorities for future research.
As ever in the history of science, this wave of advances is driven by the rapid development of new methods and techniques. New methods of extracting and studying fossils have vastly improved understanding of Palaeozoic arthropods. New non-invasive, non-destructive techniques, such as micro-computed tomography, have revolutionised anatomical analysis and imaging. Arthropod comparative genomics is still in its infancy but high-throughput sequencing together with next-generation sequencing has facilitated spectacular growth in volumes of sequence data, which in turn has driven advances in bioinformatics. These novel methods have generated a wealth of data which has been critically reviewed by the chapter authors, to provide a new perspective on arthropod biology and evolution.
The concise factual summaries and the questions articulated in this book will be of interest to evolutionary biologists, palaeontologists, developmental geneticists and invertebrate zoologists. It will be of special interest to advanced graduate and post-graduate students and have the potential to stimulate younger researchers to address questions in arthropod biology from the vantage point of a phylum-wide comparative perspective
Variación morfológica y un nuevo y remarcable tipo de dimorfismo sexual en la población de Pseudocyclops xiphophorus del Lago Faro en el noreste de Sicilia
Get PDFThe population of P. xiphophorus in Lake Faro exhibits variation in the form of caudal seta V. In some specimens of both sexes, this seta is spatulate but in others it is slender and unmodified. Occasional specimens are asymmetrical. In addition to this variation in caudal seta form, the Lake Faro population displays variation in male body length and in the extent of the sexually dimorphic specialisation of the right swimming leg 2. The scale of these differences between the morphotypes might suggest their taxonomic treatment as distinct species. The modification of the distal two segments of the exopod of right leg 2 in the male is a unique sexual dimorphism. We infer, from the presence of this hook on the right exopod in adult males only, that it is involved in mating behaviour. Laboratory-based breeding experiments between females and males showing different combinations of these characters were also performed. Experiments comparing egg production rates in females that have mated with modified or unmodified males revealed no significant differences. It appears therefore that gene flow is not interrupted between the morphotypes and that reproductive segregation does not occur. Observations of male leg 5 morphology and musculature revealed no significant differences between the two P. xiphophorus morphotypes.La población de P. xiphophorus del Lago Faro muestra variación en la forma de la seda caudal V. En algunos especímenes de ambos sexos presenta una morfología espatulada, pero en otros es esbelta y sin modificaciones. Ocasionalmente, es asimétrica en un mismo individuo. La población del Lago Faro muestra también variabilidad en la longitud corporal del macho y en el grado de dimorfismo sexual de la segunda pata natatoria derecha. La escala de estas diferencias entre morfotipos podría sugerir un tratamiento específico diferente para ellos. La modificación en el macho de los dos segmentos distales del exópodo de la segunda pata natatoria derecha es un carácter desconocido en otras especies del género. La presencia de un gancho en el exópodo derecho de los machos sugiere que esta modificación está relacionada con el comportamiento de apareamiento. Se han realizado cruzamientos en laboratorio entre hembras y machos que mostraban diferentes combinaciones de estos caracteres. La comparación de las tasas de producción de huevos en hembras que se han cruzado con machos con o sin modificaciones no muestra diferencias significativas. Parece por tanto que el flujo génico entre morfotipos no está interrumpido y que no tiene lugar segregación reproductiva. La observación de la morfología y del patrón muscular de la pata quinta del macho no ha revelado tampoco diferencias significativas entre los dos morfotipos de P. xiphophorus
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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