1,720,967 research outputs found
Co-introduction success of monogeneans infecting the fisheries target Limnothrissa miodon differs between two non-native areas: the potential of parasites as a tag for introduction pathway
No full textFish have been widely translocated into non-native areas, commonly as fishery targets. Since fish figure as hosts of various parasite taxa, their introduction may pose often-underestimated threats to ecosystems. However, parasites can also serve to track host species’ introduction routes when these would otherwise be unknown. To verify the potential of parasites in reconstructing invasion routes, we investigated two of the best-documented introductions: those of Limnothrissa miodon into lakes Kivu and Kariba. As a proof of concept, we investigate the possibility of using parasites to evaluate the effect of host size in the introduction pathway and to track the host origins of L. miodon. Combining historical collections and recent field samples, specimens of L. miodon from Lake Kivu and Lake Kariba were examined for monogenean flatworms. Intraspecific variation was investigated using morphometrics of the parasite’s sclerotised structures. Three markers from the ribosomal DNA region were used for genetic parasite identification. In Lake Tanganyika, L. miodon is infected by two species of monogeneans, Kapentagyrus limnotrissae and K. tanganicanus. One of these species, K. limnotrissae, was found on L. miodon from Lake Kariba. In contrast, not a single monogenean individual was found in specimens from Lake Kivu. Morphometric results suggested that the origin of K. limnotrissae introduced into Lake Kariba may be the southern part of Lake Tanganyika, which corresponds to historical reports. Moreover, differences in the size of introduced fish, fry versus juveniles, were proposed as one of the factors influencing parasite occurrence in non-native areas. This supports the potential use of monogeneans as markers for host origin.This study was supported by ECIP (European Centre of Ichthyoparasitology); project No. P505/12/G112. Work in the collections of RMCA (Royal Museum for Central Africa) was financed by the SYNTHESYS Project (http://www.synthesys.info/) (BE-TAF-5731) which is financed by European Community Research Infrastructure Action under the FP7 Integrating Activities Programme
Comparative population mitogenomics of fish parasites reveals contrasting geographic pattern in the pelagic zone of Lake Tanganyika
No full textAfrican Great Lakes and their fauna are among the prime model systems for evolutionary research. Lake Tanganyika is the second deepest lake in the world and its permanently stratified, relatively species-poor and well-delimited pelagic zone offers a simple model for ecosystem dynamics of open water areas worldwide. In our study, we focused on mitogenomic differentiation of directly transmitted parasites (Monogenea, Kapentagyrus) infecting two species of pelagic clupeid fishes across two subbasins of Lake Tanganyika, to unravel patterns of migration and population dynamics in the pelagic zone of large water bodies. Starting from pooled population samples, altogether containing more than 800 specimens, we provide the first population-genomic study on any parasite in the African Great Lakes. Our results indicate a lack of spatial population structuring in Kapentagyrus tanganicanus infecting its two clupeid hosts. In Kapentagyrus limnotrissae, a parasite specific to only one of the two clupeid hosts, spatial and seasonal restriction in gene flow are observed. Contrasting patterns in spatial population structuring between K. tanganicanus and K. limnotrissae reflect their differences in host range and in the life histories, migration and habitat preference of their respective hosts. This is a proof-of-concept of how parasites can be reliable tags for hardly traceable hosts, in this case indicating host and parasite connectivity throughout the hosts' spatial distribution. Comparison of population-genetic parameters based on individual specimens versus pooled samples proofs PoolSeq as a suitable method in (mito)genomics of minute taxa that are hard to access in the field
Monogeneans from Catfishes in Lake Tanganyika. I: Two new species of Bagrobdella (Dactylogyridae) from Auchenoglanis occidentalis (Siluriformes: Claroteidae)
No full textIn the framework of the study of Siluriform fish monogeneans of Lake Tanganyika, we described two new species of Bagrobdella Paperna, 1969 from Auchenoglanis occidentalis (Valenciennes, 1840). Bagrobdella vanhovei sp. nov. is characterized by the morphology of its MCO which is unique among its congeners, presenting a non-terminal opening, whereas the other species have a terminal opening, and Bagrobdella vansteenbergei sp. nov. characterized by the size of its hooks, which are almost all of the same size, and its male copulating organ with a unique shape: a sub-terminal opening and no membrane surrounding. The Multivariate analysis done on morphometrical characters shows that the new and already described spe-cies are well individualized, except for Bagrobdella parauchenoglanii Akoumba, Pariselle, Tombi & Bilong Bilong, 2017 and Bagrobdella fraudulenta Euzet & Le Brun, 1990 (but these two species are easily distinguishable by their morphology), and that B. vanhovei sp. nov. has a great intra-specific morphometrical variation
Complete mitochondrial genomes and updated divergence time of the two freshwater clupeids endemic to Lake Tanganyika (Africa) suggest intralacustrine speciation
No full textAbstract
BackgroundThe hydro-geological history of Lake Tanganyika paints a complex image of several colonization and adaptive radiation events. The initial basin was formed around 9-12 million years ago (MYA) from the predecessor of the Malagarasi–Congo River and only 5-6 MYA, its sub-basins fused to produce the clear, deep waters of today. Next to the well-known radiations of cichlid fishes, the lake also harbours a modest clade of only two clupeid species, Stolothrissa tanganicae and Limnothrissa miodon. They are members of Pellonulini, a tribe of clupeid fishes that mostly occur in freshwater and that colonized West- and Central-Africa during a period of high sea levels during the Cenozoic. There is no consensus on the phylogenetic relationships between members of Pellonulini and the timing of the colonization of Lake Tanganyika by clupeids. ResultsWe use short-read next generation sequencing of 10X Chromium libraries to sequence and assemble the full mitochondrial genomes of S. tanganicae and L. miodon. We then use Maximum Likelihood and Bayesian methods to place them into the phylogeny of Pellonulini and other clupeiforms, taking advantage of all available full mitochondrial clupeiform genomes. We identify Potamothrissa obtusirostris as the closest living relative of the Tanganyika sardines and establish paraphyly for Microthrissa. Our results indicate a relatively recent divergence of the Tanganyika sardines around 4.07 MYA [95% CI: 1.66-7.06], and from P. obtusirostris around 11.88 MYA [95% CI: 6.09-17.27]. ConclusionsThese young estimates imply that the ancestor of the Tanganyika sardines diverged from a riverine ancestor and entered the proto-lake Tanganyika around the time of its formation from the Malagarasi–Congo river, and diverged into the two extant species at the onset of deep clearwater conditions. Our results prompt a more thorough examination of the relationships within Pellonulini, and the new mitochondrial genomes provide an important resource for the future study of this tribe, e.g. as a reference for species identification, genetic diversity, and macroevolutionary studies.</jats:p
Lifestyle and not density of fish hosts determines parasite distribution over time and space
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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
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe 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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