Natural and Experimental Infection of Caenorhabditis Nematodes by Novel Viruses Related to Nodaviruses

Novel viruses have been discovered in wild Caenorahbditis nematode isolates and can now be used to explore host antiviral pathways, nematode ecology, and host-pathogen co-evolution

Genetic and ecological differentiation among aphid populations of Brachycaudus helichrysi (Hemiptera Aphididae) : an evidence of two sibling species with contrasted life cycles

Brachycaudus helichrysi est un puceron ravageur des cultures qui inflige de sérieux dégâts à ses hôtes primaires (arbres fruitiers du genre Prunus) ainsi qu'à plusieurs herbacées cultivées correspondant à ses hôtes secondaires (par exemple les tournesols et les chrysanthèmes).L'étude phylogéographique de l'espèce basée sur un échantillonnage mondial, montre que B. helichrysi rassemble deux taxa appelés B. helichrysi H1 et H2. Cette étude, basée sur plusieurs marqueurs génétiques (mitochondriaux, nucléaire et bactériens), révèle une divergence génétique de l'ordre de celle observée entre espèce du genre Brachycaudus. Ceci suggère que B. helichrysi H1 et H2 sont deux espèces sœurs. Comme H1 et H2 sont morphologiquement indistinguables, nous avons mis au point un test de discrimination génétique par PCR-RFLP.L'analyse des génotypes (14 loci microsatellites) combinés aux données écologiques suggère que ces deux espèces sœurs ont des histoires évolutives différentes. Le cycle de vie de B. helichrysi H1 correspondrait à la parthénogenèse cyclique, utilisant les pruniers comme hôte primaire. Nous avons montré qu'il existe chez H1 des clusters génétiques structurés géographiquement. Au contraire, B. helichrysi H2 rassemble principalement des lignées clonales polyphages, persistantes et largement distribuées dans le monde (i.e. superclones), ainsi qu'une lignée sexuée, probablement hétéroécique, qui a été trouvée sur pêchers en Inde. Les individus des deux espèces colonisent fréquemment une même plante herbacée, composant ainsi des colonies « mixtes ». Cette étude apportera un éclairage sur comment l'évolution des cycles de vie, en particulier la perte de la reproduction sexuée, a pu jouer un rôle dans les processus de spéciation au sein du complexe B. helichrysiBrachycaudus helichrysi is a worldwide polyphagous aphid pest that seriously damages its primary hosts (Prunus spp.) and the various cultivated plants among its secondary hosts (e.g. sunflower, chrysanthemums).In a phylogeographic study based on a worldwide sampling, I have shown that this species is actually an amalgamation of two sibling taxa called B. helichrysi H1 and B. helichrysi H2. This study based on mitochondrial, nuclear and Buchnera aphidicola (the primary symbiont of aphids) DNA markers revealed that these two taxa display levels of genetic divergence as great as those generally found between sister species in the Brachycaudus genus, suggesting that they actually correspond to two distinct sibling species. As these two species are morphologically indistinguishable, we developed a PCR-RFLP test to genetically discriminate them.Further investigations, based on microsatellites data combined with ecological information suggest that these two species have two very different evolutionary histories. Brachycaudus helichrysi H1 exhibits a typical signature of cyclical parthenogenesis, using plum trees during the sexual phase, and we demonstrate the existence of distinct geographic genetic clusters within this species. By contrast B. helichrysi H2 comprises two types of lineages. First, it gathers several persistent obligate clonal lineages distributed worldwide (i.e. superclones) and highly polyphagous, and second, we reveal the existence of a cyclical parthenogenetic H2 lineage that uses peach trees as primary hosts and has so far only been found in India. All B. helichrysi lineages of H1 and H2 co-occurred in mixed colonies on herbaceous hosts all around the world.This study will shed light on how life cycle evolution, especially the loss of sexual reproduction, could explain the ongoing speciation process in the B. helichrysi species complex

Différenciation génétique et écologique au sein des populations du puceron Brachycaudus helichrysi (Hemiptera : Aphididae) : mise en évidence de deux espèces soeurs au cycles de vie contrastés

Brachycaudus helichrysi est un puceron ravageur des cultures qui inflige de sérieux dégâts à ses hôtes primaires (arbres fruitiers du genre Prunus) ainsi qu'à plusieurs herbacées cultivées correspondant à ses hôtes secondaires (par exemple les tournesols et les chrysanthèmes). L'étude phylogéographique de l'espèce basée sur un échantillonnage mondial, montre que B. helichrysi rassemble deux taxa appelés B. helichrysi H1 et H2. Cette étude, basée sur plusieurs marqueurs génétiques (mitochondriaux, nucléaire et bactériens), révèle une divergence génétique de l'ordre de celle observée entre espèce du genre Brachycaudus. Ceci suggère que B. helichrysi H1 et H2 sont deux espèces sœurs. Comme H1 et H2 sont morphologiquement indistinguables, nous avons mis au point un test de discrimination génétique par PCR-RFLP. L'analyse des génotypes (14 loci microsatellites) combinés aux données écologiques suggère que ces deux espèces sœurs ont des histoires évolutives différentes. Le cycle de vie de B. helichrysi H1 correspondrait à la parthénogenèse cyclique, utilisant les pruniers comme hôte primaire. Nous avons montré qu'il existe chez H1 des clusters génétiques structurés géographiquement. Au contraire, B. helichrysi H2 rassemble principalement des lignées clonales polyphages, persistantes et largement distribuées dans le monde (i.e. superclones), ainsi qu'une lignée sexuée, probablement hétéroécique, qui a été trouvée sur pêchers en Inde. Les individus des deux espèces colonisent fréquemment une même plante herbacée, composant ainsi des colonies « mixtes ». Cette étude apportera un éclairage sur comment l'évolution des cycles de vie, en particulier la perte de la reproduction sexuée, a pu jouer un rôle dans les processus de spéciation au sein du complexe B. helichrysi

Différenciation génétique et écologique au sein des populations du puceron Brachycaudus helichrysi (Hemiptera Aphididae) (mise en évidence de deux espèces soeurs au cycles de vie contrastés)

Brachycaudus helichrysi est un puceron ravageur des cultures qui inflige de sérieux dégâts à ses hôtes primaires (arbres fruitiers du genre Prunus) ainsi qu'à plusieurs herbacées cultivées correspondant à ses hôtes secondaires (par exemple les tournesols et les chrysanthèmes).L'étude phylogéographique de l'espèce basée sur un échantillonnage mondial, montre que B. helichrysi rassemble deux taxa appelés B. helichrysi H1 et H2. Cette étude, basée sur plusieurs marqueurs génétiques (mitochondriaux, nucléaire et bactériens), révèle une divergence génétique de l'ordre de celle observée entre espèce du genre Brachycaudus. Ceci suggère que B. helichrysi H1 et H2 sont deux espèces sœurs. Comme H1 et H2 sont morphologiquement indistinguables, nous avons mis au point un test de discrimination génétique par PCR-RFLP.L'analyse des génotypes (14 loci microsatellites) combinés aux données écologiques suggère que ces deux espèces sœurs ont des histoires évolutives différentes. Le cycle de vie de B. helichrysi H1 correspondrait à la parthénogenèse cyclique, utilisant les pruniers comme hôte primaire. Nous avons montré qu'il existe chez H1 des clusters génétiques structurés géographiquement. Au contraire, B. helichrysi H2 rassemble principalement des lignées clonales polyphages, persistantes et largement distribuées dans le monde (i.e. superclones), ainsi qu'une lignée sexuée, probablement hétéroécique, qui a été trouvée sur pêchers en Inde. Les individus des deux espèces colonisent fréquemment une même plante herbacée, composant ainsi des colonies mixtes . Cette étude apportera un éclairage sur comment l'évolution des cycles de vie, en particulier la perte de la reproduction sexuée, a pu jouer un rôle dans les processus de spéciation au sein du complexe B. helichrysiBrachycaudus helichrysi is a worldwide polyphagous aphid pest that seriously damages its primary hosts (Prunus spp.) and the various cultivated plants among its secondary hosts (e.g. sunflower, chrysanthemums).In a phylogeographic study based on a worldwide sampling, I have shown that this species is actually an amalgamation of two sibling taxa called B. helichrysi H1 and B. helichrysi H2. This study based on mitochondrial, nuclear and Buchnera aphidicola (the primary symbiont of aphids) DNA markers revealed that these two taxa display levels of genetic divergence as great as those generally found between sister species in the Brachycaudus genus, suggesting that they actually correspond to two distinct sibling species. As these two species are morphologically indistinguishable, we developed a PCR-RFLP test to genetically discriminate them.Further investigations, based on microsatellites data combined with ecological information suggest that these two species have two very different evolutionary histories. Brachycaudus helichrysi H1 exhibits a typical signature of cyclical parthenogenesis, using plum trees during the sexual phase, and we demonstrate the existence of distinct geographic genetic clusters within this species. By contrast B. helichrysi H2 comprises two types of lineages. First, it gathers several persistent obligate clonal lineages distributed worldwide (i.e. superclones) and highly polyphagous, and second, we reveal the existence of a cyclical parthenogenetic H2 lineage that uses peach trees as primary hosts and has so far only been found in India. All B. helichrysi lineages of H1 and H2 co-occurred in mixed colonies on herbaceous hosts all around the world.This study will shed light on how life cycle evolution, especially the loss of sexual reproduction, could explain the ongoing speciation process in the B. helichrysi species complex.MONTPELLIER-SupAgro La Gaillarde (341722306) / SudocSudocFranceF

Molecular identification and ecological characteristics of two cryptic lineages within a cosmopolitan aphid pest, Brachycaudus helichrysi (Hemiptera: Aphididae)

International audienceThe leaf-curl plum aphid, Brachycaudus helichrysi (Kaltenbach 1843), is a polyphagous cosmopolitan aphid. This serious pest of plum and peach orchards affects the growth of its host plants by curling infested leaves, and can transmit viruses such as the plum pox virus. Phylogenetic analyses have recently shown that B. helichrysi actually comprises two lineages that are morphologically similar but genetically different. In this study, we developed a PCR-RFLP test for differentiating between these two lineages, based on a mitochondrial DNA fragment. We used this test to investigate the patterns of host plant association and the geographical distribution of these lineages, with a large sample of individuals collected from numerous host plants and locations worldwide. We found that one of the lineages was never present on plum trees, and that individuals from both lineages coexisted on many secondary herbaceous hosts at almost all of the sites studied. We then carried out principal component analysis to determine whether the distribution of the two lineages could be explained by climatic features. We found that the lineage absent from plum trees was not found in regions with harsh winters. This suggests that one of the lineages within B. helichrysi may be an obligate parthenogenetic aphid

Molecular phylogeny reveals the existence of two sibling species in the aphid pest Brachycaudus helichrysi (Hemiptera: Aphididae)

Contacts : [email protected]; [email protected]; [email protected]; [email protected]; [email protected]; [email protected] audienceBrachycaudus helichrysi is a worldwide polyphagous aphid pest that seriously damages its primary hosts (Prunus spp.) and the various cultivated plants among its secondary hosts (e. g. sunflower). A recent study of the Brachycaudus genus suggested that this species might encompass two differentiated lineages. We tested this hypothesis, by carrying out a phylogenetic study of this aphid pest based on worldwide sampling and the evaluation of mitochondrial, nuclear and Buchnera aphidicola DNA markers. We show that this species is actually an amalgamation of two sibling taxa, B. helichrysi H1 and B. helichrysi H2, that seem to have overlapping geographic ranges and herbaceous host plant preferences. These two taxa displayed levels of genetic divergence as great as those generally found between sister species in the Brachycaudus genus, suggesting that they actually correspond to two distinct species. Our phylogenetic reconstructions revealed a degree of incongruence between the topologies obtained with the aphid gene data set and with data for a DNA marker from its primary endosymbiont. We identified possible reasons for this observation and discuss the ecological and genotypic data suggesting that B. helichrysi H1 and B. helichrysi H2 have different life cycles

Regular or covert sex defines two lineages and worldwide superclones within the leaf-curl plum aphid (Brachycaudus helichrysi, Kaltenbach)

International audienceAsexual reproduction occurs widely in plants and animals, particularly in insects. Aphid species usually reproduce by cyclic parthenogenesis, but many species include obligate asexual lineages. We recently showed that the leaf-curl plum aphid, Brachycaudus helichrysi, actually encompasses two lineages, B.helichrysi H1 and H2. Ecological data suggest that these lineages have different life cycles. We conducted a large population genetics study, based on 14 microsatellite loci, to infer their respective life cycles and investigate their population structure and geographical distribution. Brachycaudus helichrysi H1 displayed the genetic signature of cyclical parthenogenesis, using plum trees as primary hosts for sexual reproduction, as classically described for B.helichrysi. B.helichrysi H2 displayed the typical signature of obligate asexual reproduction. H2 encompassed at least eight highly successful genotypes or superclones. B.helichrysi H2 population that underwent sexual reproduction, which was collected from peach trees, in Northern India. Our results confirm that H1 and H2 have different life cycles. Brachycaudus helichrysi H1 is clearly heteroecious using plum trees as primary hosts, while B.helichrysi H2 encompasses several anholocyclic lineages, and some heteroecious populations that until now have only been found associated with peach trees as primary hosts. We discuss implications of these findings for the pest status of B.helichrysi lineages

Large-scale phylogeographic study of the cosmopolitan aphid pest Brachycaudus helichrysi reveals host plant associated lineages that evolved in allopatry

International audienceMany cosmopolitan plant-eating insect species comprise reproductively isolated population clusters that exhibit contrasting biological (e.g. life cycle) and ecological (e.g. host plant association) characteristics. Phylogeographical studies can untangle such complexities and shed light on the evolutionary forces that drove the divergence between population clusters. In the present study, we investigated the phylogeography of the leaf curl plum aphid (Brachycaudus helichrysi), a cosmopolitan pest of Prunus orchards. Using a combination of DNA markers on a set of specimens sampled worldwide, we confirmed the existence of two main lineages (H1 and H2), with differing life cycles. H1 is a sexually reproducing lineage found across the Holarctic on plum trees, whereas H2 consists of globally distributed asexual lineages and few sexual populations that are restricted to West Asia and use peach trees as primary hosts. We further characterized a third lineage (H3), restricted to East Asia, which is associated with apricot trees and Prunus species that are endemic to this region. The divergence of the lineages postdates the speciation of associated Prunus species but precedes their domestication. Our results suggest that, in B. helichrysi, the differentiation between host-specific lineages initially started in geographically isolated populations, which subsequently each adapted to local Prunus species. (C) 2016 The Linnean Society of Londo