1,720,979 research outputs found
Reproduction and migration in relation to senescence in the barn swallow Hirundo rustica : A study of avian “centenarians”
No full textA. P. Moller, F. de Lope and N. Saino: Reproduction and migration in relation to senescence in the barn swallow Hirundo rustica: A study of avian 'centenarians'. Senescence reflects the decrease in age-dependent residual reproductive value, and a previous study of a cohort of migratory barn swallows (Hirundo rustica) that had reached advanced ages for this species (at least five years old) provided evidence consistent with senescence such as reduced reproductive performance and increased abundance of parasites. We studied a population of migratory barn swallows over a number of years. Several questions were asked including 1) how do longer lived birds compare to shorter lived individuals of the same species, 2) is there a difference in individuals of the same species that live in different geographical regions, and 3) how do patterns of reproduction change during aging? We compared the phenotypes of 87 individuals from three populations in Denmark, Italy and Spain that had reached at least five years old with those of control individuals matched for sex, arrival date and breeding site. These controls only became one year old, i.e., they were not found thereafter and both groups of individuals were compared in their first year of life. Results showed that there were no significant differences in any of 11 morphological characters or in the abundance of three ectoparasites between the two groups of birds. Females that eventually became very old had relatively smaller first clutches as one year olds than did one year old controls, while males that eventually became very old had mates that laid clutches that were relatively larger than those of controls. Annual fecundity showed a similar pattern, with an increased sex difference in fecundity between birds from Spain than in Italy and in Denmark. Danish barn swallows that achieved older ages had relatively lower haematocrits than control individuals of the same sex, age and arrival date captured at the same site, while the difference in haematocrits between these two categories of individuals was small for Italian birds. Spring arrival date was relatively earlier in Danish males that eventually became very old compared to control males of the same age and tail length (a correlate of fitness) that arrived at the same site, while the two age categories of females did not differ in arrival date. In the Spanish population there was no difference in arrival date between the birds that aged most successfully and controls for either sex. We will discuss these findings in relation to current senescence theories
Parasitism, immunity and arrival date in a migratory bird
No full textLong-distance bird migration is expensive, and individuals in prime condition are therefore expected to arrive at the breeding grounds earlier than the average individual in the population. We tested whether arrival date during spring migration was associated with low parasite burden and strong T-cell-dependent immune response in populations of the transequatorially migrating Barn Swallow Hirundo rustica from Denmark, Italy, and Spain. Male Barn Swallows with heavy infestations of the chewing louse Hirundoecus malleus L. arrived later than other males, whereas that was not the case for females. This negative relationship remained after controlling the relationship between parasite load and arrival for tail length. Infection with blood parasites of the species Haemoproteus prognei was associated with delayed arrival in the Spanish population, which was the only one with a high prevalence of blood parasites. High intensities of infestation with a commensal feather mite were associated with early arrival by females, but also by males when the independent relationship between tail length and intensity of mite infestation was controlled statistically. Experimental manipulation of nest infestation with the hematophagous mite Ornithonyssus bursa Berlese affected the arrival date of adult males, but not of females in the following year, with arrival date being inversely related to the experimental mite population size. Males with strong T-cell responses arrived earlier than males with weak responses, independent of their tail length in two of three populations, but there was no significant relationship in females. These findings are in accordance with predictions based on the hypothesis that bird migration is dependent on condition, with individuals in prime condition arriving early
Elevated frequency of abnormalities in barn swallows from Chernobyl
No full textEver since the Chernobyl accident in 1986, that contaminated vast areas in surrounding countries with radiation, abnormalities and birth defects have been reported in human populations. Recently, several studies suggested that the elevated frequency of such abnormalities can be attributed to poverty and stress in affected human populations. Here, we present long-term results for a free-living population of barn swallows, Hirundo rustica, demonstrating the presence of 11 morphological abnormalities in populations around Chernobyl, but much less frequently in an uncontaminated Ukrainian control population and three more distant control populations. The presence of these abnormalities in barn swallows is associated with reduced viability. These findings demonstrate a link between morphological abnormalities and radiation in an animal population that cannot be attributed to poverty and stress. The most parsimonious hypothesis for abnormalities in animal and human populations alike is that the effects are caused by the same underlying cause, viz. radiation derived from the Chernobyl accident
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
Geographic variation in tha G matrices of wild populations of the barn swallow
No full textIn this paper, we present an analysis of genetic variation in three wild populations of the barn swallow, Hirundo rustics. We estimated the P, E, and G matrices for six linear morphological measurements and tested for variation among populations using the Flury hierarchical method and the jackknife followed by MANOVA method. Because of nonpositive-definite matrices, we had to employ 'bending' to analyse the G and E matrices with the Flury method. Both statistical methods agree in finding that the P and G matrices are significantly different but comparison between the analysis of the P matrices and pairwise analyses of the P, E, and G matrices suggests caution in interpreting the Flury results concerning differences in matrix structure. The significant variation among the populations in the G matrices appears to be due in large measure to the most geographically distant population
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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