1,721,032 research outputs found
The diverse prey spectrum of the Tanganyikan scale-eater Perissodus microlepis (Boulenger, 1898)
Get PDFFeeding upon the scales of other fish—lepidophagy—is a highly specialized foraging strategy in fish. Scale-eating is rare in teleosts, yet has evolved several times in East African cichlids, the most famous case being the Perissodini clade in Lake Tanganyika. Here, we examined the prey spectrum of the scaleeater Perissodus microlepis (Boulenger, 1898) via morphological assessment and targeted sequencing (barcoding) of ingested scales. We found that the size of the ingested scales, but not their number, correlates with the body size of scale-eaters. Sequencing of a segment of the mitochondrial ND2 gene in more than 300 scales revealed that P. microlepis feed upon a broad spectrum of prey species. In total, we detected 39 different prey species, reflecting the cichlid community in the rocky littoral zone of Lake Tanganyika. The most common prey were the algae-eaters Petrochromis polyodon, Pe. ephippium, Eretmodus cyanostictus, Tropheus moorii, and Simochromis diagramma, which make up more than half of the diet. The diversity of scales found within scale-eaters and the overall broad prey spectrum suggest that P. microlepis is an opportunistic feeder. Mouth-handedness and body color hue of the scale-eaters do not seem to have an influence on prey choice
Evolution: An Archipelago Replete with Replicates
No full textAdaptive radiations, in which repeated bouts of diversification lead to phenotypically similar species, highlight the power of natural selection and predictability in evolution. A newly discovered radiation of stick spiders on Hawaii helps shed new light on this phenomenon
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
Convergence and plasticity in the adaptive radiation of cichlid fishes
Get PDFEver since Charles Darwin and Alfred Wallace (1858) propelled our understanding about the importance of natural selection in the transformation of species, researchers endeavoured to use this intellectual foundation to explain larger patterns of biodiversity. One pattern emerging from the observation of phylogenetic relationships and ecological adaptations of species is the abundance of lineages, which are apparently rapidly diversifying, resulting in ecologically diverse clades of species. Most of the biodiversity we know is made up by such clades, being the result of so-called adaptive radiations. Phenotypic diversification and lineage accumulation in adaptive radiations have received considerable attention and great progress has been made in understanding these aspects. Adaptive radiations can be triggered by an ecological opportunity, i.e. a newly formed or colonized habitat lacking competing species or the formation of a key-innovation, a novel trait that allows for the invasion of a completely novel set of niches. The radiation of East African cichlid fishes, and other groups of fishes, are hypothesized to have been triggered by a key-innovation, namely a reorganisation of the pharyngeal jaw apparatus (Liem 1973). Liem’s hypothesis attributes the evolutionary success of groups with certain pharyngeal jaw modifications to an increased versatility in exploiting resources. Although morphological descriptions of the pharyngeal jaw apparatus for many taxa of fishes abound in the literature, and studies with functional, biomechanical or ecological perspectives are numerous as well, as of yet no concise treatise about the evolutionary implications of the different aspects and characteristics of the pharyngeal jaw has been published. This gap I thrive to close with the first chapter of this thesis.
The course of adaptive radiations might be influenced by a phenomenon only little studied in this context so far. Phenotypic plasticity, the ability of a genotype to produce different phenotypes depending on environmental cues, might increase a founding populations chance of persistence. Novel niches might also be invaded more quickly, since the phenotypic shift due to plasticity might place a population in the ‘realm of attraction’ of a peak on the adaptive landscape. If plasticity is only exhibited in some directions in morphospace, but not in others it has the potential of biasing evolutionary trajectories in adaptive radiations. To better understand if phenotypic plasticity in the pharyngeal jaw might have influenced the adaptive radiations of cichlids, I studied the Nicaraguan Midas cichlid in a common garden experiment. My demonstration of plasticity in the cichlids’ pharyngeal jaw, reported in chapter 2, suggests it as a factor to be considered in answering the question of why there are so many cichlid species.
The concept of adaptive radiation is intimately related to ecological adaptation by means of natural selection. Thus, one would not be surprised if phenomena indicative of natural selection would be common in adaptive radiations. One of the strongest cases for the action of natural selection, since the birth of the idea, has been made with the argument of convergent evolution. Separation in time or by geography was, however, assumed to be necessary due to competitive exclusion (Osborn 1902). This principle, later formulated by Gause (1934), was questioned to be applicable to some communities of organisms, one of them being the cichlid species flocks of East Africa. Ernst Mayr (1984) asked:
“The coexistence of hundreds of closely related species in the same lake poses some fundamental questions concerning competition and resource utilization. To what extent, if any, is the existence of fish flocks in freshwater lakes in conflict with the concept of competitive exclusion?”
This question is investigated in chapter 3, which is concerned with convergence within the cichlid radiation in Lake Tanganyika. The revealed abundance of ecomorphological convergence without geographical or chronological separation indeed seems to defy Gause’s principle. Furthermore, it suggests the facility of coexistence of convergent species to be another key factor for the cichlids’ species richness that has been previously overlooked.
The large overlap in morpho- and ecospace between subclades of Tanganyikan cichlids is not unique, but emerges as a common feature of adaptive radiations. This is exemplified by the adaptive radiation of Antarctic notothenioid fishes, the topic of chapter 4, comprising several families, which diversified in parallel along the benthic-pelagic axis. Thus, an adaptive radiation of fishes, taking place in a most different setting than the tropical, confined, freshwater environment in which cichlids diversified, nevertheless exhibits intriguing parallels in subclade overlap. Convergence might hence be a feature of radiations in general
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
koamabayili/VECTRON-author-checklist: VECTRON author checklist
No full textWe have done our best to complete the author checklist relating to the use of animals in the hut study. Note that the objective for the hut study was to evaluate the IRS treatment applications for residual efficacy against Anopheles mosquitoes, including the local An. coluzzii mosquito population. Cows were only used to attract mosquitoes into the huts and no tests were carried out directly on the cows. The author checklist is intended for use with studies where experiments are carried out on animals, which is why we have had such difficulty in completing this for the hut study, as many of the questions do not relate to how the cows were used
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