1,720,990 research outputs found
Oleic acid is elevated in cell membranes during rapid cold-hardening and pupal diapause in the flesh fly, Sarcophaga crassipalpis.
Full text linkThe integrity of cellular membranes is critical to the survival of insects at low temperatures, thus there is tremendous advantage conferred to insects that can adjust their composition of membrane fatty acids (FA’s). Such changes, known as homeoviscous adaptation, allow cellular membranes to maintain a liquid-crystalline state at temperatures that are normally low enough to cause the membrane to enter the gel state and lose the ability to maintain homeostasis.
Flesh flies (Sarcophaga crassipalpis) were subjected to two experimental conditions that elicit low temperature tolerance: rapid cold-hardening and diapause. FA’s were isolated and analyzed using gas chromatography-mass spectrometry. FA’s changed in response to both rapid cold-hardening and diapause. In response to rapid cold-hardening, the proportion of oleic acid (18:1n-9) in pharate adults increased from 30% to 47% of the total fatty acid pool. The proportion of almost every other FA was reduced. Diapausing pupae experienced an even greater increase in oleic acid proportion to 58% of the total FA pool. Oleic acid not only increases membrane fluidity at low temperature, but also allows the cell membrane to maintain a liquid crystalline state should the temperature increase. This is the first demonstration of homeoviscous adaptation in a cold-hardy insect with a pupal diapause
RNAi of rpS3a suggests a link between this gene and arrested ovarian development during adult diapause in Culex pipiens
Full text linkIn mosquitoes that do not enter diapause, rpS3a is consistently expressed, but in mosquitoes programmed for diapause, expression of rpS3a is intermitted during early diapause, but is then consistently elevated in females 1 month and older. RNAi was performed to evaluate a possible function for rpS3a related to the arrested ovarian development during diapause. dsRNA injected into non-diapausing females suppressed ovarian development. Decreased expression of rpS3a following dsRNA injection was confirmed by Northern blot hybridization. Topical application of JHIII, an endocrine trigger for diapause termination in this species, yielded an almost complete recovery from the RNAi effect. We propose that rpS3a is involved in the shut down of ovarian development that characterizes the adult diapause of Cx. pipiens
Prolonged dehydration resistance by the northern house mosquito, Culex pipiens, during its overwintering diapause
Full text linkThroughout the winter, the northern house mosquito, Culex pipiens, is continually exposed to desiccating conditions, and this water deficit is further exacerbated by long periods with no access to free water. In this study, we report that mosquitoes in diapause are more tolerant of xeric conditions than their nondiapausing counterparts. To counter water loss female mosquitoes reared under conditions that induce diapause have a lower percent water content that results from a higher dry mass which in turn decreases their surface area to volume ratio. Both diapausing and nondiapausing females can tolerate a loss of approximately 30%, but diapausing females conserve their water reserves more do not reach this limit as readily. This mosquito relies solely on drinking free water to replenish its water supply and has no ability to absorb water vapor from the atmosphere. Cuticular hydrocarbon content was nearly 3x higher in diapausing female mosquitoes than nondiapausing individuals, this enhancement impedes water loss through the cuticle. No differences were noted in sorbitol, trehalose, glycerol or the total sugar contents during diapause. Additionally, the utilization on internal lipids by diapausing C. pipiens was significantly lower than nondiapausing female. Thus, the increased dehydration resistance of diapausing females C. pipiens results from the combination of their larger size, accumulation of additional cuticular lipids, and a suppression of metabolism
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
Life history adaptations to polar and alpine environments
No full textThis chapter is concerned with the life-history features of terrestrial invertebrates inhabiting the cold regions of the world. It predominantly focuses on the Antarctic continent and the Arctic elements of the large northern continents, also drawing parallels with the alpine regions of the world's major mountain ranges. To human perception, these polar and montane regions of the planet are clearly challenging regions in which to live. They face environmental stresses that operate on a range of timescales, for example from chronic exposure to low temperature, high winds, freezing, or desiccation, to extreme or short-term acute events. At northern or southern latitudes beyond the polar circles, the sun remains permanently below the horizon for a period of days to months, depending on latitude, each winter, inevitably imposing considerable seasonality on organisms and ecosystems.
Focusing simply on temperature, in the absence of solar-energy input, terrestrial habitats of both regions face comparable extremely low air temperatures during winter. But the two regions are far from identical, with the Antarctic also enduring much lower typical summer temperatures than those of the Arctic (Convey, 1996a; Danks, 1999); hence lack of available energy provides a major constraint on biological activity here. However, the biological impacts of temperature are not well described simply by standard meteorological measures of mean air temperature, and scales and patterns of physical and temporal variation are also important
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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