1,720,963 research outputs found
Avian life in a seasonally arid tropical environment: Adaptations and mechanisms in breeding, moult and immune function
Full text linkThere is a growing appreciation of the diversity and uniqueness of tropical organisms, but evidence about the selection pressures that shape this diversity remains sketchy. In this thesis, I investigated how variation in life history traits arises from tropical environmental seasonality, starting with exploration of the annual cycle of the Common Bulbul Pycnonotus barbatus in Nigeria. This revealed that breeding was not seasonal, but moult was timed almost entirely to the wet season with only few individuals moulting into the dry season, suggesting that breeding and to a lesser extent moult, are decoupled from season, allowing me to test how breeding and moult affect immune function independent of seasonal conditions. On testing this, I found that season explained variation in immune function better than breeding or moult, but unexpectedly, immune indices were higher in the dry season and during breeding, contrary to expectations that infection risk is higher in the wet season, and that breeding constrains resources for immune function. Furthermore, I compared immune indices along the cool-wet to hot-dry environmental gradient in Nigeria and found that immune indices were rather similar. I then tested the effect of diet alteration on immune function, body mass and moult of bulbuls in captivity and found that bulbuls fed on fruits had better immune function, body mass and moult than those fed on invertebrates. These findings together suggest environmental conditions affect immune function more directly than via resource allocation trade-offs, but that variation in immune function does not follow simple environmental productivity pattern
Avian life in a seasonally arid tropical environment:Adaptations and mechanisms in breeding, moult and immune function
Full text linkThere is a growing appreciation of the diversity and uniqueness of tropical organisms, but evidence about the selection pressures that shape this diversity remains sketchy. In this thesis, I investigated how variation in life history traits arises from tropical environmental seasonality, starting with exploration of the annual cycle of the Common Bulbul Pycnonotus barbatus in Nigeria. This revealed that breeding was not seasonal, but moult was timed almost entirely to the wet season with only few individuals moulting into the dry season, suggesting that breeding and to a lesser extent moult, are decoupled from season, allowing me to test how breeding and moult affect immune function independent of seasonal conditions. On testing this, I found that season explained variation in immune function better than breeding or moult, but unexpectedly, immune indices were higher in the dry season and during breeding, contrary to expectations that infection risk is higher in the wet season, and that breeding constrains resources for immune function. Furthermore, I compared immune indices along the cool-wet to hot-dry environmental gradient in Nigeria and found that immune indices were rather similar. I then tested the effect of diet alteration on immune function, body mass and moult of bulbuls in captivity and found that bulbuls fed on fruits had better immune function, body mass and moult than those fed on invertebrates. These findings together suggest environmental conditions affect immune function more directly than via resource allocation trade-offs, but that variation in immune function does not follow simple environmental productivity pattern
Avian life in a seasonally arid tropical environment:Adaptations and mechanisms in breeding, moult and immune function
Full text linkThere is a growing appreciation of the diversity and uniqueness of tropical organisms, but evidence about the selection pressures that shape this diversity remains sketchy. In this thesis, I investigated how variation in life history traits arises from tropical environmental seasonality, starting with exploration of the annual cycle of the Common Bulbul Pycnonotus barbatus in Nigeria. This revealed that breeding was not seasonal, but moult was timed almost entirely to the wet season with only few individuals moulting into the dry season, suggesting that breeding and to a lesser extent moult, are decoupled from season, allowing me to test how breeding and moult affect immune function independent of seasonal conditions. On testing this, I found that season explained variation in immune function better than breeding or moult, but unexpectedly, immune indices were higher in the dry season and during breeding, contrary to expectations that infection risk is higher in the wet season, and that breeding constrains resources for immune function. Furthermore, I compared immune indices along the cool-wet to hot-dry environmental gradient in Nigeria and found that immune indices were rather similar. I then tested the effect of diet alteration on immune function, body mass and moult of bulbuls in captivity and found that bulbuls fed on fruits had better immune function, body mass and moult than those fed on invertebrates. These findings together suggest environmental conditions affect immune function more directly than via resource allocation trade-offs, but that variation in immune function does not follow simple environmental productivity pattern
Body reserves in intra-African migrants
Full text linkAvian migration has been shown to be a life history strategy for surviving environmental resource variability, but it requires increased body reserves for long distance flight. Fat reserves make excellent energy stores for barrier crossing, whereas proteins generate less energy for the same mass of fat but provide water during breakdown which may become especially useful when birds become water stressed. Intra-African migrants are probably unlikely to have to cross barriers equivalent to the Sahara and the Mediterranean and so may have different patterns of mass reserves reflecting the utility of metabolizing fat versus protein in hot, tropical environments. We examined differences in proportions of body mass gain, pectoral muscle score and fat score between intra African migrants, Palearctic migrants and resident African species. We tested whether intra-African migrants show a distinct seasonal peak in mass gain corresponding to expected peak migration period in a manner similar to Palearctic migrants, but maintain larger muscle tissues, because Palearctic migrants are more constrained by a need to heavily up regulate fat in addition to fat free reserves before migration due to the energy requirements of crossing the barrier of the Sahara. We found that intra-African migrants had a peak seasonal mass gain similar to Palearctics whereas African residents did not, and that Palearctics increased fat reserves with pectoral muscle reserves, so that they had much higher fat scores for any given level of pectoral muscle compared to intra-African migrants or resident species. Our results suggest that barrier crossing leads to a distinct increase in fat reserves rather than migration per se, and suggests that intra-African migrants are more similar in their reserve management to African residents. Mass gain devoid of visible fat accumulation in intra-African migrants may therefore suggest absence of barriers during migrationPeer reviewe
Geographic variation in baseline innate immune function does not follow variation in aridity along a tropical environmental gradient
Full text linkC.J.N. was supported by a studentship funded by the Leventis Conservation Foundation through the University of St. Andrews, UK and an Ubbo Emmius grant of the University of Groningen. B.I.T. was supported by the Netherlands Organisation for Scientific Research (NWO-Vidi 864.10.012). This is publication number 141 of the A.P. Leventis Ornithological Research Institute, Nigeria and chapter 7 of the thesis ‘Avian life in a seasonally arid tropical environment: adaptations and mechanisms in breeding, molt and immune function’91, submitted for the award of a doctorate degree by the University of Groningen, the Netherlands and University of St. Andrews, UK.Geographic variation in aridity determines environmental productivity patterns, including large-scale variability in pathogens, vectors and associated diseases. If disease risk decreases with increasing aridity and is matched by immune defense, we predict a decrease in innate immune function along a gradient of increasing aridity from the cool-wet forest to the hot-dry Sahel, from south to north in Nigeria. We sampled blood and measured five innate immune indices from 286 Common Bulbuls Pycnonotus barbatus between 6 and 13°N. We sampled in the dry season; we resampled the first location (Jos) also as the last sample location to test temporal change in immune function. Immune indices did not decrease with aridity. One immune index, nitric oxide concentration showed a weak quadratic pattern. In Jos, ovotransferrin concentration, haemagglutination and haemolysis titres increased 12 weeks into the dry season, contrary to expectations that immune indices should decrease with increased dryness. In this tropical system, innate immune function does not decrease with increasing aridity but temporal factors within a location may influence immune function more strongly than spatial variation in aridity, suggesting that immune variation does not follow a simple environmental productivity pattern. Consequently, caution should probably be exercised in predicting effects of climate variability on immune function or disease risk.Peer reviewe
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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