1,720,961 research outputs found
Insights into the Taxonomically Challenging Hexaploid Alpine Shrub Willows of Salix Sections Phylicifoliae and Nigricantes (Salicaceae)
No full textThe complex genomic composition of allopolyploid plants leads to morphologically diverse species. The traditional taxonomical treatment of the medium-sized, hexaploid shrub willows distributed in the Alps is difficult based on their variable morphological characters. In this study, RAD sequencing data, infrared-spectroscopy, and morphometric data are used to analyze the phylogenetic relationships of the hexaploid species of the sections Nigricantes and Phylicifoliae in a phylogenetic framework of 45 Eurasian Salix species. Both sections comprise local endemics as well as widespread species. Based on the molecular data, the described morphological species appeared as monophyletic lineages (except for S. phylicifolia s.str. and S. bicolor, which are intermingled). Both sections Phylicifoliae and Nigricantes are polyphyletic. Infrared-spectroscopy mostly confirmed the differentiation of hexaploid alpine species. The morphometric data confirmed the molecular results and supported the inclusion of S. bicolor into S. phylicifolia s.l., whereas the alpine endemic S. hegetschweileri is distinct and closely related to species of the section Nigricantes. The genomic structure and co-ancestry analyses of the hexaploid species revealed a geographical pattern for widespread S. myrsinifolia, separating the Scandinavian from the alpine populations. The newly described S. kaptarae is tetraploid and is grouped within S. cinerea. Our data reveal that both sections Phylicifoliae and Nigricantes need to be redefined
Hybrid zones in the European Alps impact the phylogeography of alpine vicariant willow species (Salix L.)
Full text linkIn the European Alps, Pleistocene climate oscillations resulted in geographical range expansions and restrictions of species. Postglacial recolonizations often result in secondary contact hybridization of vicariant species, thereby creating hybrid zones with patterns of introgression. Here, we compare the genetic structure of two secondary contact hybrid zones between two vicariant willow species pairs occurring in the European Alpine System. Supplemented by morphological and ecological data, we try to understand the factors shaping the hybrid zones and their influence on geographical range filling patterns.Open-Access-Publikationsfonds 202
Challenge accepted: Evolutionary lineages versus taxonomic classification of North American shrub willows ( Salix )
No full textAbstract Premise The huge diversity of Salix subgenus Chamaetia/Vetrix clade in North America and the lack of phylogenetic resolution within this clade has presented a difficult but fascinating challenge for taxonomists to resolve. Here we tested the existing taxonomic classification with molecular tools. Methods In this study, 132 samples representing 46 species from 22 described sections of shrub willows from the United States and Canada were analyzed and combined with 67 samples from Eurasia. The ploidy levels of the samples were determined using flow cytometry and nQuire. Sequences were produced using a RAD sequencing approach and subsequently analyzed with ipyrad, then used for phylogenetic reconstructions (RAxML, SplitsTree), dating analyses (BEAST, SNAPPER), and character evolution analyses of 14 selected morphological traits (Mesquite). Results The RAD sequencing approach allowed the production of a well‐resolved phylogeny of shrub willows. The resulting tree showed an exclusively North American (NA) clade in sister position to a Eurasian clade, which included some North American endemics. The NA clade began to diversify in the Miocene. Polyploid species appeared in each observed clade. Character evolution analyses revealed that adaptive traits such as habit and adaxial nectaries evolved multiple times independently. Conclusions The diversity in shrub willows was shaped by an evolutionary radiation in North America. Most species were monophyletic, but the existing sectional classification could not be supported by molecular data. Nevertheless, monophyletic lineages share several morphological characters, which might be useful in the revision of the taxonomic classification of shrub willows
Evolution of a hybrid zone of willows (Salix L.) in the Alps analysed by RAD-seq and morphometrics
Full text linkNatural hybridization of plants can result in many outcomes with several evolutionary consequences, such as hybrid speciation and introgression. Natural hybrid zones can arise as a result of fluctuating climate during the exchange of glacial and interglacial periods, where species retract and expand their territories, resulting in secondary contacts. On mountain ranges, such as the European Alps, hybrid zones of alpine species are frequently formed where different lineages meet. Willows are a large genus of woody plants with an immense capability of interspecific crossing. About 33 species of this genus inhabit the Alps, where intermediate phenotypes were frequently observed and proclaimed as hybrids, but rarely examined in detail. One of the reasons was a lack of informative molecular markers and suitable analytical tools to analyse this highly diverse and convergent genus. With the development of the RAD-seq technology, several questions regarding willow phylogeny and hybridization could be answered. In this study, a putative hybrid zone of two sister species, S. foetida and S. waldsteiniana, was investigated to study the genomic structure of populations within and outside their contact zone, to find evidence for hybrid speciation or introgression, and to analyse if morphological phenotypes are reflected by their genotypes. Individuals of the two species were sampled across their distribution range in the Alps and examined with the use of RADseq data and morphometric analyses. The results showed that a hybrid zone between the two species was established within the range of their contact zone. Patterns of genetic admixture in homoploid hybrids indicated introgression with asymmetric backcrossing to one of the parental species. Morphometric characteristics of hybrids supported the molecular data and showed intermediacy with a bias towards S. waldsteiniana. Only one potentially divergent hybrid lineage was observed, hinting to a possibility of localised hybrid speciation events
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
Ancient DNA extraction methods for herbarium specimens: When is it worth the effort?
No full textPremise
Herbaria harbor a tremendous number of plant specimens that are rarely used for molecular systematic studies, largely due to the difficulty in extracting sufficient amounts of high-quality DNA from the preserved plant material.
Methods
We compared the standard Qiagen DNeasy Plant Mini Kit and a specific protocol for extracting ancient DNA (aDNA) (the N-phenacylthiazolium bromide and dithiothreitol [PTB–DTT] extraction method) from two different plant genera (Xanthium and Salix). The included herbarium materials covered about two centuries of plant collections. To analyze the success of DNA extraction using each method, a subset of samples was subjected to a standard library preparation as well as target-enrichment approaches.
Results
The PTB–DTT method produced a higher DNA yield of better quality than the Qiagen kit; however, extracts from the Qiagen kit over a certain DNA yield and quality threshold produced comparable sequencing results. The sequencing resulted in high proportions of endogenous reads. We were able to successfully sequence 200-year-old samples.
Discussion
This method comparison revealed that, for younger specimens, DNA extraction using a standard kit might be sufficient. For old and precious herbarium specimens, aDNA extraction methods are better suited to meet the requirements for next-generation sequencing.Open-Access-Publikationsfonds 202
Spatio-temporal evolution of shrub willows (Salix subgenus Vetrix clade) on a global scale
No full texthttp://dx.doi.org/10.13039/501100001824 Czech Science Foundationhttp://dx.doi.org/10.13039/100000076 National Science Foundation Directorate for Biological Scienceshttp://dx.doi.org/10.13039/501100001659 German Research Foundatio
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