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Search Results: 1 - 10 of 20809 matches for " Jean Clobert "
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The importance of habitat resistance for movement decisions in the common lizard, Lacerta vivipara
Zajitschek Susanne RK,Zajitschek Felix,Clobert Jean
BMC Ecology , 2012, DOI: 10.1186/1472-6785-12-13
Abstract: Background Movement behaviour can be influenced by a multitude of biotic and abiotic factors. Here, we investigate the speed of movement in relation to environmental and individual phenotypic properties in subadult common lizards (Lacerta vivipara). We aim to disentangle the importance of substrate, cover, humidity, basking opportunity and individual phenotype on moving tendencies in 12 treatment combinations, at which each lizard was tested. Results We find that movement behaviour depends on the starting conditions, the physical properties of the dispersal corridor, and on the individuals’ phenotype. Specifically, the presence of cover and substrate providing suitable traction in the corridor had positive effects on individual movement decisions. Additionally, we find high phenotypic variation in the propensity to move dependent on the presence of cover. Individual back patterns also strongly affected movement decisions in interaction with the physical properties of the dispersal corridor. Conclusions Our results highlight the importance of understanding the habitat resistance for movement patterns, with humid habitats with covering vegetation providing the best conditions to initiate movement in the common lizard. In addition, population effects, differences in back pattern phenotype and individual plasticity were identified as key parameters influencing movement behaviour.
Cooperative social clusters are not destroyed by dispersal in a ciliate
Nicolas Schtickzelle, Else J Fjerdingstad, Alexis Chaine, Jean Clobert
BMC Evolutionary Biology , 2009, DOI: 10.1186/1471-2148-9-251
Abstract: The propensity for social aggregation was greater in strains with reduced cell quality and lower growth performance. While we found a trade-off between costly aggregation and local dispersal in phenotypic analyses, aggregative strains showed a dispersal polymorphism by producing either highly sedentary or long-distance dispersive cells, in contrast to less aggregative strains whose cells were monomorphic local dispersers.High dispersal among aggregative strains may not destroy group stability in T. thermophila because the dispersal polymorphism allows social strains to more readily escape kin groups than less aggregative strains, yet still benefit from stable group membership among sedentary morphs. Such dispersal polymorphisms should be common in other social organisms, serving to alter the nature of the negative impact of dispersal on social evolution.Aggregative and dispersive behaviors could be antagonistic in many systems since high mobility should reduce the formation of aggregative associations. If aggregative behavior confers substantial benefits (e.g. via cooperation among kin), high dispersal destroys these benefits by reducing group stability [1]. Under these conditions, one should expect social species to have much lower dispersal than solitary species producing an aggregation-dispersal trade-off. The connection between dispersal and aggregation or cooperation, however, is far from straightforward. In a characteristically groundbreaking discussion of the issue, Hamilton and May [1] suggested that while aggregation among kin can indeed drive kin cooperation, as aggregations grow so does competition among related individuals (kin competition). Such strong competition among kin hence engenders inclusive fitness costs of aggregation that could be ameliorated by dispersal [2,3], but dispersal reduces group stability, and stability should promote cooperation [4-6]. Because aggregation can lead to more advanced forms of cooperation, including altruism [7-10], u
The co-evolution of multiply-informed dispersal: information transfer across landscapes from neighbors and immigrants
Alexis S. Chaine,Stéphane Legendre,Jean Clobert
PeerJ , 2013, DOI: 10.7717/peerj.44
Abstract: Dispersal plays a key role in natural systems by shaping spatial population and evolutionary dynamics. Dispersal has been largely treated as a population process with little attention to individual decisions and the influence of information use on the fitness benefits of dispersal despite clear empirical evidence that dispersal behavior varies among individuals. While information on local density is common, more controversial is the notion that indirect information use can easily evolve. We used an individual-based model to ask under what conditions indirect information use in dispersal will evolve. We modeled indirect information provided by immigrant arrival into a population which should be linked to overall metapopulation density. We also modeled direct information use of density which directly impacts fitness. We show that immigrant-dependent dispersal evolves and does so even when density dependent information is available. Use of two sources of information also provides benefits at the metapopulation level by reducing extinction risk and prolonging the persistence of populations. Our results suggest that use of indirect information in dispersal can evolve under conservative conditions and thus could be widespread.
Evolution of dispersal and life history strategies – Tetrahymena ciliates
Else J Fjerdingstad, Nicolas Schtickzelle, Pauline Manhes, Arnaud Gutierrez, Jean Clobert
BMC Evolutionary Biology , 2007, DOI: 10.1186/1471-2148-7-133
Abstract: Very significant among-strain differences were found with regard to dispersal rate, morphological commitment and plasticity, and almost all core life-history traits (e.g. survival, growth performance and strategy), with most of these traits being significantly intercorrelated. Some strains showed high short-distance dispersal rates, high colonization capacity, bigger cell size, elevated growth performance, and good survival abilities. These well performing strains, however, produced fewer fast-swimming dispersal morphs when subjected to environmental degradation than did philopatric strains performing poorly under normal conditions.Strong evidence was found for a genetic covariation between dispersal strategies and core life history traits in T. thermophila, with a fair fit of observed trait associations with classic colonizer models. However, the well performing strains with high colonization success and short-distance dispersal likely suffered under a long-distance dispersal disadvantage, due to producing fewer fast-swimming dispersal morphs than did philopatric strains. The smaller cell size at carrying capacity of the latter strains and their poor capacity to colonize as individual cells suggest that they may be adapted to greater levels of dependency on clone-mates (stronger sociality). In summary, differential exposure to selection on competitive and cooperative abilities, in conjunction with selective factors targeting specifically dispersal distance, likely contributed importantly to shaping T. thermophila dispersal and life history evolution.Understanding the selective pressures affecting the evolution of dispersal strategies is of prime importance for a broad range of biological fields, ranging from conservation biology to research on the evolution of species, host-parasite interactions and communities of species [1-7]. Dispersal strategies of living organisms affect the dynamics, and the demographic and genetic structure of their populations [8,9], and im
Incestuous Sisters: Mate Preference for Brothers over Unrelated Males in Drosophila melanogaster
Adeline Loyau, Jérémie H. Cornuau, Jean Clobert, étienne Danchin
PLOS ONE , 2012, DOI: 10.1371/journal.pone.0051293
Abstract: The literature is full of examples of inbreeding avoidance, while recent mathematical models predict that inbreeding tolerance or even inbreeding preference should be expected under several realistic conditions like e.g. polygyny. We investigated male and female mate preferences with respect to relatedness in the fruit fly D. melanogaster. Experiments offered the choice between a first order relative (full-sibling or parent) and an unrelated individual with the same age and mating history. We found that females significantly preferred mating with their brothers, thus supporting inbreeding preference. Moreover, females did not avoid mating with their fathers, and males did not avoid mating with their sisters, thus supporting inbreeding tolerance. Our experiments therefore add empirical evidence for inbreeding preference, which strengthens the prediction that inbreeding tolerance and preference can evolve under specific circumstances through the positive effects on inclusive fitness.
Carotenoid-Based Colours Reflect the Stress Response in the Common Lizard
Patrick S. Fitze, Julien Cote, Luis Martin San-Jose, Sandrine Meylan, Caroline Isaksson, Staffan Andersson, Jean-Marc Rossi, Jean Clobert
PLOS ONE , 2009, DOI: 10.1371/journal.pone.0005111
Abstract: Under chronic stress, carotenoid-based colouration has often been shown to fade. However, the ecological and physiological mechanisms that govern colouration still remain largely unknown. Colour changes may be directly induced by the stressor (for example through reduced carotenoid intake) or due to the activation of the physiological stress response (PSR, e.g. due to increased blood corticosterone concentrations). Here, we tested whether blood corticosterone concentration affected carotenoid-based colouration, and whether a trade-off between colouration and PSR existed. Using the common lizard (Lacerta vivipara), we correlatively and experimentally showed that elevated blood corticosterone levels are associated with increased redness of the lizard's belly. In this study, the effects of corticosterone did not depend on carotenoid ingestion, indicating the absence of a trade-off between colouration and PSR for carotenoids. While carotenoid ingestion increased blood carotenoid concentration, colouration was not modified. This suggests that carotenoid-based colouration of common lizards is not severely limited by dietary carotenoid intake. Together with earlier studies, these findings suggest that the common lizard's carotenoid-based colouration may be a composite trait, consisting of fixed (e.g. genetic) and environmentally elements, the latter reflecting the lizard's PSR.
Integrated Optimization of Mechanisms with Genetic Algorithms  [PDF]
Jean-Luc Marcelin
Engineering (ENG) , 2010, DOI: 10.4236/eng.2010.26057
Abstract: This paper offers an integrated optimization of mechanisms with genetic algorithm, the principle of which is to use a neural network as a global calculation program and to couple the network with stochastic methods of optimization. In other words, this paper deals with the integrated optimization of mechanisms with genetic algorithms, and, in conclusion, the possible use of neural networks for complex mechanisms or processes.
Extremely Early Diagnostic Test for Prostate Cancer  [PDF]
Veronica Jean James
Journal of Cancer Therapy (JCT) , 2011, DOI: 10.4236/jct.2011.23051
Abstract: Purpose: This article reports the results of a blinded fibre diffraction study of skin samples taken from TRAMP mice and age-matched controls to determine whether changes noted in fibre diffraction studies of human skin were present in these TRAMP mice studies. These mice are bred to progress to Gleeson Type 3 to Type 5 prostate cancer. Methods: Small strips, 1 mm × 5 mm, cut from the mouse skin samples were loaded into cells in the same way as human samples and slightly stretched to remove the crimp. They remained fully hydrated throughout exposure to the synchrotron beam. Results: The added change that was reported for prostate cancer in 2009 was obtained for all TRAMP mice samples, indicating that this change can be read as High Grade Cancer in human diagnostic tests. Discussion: These changes were evident for all 3 and 7 week old TRAMP mice samples but not for any of the control samples. This indicates that the changes in the fibre diffraction patterns appear much earlier than in any other available prostate cancer diagnostic test, as none of these can verify the presence of prostate cancer in the TRAMP mice before 10 weeks of age. The fibre diffraction test is therefore the most accurate and earliest test for high grade prostate cancer.
LeChatelier Principle and the Effects of Trade Policy under Induced Innovation  [PDF]
Jean-Paul Chavas
Theoretical Economics Letters (TEL) , 2012, DOI: 10.4236/tel.2012.23044
Abstract: This paper explores the effects of trade policy under induced innovation in general equilibrium. The analysis considers the effects of discrete changes in tariffs and import quotas, allowing for heterogeneous technologies among firms. The interactions between induced innovation and the effects of trade policy give a set of “LeChatelier effects” comparing short run versus long run market equilibrium. We investigate how induced innovation can reduce the adverse effects of tariffs on trade, and influence the effects of quotas on corresponding quota rents. The analysis presents new LeChatelier results that apply globally, i.e. under any discrete change in trade policy.
Is Dark Matter Made up of Xons?  [PDF]
Jean-Paul Auffray
Journal of Modern Physics (JMP) , 2013, DOI: 10.4236/jmp.2013.48A011

Three months before his untimely death in Paris in July 1912, Henri Poincaré formulated the conjecture that Planck’s action element could (should) be regarded as constituting a “véritable atome”, i.e. an “atom of motion”, whose integrity arises from the fact that the “points” it contains are equivalent to one another from the standpoint of probability. In this paper we investigate the possibility that this conjecture provides a clue to the origin and nature of dark matter.

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