1,720,973 research outputs found
ECOLOGIE ALIMENTAIRE COMPAREE DE LIMNOTHRISSA MIODON ET DE LAMPRICHTHYS TANGANICANUS AU LAC KIVU (AFRIQUE DE L'EST)
No full textLimnothrissa miodon, a clupeid endemic to Lake Tanganyika, was voluntarily introduced in Lake Kivu between 1958-1959 and enabled the development of a flourishing pelagic fishery. Recently, Lamprichthys tanganicanus, a poeciliid also endemic to Lake Tanganyika, was accidentally introduced into Lake Kivu. Because potential preys for both species are scarce in the lake, L. tanganicanus could compete with L. miodon and could constitute a threat to pelagic fisheries which rely mainly on L. miodon. The objective of this work was to study the feeding ecology of these two fish species using several methods: analysis of stomach contents, identification of dietary patterns, analysis of stable isotopes of C and N and analysis of fatty acids in fishes and in the main components of plankton. The results showed a strong diet overlap between these two fish species, indicating some level of interspecific competition. However, their differing feeding activities patterns and differing use of terrestrial, littoral and pelagic food resources could reduce this competition. Indeed, although both species occupy a similar trophic position, L. miodon is dependent much more on pelagic food resources than L. tanganicanus which has a stronger link with the littoral food web. The profiles of fatty acids in fishes and plankton components indicate that the fatty acids compositions of both species are very close, and that the nutritional quality of zooplankton varies relatively little during the year. As for the productivity of zooplankton, it undergoes significant seasonal variations, which are dependent on both quantity and composition of phytoplankton. Finally, fatty acid profiles also revealed that bacteria do contribute significantly to zooplankton and fish biomass, highlighting the contribution of the microbial food web to consumer production.Limnothrissa miodon, Clupéidé endémique au lac Tanganyika, a été volontairement introduit au lac Kivu entre 1958-1959 et y a permis le développement d’une pêcherie florissante. Récemment, Lamprichthys tanganicanus, un Poeciliidé aussi endémique au lac Tanganyika, a été accidentellement introduit au lac Kivu. Comme les proies potentielles de ces deux espèces sont peu abondantes dans le lac, L. tanganicanus pourrait être en compétition avec L. miodon et constituerait alors une menace pour la pêche en milieu pélagique, qui repose principalement sur L. miodon. Ce travail a consisté à étudier l’écologie alimentaire de ces deux espèces par différentes méthodes: analyse des contenus stomacaux, détermination des rythmes alimentaires, mesure des isotopes stables du C et du N et analyses des acides gras dans les poissons et les principaux composants du plancton. Les résultats ont révélé un fort recouvrement du régime alimentaire entre ces deux poissons, signe d’une probable compétition interspécifique. Cette compétition serait cependant atténuée par leurs rythmes alimentaires différents ainsi que par leur utilisation différente des ressources littorales, terrestres et pélagiques. En effet, bien que les deux espèces occupent pratiquement la même position trophique, L. miodon est beaucoup plus dépendant des ressources alimentaires pélagiques que L. tanganicanus, qui s’insère plus dans le réseau trophique littoral. Les profils des acides gras dans les poissons et les composants du plancton indiquent que les deux espèces de poissons ont des compositions en acides gras très proches et que la qualité nutritionnelle du zooplancton varie relativement peu au cours de l’année. Quant à la productivité du zooplancton, elle subit des variations saisonnières importantes, qui sont dépendantes à la fois de la quantité et de la composition du phytoplancton. Enfin, les profils d’acides gras ont aussi révélé que les bactéries contribuent significativement à la biomasse du zooplancton et des poissons, ce qui démontre la contribution de la boucle microbienne à la production des consommateurs.(DOCSC03) -- FUNDP, 201
Mystery of the parasites inhabiting pelagic zones: the case of monogeneans in Lake Tanganyika
No full textPelagic zones are characterised by consistent large-scale patterns of circulation. Lake Tanganyika is
the deepest of the African Great Lakes and harbours one of the most diverse fish assemblages. A high
species richness in the littoral zone contrast with a lower diversity in the open waters. Therefore, Lake
Tanganyika, as an enclosed ecosystem, provides a plying field to study evolutionary and ecological
processes in open water areas worldwide. Research on parasite diversity and dynamics on ecosystem level
is underrepresented in the Global South. Our teamwork is based on a multilateral North-South collaboration
with the shared goal to uncover diversity and pelagic ecosystem dynamics in this biodiversity hotspot. To
explore evolutionary and ecological patterns of parasitic flatworms in this barrier-free habitat, we examined
spatiotemporal dynamics of the monogenean fauna infecting two endemic species of pelagic clupeid hosts
in the lake.
We combined data on spatiotemporal dynamics (1730 screened fishes, 3710 parasites) of two
parasite species (Kapentagyrus spp., Monogenea) with morphological variation of their clupeid hosts to
investigate general patterns of host-parasite interactions in the lake’s pelagic zone of this ancient lake.
Starting from pooled population samples, altogether containing more than 800 parasite specimens, we
provide the first population-genomic study on any parasite in the African Great Lakes, using the relatively
new DNA PoolSeq technique.
Combining ecological and genomic data, we show that the distribution of parasitic flatworms is
geographically restricted by host life strategies even in this ecosystem which lacks obvious physical
barriers. Contrasting levels of variation across mitochondrial protein coding regions within and across
monogenean species are likely linked to the age of diversification. Furthermore, we highlight PoolSeq as
suitable method for (mito–)genomics of minute taxa that are hard to access in the field through a
comparison of population-genetic parameters based on individual specimens vs. pooled samples
Mystery of the parasites inhabiting pelagic zones: the case of monogeneans in Lake Tanganyika
No full textPelagic zones are characterised by consistent large-scale patterns of circulation. Lake Tanganyika is
the deepest of the African Great Lakes and harbours one of the most diverse fish assemblages. A high
species richness in the littoral zone contrast with a lower diversity in the open waters. Therefore, Lake
Tanganyika, as an enclosed ecosystem, provides a plying field to study evolutionary and ecological
processes in open water areas worldwide. Research on parasite diversity and dynamics on ecosystem level
is underrepresented in the Global South. Our teamwork is based on a multilateral North-South collaboration
with the shared goal to uncover diversity and pelagic ecosystem dynamics in this biodiversity hotspot. To
explore evolutionary and ecological patterns of parasitic flatworms in this barrier-free habitat, we examined
spatiotemporal dynamics of the monogenean fauna infecting two endemic species of pelagic clupeid hosts
in the lake.
We combined data on spatiotemporal dynamics (1730 screened fishes, 3710 parasites) of two
parasite species (Kapentagyrus spp., Monogenea) with morphological variation of their clupeid hosts to
investigate general patterns of host-parasite interactions in the lake’s pelagic zone of this ancient lake.
Starting from pooled population samples, altogether containing more than 800 parasite specimens, we
provide the first population-genomic study on any parasite in the African Great Lakes, using the relatively
new DNA PoolSeq technique.
Combining ecological and genomic data, we show that the distribution of parasitic flatworms is
geographically restricted by host life strategies even in this ecosystem which lacks obvious physical
barriers. Contrasting levels of variation across mitochondrial protein coding regions within and across
monogenean species are likely linked to the age of diversification. Furthermore, we highlight PoolSeq as
suitable method for (mito–)genomics of minute taxa that are hard to access in the field through a
comparison of population-genetic parameters based on individual specimens vs. pooled samples
Monogenean parasites of sardines in Lake Tanganyika: diversity, origin and intraspecific variability
No full textWhereas Lake Tanganyika’s littoral and benthic zones are famous for their diverse fish communities, its pelagic zone is dominated by few species, of which two representatives of Clupeidae (Limnothrissa miodon and Stolothrissa tanganicae) take a pivotal role. We investigated the monogenean fauna infecting these freshwater clupeids to explore the link between parasite morphology and host species identity, or seasonal and geographical origin, which may reveal host population structure. Furthermore, we conducted phylogenetic analyses to test whether these parasitic flatworms mirror their host species’ marine origin. Based on 406 parasite specimens infecting 385 host specimens, two monogenean species of Kapentagyrus Kmentová, Gelnar and Vanhove, gen. nov. were morphologically identified and placed in the phylogeny of Dactylogyridae using three molecular markers. One of the species, Kapentagyrus limnotrissae comb. nov., is host-specific to L. miodon while its congener, which is new to science and described as Kapentagyrus tanganicanus Kmentová, Gelnar and Vanhove, sp. nov., is infecting both clupeid species. Morphometrics of the parasites’ hard parts showed intra-specific variability, related to host species identity and seasonality in K. tanganicanus. Significant intra-specific differences in haptor morphometrics between the northern and southern end of Lake Tanganyika were found, and support the potential use of monogeneans as tags for host population structure. Based on phylogenetic inference, we suggest a freshwater origin of the currently known monogenean species infecting clupeids in Africa, with the two species from Lake Tanganyika representing a quite distinct lineage
Monogenean parasites of sardines in Lake Tanganyika: diversity, origin and intraspecific variability
No full textWhereas Lake Tanganyika’s littoral and benthic zones are famous for their diverse fish communities, its pelagic zone is dominated by few species, of which two representatives of Clupeidae (Limnothrissa miodon and Stolothrissa tanganicae) take a pivotal role. We investigated the monogenean fauna infecting these freshwater clupeids to explore the link between parasite morphology and host species identity, or seasonal and geographical origin, which may reveal host population structure. Furthermore, we conducted phylogenetic analyses to test whether these parasitic flatworms mirror their host species’ marine origin. Based on 406 parasite specimens infecting 385 host specimens, two monogenean species of Kapentagyrus Kmentová, Gelnar and Vanhove, gen. nov. were morphologically identified and placed in the phylogeny of Dactylogyridae using three molecular markers. One of the species, Kapentagyrus limnotrissae comb. nov., is host-specific to L. miodon while its congener, which is new to science and described as Kapentagyrus tanganicanus Kmentová, Gelnar and Vanhove, sp. nov., is infecting both clupeid species. Morphometrics of the parasites’ hard parts showed intra-specific variability, related to host species identity and seasonality in K. tanganicanus. Significant intra-specific differences in haptor morphometrics between the northern and southern end of Lake Tanganyika were found, and support the potential use of monogeneans as tags for host population structure. Based on phylogenetic inference, we suggest a freshwater origin of the currently known monogenean species infecting clupeids in Africa, with the two species from Lake Tanganyika representing a quite distinct lineage
Host lifestyle and parasite interspecific facilitation mediate co-infection in a species-poor host–parasite system
Full text linkDespite their important ecological role, questions remain on mechanisms structuring parasite assemblages. We present an endemic and species-poor parasite–host system of two species of clupeid fishes Limnothrissa miodon, Stolothrissa tanganicae) and two species of monogenean parasites (Kapentagyrus, Dactylogyridae) from Lake Tanganyika as a model to study parasite distribution patterns and co-infection dynamics in nature. We modelled spatiotemporal dynamics of parasite–host interaction using infection data along the north–south axis of Lake Tanganyika (660 km) over the course of two seasons and four years (1730 fish, 3710 parasites). We found temporal stability of parasite infection, which contrasts with previously reported seasonally driven fluctuations of fish host abundances. We found a difference in spatial structure between the parasite species which follows the contrasting dispersal pattern of their respective host species. On L. miodon, the host species that is infected by the two parasite species, we discovered a positive correlation with host body size for one parasite species, and a negative correlation for the other species. The apparent host-size related replacement in the two parasite species infecting L. miodon contrasts with the beneficial influence that each of the parasite species has on the other. Parasites have been reported in previous studies to change habitat depending on host size/age. Differences in abundance and prevalence here reported between parasite species infecting the same host species related to the host body length further illustrate the parasites’ dependence on changes in lifestyle of the host during its ontogenetic development. Also, possible mechanisms underlying the reported facilitation of infection are discussed. In conclusion, we show that in this closed, species-poor system parasite infection dynamics are dependent on a combination of host mobility, host lifestyle changes over ontogenetic development, and interspecific interactions between parasites.Acknowledgements –
We would like to thank Stephan Koblmüller,Holger Zimmermann, Jiří Vorel, Simona Georgieva, GyrhaissKapepula Kasembele, Cyprian Katongo, Taylor Banda, Aneesh P.H. Bose, Filip A. M. Volckaert and Els De Keyzer for their helpin organising and conducting field work. Pierre-Denis Plisnier isacknowledged for providing bathymetric data of Lake Tanganyika.Funding – The study was supported by the Czech ScienceFoundation (GACR) project no. P505/12/G112 – EuropeanCentre of Ichtyoparasitology (ECIP) and standard project GA19-13573S, research grant 1513419N and project GOH3817N(European Marine Biological Research Centre (EMBRC) Belgium)of the Research Foundation – Flanders (FWO-Vlaanderen), GlobalMinds project GM2O18INITO7 and ERC incentive fundingBOF21INCENT09 of Hasselt University and South InitiativeCD2018SIN218A101 of VLIR-UOS. AJCL (BOF19OWB02),NK (BOF21PD01) and MPMV (BOF20TT06) received supportfrom the Special Research Fund of Hasselt University.Permits – Fieldwork was carried out with the approval of thecompetent local authorities under mission statement 031/MINRST/CRH-U/2016 and the permission of the Fisheries Department ofZambia and under a study permit issued by the government ofZambia (SP 00873
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
- …
