N. Le Brun | Université de Montpellier (original) (raw)

Papers by N. Le Brun

Research paper thumbnail of Interspecific competition between entomopathogenic nematodes (Steinernema) is modified by their bacterial symbionts (Xenorhabdus)

BMC evolutionary biology, 2006

Symbioses between invertebrates and prokaryotes are biological systems of particular interest in ... more 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 ...

Research paper thumbnail of Isolation and identification of entomopathogenic nematodes and their symbiotic bacteria from Hérault and Gard (Southern France)

Journal of Invertebrate Pathology, 2008

Isolation and identification of native nematode-bacterial associations in the field are necessary... more Isolation and identification of native nematode-bacterial associations in the field are necessary for successful control of endemic pests in a particular location. No study has yet been undertaken to recover and identify EPN in metropolitan France. In the present paper, we provide results of a survey of EPN and their symbiotic bacteria conducted in Hérault and Gard regions in Southern France. Molecular characterization of isolated nematodes depicted three different Steinernema species and one Heterorhabditis species, H. bacteriophora. Steinernema species recovered were identified as: S. feltiae and S. affine and an undescribed species. Xenorhabdus symbionts were identified as X. bovienii for both S. feltiae and S. affine. Phylogenetic analysis placed the new undescribed Steinernema sp. as closely related to S. arenarium but divergent enough to postulate that it belongs to a new species within the ''glaseri-group". The Xenorhabdus symbiont from this Steinernema sp. was identified as X. kozodoii. All Heterorhabditis isolates recovered were diagnosed as H. bacteriophora and their bacterial symbionts were identified as Photorhabdus luminescens. Molecular characterization of these nematodes enabled the distinction of two different H. bacteriophora strains. Bacterial symbiontic strains of these two H. bacteriophora strains were identified as P. luminescens ssp. kayaii and P. luminescens ssp. laumondii.

Research paper thumbnail of Specialization of the entomopathogenic nematode Steinernema scapterisci with its mutualistic Xenorhabdus symbiont

Naturwissenschaften, 2005

The level of specialization of the entomopathogenic nematode Steinernema scapterisci with its nat... more The level of specialization of the entomopathogenic nematode Steinernema scapterisci with its native Xenorhabdus symbiont was investigated by testing (1) the influence of non-native bacterial strains on nematode fitness within an insect-host (Galleria mellonella) and (2) specificity of the association between the nematode infective juveniles and non-native bacteria. All non-native Xenorhabdus spp. or Photorhabdus spp. strains tested were mutualistically associated with other entomopathogenic nematodes in nature. We showed that most of the Xenorhabdus spp. strains tested led to an insignificant difference of the nematode's fitness compared to the one obtained with the native bacterium. Conversely, Photorhabdus spp. strains almost entirely abolished nematode reproduction. The phylogenetic analysis of bacterial strains tested, showed that there was a negative correlation between S. scapterisci's reproduction rate with a bacterial strain and the genetic distance of this bacterial strain from the native one. We also showed that the native bacterium was the only one which was transmitted by S. scapterisci's infective juveniles. All these results, suggested a specialization between S. scapterisci and its native Xenorhabdus. As the same phenomenon was already demonstrated in the association between S. carpocapsae and X. nematophila, specialization between partners would not be an exception in entomopathogenic nematode-bacteria interactions. Nevertheless, S. scapterisci showed a dramatically higher compatibility with non-native Xenorhabdus spp. strains than did S. carpocapsae, suggesting differences in the co-evolutionary processes between nematodes and bacteria in these two model systems.

Research paper thumbnail of Effect of native Xenorhabdus on the fitness of their Steinernema hosts: contrasting types of interaction

Parasitology Research, 2003

Steinernema species are entomopathogenic nematodes. They are symbiotically associated with Entero... more Steinernema species are entomopathogenic nematodes. They are symbiotically associated with Enterobacteriaceae of the genus Xenorhabdus. These nematode-bacteria symbioses are extremely diversified and constitute an important new model in ecology and evolution to investigate symbioses between microbes and invertebrates. However, no study has so far adequately evaluated either the outcome of the interactions or the obligate nature of interactions in different Steinernema species in the same way. Studying three different species of Steinernema, we showed that symbiotic nematodes are always fitter than aposymbiotic ones. Nevertheless, we revealed contrasting types of interaction in terms of outcome and obligate nature of the interaction. Bacterial analyses showed that nematode species differed dramatically in the number of symbiotic Xenorhabdus they carried. We suggested that when the interaction appeared more facultative for a nematode species, the nematodes carried fewer Xenorhabdus cells than strongly dependent worm species. Thus, the symbiont transmission appeared to become more efficient as the relationship between the nematode and the bacteria became tighter.

Research paper thumbnail of Crowdsourcing Word-Color Associations

Lecture Notes in Computer Science, 2014

In Natural Language Processing and semantic analysis in particular, color information may be impo... more In Natural Language Processing and semantic analysis in particular, color information may be important in order to properly process textual information (word sense disambiguation, and indexing). More specifically, knowing what colors are generally associated with what terms is crucial information. In this paper, we explore how crowdsourcing through a game with a purpose (GWAP) can be an adequate strategy to collect such lexico-semantic data.

Research paper thumbnail of Experimental evidence of genetic determinism in high susceptibility to intestinal pinworm infection in mice: a hybrid zone model

Parasitology, 1993

In the hybrid zone of the two mouse subspecies Mus musculus musculus and Mus musculus domesticus,... more In the hybrid zone of the two mouse subspecies Mus musculus musculus and Mus musculus domesticus, mice with hybrid genotypes harbour, on the average, more helminth parasites (cestodes and nematodes) than mice of the two parental taxa. In order to determine the roles played by genetic parameters in this phenomenon, mice with recombined and parental genotypes were experimentally infected with the intestinal pinworm Aspiculuris tetraptera, a natural parasite of the house mouse. The results showed that the high susceptibility of the hybrid zone mice is genetically determined. In addition, this study shows the occurrence of variability among resistant parental populations.

Research paper thumbnail of When mutualists are pathogens: an experimental study of the symbioses between Steinernema (entomopathogenic nematodes) and Xenorhabdus (bacteria)

Journal of Evolutionary Biology, 2004

In this paper, we investigate the level of specialization of the symbiotic association between an... more In this paper, we investigate the level of specialization of the symbiotic association between an entomopathogenic nematode (Steinernema carpocapsae) and its mutualistic native bacterium (Xenorhabdus nematophila). We made experimental combinations on an insect host where nematodes were associated with non-native symbionts belonging to the same species as the native symbiont, to the same genus or even to a different genus of bacteria. All nonnative strains are mutualistically associated with congeneric entomopathogenic nematode species in nature. We show that some of the non-native bacterial strains are pathogenic for S. carpocapsae. When the phylogenetic relationships between the bacterial strains was evaluated, we found a clear negative correlation between the effect a bacterium has on nematode fitness and its phylogenetic distance to the native bacteria of this nematode. Moreover, only symbionts that were phylogenetically closely related to the native bacterial strain were transmitted. These results suggest that co-evolution between the partners has led to a high level of specialization in this mutualism, which effectively prevents horizontal transmission. The pathogenicity of some non-native bacterial strains against S. carpocapsae could result from the incapacity of the nematode to resist specific virulence factors produced by these bacteria.

Research paper thumbnail of The genus Diplozoon (Monogenea, Polyopisthocotylea) in southern france: Speculation and specificity

International Journal for Parasitology, 1988

... individuals fused in permanent cross copula (Bovet, 1967; Lambert, Le Brun and Renaud, 1987).... more ... individuals fused in permanent cross copula (Bovet, 1967; Lambert, Le Brun and Renaud, 1987). Based on an analysis of the geographic distribution of Diplowon, it appears that this parasite probably originated from Asia and then spread throughout Eurasia, as suggested by ...

Research paper thumbnail of A SURVIVAL-REPRODUCTION TRADE-OFF IN ENTOMOPATHOGENIC NEMATODES MEDIATED BY THEIR BACTERIAL SYMBIONTS

Evolution, 2008

showed benefits to the association for the nematode during the parasitic stage, but preliminary d... more showed benefits to the association for the nematode during the parasitic stage, but preliminary data suggest the existence of costs to the association for the nematode in free stage. IJs deprived from their bacteria indeed survive longer than symbiotic ones.

Research paper thumbnail of Manifold aspects of specificity in a nematode-bacterium mutualism

Journal of Evolutionary Biology, 2009

Coevolution in mutualistic symbiosis can yield, because the interacting partners share common int... more Coevolution in mutualistic symbiosis can yield, because the interacting partners share common interests, to coadaptation: hosts perform better when associated with symbionts of their own locality than with others coming from more distant places. However, as the two partners of a symbiosis might also experience conflicts over part of their life cycle, coadaptation might not occur for all life-history traits. We investigated this issue in symbiotic systems where nematodes (Steinernema) and bacteria (Xenorhabdus) reproduce in insects they have both contributed to kill. Newborn infective juveniles (IJs) that carry bacteria in their intestine then disperse from the insect cadaver in search of a new host to infect. We ran experiments where nematodes coinfect insects with bacteria that differ from their native symbiont. In both Steinernema carpocapsae/Xenorhabdus nematophila and Steinernema feltiae/Xenorhabdus bovienii symbioses, we detected an overall specificity which favours the hypothesis of a fine-tuned co-adaptation process. However, we also found that the life-history traits involved in specificity strongly differ between the two model systems: when associated with strains that differ too much from their native symbionts, S. carpocapsae has low parasitic success, whereas S. feltiae has low survival in dispersal stage.

Research paper thumbnail of Interspecific competition between entomopathogenic nematodes (Steinernema) is modified by their bacterial symbionts (Xenorhabdus)

BMC evolutionary biology, 2006

Symbioses between invertebrates and prokaryotes are biological systems of particular interest in ... more 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 ...

Research paper thumbnail of Isolation and identification of entomopathogenic nematodes and their symbiotic bacteria from Hérault and Gard (Southern France)

Journal of Invertebrate Pathology, 2008

Isolation and identification of native nematode-bacterial associations in the field are necessary... more Isolation and identification of native nematode-bacterial associations in the field are necessary for successful control of endemic pests in a particular location. No study has yet been undertaken to recover and identify EPN in metropolitan France. In the present paper, we provide results of a survey of EPN and their symbiotic bacteria conducted in Hérault and Gard regions in Southern France. Molecular characterization of isolated nematodes depicted three different Steinernema species and one Heterorhabditis species, H. bacteriophora. Steinernema species recovered were identified as: S. feltiae and S. affine and an undescribed species. Xenorhabdus symbionts were identified as X. bovienii for both S. feltiae and S. affine. Phylogenetic analysis placed the new undescribed Steinernema sp. as closely related to S. arenarium but divergent enough to postulate that it belongs to a new species within the ''glaseri-group". The Xenorhabdus symbiont from this Steinernema sp. was identified as X. kozodoii. All Heterorhabditis isolates recovered were diagnosed as H. bacteriophora and their bacterial symbionts were identified as Photorhabdus luminescens. Molecular characterization of these nematodes enabled the distinction of two different H. bacteriophora strains. Bacterial symbiontic strains of these two H. bacteriophora strains were identified as P. luminescens ssp. kayaii and P. luminescens ssp. laumondii.

Research paper thumbnail of Specialization of the entomopathogenic nematode Steinernema scapterisci with its mutualistic Xenorhabdus symbiont

Naturwissenschaften, 2005

The level of specialization of the entomopathogenic nematode Steinernema scapterisci with its nat... more The level of specialization of the entomopathogenic nematode Steinernema scapterisci with its native Xenorhabdus symbiont was investigated by testing (1) the influence of non-native bacterial strains on nematode fitness within an insect-host (Galleria mellonella) and (2) specificity of the association between the nematode infective juveniles and non-native bacteria. All non-native Xenorhabdus spp. or Photorhabdus spp. strains tested were mutualistically associated with other entomopathogenic nematodes in nature. We showed that most of the Xenorhabdus spp. strains tested led to an insignificant difference of the nematode's fitness compared to the one obtained with the native bacterium. Conversely, Photorhabdus spp. strains almost entirely abolished nematode reproduction. The phylogenetic analysis of bacterial strains tested, showed that there was a negative correlation between S. scapterisci's reproduction rate with a bacterial strain and the genetic distance of this bacterial strain from the native one. We also showed that the native bacterium was the only one which was transmitted by S. scapterisci's infective juveniles. All these results, suggested a specialization between S. scapterisci and its native Xenorhabdus. As the same phenomenon was already demonstrated in the association between S. carpocapsae and X. nematophila, specialization between partners would not be an exception in entomopathogenic nematode-bacteria interactions. Nevertheless, S. scapterisci showed a dramatically higher compatibility with non-native Xenorhabdus spp. strains than did S. carpocapsae, suggesting differences in the co-evolutionary processes between nematodes and bacteria in these two model systems.

Research paper thumbnail of Effect of native Xenorhabdus on the fitness of their Steinernema hosts: contrasting types of interaction

Parasitology Research, 2003

Steinernema species are entomopathogenic nematodes. They are symbiotically associated with Entero... more Steinernema species are entomopathogenic nematodes. They are symbiotically associated with Enterobacteriaceae of the genus Xenorhabdus. These nematode-bacteria symbioses are extremely diversified and constitute an important new model in ecology and evolution to investigate symbioses between microbes and invertebrates. However, no study has so far adequately evaluated either the outcome of the interactions or the obligate nature of interactions in different Steinernema species in the same way. Studying three different species of Steinernema, we showed that symbiotic nematodes are always fitter than aposymbiotic ones. Nevertheless, we revealed contrasting types of interaction in terms of outcome and obligate nature of the interaction. Bacterial analyses showed that nematode species differed dramatically in the number of symbiotic Xenorhabdus they carried. We suggested that when the interaction appeared more facultative for a nematode species, the nematodes carried fewer Xenorhabdus cells than strongly dependent worm species. Thus, the symbiont transmission appeared to become more efficient as the relationship between the nematode and the bacteria became tighter.

Research paper thumbnail of Crowdsourcing Word-Color Associations

Lecture Notes in Computer Science, 2014

In Natural Language Processing and semantic analysis in particular, color information may be impo... more In Natural Language Processing and semantic analysis in particular, color information may be important in order to properly process textual information (word sense disambiguation, and indexing). More specifically, knowing what colors are generally associated with what terms is crucial information. In this paper, we explore how crowdsourcing through a game with a purpose (GWAP) can be an adequate strategy to collect such lexico-semantic data.

Research paper thumbnail of Experimental evidence of genetic determinism in high susceptibility to intestinal pinworm infection in mice: a hybrid zone model

Parasitology, 1993

In the hybrid zone of the two mouse subspecies Mus musculus musculus and Mus musculus domesticus,... more In the hybrid zone of the two mouse subspecies Mus musculus musculus and Mus musculus domesticus, mice with hybrid genotypes harbour, on the average, more helminth parasites (cestodes and nematodes) than mice of the two parental taxa. In order to determine the roles played by genetic parameters in this phenomenon, mice with recombined and parental genotypes were experimentally infected with the intestinal pinworm Aspiculuris tetraptera, a natural parasite of the house mouse. The results showed that the high susceptibility of the hybrid zone mice is genetically determined. In addition, this study shows the occurrence of variability among resistant parental populations.

Research paper thumbnail of When mutualists are pathogens: an experimental study of the symbioses between Steinernema (entomopathogenic nematodes) and Xenorhabdus (bacteria)

Journal of Evolutionary Biology, 2004

In this paper, we investigate the level of specialization of the symbiotic association between an... more In this paper, we investigate the level of specialization of the symbiotic association between an entomopathogenic nematode (Steinernema carpocapsae) and its mutualistic native bacterium (Xenorhabdus nematophila). We made experimental combinations on an insect host where nematodes were associated with non-native symbionts belonging to the same species as the native symbiont, to the same genus or even to a different genus of bacteria. All nonnative strains are mutualistically associated with congeneric entomopathogenic nematode species in nature. We show that some of the non-native bacterial strains are pathogenic for S. carpocapsae. When the phylogenetic relationships between the bacterial strains was evaluated, we found a clear negative correlation between the effect a bacterium has on nematode fitness and its phylogenetic distance to the native bacteria of this nematode. Moreover, only symbionts that were phylogenetically closely related to the native bacterial strain were transmitted. These results suggest that co-evolution between the partners has led to a high level of specialization in this mutualism, which effectively prevents horizontal transmission. The pathogenicity of some non-native bacterial strains against S. carpocapsae could result from the incapacity of the nematode to resist specific virulence factors produced by these bacteria.

Research paper thumbnail of The genus Diplozoon (Monogenea, Polyopisthocotylea) in southern france: Speculation and specificity

International Journal for Parasitology, 1988

... individuals fused in permanent cross copula (Bovet, 1967; Lambert, Le Brun and Renaud, 1987).... more ... individuals fused in permanent cross copula (Bovet, 1967; Lambert, Le Brun and Renaud, 1987). Based on an analysis of the geographic distribution of Diplowon, it appears that this parasite probably originated from Asia and then spread throughout Eurasia, as suggested by ...

Research paper thumbnail of A SURVIVAL-REPRODUCTION TRADE-OFF IN ENTOMOPATHOGENIC NEMATODES MEDIATED BY THEIR BACTERIAL SYMBIONTS

Evolution, 2008

showed benefits to the association for the nematode during the parasitic stage, but preliminary d... more showed benefits to the association for the nematode during the parasitic stage, but preliminary data suggest the existence of costs to the association for the nematode in free stage. IJs deprived from their bacteria indeed survive longer than symbiotic ones.

Research paper thumbnail of Manifold aspects of specificity in a nematode-bacterium mutualism

Journal of Evolutionary Biology, 2009

Coevolution in mutualistic symbiosis can yield, because the interacting partners share common int... more Coevolution in mutualistic symbiosis can yield, because the interacting partners share common interests, to coadaptation: hosts perform better when associated with symbionts of their own locality than with others coming from more distant places. However, as the two partners of a symbiosis might also experience conflicts over part of their life cycle, coadaptation might not occur for all life-history traits. We investigated this issue in symbiotic systems where nematodes (Steinernema) and bacteria (Xenorhabdus) reproduce in insects they have both contributed to kill. Newborn infective juveniles (IJs) that carry bacteria in their intestine then disperse from the insect cadaver in search of a new host to infect. We ran experiments where nematodes coinfect insects with bacteria that differ from their native symbiont. In both Steinernema carpocapsae/Xenorhabdus nematophila and Steinernema feltiae/Xenorhabdus bovienii symbioses, we detected an overall specificity which favours the hypothesis of a fine-tuned co-adaptation process. However, we also found that the life-history traits involved in specificity strongly differ between the two model systems: when associated with strains that differ too much from their native symbionts, S. carpocapsae has low parasitic success, whereas S. feltiae has low survival in dispersal stage.