1,720,958 research outputs found
Genetic heterogeneity, reproductive isolation and host preferences in mealy aphids of the Hyalopterus pruni complex (Homoptera, Aphidoidea).
No full textThree taxa were detected by allozyme markers within the mealy aphids of the Hyalopterus pruni complex, having different cultivated Prunus species as main primary hosts. The genetically closer H. pruni and H. amygdali A (DNei= 0.10) never share primary hosts, whereas H. amygdali A and B (DNei= 0.32) may occasionally share them, producing few F1 hybrids. The three species proved reproductively isolated in the field, with no gene exchange. Their speciation seem to have occurred long before the agricultural revolution, crop colonization representing a host range expansion rather than a host shift, as in sympatric speciatio
Interspecific hybridization as a source of new species in orchids of the genus Dactylorhiza
No full textThe Palaearctic genus Dactylorhiza includes 8 diploid,10 autotetraploid,and about 40 allopolyploid species. Most of the latter derived by multiple crosses in space and time between the diploid (2n=40) D.saccifera s.l. and either D.incarnata s.l. or D.euxina; they have 4x=80 and reproduce sexually (Allotetraploid Marsh Orchids,AMOs). AMO species are differentiated morphologically, ecologically and genetically, have distinct ranges and show different combinations of alleles from local races of their parental species. Hybridization between D.saccifera s.l. and D.incarnata s.l. also gave origin to a few allotriploid taxa, as yet undescribed, with apomictic reproduction and clonal structure. Other Dactylorhiza hybrid species originated from crosses between the diploid (2n=40) D.romana and D.sambucina. They include: 1) the apomictic allotriploid D.insularis (3x=60), which combines two genomes of D.romana and one of D.sambucina, and had a single origin in an Iberian hybrid zone; 2) the sexual allotetraploid D.cantabrica, which combines two genomes of each parental species, and had a single quite recent origin, as indicated by its very restricted range, much smaller than that of D.insularis. The ecological and evolutionary success of Dactylorhiza hybrid species is considered, with particular regard to their mode of reproduction, environmental adaptations, and competitive success
Speciation by hybridization in European orchids: evidence by nuclear and chloroplastic markers
No full textA number of hybrid species has been recently detected in orchids of the genus Dacylorhiza, by the use of codominant single copy nuclear markers (e.g. enzyme loci). They differ in ploidy level, mode of reproduction, genetic variation and single versus multiple origin. The Allotetraploid Marsh Orchids (D. elata s.l.) show sexual reproduction and have 4x=80; their parental species are D. saccifera s.l. (2n=40) and D. incarnata s.l. (2n=40), as suggested on chromosome basis by Heslop-Harrison (1953, 1954, 1957) and assessed on allozyme basis (Hedrén, 1996a, b; Bullini et al., 2002). Genetic comparison of various AMO taxa from Europe and Caucasus showed their multiple origin, both in time and space; the maternal species was generally D. saccifera s.l., as shown by cpDNA. Other hybrid Dactylorhiza species are allotriploid and reproduce by apomixis. Among marsh orchids, four triploid apomictic taxa, as yet undescribed, have been evidenced: three of them show 2 genomes from D. incarnata and 1 from D. saccifera, the fourth has 2 saccifera and 1 incarnata genomes. Their origin from occasionally fertile backcrosses of AMOs with either parental species has been suggested; according to the taxon, cpDNA was contributed from either D. saccifera or D. incarnata (Bullini et al., in press). The Western Mediterranean orchid D. insularis (3x=60) shows sporophytic polyembriony; this species derived from hybridization between D. romana (2n=40) and D. sambucina (2n=40), which contributed two and one genomes, respectively, as assessed by allozyme markers; the maternal species was D. romana. D. insularis had a single, recent origin and shows limited clonal variation (Bullini et al., 2001). Genetic relationships between Dactylorhiza hybrid taxa and their parental species, as inferred from cpDNA, are generally similar to those reported for nuclear ribosomal intergenic spacer (ITS; Bateman et al., 1997; Bateman, 2001). These findings suggest that concerted evolution, i.e. homogenization towards one parental species, has occurred in hybrid Dactylorhiza taxa at ITS level, highly biased towards the maternal parent
Allopolyploid speciation in primroses of the Auricula section (genus Primula, subgenus Auriculastrum)
No full textIn the present study, we show that the hexaploid primroses (6x=66) of section Auricula arose from crosses between species of Dodecatheon (4x=44) and of Primula, section Cuneifolia (2x=22), that came into secondary contact in the Alps. Genetic studies at codominant nuclear markers (enzyme loci) indicate that the most likely parental species of the Auricula taxa were D. pulchellum, D. frigidum and P. cuneifolia. Among the alleles detected in Auricula species, 9 were found in a diploid population of P.cuneifolia from Siberia, 17 in allotetraploid D.
pulchellum s.l./D. frigidum respectively from NW Canada and Alaska, whereas few were shared by both P .cuneifolia and Dodecatheon spp. Nine missing alleles were detected; their relative low frequency (about 1/4 of the total alleles) suggests that the Auricula section had a recent origin, during one of the last Ice Ages. We suggest that triploid P.cuneifolia x Dodecatheon spp. hybrids acquired sexuality by a chromosome doubling, allowing normal meiosis. Data from cpDNA indicate D.pulchellum s.l./D.frigidum as the maternal species of the Auricula complex. The putative parental species are now extinct from all Europe, possibly due to competitive exclusion by their allohexaploid derivatives, able to exploit a wide range of environments, from sea-level (i.e. P.palinuri) up to 3000m
Speciation by hybridization and polyploidy in European orchids of the genus Dactylorhiza
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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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