Density-and trait-mediated effects of a parasite and a predator in a tri-trophic food web

1. Despite growing interest in ecological consequences of parasitism in food webs, relatively little is known about effects of parasites on long-term population dynamics of non-host species or about whether such effects are density- or trait- mediated. 2. We studied a tri-trophic food chain comprised of: (i) a bacterial basal resource (Serratia fonticola), (ii) an intermediate consumer (Paramecium caudatum), (iii) a top predator (Didinium nasutum), and (iv) a parasite of the intermediate consumer (Holospora undulata). A fully-factorial experimental manipulation of predator and parasite presence/absence was combined with analyses of population dynamics, modelling, and analyses of host (Paramecium) morphology and behavior. 3. Predation and parasitism each reduced the abundance of the intermediate consumer (Paramecium), and parasitism indirectly reduced the abundance of the basal resource (Serratia). However, in combination, predation and parasitism had non-additive effects on the abundance of the intermediate consumer, as well as on that of the basal resource. In both cases, the negative effect of parasitism seemed to be effaced by predation. 4. Infection of the intermediate consumer reduced predator abundance. Modelling and additional experimentation revealed that this was most likely due to parasite reduction of intermediate host abundance (a density-mediated effect), as opposed to changes in predator functional or numerical response. 5. Parasitism altered morphological and behavioural traits, by reducing host cell length and increasing the swimming speed of cells with moderate parasite loads. Additional tests showed no significant difference in Didinium feeding rate on infected and uninfected hosts, suggesting that the combination of these modifications does not affect host vulnerability to predation. However, estimated rates of encounter with Serratia based on these modifications were higher for infected Paramecium than for uninfected Paramecium. 6. A mixture of density-mediated and trait-mediated indirect effects of parasitism on non- host species creates rich and complex possibilities for effects of parasites in food webs that should be included in assessments of possible impacts of parasite eradication or introduction

Statistical interpretations and new findings on Variation in Cancer Risk Among Tissues

Tomasetti and Vogelstein (2015a) find that the incidence of a set of cancer types is correlated with the total number of normal stem cell divisions. Here, we separate the effects of standing stem cell number (i.e., organ or tissue size) and per stem cell lifetime replication rate. We show that each has a statistically significant and independent effect on explaining variation in cancer incidence over the 31 cases considered by Tomasetti and Vogelstein. When considering the total number of stem cell divisions and when removing cases associated with disease or carcinogens, we find that cancer incidence attains a plateau of approximately 0.6% incidence for the cases considered by these authors. We further demonstrate that grouping by anatomical site explains most of the remaining variation in risk between cancer types. This new analysis suggests that cancer risk depends not only on the number of stem cell divisions but varies enormously ($\sim$10,000 times) depending on the stem cell's environment. Future research should investigate how tissue characteristics (anatomical site, type, size, stem cell divisions) explain cancer incidence over a wider range of cancers, to what extent different tissues express specific protective mechanisms, and whether any differential protection can be attributed to natural selection

Shear coaxial injector instability mechanisms

There is no definitive knowledge of which of several concurrent processes ultimately results in unstable combustion within liquid rocket chambers employing shear coaxial injectors. Possible explanations are a detrimental change in the atomization characteristics due to a decrease in the gas-to-liquid velocity ratio, a change in the gas side injector pressure drop allowing acoustic coupling to the propellant feed system or the disappearance of a stabilizing recirculation region at the base of the LOX post. The aim of this research effort is to investigate these proposed mechanisms under conditions comparable to actual engine operation. Spray characterization was accomplished with flash photography and planar laser imaging to examine the overall spray morphology and liquid jet breakup processes and with a PDPA to quantify the spatial distribution of droplet size and mean axial velocity. A simplified stability model based on the Rayleigh criterion was constructed for the flow dynamics occurring within the chamber and injector to evaluate the potential coupling between the chamber and injector acoustic modes and was supported by high frequency measurements of chamber and injector pressure oscillations. To examine recirculation within the LOX post recess, velocity measurements were performed in the recess region by means of LDV. Present experiments were performed under noncombusting conditions using LOX/GH2 stimulants at pressures up to 4 MPa

Effects of shortened host life span on the evolution of parasite life history and virulence in a microbial host-parasite system

<p>Abstract</p> <p>Background</p> <p>Ecological factors play an important role in the evolution of parasite exploitation strategies. A common prediction is that, as shorter host life span reduces future opportunities of transmission, parasites compensate with an evolutionary shift towards earlier transmission. They may grow more rapidly within the host, have a shorter latency time and, consequently, be more virulent. Thus, increased extrinsic (i.e., not caused by the parasite) host mortality leads to the evolution of more virulent parasites. To test these predictions, we performed a serial transfer experiment, using the protozoan <it>Paramecium caudatum </it>and its bacterial parasite <it>Holospora undulata</it>. We simulated variation in host life span by killing hosts after 11 (<it>early </it>killing) or 14 (<it>late </it>killing) days post inoculation; after killing, parasite transmission stages were collected and used for a new infection cycle.</p> <p>Results</p> <p>After 13 cycles (≈ 300 generations), parasites from the <it>early-killing </it>treatment were less infectious, but had shorter latency time and higher virulence than those from the <it>late-killing </it>treatment. Overall, shorter latency time was associated with higher parasite loads and thus presumably with more rapid within-host replication.</p> <p>Conclusion</p> <p>The analysis of the means of the two treatments is thus consistent with theory, and suggests that evolution is constrained by trade-offs between virulence, transmission and within-host growth. In contrast, we found little evidence for such trade-offs across parasite selection lines within treatments; thus, to some extent, these traits may evolve independently. This study illustrates how environmental variation (experienced by the host) can lead to the evolution of distinct parasite strategies.</p

Herstellung pfropfpolymerisierter Ionenaustauscher mit Aufklärung des Reaktionsmechanismus

In dieser Arbeit wurde eine reproduzierbare Methode zur Herstellung von Anionenaustauschern auf Basis von Polystyrol/Divinylbenzol-Copolymeren entwickelt und diese eingehend untersucht. Die Methode beruht auf der radikalischen Pfropfpolymerisation ionischer Styrolderivate mithilfe eines Radikalstarters an den vinylischen Doppelbindungen des Grundmaterials. Diese Untersuchungen hatten das Ziel Zusammenhänge zwischen chemischer Struktur und den Eigenschaften der Anionenaustauscher zu identifizieren und diese mithilfe der Methode zu steuern. Es konnte identifiziert werden, dass die radikalische Pfropfpolymerisation sowohl in freier Lösung als auch auf der Oberfläche des Polymer initiiert werden kann und dass sowohl Radikalstarter als auch das verwendete organische Lösungsmittel den Ort der Initiierung beeinflussen. Es gelang außerdem den Einfluss verschiedener Reaktionsparameter auf die Selektivität und die Trenneffizienz, sowie die chemische Struktur der Anionenaustauscher zu identifizieren. Dabei konnte gezeigt werden, dass auf der Polymeroberfläche nur sehr kurze Ketten an Austauschergruppen generiert werden und die Kettenlänge in diesem Bereich keinen Einfluss auf die Selektivität besitzt. Weitere Untersuchungen der Austauscher konnten stattdessen Hinweise darauf liefern, dass die zur Pfropfpolymerisation parallel ablaufende Oxidation des Grundpolymers durch den Radikalstarter die Selektivität der Austauschermaterialien bestimmt

Analyse d'un discours androcentrique: La Pornocratie ou Les femmes dans les temps modernes, de Pierre Joseph Proudhon

L'auteur se propose d'étudier la dimension langagière du discours proudhonien sur la question de la femme, notamment dans son ouvrage posthume La Pornocratie. Quelques éléments d'information sur les conditions de production de ce discours sont rassemblés à la suite d'une reconstruction de ses antécédents. Dans l'étude proprement dite de l'ouvrage, l'accent est mis sur les différentes "stratégies discursives" (recours aux métaphores, aux oppositions sémantiques, à l'identification de termes non équivalents, entre autres). Ces stratégies, intégrées dans un ensemble de "registres" alternants (scientifique, polémique, lyrique), expliquent l'intensité du discours proudhonien sur la femme

An Engineering Method for Adaptive, Context-aware Web Applications

Users of Web-based software encounter growing complexity of the software resulting from the increasing amount of information and service offering. As a consequence, the likelihood that users employ the software in a manner compatible with the provider's interest decreases. Depending on the purpose of the Web application, a provider's goal can be to guide and influence user choices in information and service selection, or to assure user productivity. An approach at addressing these goals is to adapt the software's behavior during operation to the context in which it is being used. The term context-awareness originates in mobile computing, where research projects have studied context recognition and adaptation in specific scenarios. Context-awareness is now being studied in a variety of systems, including Web applications. However, how to account for context in a Web Engineering process is not yet established, nor is a generic means of using context in a Web software architecture. This dissertation addresses the question of how context-awareness can be applied in a general-purpose, systematic process for Web application development: that is, in a Web Engineering process. A model for representing an application's context factors in ontologies is presented. A general-purpose methodology for Web Engineering is extended to account for context, by putting in relation context ontologies with elements of the application domain. The application model is extended with adaptation specifications, defining at which places in the application adaptation to context is to occur, and according to what strategy. Application and context models are system interpretable, in order to support automatic adaptation of a system's behavior during its operation, that is, consequently to user requests. Requirements for a corresponding Web software architecture for context are established first at the conceptual level, then specifically in a content-based architecture based on an XML stack. The CATWALK software framework, an implementation of an architecture enabling adaptation to context is described. The framework provides mechanisms for interpreting application and context models to generate an adaptive application, meaning to generate responses to user requests, where the generation process makes decisions based on context information. For this purpose, the framework contains default implementations for context recognition and adaptation mechanisms. The approach presented supports a model-based development of Web applications which adapt to context. The CATWALK framework is an mplementation for model interpretation in a run-time system and thus simplifies the development of Web applications which adapt to context. As the framework is component-based and follows a strict separation of concerns, the default mechanisms can be extended or replaced, allowing to reduce the amount of custom code required to implement specific context-aware Web applications or to study alternative context inference or adaptation strategies. The use of the framework is illustrated in a case study, in which models are defined for a prototypical application, and this application is generated by the framework. The purpose of the case study is to illustrate effects of adaptation to context, based on context description and adaptation specifications in the application model

Overestimating the Role of Environment in Cancers

In a recent article, Wu and colleagues (Nature 2016;529:43-47) review previous studies and present new estimates for the contribution of extrinsic factors to cancer development. The new estimates are generally close to 100%, even for bone and brain cancers that have no known associations with lifestyle and are typically not considered to be preventable. We find that the results of Wu and colleagues are incompatible with previous estimates derived from epidemiological and genetic data. We further argue that their methods are fundamentally flawed because they overlook important effects of tissue type on cancer risk. We therefore conclude that their results give a misleading view of cancer etiology and preventability. Cancer Prev Res; 9(10); 773-6. ©2016 AACR

Tracking costs of virulence in natural populations of the wheat pathogen, Puccinia striiformis f.sp.tritici

<p>Abstract</p> <p>Background</p> <p>Costs of adaptation play an important role in host-parasite coevolution. For parasites, evolving the ability to circumvent host resistance may trade off with subsequent growth or transmission. Such costs of virulence (<it>sensu </it>plant pathology) limit the spread of all-infectious genotypes and thus facilitate the maintenance of genetic polymorphism in both host and parasite. We investigated costs of three virulence factors in <it>Puccinia striiformis </it>f.sp.<it>tritici</it>, a fungal pathogen of wheat (<it>Triticum aestivum</it>).</p> <p>Results</p> <p>In pairwise competition experiments, we compared the fitness of near-isogenic genotypes that differed by a single virulence factor. Two virulence factors (<it>vir4</it>, <it>vir6</it>) imposed substantial fitness costs in the absence of the corresponding resistance genes. In contrast, the <it>vir9 </it>virulence factor conferred a strong competitive advantage to several isolates, and this for different host cultivars and growing seasons. In part, the experimentally derived fitness costs and benefits are consistent with frequency changes of these virulence factors in the French pathogen population.</p> <p>Conclusion</p> <p>Our results illustrate the variation in the evolutionary trajectories of virulence mutations and the potential role of compensatory mutations. Anticipation of such variable evolutionary outcomes represents a major challenge for plant breeding strategies. More generally, we believe that agro-patho-systems can provide valuable insight in (co)evolutionary processes in host-parasite systems.</p