Invasions biologiques : le rôle des microorganismes symbiotiques

National audienceUne des principales causes de perte de biodiversité à l'échelle planétaire est l'introduction par l'homme, volontaire ou non, d'espèces animales et végétales en dehors de leur aire de répartition naturelle. Les individus introduits peuvent parfois fonder une population qui s'installe durablement dans le nouvel environnement, voire qui l'envahisse. Certains biologistes ont récemment suggéré que les microorganismes symbiotiques vivant en association avec les envahisseurs pourraient jouer un rôle clé dans les invasions biologiques. Le projet Xylobiotic, financé par la Région Centre Val-de-Loire et conduit par des chercheurs affiliés à quatre unités de recherche de cette Région, aborde la question du rôle des symbiotes mutualistes dans le succès invasif de plusieurs insectes xylophages introduits en France, afin d'améliorer les méthodes de lutte contre les insectes invasifs

Invasions biologiques : le rôle des microorganismes symbiotiques

[Notes_IRSTEA]titre de la revue : Microscoop, le magazine de la Délégation CNRS Centre Limousin Poitou-Charentes [Departement_IRSTEA]Territoires [TR1_IRSTEA]SEDYVINNational audienceUne des principales causes de perte de biodiversité à l'échelle planétaire est l'introduction par l'homme, volontaire ou non, d'espèces animales et végétales en dehors de leur aire de répartition naturelle. Les individus introduits peuvent parfois fonder une population qui s'installe durablement dans le nouvel environnement, voire qui l'envahisse. Certains biologistes ont récemment suggéré que les microorganismes symbiotiques vivant en association avec les envahisseurs pourraient jouer un rôle clé dans les invasions biologiques. Le projet Xylobiotic, financé par la Région Centre Val-de-Loire et conduit par des chercheurs affiliés à quatre unités de recherche de cette Région, aborde la question du rôle des symbiotes mutualistes dans le succès invasif de plusieurs insectes xylophages introduits en France, afin d'améliorer les méthodes de lutte contre les insectes invasifs

Disentangling the effects of recombination, selection, and demography on the genetic variation at a major histocompatibility complex class II gene in the alpine chamois.

The major histocompatibility complex (MHC) harbours some of the most polymorphic loci in vertebrate genomes. MHC genes are thought to be subject to some form of balancing selection, most likely pathogen-mediated selection. Hence, MHC genes are excellent candidates for exploring adaptive processes. In this study, we investigated the genetic variation at exon 2 of the DRB class II MHC locus in 191 alpine chamois (Rupicapra rupicapra) from 10 populations in the eastern Alps of Italy. In particular, we were interested in distinguishing and estimating the relative impact of selective and demographic factors, while taking into account the confounding effect of recombination. The extremely high d(n)/d(s) ratio and the presence of trans-species polymorphisms suggest that a strong long-term balancing selection effect has been operating at this locus throughout the evolutionary history of this species. We analysed patterns of genetic variation within and between populations, and the mitochondrial D-loop polymorphism patterns were analysed to provide a baseline indicator of the effects of demographic processes. These analyses showed that (i) the chamois experienced a demographic decline in the last 5000-30 000 years, most likely related to the postglacial elevation in temperature; (ii) this demographic process can explain the results of neutrality tests applied to MHC variation within populations, but cannot justify the much weaker divergence between populations implied by MHC as opposed to mitochondrial DNA; (iii) similar sets of divergent alleles are probably maintained with similar frequencies by balancing selection in different populations, and this mechanism is also operating in small isolated populations, which are strongly affected by drift

Disentangling the effects of recombination, selection and demography on the genetic variation at a major histocompatibility complex class II gene in the alpine chamois

The major histocompatibility complex (MHC) harbours some of the most polymorphic loci in vertebrate genomes. MHC genes are thought to be subject to some form of balancing selection, most likely pathogen-mediated selection. Hence, MHC genes are excellent candidates for exploring adaptive processes. In this study, we investigated the genetic variation at exon 2 of the DRB class II MHC locus in 191 alpine chamois (Rupicapra rupicapra) from 10 populations in the eastern Alps of Italy. In particular, we were interested in distinguishing and estimating the relative impact of selective and demographic factors, while taking into account the confounding effect of recombination. The extremely high dn/ds ratio and the presence of trans-species polymorphisms suggest that a strong long-term balancing selection effect has been operating at this locus throughout the evolutionary history of this species. We analysed patterns of genetic variation within and between populations, and the mitochondrial D-loop polymorphism patterns were analysed to provide a baseline indicator of the effects of demographic processes. These analyses showed that (i) the chamois experienced a demographic decline in the last 5000–30 000 years, most likely related to the postglacial elevation in temperature; (ii) this demographic process can explain the results of neutrality tests applied to MHC variation within populations, but cannot justify the much weaker divergence between populations implied by MHC as opposed to mitochondrial DNA; (iii) similar sets of divergent alleles are probably maintained with similar frequencies by balancing selection in different populations, and this mechanism is also operating in small isolated populations, which are strongly affected by drif

Responses of the hyper‐diverse community of canopy‐dwelling Hymenoptera to oak decline

The data that support the findings of this study are openly available in Recherche Data Gouv at https://entrepot.recherche.data.gouv.fr/dataset.xhtml?persistentId=doi:10.57745/H8CBG1. Representative specimens of Braconidae, Ichneumonidae, Halictidae, Andrenidae, Crabronidae and Pemphredonidae are housed at the Orléans Museum for Biodiversity and Environment (MOBE, Orléans, France).International audience1. Forest decline and dieback are growing phenomena worldwide, resulting in severe, large-scale degradation of the canopy. This can profoundly alter the provision of trophic resources and microhabitats for canopy-dwelling arthropods.2. In 2019, we assessed the effect of oak decline on the community of canopy-dwelling Hymenoptera. We selected 21 oak stands and 42 plots, located in three forests in France, presenting contrasting levels of decline. Insects were sampled at the canopy level with green multi-funnel and flight-interception traps.3. We collected a particularly diverse community of 19,289 insect individuals belonging to 918 taxa, 10 larval trophic guilds and 7 nesting guilds.4. Oak decline had no effect on the abundance or richness of the overall community but significantly reshaped the community assemblages. Decline had contrasting effects depending on the taxa and guilds considered. Specialist parasitoids were more abundant at intermediate levels of decline severity while generalists were negatively affected. Taxa depending on ground-related resources and microhabitats were promoted. Saproxylic taxa were more abundant while xylophagous insects were negatively impacted.5. Reduced leaf area index promoted several guilds and the diversity of the overall community. While an increasing tree mortality rate enhanced the abundance and diversity of deadwood resources, it had negative impacts on several Hymenoptera guilds. Our results suggest that micro-environmental changes at the ground level due to canopy decline have major cascading effects on the communities of canopy-dwelling Hymenoptera.6. Our study highlights the relevance of studying Hymenoptera communities to investigate the outcomes of disturbances on forest biodiversity

Permanent Genetic Resources added to Molecular Ecology Resources Database 1 October 2011-30 November 2011

This article documents the addition of 139 microsatellite marker loci and 90 pairs of single-nucleotide polymorphism sequencing primers to the Molecular Ecology Resources Database. Loci were developed for the following species: Aglaoctenus lagotis, Costus pulverulentus, Costus scaber, Culex pipiens, Dascyllus marginatus, Lupinus nanus Benth, Phloeomyzus passerini, Podarcis muralis, Rhododendron rubropilosum Hayata var. taiwanalpinum and Zoarces viviparus. These loci were cross-tested on the following species: Culex quinquefasciatus, Rhododendron pseudochrysanthum Hay. ssp. morii (Hay.) Yamazaki and R.pseudochrysanthum Hayata. This article also documents the addition of 48 sequencing primer pairs and 90 allele-specific primers for Engraulis encrasicolus.12237437

Unraveling the tripartite interactions among the woolly poplar aphid, its host tree, and their environment: a lead to improve the management of a major tree plantation pest?

Article en open accessInternational audienceKey message For an optimal deployment of poplar resistance to the gall-inducing aphid Phloeomyzus passerinii, a laboratory susceptibility assay has been developed. The nature of aphid–tree interactions during compatible and incompatible situations has been studied in detail. This should help at identifying specific resistance markers and at testing effects of site conditions on tree–pest interactions. Context P. passerinii is a major pest of poplar plantations in Europe, and the plantation of resistant poplar genotypes is regarded as the best long-term management strategy for this pest. This requires a sound knowledge of the interactions among the pest, its host and their environment. Aims Here, we review the recent advances aiming at developing an optimal deployment of host resistance versus P. passerinii. Results Investigations on aphid-host interactions demonstrated that P. passerinii induces pseudogalls within the bark of susceptible hosts. This results in a reduction of starch bark content during aphid outbreaks, which could be involved in tree death. The constitutive level of starch in the bark could be related to the tolerance level of trees. A susceptibility test has been designed for poplar genotypes, discriminating three categories of susceptibility depending on tree’s ability to totally or partially inhibit pseudogall induction. The test still has several limitations however. It neither takes into account the large level of individual genetic diversity of the aphid in France, nor the environmental modulation of tree resistance and tolerance, while water deficit and fertilization could potentially affect these parameters. Conclusion The hypotheses drawn regarding the processes leading to tree death or resistance should help at identifying resistance markers, and at testing effects of site conditions on tree–pest interactions