1,720,966 research outputs found
Forgotten in the ocean: systematics, biogeography and evolution of the Trachylepis skinks of the Socotra Archipelago
Full text linkSperm removal and ejaculate size correlate with chelae asymmetry in a freshwater crayfish species
No full textAsymmetry in traits of sexual relevance may impair copulation behaviour and sexual performance of males, ultimately resulting in a fitness cost. Freshwater crayfish males use chelae, a sexually selected trait, to secure and position the female prior to and during mating. Thus, a relatively large chelae asymmetry, resulting from accidental loss and regeneration of one cheliped after autotomy, could have great consequences for male sexual behaviour. We studied copulatory behaviour and sperm expenditure of males paired to a mated female in Austropotamobius italicus, a freshwater crayfish species where both male and female mate multiply and where last-mating males are able to actively remove previously deposited sperm. We aimed at assessing whether male sperm removal and expenditure varied according to sperm allocated by first-mating males, and according to copulation behaviour and phenotypic traits (carapace length, chelae length and relative chelae asymmetry) of second-mating males. Second-mating males did not adjust their ejaculate size in relation to first-mating male ejaculate, nor to the first-mating male’s sperm removed. Moreover, the amount of sperm removed by second-mating males increased with increasing first-mating males ejaculate size, and first-mating male sperm remaining after removal did not correlate with the original first-mating male ejaculate size. Interestingly, the amount of sperm removed by second-mating males decreased with increasing relative chelae asymmetry, while increasing with male body size. However, second-mating (but not first-mating) asymmetric-clawed males produced larger ejaculates than symmetric-clawed ones. Importantly, the proportion of second-mating male sperm remaining after the two matings did not vary with relative chelae asymmetry nor with body size of second-mating males. Thus, small, asymmetric-clawed crayfish males appear to adopt sperm allocation tactics that allow them to fully compensate for their inferior sperm removal ability
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
Effects of female mating status on copulation behaviour and sperm expenditure in the freshwater crayfish Austropotamobius italicus
No full textSperm competition models predict that males should adjust their sperm expenditure according to the risk and/or intensity of sperm competition. In this paper, we analysed copulatory behaviour of both sexes and sperm expenditure in relation to female mating status (virgin or mated) in the freshwater crayfish Austropotamobius italicus, a species where males have been reported to feed on and remove sperm laid by other males. The same females were allowed to be inseminated sequentially by two males, and we compared the sexual behaviours of partners between the first (virgin females) and the second mating (mated females). We found that female resistance did not differ between the first and the second mating, nor males refused or took more time to mount a mated female. However, when mating with a mated female, males reached an effective copulation position significantly later. This occurred because second-mating males removed, by eating, all or most spermatophores previously deposited by first males. As removal was often incomplete, this resulted in a larger amount of sperm being deposited on female ventral parts after the second mating, although second males did not allocate more sperm to mated females than first males did. Thus, the peculiar mode of sperm competition, where males remove previously deposited sperm, and the consequent predictable strong last male prevalence in paternity likely led to the observed lack of adjustment of sperm expenditure to female mating status in this species
Morph-specific immunity in male Podarcis muralis
No full textPermanent colour polymorphism in lizards is maintained by complex interactions between environmental pressures and physiological traits (such as immune responsiveness) that differ among morphs. In this study we investigated whether T-cell mediated immune response vary among male colour morphs in the trimorphic (white, yellow and red) common wall lizard, Podarcis muralis. We found that yellow males showed a lower immune response compared to both red and white males, whose responses were similar. Thus, immune responsiveness is morph-specific in male common wall lizards, suggesting that this physiological trait could play an important role in maintaining colour polymorphism in this species. Moreover, immune responsiveness significantly increased with increasing male size, irrespective of colour morph, indicating that it could be regarded as a condition-dependent trait
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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