staff

Jérémy Gauthier

Postdoctoral fellow in MuseumLab

  • T: +41 22 418 63 54
  • office 4006 (Sciences III)
  • HyRAD-X exome capture museomics unravels giant ground beetle evolution. Genome Biol Evol 2021 May;():. 6275686. 10.1093/gbe/evab112.

    abstract

    Advances in phylogenomics contribute towards resolving long-standing evolutionary questions. Notwithstanding, genetic diversity contained within more than a billion biological specimens deposited in natural history museums remains recalcitrant to analysis owing to challenges posed by its intrinsically degraded nature. Yet that tantalizing resource could be critical in overcoming taxon sampling constraints hindering our ability to address major evolutionary questions. We addressed this impediment by developing phyloHyRAD, a new bioinformatic pipeline enabling locus recovery at a broad evolutionary scale from HyRAD-X exome capture of museum specimens of low DNA integrity using a benchtop RAD-derived exome-complexity-reduction probe set developed from high DNA integrity specimens. Our new pipeline can also successfully align raw RNAseq transcriptomic and UCE reads with the RAD-derived probe catalog. Using this method, we generated a robust timetree for Carabinae beetles, the lack of which had precluded study of macroevolutionary trends pertaining to their biogeography and wing-morphology evolution. We successfully recovered up to 2945 loci with a mean of 1788 loci across the exome of specimens of varying age. Coverage was not significantly linked to specimen age, demonstrating the wide exploitability of museum specimens. We also recovered fragmentary mitogenomes compatible with Sanger-sequenced mtDNA. Our phylogenomic timetree revealed a Lower Cretaceous origin for crown group Carabinae, with the extinct Aplothorax nested within the genus Calosoma demonstrating the junior synonymy of Aplothorax syn. nov., resulting in the new combination Calosoma (Ctenosta) burchellii (Waterhouse, 1841) comb. nov. This study compellingly illustrates that HyRAD-X and phyloHyRAD efficiently provide genomic-level datasets informative at deep evolutionary scales.

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  • Chromosomal scale assembly of parasitic wasp genome reveals symbiotic virus colonization Commun Biol. 2021 Jan 22;4(1):104. doi: 10.1038/s42003-020-01623-8.

    abstract

    Endogenous viruses form an important proportion of eukaryote genomes and a source of novel functions. How large DNA viruses integrated into a genome evolve when they confer a benefit to their host, however, remains unknown. Bracoviruses are essential for the parasitism success of parasitoid wasps, into whose genomes they integrated ~103 million years ago. Here we show, from the assembly of a parasitoid wasp genome at a chromosomal scale, that bracovirus genes colonized all ten chromosomes of Cotesia congregata. Most form clusters of genes involved in particle production or parasitism success. Genomic comparison with another wasp, Microplitis demolitor, revealed that these clusters were already established ~53 mya and thus belong to remarkably stable genomic structures, the architectures of which are evolutionary constrained. Transcriptomic analyses highlight temporal synchronization of viral gene expression without resulting in immune gene induction, suggesting that no conflicts remain between ancient symbiotic partners when benefits to them converge.

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  • What do tropical cryptogams reveal? Strong genetic structure in Amazonian bryophytes New Phytol. 2020 Oct;228(2):640-650. doi: 10.1111/nph.16720.

    abstract

    Lowland tropical bryophytes have been perceived as excellent dispersers. In such groups, the inverse isolation hypothesis proposes that spatial genetic structure is erased beyond the limits of short-distance dispersal. Here, we determine the influence of environmental variation and geographic barriers on the spatial genetic structure of a widely dispersed and phylogenetically independent sample of Amazonian bryophytes. Single nucleotide polymorphism data were produced from a restriction site-associated DNA sequencing protocol for 10 species and analyzed through F-statistics and Mantel tests. Neither isolation-by-environment nor the impact of geographic barriers were recovered from the analyses. However, significant isolation-by-distance patterns were observed for 8 out of the 10 investigated species beyond the scale of short-distance dispersal (> 1 km), offering evidence contrary to the inverse isolation hypothesis. Despite a cadre of life-history traits and distributional patterns suggesting that tropical bryophytes are highly vagile, our analyses reveal spatial genetic structures comparable to those documented for angiosperms, whose diaspores are orders of magnitude larger. Dispersal limitation for tropical bryophytes flies in the face of traditional assumptions regarding their dispersal potential, and suggests that the plight of this component of cryptic biodiversity is more dire than previously considered in light of accelerated forest fragmentation in the Amazon.

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  • DiscoSnp-RAD: de novo detection of small variants for RAD-Seq population genomics. PeerJ 2020 ;8():e9291. 10.7717/peerj.9291. 9291. PMC7293188.

    abstract

    Restriction site Associated DNA Sequencing (RAD-Seq) is a technique characterized by the sequencing of specific loci along the genome that is widely employed in the field of evolutionary biology since it allows to exploit variants (mainly Single Nucleotide Polymorphism-SNPs) information from entire populations at a reduced cost. Common RAD dedicated tools, such as or , are based on all-vs-all read alignments, which require consequent time and computing resources. We present an original method, DiscoSnp-RAD, that avoids this pitfall since variants are detected by exploiting specific parts of the assembly graph built from the reads, hence preventing all-vs-all read alignments. We tested the implementation on simulated datasets of increasing size, up to 1,000 samples, and on real RAD-Seq data from 259 specimens of flies, morphologically assigned to seven species. All individuals were successfully assigned to their species using both STRUCTURE and Maximum Likelihood phylogenetic reconstruction. Moreover, identified variants succeeded to reveal a within-species genetic structure linked to the geographic distribution. Furthermore, our results show that DiscoSnp-RAD is significantly faster than state-of-the-art tools. The overall results show that DiscoSnp-RAD is suitable to identify variants from RAD-Seq data, it does not require time-consuming parameterization steps and it stands out from other tools due to its completely different principle, making it substantially faster, in particular on large datasets.

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  • DiscoSnp-RAD: de novo detection of small variants for RAD-Seq population genomics PeerJ. 2020 Jun 10;8:e9291. doi: 10.7717/peerj.9291.

    abstract

    Restriction site Associated DNA Sequencing (RAD-Seq) is a technique characterized by the sequencing of specific loci along the genome that is widely employed in the field of evolutionary biology since it allows to exploit variants (mainly Single Nucleotide Polymorphism-SNPs) information from entire populations at a reduced cost. Common RAD dedicated tools, such as STACKS or IPyRAD, are based on all-vs-all read alignments, which require consequent time and computing resources. We present an original method, DiscoSnp-RAD, that avoids this pitfall since variants are detected by exploiting specific parts of the assembly graph built from the reads, hence preventing all-vs-all read alignments. We tested the implementation on simulated datasets of increasing size, up to 1,000 samples, and on real RAD-Seq data from 259 specimens of Chiastocheta flies, morphologically assigned to seven species. All individuals were successfully assigned to their species using both STRUCTURE and Maximum Likelihood phylogenetic reconstruction. Moreover, identified variants succeeded to reveal a within-species genetic structure linked to the geographic distribution. Furthermore, our results show that DiscoSnp-RAD is significantly faster than state-of-the-art tools. The overall results show that DiscoSnp-RAD is suitable to identify variants from RAD-Seq data, it does not require time-consuming parameterization steps and it stands out from other tools due to its completely different principle, making it substantially faster, in particular on large datasets.

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  • Museomics identifies genetic erosion in two butterfly species across the 20th century in Finland. Mol Ecol Resour 2020 Apr;():. 10.1111/1755-0998.13167.

    abstract

    Erosion of biodiversity generated by anthropogenic activities has been studied for decades and in many areas at the species level, using taxa monitoring. In contrast, genetic erosion within species has rarely been tracked, and is often studied by inferring past population dynamics from contemporaneous estimators. An alternative to such inferences is the direct examination of past genes, by analysing museum collection specimens. While providing direct access to genetic variation over time, historical DNA is usually not optimally preserved, and it is necessary to apply genotyping methods based on hybridization-capture to unravel past genetic variation. In this study, we apply such a method (i.e., HyRAD), to large time series of two butterfly species in Finland, and present a new bioinformatic pipeline, namely PopHyRAD, that standardizes and optimizes the analysis of HyRAD data at the within-species level. In the localities for which the data retrieved have sufficient power to accurately examine genetic dynamics through time, we show that genetic erosion has increased across the last 100 years, as revealed by signatures of allele extinctions and heterozygosity decreases, despite local variations. In one of the two butterflies (Erebia embla), isolation by distance also increased through time, revealing the effect of greater habitat fragmentation over time.

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  • Contrasting genomic and phenotypic outcomes of hybridization between pairs of mimetic butterfly taxa across a suture zone Mol Ecol. 2020 Apr;29(7):1328-1343. doi: 10.1111/mec.15403.

    abstract

    Hybrid zones, whereby divergent lineages come into contact and eventually hybridize, can provide insights on the mechanisms involved in population differentiation and reproductive isolation, and ultimately speciation. Suture zones offer the opportunity to compare these processes across multiple species. In this paper we use reduced-complexity genomic data to compare the genetic and phenotypic structure and hybridization patterns of two mimetic butterfly species, Ithomia salapia and Oleria onega (Nymphalidae: Ithomiini), each consisting of a pair of lineages differentiated for their wing colour pattern and that come into contact in the Andean foothills of Peru. Despite similarities in their life history, we highlight major differences, both at the genomic and phenotypic level, between the two species. These differences include the presence of hybrids, variations in wing phenotype, and genomic patterns of introgression and differentiation. In I. salapia, the two lineages appear to hybridize only rarely, whereas in O. onega the hybrids are not only more common, but also genetically and phenotypically more variable. We also detected loci statistically associated with wing colour pattern variation, but in both species these loci were not over-represented among the candidate barrier loci, suggesting that traits other than wing colour pattern may be important for reproductive isolation. Our results contrast with the genomic patterns observed between hybridizing lineages in the mimetic Heliconius butterflies, and call for a broader investigation into the genomics of speciation in Ithomiini - the largest radiation of mimetic butterflies.

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  • Relative Influence of Host, Wolbachia, Geography and Climate on the Genetic Structure of the Sub-saharan Parasitic Wasp Cotesia sesamiae Front. Ecol. Evol. 7:309.doi: 10.3389/fevo.2019.00309.

    abstract

    The parasitoid lifestyle represents one of the most diversified life history strategies on earth. There are however very few studies on the variables associated with intraspecific diversity of parasitoid insects, especially regarding the relationship with spatial, biotic and abiotic ecological factors. Cotesia sesamiae is a Sub-Saharan stenophagous parasitic wasp that parasitizes several African stemborer species with variable developmental success. The different host-specialized populations are infected with different strains of Wolbachia, an endosymbiotic bacterium widespread in arthropods that is known for impacting life history traits, notably reproduction, and consequently species distribution. In this study, first we analyzed the genetic structure of C. sesamiae across Sub-Saharan Africa, using 8 microsatellite markers. We identified five major population clusters across Sub-Saharan Africa, which probably originated in the East African Rift region and expanded throughout Africa in relation to host genus and abiotic factors, such as Köppen-Geiger climate classification. Using laboratory lines, we estimated the incompatibility between the different strains of Wolbachia infecting C. sesamiae. We observed that incompatibility between Wolbachia strains was asymmetric, expressed in one direction only. Based on these results, we assessed the relationships between the direction of gene flow and Wolbachia infections in the genetic clusters. We found that host specialization was more influential on genetic structure than Wolbachia-induced reproductive incompatibility, which in turn was more influential than geography and current climatic conditions. These results are discussed in the context of African biogeography, and co-evolution between Wolbachia, virus parasitoid and host, in the perspective of improving biological control efficiency through a better knowledge of biological control agents' evolutionary ecology.

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  • Discovering millions of plankton genomic markers from the Atlantic Ocean and the Mediterranean Sea Mol Ecol Resour . 2019 Mar;19(2):526-535. doi: 10.1111/1755-0998.12985.

    abstract

    Comparison of the molecular diversity in all plankton populations present in geographically distant water columns may allow for a holistic view of the connectivity, isolation and adaptation of organisms in the marine environment. In this context, a large-scale detection and analysis of genomic variants directly in metagenomic data appeared as a powerful strategy for the identification of genetic structures and genes under natural selection in plankton. Here, we used discosnp++, a reference-free variant caller, to produce genetic variants from large-scale metagenomic data and assessed its accuracy on the copepod Oithona nana in terms of variant calling, allele frequency estimation and population genomic statistics by comparing it to the state-of-the-art method. discosnp ++ produces variants leading to similar conclusions regarding the genetic structure and identification of loci under natural selection. discosnp++ was then applied to 120 metagenomic samples from four size fractions, including prokaryotes, protists and zooplankton sampled from 39 tara Oceans sampling stations located in the Atlantic Ocean and the Mediterranean Sea to produce a new set of marine genomic markers containing more than 19 million of variants. This new genomic resource can be used by the community to relocate these markers on their plankton genomes or transcriptomes of interest. This resource will be updated with new marine expeditions and the increase of metagenomic data (availability: http://bioinformatique.rennes.inria.fr/taravariants/).

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  • Genomic divergence footprints in the bracovirus of Cotesia sesamiae identified by targeted re-sequencing approach Mol Ecol . 2018 Apr;27(8):2109-2123. doi: 10.1111/mec.14574.

    abstract

    The African parasitoid wasp Cotesia sesamiae is a generalist species structured in locally adapted populations showing differences in host range. The recent discovery of Cotesia typhae, a specialist, sister species to C. sesamiae, provides a good framework to study the genetic determinants of parasitoid host range. To investigate the genomic bases of divergence between these populations and species, we used a targeted sequencing approach on 24 samples. We targeted the bracovirus genomic region encoding virulence genes involved in the interaction with the lepidopteran hosts of the wasps. High sequencing coverage was obtained for all samples, allowing the study of genetic variation between wasp populations and species. By combining population genetic estimations, such as nucleotide diversity (π), relative differentiation (FST) and absolute divergence (dxy), with branch‐site dN/dS measures, we identified six of 98 bracovirus genes showing significant divergence and evidence of positive selection. These genes, belonging to different gene families, are potentially involved in host adaptation and in the specialization process. Fine‐scale analyses of genetic variation also revealed mutations and large deletions in certain genes inducing pseudogenization and loss of function. The image emerging from these results is that adaptation mediated by bracovirus genes happens through selection of particularly adaptive alleles and loss of nonadaptive genes. These results highlight the central role of the bracovirus in the molecular interactions between the wasps and their hosts and in the evolutionary processes of specialization.

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  • Impact of Lateral Transfers on the Genomes of Lepidoptera Genes (Basel) . 2017 Nov 9;8(11):315. doi: 10.3390/genes8110315.

    abstract

    Transfer of DNA sequences between species regardless of their evolutionary distance is very common in bacteria, but evidence that horizontal gene transfer (HGT) also occurs in multicellular organisms has been accumulating in the past few years. The actual extent of this phenomenon is underestimated due to frequent sequence filtering of "alien" DNA before genome assembly. However, recent studies based on genome sequencing have revealed, and experimentally verified, the presence of foreign DNA sequences in the genetic material of several species of Lepidoptera. Large DNA viruses, such as baculoviruses and the symbiotic viruses of parasitic wasps (bracoviruses), have the potential to mediate these transfers in Lepidoptera. In particular, using ultra-deep sequencing, newly integrated transposons have been identified within baculovirus genomes. Bacterial genes have also been acquired by genomes of Lepidoptera, as in other insects and nematodes. In addition, insertions of bracovirus sequences were present in the genomes of certain moth and butterfly lineages, that were likely corresponding to rearrangements of ancient integrations. The viral genes present in these sequences, sometimes of hymenopteran origin, have been co-opted by lepidopteran species to confer some protection against pathogens.

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  • The Cotesia sesamiae story: insight into host-range evolution in a Hymenoptera parasitoid and implication for its use in biological control programs Genetica . 2017 Dec;145(6):455-468. doi: 10.1007/s10709-017-9989-3.

    abstract

    This review covers nearly 20 years of studies on the ecology, physiology and genetics of the Hymenoptera Cotesia sesamiae, an African parasitoid of Lepidoptera that reduces populations of common maize borers in East and South Africa. The first part of the review presents studies based on sampling of C. sesamiae from maize crops in Kenya. From this agrosystem including one host plant and three main host borer species, studies revealed two genetically differentiated populations of C. sesamiae species adapted to their local host community, and showed that their differentiation involved the joint evolution of virulence genes and sensory mechanisms of host acceptance, reinforced by reproductive incompatibility due to Wolbachia infection status and natural inbreeding. In the second part, we consider the larger ecosystem of wild Poales plant species hosting many Lepidoptera stem borer species that are potential hosts for C. sesamiae. The hypothesis of other host-adapted C. sesamiae populations was investigated based on a large sampling of stem borer larvae on various Poales across sub-Saharan Africa. The sampling provided information on the respective contribution of local hosts, biogeography and Wolbachia in the genetic structure of C. sesamiae populations. Molecular evolution analyses highlighted that several bracovirus genes were under positive selection, some of them being under different selection pressure in C. sesamiae populations adapted to different hosts. This suggests that C. sesamiae host races result from co-evolution acting at the local scale on different bracovirus genes. The third part considers the mechanisms driving specialization. C. sesamiae host races are more or less host-specialized. This character is crucial for efficient and environmentally-safe use of natural enemies for biological control of pests. One method to get an insight in the evolutionary stability of host-parasite associations is to characterize the phylogenetic relationships between the so-called host-races. Based on the construction of a phylogeny of C. sesamiae samples from various host- and plant species, we revealed three main lineages. Mechanisms of differentiation are discussed with regard to the geography and ecology of the samples. One of the lineage presented all the hallmarks of a distinct species, which has been morphologically described and is now studied in the perspective of being used as biological control agent against Sesamia nonagrioides Lefèbvre (Lepidoptera: Noctuidae), a major maize pest in West Africa and Mediterranean countries (see Benoist et al. 2017). The fourth part reviews past and present use of C. sesamiae in biological control, and points out the interest of such molecular ecology studies to reconcile biodiversity and food security stakes in future biological control.

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  • Foreign DNA acquisition by invertebrate genomes J Invertebr Pathol . 2017 Jul;147:157-168. doi: 10.1016/j.jip.2016.09.004.

    abstract

    Recent studies have highlighted that the accidental acquisition of DNA from other species by invertebrate genomes is much more common than originally thought. The transferred DNAs are of bacterial or eukaryote origin and in both cases the receiver species may end up utilising the transferred genes for its own benefit. Frequent contact with prokaryotic DNA from symbiotic endocellular bacteria may predispose invertebrates to incorporate this genetic material into their genomes. Increasing evidence also points to viruses as major players in transferring genes and mobile elements between the species they infect. Unexpectedly a gene flux between Hymenoptera and Lepidoptera mediated by endogenous viruses of parasitic wasps has been recently unravelled, suggesting we are probably just seeing the tip of the iceberg concerning horizontal gene transfers in invertebrates. In the context of insect for feed and food, if the new technology of insect genome editing (such as Crisper/Cas9) were used to modify the genome of reared insects it is important to take into account the risk that an introduced gene can be transferred. More generally, although insects are traditionally consumed in Asia and Africa, knowledge on insect viruses is still limited rendering it difficult to predict the impact they might have in the context of insect rearing at an industrial scale.

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  • The recurrent domestication of viruses: major evolutionary transitions in parasitic wasps Parasitology . 2018 May;145(6):713-723. doi: 10.1017/S0031182017000725.

    abstract

    Several lineages of endoparasitoid wasps, which develop inside the body of other insects, have domesticated viruses, used as delivery tools of essential virulence factors for the successful development of their progeny. Virus domestications are major evolutionary transitions in highly diverse parasitoid wasps. Much progress has recently been made to characterize the nature of these ancestrally captured endogenous viruses that have evolved within the wasp genomes. Virus domestication from different viral families occurred at least three times in parasitoid wasps. This evolutionary convergence led to different strategies. Polydnaviruses (PDVs) are viral gene transfer agents and virus-like particles of the wasp Venturia canescens deliver proteins. Here, we take the standpoint of parasitoid wasps to review current knowledge on virus domestications by different parasitoid lineages. Then, based on genomic data from parasitoid wasps, PDVs and exogenous viruses, we discuss the different evolutionary steps required to transform viruses into vehicles for the delivery of the virulence molecules that we observe today. Finally, we discuss how endoparasitoid wasps manipulate host physiology and ensure parasitism success, to highlight the possible advantages of viral domestication as compared with other virulence strategies.

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  • Experimentally evolved populations of the potato cyst nematode Globodera pallida allow the targeting of genomic footprints of selection due to host adaptation Plant Pathol, 66: 1022-1030. https://doi.org/10.1111/ppa.12646

    abstract

    In the current agronomical context of pesticide use reduction, deciphering the genetic bases of pathogen adaptation to plant defences is of major importance to improve durability of resistance. Indeed, knowledge of virulence gene frequencies in pathogen populations could allow the prediction of resistance durability before deployment. Globodera pallida is a major pest of potato crops for which a promising resistance QTL, GpaVvrn, has been identified in Solanum vernei. An experimental evolution study, in which G. pallida lineages evolved on resistant or susceptible potato genotypes for up to eight generations, previously showed that G. pallida was able to rapidly overcome GpaVvrn resistance. However, it was not known if enough genetic mixing occurred in these lineages to be able to detect islands of differentiation in a genome scan approach. Here, this question was investigated using 53 polymorphic microsatellite markers distributed along the genome and three different tests based on genetic differentiation and heterozygosity. Eight outlier loci were identified, indicative of genomic regions putatively involved in host adaptation. Several loci were identified by multiple detection methods and/or in two independent adapted lineages. Some candidate genomic regions identified also seemed to be involved in overcoming resistance to nematodes in a plant genotype harbouring the same resistance QTL in a different genetic background. These results validate the feasibility of a genome scan approach on biological material coming from short experimental evolution, and encourage the use of a high coverage genome scan by whole genome resequencing.

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  • Recurrent DNA virus domestication leading to different parasite virulence strategies Science Advances 27 Nov 2015: Vol. 1, no. 10, e1501150 DOI: 10.1126/sciadv.1501150

    abstract

    Relics of ancient infections are abundant in eukaryote genomes, but little is known about how they evolve when they confer a functional benefit on their host. We show here, for the first time, that the virus-like particles shown to protect Venturia canescens eggs against host immunity are derived from a nudivirus genome incorporated by the parasitic wasp into its own genetic material. Nudivirus hijacking was also at the origin of protective particles from braconid wasps. However, we show here that the viral genes produce “liposomes” that wrap and deliver V. canescens virulence proteins, whereas the particles are used as gene transfer agents in braconid wasps. Our findings indicate that virus domestication has occurred repeatedly during parasitic wasp evolution but with different evolutionary trajectories after endogenization, resulting in different virulence molecule delivery strategies.

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  • Recurrent Domestication by Lepidoptera of Genes from Their Parasites Mediated by Bracoviruses PLoS Genet . 2015 Sep 17;11(9):e1005470. doi: 10.1371/journal.pgen.1005470.

    abstract

    Bracoviruses are symbiotic viruses associated with tens of thousands of species of parasitic wasps that develop within the body of lepidopteran hosts and that collectively parasitize caterpillars of virtually every lepidopteran species. Viral particles are produced in the wasp ovaries and injected into host larvae with the wasp eggs. Once in the host body, the viral DNA circles enclosed in the particles integrate into lepidopteran host cell DNA. Here we show that bracovirus DNA sequences have been inserted repeatedly into lepidopteran genomes, indicating this viral DNA can also enter germline cells. The original mode of Horizontal Gene Transfer (HGT) unveiled here is based on the integrative properties of an endogenous virus that has evolved as a gene transfer agent within parasitic wasp genomes for ≈100 million years. Among the bracovirus genes thus transferred, a phylogenetic analysis indicated that those encoding C-type-lectins most likely originated from the wasp gene set, showing that a bracovirus-mediated gene flux exists between the 2 insect orders Hymenoptera and Lepidoptera. Furthermore, the acquisition of bracovirus sequences that can be expressed by Lepidoptera has resulted in the domestication of several genes that could result in adaptive advantages for the host. Indeed, functional analyses suggest that two of the acquired genes could have a protective role against a common pathogen in the field, baculovirus. From these results, we hypothesize that bracovirus-mediated HGT has played an important role in the evolutionary arms race between Lepidoptera and their pathogens.

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Natural history collections are witnesses to the history of past biodiversity, their study at the genomic level makes it possible to identify macro- and micro-evolutionary processes involved in diversification. At the Museum of Geneva, I use and develop bioinformatic methods to reconstruct the evolutionary history of populations.