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bioRxiv 717702 ver. 3 Ce rapport est disponible dans : Peer Community in Evolutionary Biology; Environmentally acquired microbial symbionts could contribute to host adaptation to local conditions like vertically transmitted symbionts do. This scenario necessitates symbionts to have different effects in different environments. We investigated this idea in Drosophila melanogaster, a species which communities of bacterial symbionts vary greatly among environments.We isolatedfour bacterial strains isolated from the feces of a D. melanogasterlaboratory strain and tested their effects in two conditions:the ancestral environment (i.e. the laboratory medium) and a new environment (i.e. fresh fruit with live yeast). All bacterial effects on larval and adult traits differed among environments, ranging from very beneficial to marginally deleterious. The joint analysis of larval development speed and adult size further shows bacteria affected developmental plasticity more than resource acquisition. This effect was largely driven by the contrasted effects of the bacteria in each environment. Our study illustrates that understanding D. melanogastersymbiotic interactions in the wild will necessitate working in ecologically realistic conditions. Besides, context-dependent effects of symbionts, and their influence on host developmental plasticity, shed light on howenvironmentally acquired symbionts may contribute to host evolution.Keywords:symbiosis; extracellular bacteria; Drosophila melanogaster; life history traits; developmentalplasticity; resource acquisition

Little is known on the origin and maintenance of symbionts associated with Drosophila larvae in natura, which restricts the understanding of Drosophila-extracellular microorganism symbiosis in the light of evolution. Here, we studied the origin and maintenance of symbionts of Drosophila larvae under ecologically realistic conditions, to our knowledge for the first time, using yeast and bacterial isolates and two Drosophila species: the model organism D. melanogaster and the invasive pest D. suzukii. We discovered that Drosophila females and males both transmit yeast and bacteria symbionts to larvae. In addition, several symbiotic yeasts initially associated with larvae were conserved throughout host life cycle and transmitted to offspring. Our results suggest that stable associations of Drosophila flies with bacteria and yeasts may exist in natura and constitute a step forward in the understanding of wild Drosophila-microorganism symbioses.

Interactions between microbial symbionts of metazoan hosts are emerging as key features of symbiotic systems. Little is known about the role of such interactions on the maintenance of symbiosis through host’s life cycle. We studied the influence of symbiotic bacteria on the maintenance of symbiotic yeast through metamorphosis of the fly Drosophila melanogaster. To this end we mimicked the development of larvae in natural fruit. In absence of bacteria yeast was never found in young adults. However, yeast could maintain through metamorphosis when larvae were inoculated with symbiotic bacteria isolated from D. melanogaster faeces. Furthermore, an Enterobacteriaceae favoured yeast transstadial maintenance. Because yeast is a critical symbiont of D. melanogaster flies, bacterial influence on host-yeast association may have consequences for the evolution of insect-yeast-bacteria tripartite symbiosis and their cooperation.Summary statementBacterial symbionts of Drosophila influence yeast maintenance through fly metamorphosis, a novel observation that may have consequences for the evolution of insect-yeast-bacteria interactions.

Species that share resources often avoid competition with context-dependent behaviors. This is the case for the invasive insect pest Drosophila suzukii, whose larval ecological niche overlaps with that of Drosophila melanogaster in ripe, but not rotten, fruit. We discovered D. suzukii females prevent costly interspecific larval competition by avoiding oviposition on substrates previously visited by D. melanogaster. More precisely, D. melanogaster association with gut bacteria of the genus Lactobacillus triggers D. suzukii avoidance. However, D. suzukii avoidance behavior is condition-dependent, and D. suzukii females that themselves carry D. melanogaster bacteria stop avoiding sites visited by D. melanogaster. The adaptive significance of avoiding cues from the competitor’s microbiota was revealed by experimentally reproducing in-fruit larval competition: reduced survival of D. suzukii larvae was dependent on the presence of gut bacteria in the competitor. This study unveils a new role for the symbiotic microbiota and plastic behaviors in mediating interspecific competition.

Many symbionts provide nutrients to their host and/or affect its phenotypic plasticity. Such symbiont effects on host resource acquisition and allocation are often simultaneous and difficult to disentangle. Here we partitioned symbiont effects on host resource acquisition and allocation using a new framework based on the analysis of a well-established trade-off between host fitness components. This framework was used to analyze the effect of symbiotic yeast on the larval development of Drosophila larvae in field-realistic conditions. The screening of eighteen yeast fresh isolates showed they had similar effects on the resource acquisition in Drosophila melanogaster, D. simulans and D. suzukii but species-specific effects on resource allocation between either larval development speed or adult size. These differences shed light on the ecology of Drosophila flies and illustrate why distinguishing between these qualitatively different effects of microorganisms on hosts is essential to understand and predict symbiosis evolution.

International audience; Transgenerational epigenetic inheritance (TEI) describes the transmission of alternative functional states through multiple generations in the presence of the same genomic DNA sequence. Very little is known about the principles and the molecular mechanisms governing this type of inheritance. Here, by transiently enhancing 3D chromatin interactions, we established stable and isogenic Drosophila epilines that carry alternative epialleles, as defined by differential levels of Polycomb-dependent trimethylation of histone H3 Lys27 (forming H3K27me3). After being established, epialleles can be dominantly transmitted to naive flies and can induce paramutation. Importantly, epilines can be reset to a naive state by disruption of chromatin interactions. Finally, we found that environmental changes modulate the expressivity of the epialleles, and we extended our paradigm to naturally occurring phenotypes. Our work sheds light on how nuclear organization and Polycomb group (PcG) proteins contribute to epigenetically inheritable phenotypic variability.

Environmentally acquired microbial symbionts could contribute to host adaptation to local adaptation like vertically transmitted symbionts do. This scenario necessitates symbionts to have different effects in different environments. In Drosophila melanogaster, communities of extracellular bacterial symbionts vary largely among environments, which could be due to variable effects on phenotype. We investigated this idea with four bacterial strains isolated from the feces of a D. melanogaster lab strain, and tested their effects in two environments: the environment of origin (i.e. the laboratory medium) and a new one (i.e. fresh fruit with live yeast). All bacterial effects on larval and adult traits differed among environments, ranging from very beneficial to marginally deleterious. The joint analysis of larval development speed and adult size further suggests bacteria would affect developmental plasticity more than resource acquisition in males. The context-dependent effects of bacteria we observed, and its underlying mechanisms, sheds light on how environmentally acquired symbionts may contribute to host evolution.

Drosophila suzukii (Matsumura) is one of the most damaging and costly pests to invade temperate horticultural regions in recent history. Conventional control of this pest is challenging, and an environmentally benign microbial biopesticide is highly desirable. A thorough exploration of the pathogens infecting this pest is not only the first step on the road to the development of an effective biopesticide, but also provides a valuable comparative dataset for the study of viruses in the model family Drosophilidae. Here we use a metatransciptomic approach to identify viruses infecting this fly in both its native (Japanese) and invasive (British and French) ranges. We describe eighteen new RNA viruses, including members of the Picornavirales, Mononegavirales, Bunyavirales, Chuviruses, Nodaviridae, Tombusviridae, Reoviridae, and Nidovirales, and discuss their phylogenetic relationships with previously known viruses. We also detect 18 previously described viruses of other Drosophila species that appear to be associated with D. suzukii in the wild.

Drosophila suzukii(Matsumura) is one of the most damaging and costly pests to invade temperate horticultural regions in recent history. Conventional control of this pest is challenging, and an environmentally benign microbial biopesticide is highly desirable. A thorough exploration of the pathogens infecting this pest is not only the first step on the road to the development of an effective biopesticide, but also provides a valuable comparative dataset for the study of viruses in the model familyDrosophilidae.Here we use a metatransciptomic approach to identify viruses infecting this fly in both its native (Japanese) and invasive (British and French) ranges. We describe 18 new RNA viruses, including members of the Picornavirales, Mononegavirales, Bunyavirales, Chuviruses,Nodaviridae, Tombusviridae, Reoviridae,and Nidovirales, and discuss their phylogenetic relationships with previously known viruses. We also detect 18 previously described viruses of otherDrosophilaspecies that appear to be associated withD. suzukiiin the wild.

How do invasive pests affect interactions between members of pre-existing agrosystems? The invasive pest Drosophila suzukii is suspected to be involved in the aetiology of sour rot, a grapevine disease that otherwise develops following Drosophila melanogaster infestation of wounded berries. We combined field observations with laboratory assays to disentangle the relative roles of both Drosophila in disease development. We observed the emergence of numerous D. suzukii , but no D. melanogaster flies, from bunches that started showing mild sour rot symptoms days after field collection. However, bunches that already showed severe rot symptoms in the field mostly contained D. melanogaster . In the laboratory, oviposition by D. suzukii triggered sour rot development. An independent assay showed the disease increased grape attractiveness to ovipositing D. melanogaster females. Our results suggest that in invaded vineyards, D. suzukii facilitates D. melanogaster infestation and, consequently, favours sour rot outbreaks. Rather than competing with close species, the invader subsequently permits their reproduction in otherwise non-accessible resources and may cause more frequent, or more extensive, disease outbreaks.

Rodent host dynamics and dispersal are thought to be critical for hantavirus epidemiology as they determine pathogen persistence and transmission within and between host populations. We used landscape genetics to investigate how the population dynamics of the bank vole Myodes glareolus, the host of Puumala hantavirus (PUUV), vary with forest fragmentation and influence PUUV epidemiology. We sampled vole populations within the Ardennes, a French PUUV endemic area. We inferred demographic features such as population size, isolation and migration with regard to landscape configuration. We next analysed the influence of M. glareolus population dynamics on PUUV spatial distribution. Our results revealed that the global metapopulation dynamics of bank voles were strongly shaped by landscape features, including suitable patch size and connectivity. Large effective size in forest might therefore contribute to the higher observed levels of PUUV prevalence. By contrast, populations from hedge networks highly suffered from genetic drift and appeared strongly isolated from all other populations. This might result in high probabilities of local extinction for both M. glareolus and PUUV. Besides, we detected signatures of asymmetric bank vole migration from forests to hedges. These movements were likely to sustain PUUV in fragmented landscapes. In conclusion, our study provided arguments in favour of source-sink dynamics shaping PUUV persistence and spread in heterogeneous, Western European temperate landscapes. It illustrated the potential contribution of landscape genetics to the understanding of the epidemiological processes occurring at this local scale.

The game theory is an interesting framework for the dialogue modeling, both the human dialogue and the human-machine dialogue. Indeed, the dialogue comes as a series of turn talking oriented towards achieving a goal. Each turn is composed by speech acts - can be likened to “moves” of game theory - which produces the effects of gains or losses during the dialogue. The main advantage concerning the application of the game theory in dialogue is that it does not require knowledge of cognitive processes or intentions of the participants, but assumes only that they have issues and interests in the dialogue they seek to satisfy. This article describes our contribution on the pragmatics of the dialogue: (a) the dialogue is not only a cognitive processing and relevant statements of the utterances produced by the other (the alter-ego) nor a social game using domination through a more or less logical argument to reach its goals or rhetorical means to achieve his ends, but also (b) a co-construction of self through gains advancing its own goals. In this paper we consider dialogue as a double process around the choice of ends and the means. Finally, we propose a general model of dialogue based on game theory.

Background Puumala virus, the agent of nephropathia epidemica (NE), is the most prevalent hantavirus in Europe. The risk for human infection seems to be strongly correlated with the prevalence of Puumala virus (PUUV) in populations of its reservoir host species, the bank vole Myodes glareolus. In humans, the infection risks of major viral diseases are affected by the presence of helminth infections. We therefore proposed to analyse the influence of both helminth community and landscape on the prevalence of PUUV among bank vole populations in the Ardennes, a PUUV endemic area in France. Results Among the 313 voles analysed, 37 had anti-PUUV antibodies. Twelve gastro-intestinal helminth species were recorded among all voles sampled. We showed that PUUV seroprevalence strongly increased with age or sexual maturity, especially in the northern forests (massif des Ardennes). The helminth community structure significantly differed between this part and the woods or hedgerows of the southern cretes pre-ardennaises. Using PUUV RNA quantification, we identified significant coinfections between PUUV and gastro-intestinal helminths in the northern forests only. More specifically, PUUV infection was positively associated with the presence of Heligmosomum mixtum, and in a lesser extent, Aonchotheca muris-sylvatici. The viral load of PUUV infected individuals tended to be higher in voles coinfected with H. mixtum. It was significantly lower in voles coinfected with A. muris-sylvatici, reflecting the influence of age on these latter infections. Conclusions This is the first study to emphasize hantavirus - helminth coinfections in natural populations. It also highlights the importance to consider landscape when searching for such associations. We have shown that landscape characteristics strongly influence helminth community structure as well as PUUV distribution. False associations might therefore be evidenced if geographic patterns of helminths or PUUV repartition are not previously identified. Moreover, our work revealed that interactions between helminths and landscape enhance/deplete the occurrence of coinfections between PUUV and H. mixtum or A. muris-sylvatici. Further experimental analyses and long-term individual surveys are now required to confirm these correlative results, and to ascertain the causal links between helminth and PUUV infection risks.

International audience; The tumor necrosis factor-alpha (TNF-alpha) influences the ability to limit parasite infection but its over-production might result in inflammatory disorders. The level of Tnf-alpha gene expression could thus mediate a balance of tolerance/resistance to infections. This study focused on Puumala hantavirus (PUUV) infection in its rodent host, the bank vole (Myodes glareolus). In humans, PUUV is responsible of a mild form of hemorrhagic fever with renal syndrome, nephropathia epidemica (NE). The severity of NE is associated with an over-production of TNF-alpha. By contrast, PUUV infection in bank vole is chronic and asymptomatic. It is likely that different coevolutionary histories between PUUV and its hosts could lead to different balances of resistance/tolerance to PUUV infection, at least partly mediated by variable production levels of TNF-alpha. We investigated the hypothesis that bank voles from PUUV endemic areas should exhibit higher levels of tolerance, i.e. lower levels of TNF-alpha production, than bank voles from areas where PUUV prevalence is low. For this purpose, we analysed variations of Tnf-alpha gene expression and promoter sequences among European populations of bank voles. Our results revealed an absence of up-regulation of Tnf-alpha gene expression in PUUV infected bank voles and significant differences in Tnf-alpha gene expression level with regard to PUUV endemicity. These results corroborated the hypothesis of different balances of tolerance/resistance to PUUV. Two single-nucleotide polymorphism genotypes within the Tnf-alpha promoter (-302 GG/GG and -296 A/A) were associated with higher Tnf-alpha gene expression and were more frequent in non-endemic areas. This study emphasized the potential influence of selection acting on TNF-alpha production and mediating a tolerance/resistance balance to PUUV in bank voles. Further investigations, including the role of phenotypic plasticity and parasite communities on Tnf-alpha expression levels, should provide important keys to understand the prevalence of PUUV over Europe.

The European grapevine moth, Lobesia botrana (Lepidoptera: Tortricidae), is a polyphagous insect able to develop on grapes and wild plants. We tested the hypothesis that the parasitoid Dibrachys cavus (Hymenoptera: Pteromalidae) uses the larval frass in its host search. A two-armed olfactometer was used to measure the attractiveness of L. botrana larvae, their silk, or their frass after larvae were fed on different host plants. Frass of three Lepidoptera (L. botrana, Eupoecillia ambiguella, Sphinx ligustri) and one Orthoptera (Chorthippus brunneus) was assayed, but only L. botrana was used to test an effect of the larval host plant (two grape cultivars and three other plant species) to D. cavus females. Larvae without frass did not attract D. cavus whatever their origin, but their frass was attractive at a dose of 2-3 days equivalent of larval frass production. The silk produced by a single larva (L. botrana) was not attractive to D. cavus. The parasitoid was most attracted to the odor of S. ligustri; the frass of L. botrana was more attractive than that of E. ambiguella, irrespective of the species on which D. cavus had been reared. There was no difference in attractiveness of frass collected from L. botrana raised on food containing different plants. Chemical extracts using five different polarity solvents (acetone, dichloromethane, hexane, methanol, and water) differed in attractiveness to D. cavus. Water and dichloromethane were the most attractive. This suggests that a complex volatile signal made from intermediate to polar volatiles may be involved in attraction. D. cavus used frass to discriminate between different potential host species. Our results revealed that the larval food of L. botrana did not modify frass attractiveness, but that the moth species did.

National audience

Dataset for manuscript "Biological warfare between Drosophila species hints for sustainable crop protection" to be submitted.

Cet article présente le cadre théorique - actes de langage et SDRT (Segmented Discourse Representation Theory) - qui permet de plonger le processus de dialogue dans un formalisme efficace pour résoudre le problème de l’interprétation pragmatique dans un système de dialogue homme-machine. Après avoir montré l’intérêt de conserver la notion d’acte de langage dans la théorie standard de la SDRT, l’article propose une formalisation des relations rhétoriques à partir des actes de langage dans une perspective pragmatique. Des exemples sont donnés pour en illustrer les aspects formels., This paper presents a theoretical framework combining speech acts and Segmented Discourse Theory Representation (SDRT) which allows inserting the process of dialogue into an efficient formalism to solve the problem of pragmatic interpretation in a man-machine dialogue system. After outlining the interest to preserve the concept of speech acts in the standard theory of the SDRT, the paper describes and illustrates with examples a formalization of the discourse relations related to the pragmatic point of view.