1,720,966 research outputs found
Multi-stressor ecotoxicologische studie op Culex muggen: van toxiciteitsmechanismen tot biotische interacties
No full textNatural populations are increasingly facing multiple stressors. Their ability to deal with interacting stressor combinations will be crucial for their local persistence. Populations of target species are typically exposed to pesticide mixtures and natural stressors, and are increasingly developing resistance to single pesticides. Nevertheless, we have poor knowledge whether natural stressors and the presence of pesticide resistance shape mixture toxicity. To assess the pesticide control efficiency and to reduce ecological damage to non-target species, it is important to quantify the effect of pesticide mixtures and compare them with the effect of their single pesticides on pest species, non-target species and their predator-prey interactions. Natural stressors that are widespread in freshwater systems are predation risk and warming; both may magnify the toxicity of single pesticides. The latter pattern has been captured in the 'Climate-induced toxicant sensitivity' concept (CITS). Nevertheless, deviations from this general pattern have been reported. To advance insights, there is a pressing need to identify the underlying molecular stress mechanisms of the CITS patterns. Moreover, while many studies on the toxicity of pesticides looked at the effects of a higher mean temperature, effects of the realistic scenario of daily temperature variation (DTV, which is a key component of global warming) are understudied. In this context, developmental stages and consequences for biotic interactions such as competition have also been largely ignored.
In Chapters 1-2 (Part I), I tested the single and combined effects of the pesticide chlorpyrifos and the biopesticide Bacillus thuringiensis israelensis (Bti) on the survival of a chlorpyrifos-resistant and non-resistant strain of the Southern house mosquito Culex quinquefasciatus. In Chapter 1, I investigated whether these effects of chlorpyrifos and/or Bti were magnified by synthetic predator cues of Notonecta water bugs. Single exposure to Bti caused mortality in both strains and single exposure to chlorpyrifos caused only mortality in the non-resistant strain, while predator cues did not induce mortality. The chlorpyrifos-resistant strain was more sensitive to Bti, indicating a cost of resistance. The interaction types between chlorpyrifos and Bti (additive), between chlorpyrifos and predator cues (additive), and between Bti and predator cues (additive) were consistent in both strains. In Chapter 2, I tested the effects of chlorpyrifos and/or Bti on the mortality by predation by the pygmy backswimmer Plea minutissima. After exposure to the mixture, equal mortality by predation was caused in both mosquito strains. As expected, less mortality by predation in the chlorpyrifos-resistant mosquito strain compared to the non-resistant strain occurred after the chlorpyrifos exposure. Notably, the predator killed more mosquito larvae of the resistant strain compared to the non-resistant strain after Bti exposure indicating a predation cost of resistance in the presence of a biopesticide. Part I highlights the integrated use of Bti and natural control by predators as a promising strategy to counter the build-up of resistance and to keep vector mosquito populations under control.
In chapters 3-5 (Part II), I tested whether daily temperature variation (DTV) magnifies the toxicity of chlorpyrifos in the Northern house mosquito Culex pipiens. In Chapter 3, I also studied whether DTV magnifies the single toxicity of Bti and/or its combined toxicity with chlorpyrifos. DTV was not lethal and did not change the toxicity of the individual pesticides. Yet, a key novel finding was that high DTV increased the mortality of the mixture by changing the interaction between both pesticides from additive to synergistic. In Chapter 4, I tested whether the effect of DTV and its interaction with chlorpyrifos was dependent on the developmental stage. DTV had again no direct negative effects and did not change the toxicity of the individual pesticides. Exposure to chlorpyrifos at a constant temperature-imposed mortality and reduced the heat tolerance in both larvae and adult males, but not in adult females. This pesticide-induced decrease of heat tolerance is in line with the TICS ("toxicant-induced climate change sensitivity") concept whereby the first evidence was provided that the TICS can be sex-specific. Notably, DTV interacted synergistically with chlorpyrifos for heat tolerance of the larvae and adult females. DTV increased the chlorpyrifos-induced decrease (CITS) of heat tolerance (TICS), providing support for the reciprocal effects between DTV and contaminants, hence the coupling of the TICS and CITS concepts (CITS --> TICS). This coupling of CITS and TICS was developmental stage specific as the interaction effect between DTV and chlorpyrifos was additive for adult males. In Chapter 5, I also studied the effect of competition with the water flea Daphnia magna on the combined effects of DTV and chlorpyrifos on the mosquito larvae. In this experiment, no pesticide-induced mortality was observed in the presence of DTV due to an accelerated pesticide breakdown under DTV, which contrasts with the general pattern of the CITS concept. There was neither a significant effect of competition on mortality, nor did competition influence the interaction between the single pesticide and DTV. Together these chapters underscore the importance to consider the effects of DTV on pesticide toxicity and on pesticide exposure in risk assessment of toxicants.
In Chapters 6-7 (Part III), I tested three concentrations of the pesticide chlorpyrifos (absence, low-effect and high-effect) in the absence and presence of 4 °C warming on larvae of the Northern house mosquito Culex pipiens. In Chapter 6, I showed that both the low-effect and high-effect chlorpyrifos concentrations were lethal and generated mostly negative sublethal effects: activity of acetylcholinesterase (AChE) and total fat content decreased, and oxidative damage to lipids increased, yet growth rate increased. Warming was slightly lethal, yet had positive sublethal effects: growth rate, total fat content and metabolic rate increased, and oxidative damage decreased. The independent action model identified the expected synergistic interaction between chlorpyrifos and warming in four out of seven response variables. Notably, three variables (survival, AChE, and fat content) were strongly dependent on the chlorpyrifos concentration, and two of these (AChE and fat content) were not associated with a significant interaction in the general(ised) linear models. In Chapter 7, I tested the effects of chlorpyrifos under warming at the gene expression level. By applying the independent action model on RNA-seq data I confirmed my hypothesis that synergistic interactions between both stressors at the phenotypic level are underpinned by a higher frequency or strength of antagonistic upregulations (less upregulated than expected based on responses to the single stressors) and of synergistic downregulations (more downregulated than expected) of general stress defence response genes (protection of macromolecules, antioxidant processes, detoxification, and energy metabolism/allocation).
These results are relevant to improve vector mosquito control strategies, resistance management and ecological risk assessment of pesticides. I identified a novel cost of resistance to a chemical pesticide in terms of increased vulnerability to a biopesticide, and to predation after exposure to the biopesticide. In addition, the finding of a higher toxicity of the mixture at high DTV compared to the typically used constant test temperatures in the laboratory urges caution when evaluating the environmental impact of pesticide mixtures. Not only the effects of DTV on pesticide toxicity, but also on pesticide degradation (hence exposure) should be considered in ecotox testing. I identified several factors that may affect the detection of the CITS concept: dependence on concentration, developmental stage, genetic strain and sex, and appropriate null model testing. The identified factors are important to take into account when studying the toxicity of contaminants in a warming world. Finally, I provide guidelines to formally test the stressor interaction type for gene expression data. Following this approach, my results highlight that a quantitative analysis of the frequency and strength of the interaction types of general stress response genes, specifically focusing on antagonistic upregulations and synergistic downregulations, may advance the mechanistic understanding of how other stressors modify the toxicity of contaminants.status: Publishe
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
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
Author-wise bibliometric analysis based on entropy.
No full textAuthor-wise bibliometric analysis based on entropy.</p
Integrating trait multidimensionality, predation and autotomy to explain the maintenance of boldness
No full text© 2017 The Association for the Study of Animal Behaviour There is an ongoing debate on how personality types are maintained within populations. We tested, for the first time, the potential of trait multidimensionality and trait compensation, where prey compensate for the costs of one trait by relying more on another one, in maintaining variation in boldness within a population. We studied how four boldness-related traits and swimming escape performance covary and shape the probability of survival and autotomy of Ischnura pumilio damselfly larvae in an experiment with predatory dragonfly larvae. Our results did not support the common belief that bold individuals are selected against in terms of survival selection by predation. Instead, we found survival selection favouring individuals combining being bold for two boldness-related traits. The four boldness-related traits did not covary frequently, supporting the multidimensionality of boldness. Moreover, animals bolder for one trait (activity in the presence of predator cues) were shyer for another trait (response to predator cues), which indicated trait compensation. However, the support for trait compensation was limited. The only other case of trait compensation was that bold larvae compensated for their increased risk-taking behaviour in the presence of a predator with a higher probability of autotomy. These patterns may contribute to maintaining variation in boldness in damselfly populations. Just as boldness-related traits are multidimensional, the mechanisms underlying their persistence in natural populations are also likely to be multifaceted.sponsorship: We thank everyone in our research group and Geert Neyens, Sarah Princen, Lidia Bertjens and Robin De Croon for their support and assistance during the experiment. V.D. and S.D. are PhD fellows of the Fund for Scientific Research Flanders (FWO). Financial support came from FWO research grant G.0704.13 and the KU Leuven Centre of Excellence programme PF/2010/07. (Scientific Research Flanders (FWO), FWO|G.0704.13, KU Leuven Centre of Excellence programme|PF/2010/07)status: Publishe
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