Molekularna tipizacija tuniskih klonova vrste Myzus persicae (Hemiptera: Aphididae) pomoću mikrosatelitskih biljega

In order to assess the genetic differentiation among Tunisian clones belonging to the Myzus persicae complex (M. persicae (Sulzer), M. antirrhinii (Macchiati) and M. nicotianea Blackman), the molecular technique of microsatellites was used in this study. These markers offer sensitivity and are useful in population genetic studies of parthenogenetic organisms. Here, nine polymorphic microsatellite loci were amplified to distinguish between six parthenogenetic clones belonging to M. persicae complex collected from two different Tunisian areas. Interestingly, this technique allowed discrimination between five different genotypic classes among the six clones. Furthermore, analysis of genetic relatedness between the genotypic classes revealed that two Tunisian clones did not cluster either in M. persicae or in M. antirrhinii taxa, whereas, the four other Tunisian clones clustered into the M. persicae Sulzer taxa.U cilju utvrđivanja genetičkih razlika između tuniskih klonova kompleksa Myzus persicae (Sulzer), M. antirrhinii (Macchiati) i M. nicotianea (Blackman) upotrijebljena je molekularna mikrosatelitska tehnika. Ovi su biljezi vrlo osjetljivi i korisni u takvim istraživanjima partenogenetskih organizama. Umnoženo je devet polimorfnih lokusa mikrosatelita kako bi se razlikovalo šest partenogenetskih klonova kompleksa M. persicae sabranih u dva različita područja u Tunisu. Zanimljivo je da je ova tehnika omogućila razlikovanje između pet različitih genotipskih razreda tih šest klonova. Nadalje, analize genetičke srodnosti između genotipskih razreda pokazale su da dva tuniska klona nisu u istoj grupi niti s M. persicae, niti s M. antirrhinii, dok se četiri tuniska klona nalaze unutar vrste M. persicae Sulzer

Masculinization of the X Chromosome in the Pea Aphid

International audienceEvolutionary theory predicts that sexually antagonistic mutations accumulate differentially on the X chromosome and autosomes in species with an XY sex-determination system, with effects (masculinization or feminization of the X) depending on the dominance of mutations. Organisms with alternative modes of inheritance of sex chromosomes offer interesting opportunities for studying sexual conflicts and their resolution, because expectations for the preferred genomic location of sexually antagonistic alleles may differ from standard systems. Aphids display an XX/X0 system and combine an unusual inheritance of the X chromosome with the alternation of sexual and asexual reproduction. In this study, we first investigated theoretically the accumulation of sexually antagonistic mutations on the aphid X chromosome. Our results show that i) the X is always more favourable to the spread of male-beneficial alleles than autosomes, and should thus be enriched in sexually antagonistic alleles beneficial for males, ii) sexually antagonistic mutations beneficial for asexual females accumulate preferentially on autosomes, iii) in contrast to predictions for standard systems, these qualitative results are not affected by the dominance of mutations. Under the assumption that sex-biased gene expression evolves to solve conflicts raised by the spread of sexually antagonistic alleles, one expects that male-biased genes should be enriched on the X while asexual female-biased genes should be enriched on autosomes. Using gene expression data (RNA-Seq) in males, sexual females and asexual females of the pea aphid, we confirm these theoretical predictions. Although other mechanisms than the resolution of sexual antagonism may lead to sex-biased gene expression, we argue that they could hardly explain the observed difference between X and autosomes. On top of reporting a strong masculinization of the aphid X chromosome, our study highlights the relevance of organisms displaying an alternative mode of sex chromosome inheritance to understanding the forces shaping chromosome evolution

Large-scale gene discovery in the pea aphid Acyrthosiphon pisum (Hemiptera)

Aphids are the leading pests in agricultural crops. A large-scale sequencing of 40,904 ESTs from the pea aphid Acyrthosiphon pisum was carried out to define a catalog of 12,082 unique transcripts. A strong AT bias was found, indicating a compositional shift between Drosophila melanogaster and A. pisum. An in silico profiling analysis characterized 135 transcripts specific to pea-aphid tissues (relating to bacteriocytes and parthenogenetic embryos). This project is the first to address the genetics of the Hemiptera and of a hemimetabolous insect.Beatriz Sabater-Muñoz... et al

Molecular markers linked to breeding system differences in segregating and natural populations of the cereal aphid Rhopalosiphum padi L.

International audienc

Strong biases in the transmission of sex chromosomes in the aphid Rhopalosiphum padi

International audienceThe typical life cycle of aphids involves several parthenogenetic generations followed by a single sexual one in autumn, i.e. cyclical parthenogenesis. Sexual females are genetically identical to their parthenogenetic mothers and carry two sex chromosomes (XX). Male production involves the elimination of one sex chromosome (to produce X0) that could give rise to genetic conflicts between X-chromosomes. In addition, deleterious recessive 'mutations could accumulate on sex chromosomes during the parthenogenetic phase and affect males differentially depending on the X-chromosome they inherit. Genetic conflicts and deleterious mutations thus may induce transmission bias that could be exaggerated in males. Here, the transmission of X-chromosomes has been studied in the laboratory in two cyclically parthenogenetic lineages of the bird cherry-oat aphid Rhopalosiphum padi. X-chromosome transmission was followed, using X-linked microsatellite loci, at male production in the two lineages and in their hybrids deriving from reciprocal crosses. Genetic analyses revealed non-Mendelian inheritance of X-chromosomes in both parental and hybrid lineages at different steps of male function. Putative mechanisms and evolutionary consequences of non-Mendelian transmission of X-chromosomes to males are discusse

Modelling vertical and lateral weed seed movements during mouldboard ploughing with a skim-coulter

International audienc

Genetic architecture of sexual and asexual populations of the aphid Rhopalosiphum padi based on allozyme and microsatellite markers

International audienceCyclical parthenogens, including aphids, are attractive models for comparing the genetic outcomes of sexual and asexual reproduction, which determine their respective evolutionary advantages. In this study, we examined how reproductive mode shapes genetic structure of sexual (cyclically parthenogenetic) and asexual (obligately parthenogenetic) populations of the aphid Rhopalosiphum padi by comparing microsatellite and allozyme data sets. Allozymes showed little polymorphism, confirming earlier studies with these markers. In contrast, microsatellite loci were highly polymorphic and showed patterns very discordant from allozyme loci. In particular, microsatellites revealed strong heterozygote excess in asexual populations, whereas allozymes showed heterozygote deficits. Various hypotheses are explored that could account for the conflicting results of these two types of genetic markers. A strong differentiation between reproductive modes was found with both types of markers. Microsatellites indicated that sexual populations have high allelic polymorphism and heterozygote deficits (possibly because of population subdivision, inbreeding or selection). Little geographical differentiation was found among sexual populations confirming the large dispersal ability of this aphid. In contrast, asexual populations showed less allelic polymorphism but high heterozygosity at most loci. Two alternative hypotheses are proposed to explain this heterozygosity excess: allele sequence divergence during long‐term asexuality or hybrid origin of asexual lineages. Clonal diversity of asexual lineages of R. padi was substantial suggesting that they could have frozen genetic diversity from the pool of sexual lineages. Several widespread asexual genotypes were found to persist through time, as already seen in other aphid species, a feature seemingly consistent with the general‐purpose genotype hypothesi

Admixed sexual and facultatively asexual aphid lineages at mating sites

International audienceCyclically parthenogenetic organisms may have facultative asexual counterparts. Such organisms, including aphids, are therefore interesting models for the study of ecological and genetic interactions between lineages differing in reproductive mode. Earlier studies on aphids have revealed major differences in the genetic outcomes of populations that are possibly resulting mostly either from sexual or from asexual reproduction. Besides, notable gene flow between sexual and asexual derivatives has been suspected, which could lead to the emergence of new asexual lineages. The present study examines the interplay between these lineages and is based on analyses of population structure of individuals that may contribute to the pool of sexual reproductive forms in the host alternating aphid Rhopalosiphum padi. Using a Bayesian assignment method, we first show that the sexual forms of R. padi on mating sites encompass two genetically distinct clusters of individuals in the western part of France. The first cluster included unique genotypes of sexual lineages, while the second cluster included facultatively asexual lineages in numerous copies, the reproductive mode of the two clusters being confirmed by reference clones. Sexual reproductive forms produced by sexual and facultatively asexual lineages are thus admixed at mating sites which gives a large opportunity for the two clusters to mate with each other. Nevertheless, this study also highlights, as previously demonstrated, that the two clusters retained high genetic differentiation. Possible explanations for the inferred limited genetic exchanges are advanced in the discussion, but further dedicated investigations are required to solve this paradox