1,721,038 research outputs found
New discoveries reveal unexpectedly wide taxonomic diversity and call for a new classification of the green algal family Prasiolaceae (Trebouxiophyceae)
No full textAlgal lineages with small size and low morphological complexity are typically among the most difficult to resolve taxonomically. They are often characterized by high levels of cryptic diversity and environment-driven plasticity that complicate species recognition. Their full taxonomic diversity is even more difficult to unravel when their evolution has also resulted in great ecological diversity, encompassing many different habitats including unusual ones. An example of this case is the Prasiolaceae, a family of filamentous, leafy and packet-like green algae occurring in marine, freshwater and terrestrial environments. They are well known for their preference for habitats subject to high loads of organically derived nutrients, mainly in the form of seabird guano found in upper littoral habitats. In recent years, new surveys and new molecular phylogenetic studies have produced the surprising discovery of many new lineages, revealing an unexpected high taxonomic diversity. DNA sequence data obtained from cultured strains called for the description of several new genera and species. Prasiola, type genus of the family, was subjected to a major rearrangement. The genus was shown to be polyphyletic, which required its splitting into four genera: the real Prasiola (in which the type species Prasiola crispa belongs), Eaprasiola, Mariprasiola and Vittaprasiola. The marine species of this grouping, classified in the genus Mariprasiola, represent a remarkable case: they exhibit clear morphological and life history differences, although sequences of the most common markers used for species delimitation are identical. Conversely, in the genus Vittaprasiola DNA sequence divergence demonstrates the existence of cryptic entities that require separation at species level. Further studies of this group should expand the body of molecular markers available and, in combination with fieldbased studies making use of environmental DNA, might reveal an even higher phylogenetic and taxonomic diversity
New discoveries in the family Prasiolaceae (Trebouxiophyceae) and a new taxonomic rearrangement of the genus Prasiola
No full textPrasiolales (Trebouxiophyceae, Chlorophyta) of the Svalbard Archipelago: diversity, biogeography and description of the new genera Prasionema and Prasionella
No full textSpecies of Prasiolales (Trebouxiophyceae, Chlorophyta) are among the most common terrestrial and freshwater algae in polar regions. Comprehensive molecular studies of this group are available for Antarctica, but not yet for Arctic regions. We examined the diversity of the Prasiolales in the Svalbard Archipelago combining morphological observations of field-collected material, culture studies, molecular data (plastid rbcL and tufA sequences) and literature records. We confirmed the widespread occurrence of Prasiola crispa and P. fluviatilis, species recorded from Spitsbergen since the 19th century. Molecular phylogenetic analyses led to the discovery of two new genera of Prasiolales. Prasionema payeri is morphologically identical to filamentous stages of P. crispa, but represents an early-diverging lineage in the order. Prasionella wendyae is a colonial alga reproducing by aplanospores; its phylogenetic position is among the basal lineages of the order, but it could not be reliably reconstructed due to weak statistical support. The inclusion of P. wendyae in the prasiolalean phylogeny determined the paraphyly of Rosenvingiella, requiring the establishment of the new genus Rosenvingiellopsis for R. constricta. A poorly known species described from Spitsbergen, Ulothrix discifera, is transferred here to Rosenvingiella. Whereas some species of Prasiolales have bipolar distribution (P. crispa), others appear to be restricted to one or other of the poles. Our results suggest that polar regions are still a major repository of unknown algal diversity and highlight the importance of continued field surveys and the use of molecular data
Macroalgal biodiversity in the Beaufort Marine Biodiscovery Project
No full textAbstracts 48th European Marine Biology Symposium (Galway, 19-23 August 2013) - Poster number 1
Molecular phylogeny and taxonomic reassessment of the genus Cladostephus (Sphacelariales, Phaeophyceae)
No full textThe brown algal genus Cladostephus (Sphacelariales) is found worldwide in temperate regions. Two species are considered endemic to South America (C. antarcticus Kützing and C. hariotii Sauvageau), whilst specimens from the rest of the world are usually attributed to a third, cosmopolitan species, C. spongiosus (Hudson) C.Agardh. However, comparisons of organellar (plastid rbcL and psbC, mitochondrial COI-5P) and nuclear (ITS nrDNA) markers for samples collected throughout the geographic range of C. spongiosus suggest that two genetic entities are treated under this name, which correspond to previously recognized morphological entities. Specimens with ‘spongiose’ morphology (C. spongiosus s.s.) were found to be limited to the Atlantic coast of Western Europe. The entity showing ‘verticillate’ morphology (‘C. verticillatus’) emerged as the cosmopolitan species: specimens were found on the Atlantic coasts of western Europe and the USA, in the Mediterranean, in New Zealand, Australia and on the Pacific coast of Mexico. Since the name C. verticillatus (Lightfoot) Lyngbye is illegitimate, this entity is herein referred to as C. hirsutus (L.) Boudouresque & M.Perret. A third genetic entity was only encountered in the southern hemisphere, i.e. in New Zealand, Australia, southern Chile and Falkland Islands. Comparisons with descriptions and images of type specimens suggest that this southern entity conforms most closely to the description of Cladostephus australis Kützing, nom. illeg., and it is herein renamed as Cladostephus kuetzingii Heesch, Rindi & W.A.Nelson
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
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