Affichage des résultats 1541 à 1560 sur 1674 au total
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Symbiosis evolution is often viewed as a progress, with emergence of new adaptive properties. However, symbiosis also enhances the interdependence between partners. I describe several such interdependences, and emphasize that they arise without emergence of new property. Generally, when two partners permanently interact, a mutation in one partner can be complemented by the other. Independency is then lost without any positive selection, in a neutral evolution. The accumulation of such steps makes the reversion to independency unlikely, and drives interdependency in symbiosis.
Symbiosis evolution is often viewed as a progress, with emergence of new adaptive properties. However, symbiosis also enhances the interdependence between partners. I describe several such interdependences, and emphasize that they arise without emergence of new property. Generally, when two partners permanently interact, a mutation in one partner can be complemented by the other. Independency is then lost without any positive selection, in a neutral evolution. The accumulation of such steps makes the reversion to independency unlikely, and drives interdependency in symbiosis.
These d'Alexandra Popa - mardi 24 mai 2011 - 14h00 - Amphithéâtre du CNRS
Males and females of most species share nearly the entire genome, and yet they use many of their shared genes in radically different ways. Differential expression between males and females is thought to be product of conflicting male- and female-specific selection over optimal transcription, and to form the underlying basis of sexual dimorphism in many species. If the relationship between sex-biased gene expression and sexually dimorphic phenotypes is true, then several simple predictions can be made. First, altering sex-specific selection should elicit a response in sex-biased gene expression, and this response should be more pronounced for genes linked to sex chromosomes. Second, although sexual dimorphism is often envisaged as a dichotomous comparison between female and male forms, many species show more of a continuum, with some individuals occupying intermediate points along an axis of dimorphism. In these cases, the magnitude of sex-biased expression should reflect the degree of sexual dimorphism. Third, the degree of sex-biased expression should accumulate over time in response to continuous sex-specific selection. Case studies using both comparative and experimental evolutionary frameworks will be presented to address these predictions.
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Postcopulatory sexual selection is thought to be an important force driving the evolution of sperm design. Yet, despite numerous theoretical and empirical studies of the relationship between sperm design and sperm competition (as one postcopulatory sexual selection mechanism) is still poorly understood. A series of comparative studies in several taxonomic groups have found inconclusive and sometimes even contradictory results suggesting that in different taxonomic groups the evolution of sperm design in the context of sperm competition show markedly different patterns. We conducted the largest to date comparative study including over 250 species of passerine birds to investigate the relationship between sperm design and sperm competition and to determine the evolutionary rate of sperm design as a sexually selected trait. We did so in three ways: (I) we investigated the relationship between sperm design and sperm competition at different phylogenetic levels its association with the underlying phylogeny; (II) we tested the interspecific, the intraspecific and the intra-male variation of sperm design in the context of sperm competition; (III) we performed experiments to improve our understanding of the behavioural mechanisms influencing sperm design and function. Our results provide new insights into the evolution of sperm design as a sexually selected trait.
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Thèse de Marion Germain le mardi 16 décembre 2014 à 13 h 30 - amphithéâtre Déambulatoire 1 (Doua)
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Individual and collective reactions to threat are largely conceived as individualistic and anti-social: when exposed to threat, humans would revert to self-preservative motives, trying to flee as fast as possible, sometimes at the expense of others. This conception, which can be traced back to the non-empirical conclusions of sociologist and social psychologist Gustave Le Bon, has met immediate intellectual success and is widespread both in academic and lay audiences. However, more recent work based on interviews with survivors from a diversity of disasters has consistently shown a very different pattern: humans do not display self-preservative behaviour when exposed to threat. In fact, they show a high degree of pro-sociality in such contexts, even when their life is directly at risk. Those results remain questionable. In particular, it is not clear how the type of danger people are exposed to can modulate their individual and collective responses to it. Another important issue is the methodology being used in those studies, which does not allow comparing between different moments of the event. Indeed, it is possible that immediate reactions to threat are self-preservative, with prosocial responses overcoming individualistic ones later on. Finally, previous work does not distinguish between genuine altruistic acts (where the action is immediately costly to the agent - eg exposing oneself to danger to help another person) and apparent altruistic behaviour (clearing an access, which directly benefits the agent). We have conducted interviews with survivors from the attacks at the Bataclan (13-11-2015 in Paris) asking them to describe with precision their own actions and others' at different moments of the attacks. In this talk, I will try to clarify the interplay between individualistic and prosocial motives and their temporality during collective exposure to deadly threat, drawing from our work with survivors from the Bataclan attacks. I will also suggest future directions to better understand the evolution of prosocial traits in such circumstances, in humans and other social species.
The recent West African Ebola outbreak has been a terrible reminder for the need to gain timely situation awareness, in order to inform and guide public health intervention and maximise the chances of mitigating disease outbreaks. Unfortunately, many tools are still lacking for addressing the challenges, both statistical and technical, posed by the analysis of outbreak data. This presentation will introduce the R Epidemics Consortium (RECON), an initiative bringing together public health officers, statisticians, modellers and software developers to develop a new generation of tools for outbreak response using the R software. We will argue that R is a platform of choice for the development of cutting-edge methodology which can further our understanding of disease dynamics. This point will be illustrated using outbreaker2, a new R package for reconstructing disease outbreaks using various kinds of epidemiological and genetic data. We will also show how R can be used for addressing some of the more technical challenges inherent to the outbreak response context, taking the packages incidence and epicontacts as examples. We will conclude by reflecting on how the typical life-cycle of methodological development is altered during emergency outbreak response, and on what novel practices may be considered to address some of these issues.http://repidemicsconsortium.org/ Keywords: methods, R, statistics, software, RECON, tools
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In aquatic ecosystems, food stress (more in particular cyanoHABS, cyanobacterial harmful blooms) has a strong negative impact on zooplankton grazers, and through the food web, disrupt the whole freshwater community. Deciphering the mechanisms underlying resistance to cyanoHABS in these grazers is thus essential to predict how cyanoHABs can be prevented or controlled. In the freshwater crustacean Daphnia, resistance is influenced by prior exposure to cyanobacteria and genotype, but the underlying mechanisms remain unclear. Through gut microbiota transplants, we here show that the gut microbiota plays a crucial role, and might mediate both genetic adaptation and acclimatization to cyanoHABs. Microbiota from resistant genotypes conferred a higher resistance to recipient Daphnia than microbiota from susceptible genotypes. Resistance to cyanobacteria in recipient Daphnia was not affected by the recipient genotype, but was strongly impacted by the donor genotype. This suggests that the Daphnia genotype acts indirectly on resistance to cyanobacteria, by shaping the gut microbiota. In addition, resistance was higher when donors were previously fed cyanobacteria, suggesting that gut microbiota responded to become more efficient in dealing with cyanobacteria after prior exposure. Next generation sequencing of 16S rDNA shows that resistance is associated with changes in microbiota structure. Our results provide evidence that resistance to toxic cyanobacteria in Daphnia is driven by the gut microbiota, which might thus be an important mediator of the genetic mosaic of coevolution between toxic cyanobacteria and their grazers, and a key determinant of how freshwater ecosystems respond to climate warming.