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Search Results: 1 - 10 of 2196 matches for " Mathieu Sicard "
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Interspecific competition between entomopathogenic nematodes (Steinernema) is modified by their bacterial symbionts (Xenorhabdus)
Sicard Mathieu,Hinsinger Julie,Le Brun Nathalie,Pages Sylvie
BMC Evolutionary Biology , 2006,
Abstract: Background Symbioses between invertebrates and prokaryotes are biological systems of particular interest in order to study the evolution of mutualism. The symbioses between the entomopathogenic nematodes Steinernema and their bacterial symbiont Xenorhabdus are very tractable model systems. Previous studies demonstrated (i) a highly specialized relationship between each strain of nematodes and its naturally associated bacterial strain and (ii) that mutualism plays a role in several important life history traits of each partner such as access to insect host resources, dispersal and protection against various biotic and abiotic factors. The goal of the present study was to address the question of the impact of Xenorhabdus symbionts on the progression and outcome of interspecific competition between individuals belonging to different Steinernema species. For this, we monitored experimental interspecific competition between (i) two nematode species: S. carpocapsae and S. scapterisci and (ii) their respective symbionts: X. nematophila and X. innexi within an experimental insect-host (Galleria mellonella). Three conditions of competition between nematodes were tested: (i) infection of insects with aposymbiotic IJs (i.e. without symbiont) of both species (ii) infection of insects with aposymbiotic IJs of both species in presence of variable proportion of their two Xenorhabdus symbionts and (iii) infection of insects with symbiotic IJs (i.e. naturally associated with their symbionts) of both species. Results We found that both the progression and the outcome of interspecific competition between entomopathogenic nematodes were influenced by their bacterial symbionts. Thus, the results obtained with aposymbiotic nematodes were totally opposite to those obtained with symbiotic nematodes. Moreover, the experimental introduction of different ratios of Xenorhabdus symbionts in the insect-host during competition between Steinernema modified the proportion of each species in the adults and in the global offspring. Conclusion We showed that Xenorhabdus symbionts modified the competition between their Steinernema associates. This suggests that Xenorhabdus not only provides Steinernema with access to food sources but also furnishes new abilities to deal with biotic parameters such as competitors.
Interspecific competition between entomopathogenic nematodes (Steinernema) is modified by their bacterial symbionts (Xenorhabdus)
Mathieu Sicard, Julie Hinsinger, Nathalie Le Brun, Sylvie Pages, No?l Boemare, Catherine Moulia
BMC Evolutionary Biology , 2006, DOI: 10.1186/1471-2148-6-68
Abstract: We found that both the progression and the outcome of interspecific competition between entomopathogenic nematodes were influenced by their bacterial symbionts. Thus, the results obtained with aposymbiotic nematodes were totally opposite to those obtained with symbiotic nematodes. Moreover, the experimental introduction of different ratios of Xenorhabdus symbionts in the insect-host during competition between Steinernema modified the proportion of each species in the adults and in the global offspring.We showed that Xenorhabdus symbionts modified the competition between their Steinernema associates. This suggests that Xenorhabdus not only provides Steinernema with access to food sources but also furnishes new abilities to deal with biotic parameters such as competitors.Symbioses between the entomopathogenic nematodes Steinernema spp. and the enterobacteriacae Xenorhabdus spp. are associations in which both partners receive benefits from each other [1-3]. In the soil, the infective juveniles (IJs) of the nematodes act as vectors dispersing the bacteria from insect host to insect-host and in turn, the bacteria increase the nematode's fitness within the insects hosts [3,4]. Previous studies showed that these symbioses were highly specific and that no Steinernema spp. was able to associate with a Xenorhabdus spp. genetically distant from its natural one [2,5,6]. As the bacterial dispersion is totally dependent upon the fitness of the nematode within the insect-host, it is possible that Xenorhabdus spp. might select special traits in order to enhance their vector's fitness. It is known that Xenorhabdus spp. are beneficial to their nematodes in providing the latter with a better ability to kill the insect and feed on it [1,7,8]. Previous studies that focused on two different Steinernema species (S. carpocapsae and S. scapterisci) have provided us with insights into the association characteristics [2,5,6,9-11]. Although the two nematode species demonstrated increased fitne
High Virulence of Wolbachia after Host Switching: When Autophagy Hurts
Winka Le Clec'h,Christine Braquart-Varnier,Maryline Raimond,Jean-Baptiste Ferdy,Didier Bouchon,Mathieu Sicard
PLOS Pathogens , 2012, DOI: 10.1371/journal.ppat.1002844
Abstract: Wolbachia are widespread endosymbionts found in a large variety of arthropods. While these bacteria are generally transmitted vertically and exhibit weak virulence in their native hosts, a growing number of studies suggests that horizontal transfers of Wolbachia to new host species also occur frequently in nature. In transfer situations, virulence variations can be predicted since hosts and symbionts are not adapted to each other. Here, we describe a situation where a Wolbachia strain (wVulC) becomes a pathogen when transfected from its native terrestrial isopod host species (Armadillidium vulgare) to another species (Porcellio d. dilatatus). Such transfer of wVulC kills all recipient animals within 75 days. Before death, animals suffer symptoms such as growth slowdown and nervous system disorders. Neither those symptoms nor mortalities were observed after injection of wVulC into its native host A. vulgare. Analyses of wVulC's densities in main organs including Central Nervous System (CNS) of both naturally infected A. vulgare and transfected P. d. dilatatus and A. vulgare individuals revealed a similar pattern of host colonization suggesting an overall similar resistance of both host species towards this bacterium. However, for only P. d. dilatatus, we observed drastic accumulations of autophagic vesicles and vacuoles in the nerve cells and adipocytes of the CNS from individuals infected by wVulC. The symptoms and mortalities could therefore be explained by this huge autophagic response against wVulC in P. d. dilatatus cells that is not triggered in A. vulgare. Our results show that Wolbachia (wVulC) can lead to a pathogenic interaction when transferred horizontally into species that are phylogenetically close to their native hosts. This change in virulence likely results from the autophagic response of the host, strongly altering its tolerance to the symbiont and turning it into a deadly pathogen.
Wolbachia Mediate Variation of Host Immunocompetence
Christine Braquart-Varnier, Marion Lachat, Juline Herbinière, Monique Johnson, Yves Caubet, Didier Bouchon, Mathieu Sicard
PLOS ONE , 2008, DOI: 10.1371/journal.pone.0003286
Abstract: Background After decades during which endosymbionts were considered as silent in their hosts, in particular concerning the immune system, recent studies have revealed the contrary. In the present paper, we addressed the effect of Wolbachia, the most prevalent endosymbiont in arthropods, on host immunocompetence. To this end, we chose the A. vulgare-Wolbachia symbiosis as a model system because it leads to compare consequences of two Wolbachia strains (wVulC and wVulM) on hosts from the same population. Moreover, A. vulgare is the only host-species in which Wolbachia have been directly observed within haemocytes which are responsible for both humoral and cellular immune responses. Methodology/Principal Findings We sampled gravid females from the same population that were either asymbiotic, infected with wVulC, or infected with wVulM. The offspring from these females were tested and it was revealed that individuals harbouring wVulC exhibited: (i) lower haemocyte densities, (ii) more intense septicaemia in their haemolymph and (iii) a reduced lifespan as compared to individuals habouring wVulM or asymbiotic ones. Therefore, individuals in this population of A. vulgare appeared to suffer more from wVulC than from wVulM. Symbiotic titer and location in the haemocytes did not differ for the two Wolbachia strains showing that these two parameters were not responsible for differences observed in their extended phenotypes in A. vulgare. Conclusion/Significance The two Wolbachia strains infecting A. vulgare in the same population induced variation in immunocompetence and survival of their hosts. Such variation should highly influence the dynamics of this host-symbiont system. We propose in accordance with previous population genetic works, that wVulM is a local strain that has attenuated its virulence through a long term adaptation process towards local A. vulgare genotypes whereas wVulC, which is a widespread and invasive strain, is not locally adapted.
Cannibalism and Predation as Paths for Horizontal Passage of Wolbachia between Terrestrial Isopods
Winka Le Clec’h, Frédéric D. Chevalier, Lise Genty, Joanne Bertaux, Didier Bouchon, Mathieu Sicard
PLOS ONE , 2013, DOI: 10.1371/journal.pone.0060232
Abstract: The alpha-proteobacteria Wolbachia are the most widespread endosymbionts in arthropods and nematodes. Mainly maternally inherited, these so-called sex parasites have selected several strategies that increase their vertical dispersion in host populations. However, the lack of congruence between the Wolbachia and their host phylogenies suggests frequent horizontal transfers. One way that could be used for horizontal Wolbachia transfers between individuals is predation. The aim of this study was to test whether horizontal passage of Wolbachia is possible when an uninfected terrestrial isopod eats an infected one. After having eaten Armadillidium vulgare harbouring Wolbachia, the predator-recipients (the two woodlice A. vulgare and Porcellio dilatatus dilatatus) that were initially Wolbachia-free were tested positive for the presence of Wolbachia both by quantitative PCR and Fluorescence in situ Hybridization (FISH). Even if the titers were low compared to vertically infected individuals, this constitutes the first demonstration of Wolbachia occurrence in various organs of an initially uninfected host after eating an infected one.
A plena luz camino por la sombra
Sicard,Alain;
Atenea (Concepción) , 2004, DOI: 10.4067/S0718-04622004048900002
Abstract: this article analyzes, through the themes of light and shade, the two constitutive poetics of nerudian poetry, their articulation and inseparability. the nocturnal i then appears as the fundamental poetic i in the degree to which it exorcises its own death transforming it into a gesture of knowledge.
N. / V
Alain Sicard
Revista Chilena de Literatura , 2011,
Abstract:
L’indexation spatiale des archives ethnographiques inédites: les documents sonores et audiovisuels des pays andins
Hugues Sicard
M@ppemonde , 2005,
Abstract: Detailing the geographical context of unpublished sound and audiovisual ethnographical documents is essential while cataloguing them. A precise and effective spatial indexation system is without any doubt difficult to elaborate, especially for Andean countries, but the use of certain techniques allows us to considerably improve current cataloguing methods.
A plena luz camino por la sombra
Alain Sicard
Atenea , 2004,
Abstract: Se analizan, a través de las temáticas de la luz y de la sombra, las dos poéticas constitutivas de la poesía nerudiana, su articulación y su inseparabilidad. El yo nocturno aparece entonces como el yo poético fundamental en la medida en que exorciza la propia muerte, convirtiéndola en gesto de conocimiento.
The Lyon Clinical Olfactory Test: Validation and Measurement of Hyposmia and Anosmia in Healthy and Diseased Populations
Catherine Rouby,Thierry Thomas-Danguin,Michel Vigouroux,Gabriela Ciuperca,Tao Jiang,Jér me Alexanian,Mathieu Barges,Isabelle Gallice,Jean-Louis Degraix,Gilles Sicard
International Journal of Otolaryngology , 2011, DOI: 10.1155/2011/203805
Abstract: The LCOT is a self-administered test designed to assess olfactory deficits. Altogether, 525 subjects contributed to the validation. Elderly participants were well represented in this sample. In a validation study (study 1), 407 healthy and 17 anosmic volunteers between 15 and 91 years of age underwent threshold, supraliminal detection, and identification testing. Cutoff values for normosmia and hyposmia were calculated and applied in a second study in a group of patients with smell complaints and in a group of Alzheimer patients with age-matched controls. Incidence of smell deficit was estimated at 5.6% in the healthy population of study 1, and at 16% in the elderly control group of study 2. Assessment of the ability of each subtest to discriminate between groups showed that LCOT is relevant to differentiating between perception and identification deficits and between Alzheimer's and hyposmic patients.
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