title: Genetic signature of amphimixis allows for the detection and fine scale localization of sexual reproduction events in a mainly parthenogenetic nematode.
abstract: Asexuality is an important mode of reproduction in eukaryotic taxa and has a theoretical advantage over sexual reproduction because of the increased ability to propagate genes. Despite this advantage, hidden signs of cryptic sex have been discovered in the genomes of asexual organisms. This has provided an interesting way to address the evolutionary impact of sex in plant and animal populations. However, the identification of rare sexual reproduction events in mainly asexual species has remained a challenging task. We examined the reproductive history in populations of the plant parasitic nematode Xiphinema index by genotyping individuals collected from six grapevine fields using seven microsatellite markers. A high level of linkage disequilibrium and heterozygous excess suggested a clonality rate of 95-100%. However, we also detected rare sexual reproduction events within these highly clonal populations. By combining highly polymorphic markers with an appropriate hierarchical sampling, and using both Bayesian and multivariate analysis with phylogenetic reconstructions, we were able to identify a small number of sexually produced individuals at the overlapping zones between different genetic clusters. This suggested that sexual reproduction was favoured when and where two nematode patches came into contact. Among fields, a high degree of genetic differentiation indicated a low level of gene flow between populations. Rare genotypes that were shared by several populations suggested passive dispersal by human activities, possibly through the introduction of infected plants from nurseries. We conclude that our method can be used to detect and locate sexual events in various predominantly asexual species.
authors.affiliation: INRA, Agrocampus Ouest, University Rennes, UMR 1099 BiO3P (Biology of Organisms and Populations applied to Plant Protection), Le Rheu, France.
authors.forename: Laure
authors.initials: L
authors.lastname: Villate
authors.forename: Daniel
authors.initials: D
authors.lastname: Esmenjaud
authors.forename: Maarten
authors.initials: M
authors.lastname: Van Helden
authors.forename: Solenn
authors.initials: S
authors.lastname: Stoeckel
authors.forename: Olivier
authors.initials: O
authors.lastname: Plantard
mesh_terms: D000483:Alleles; D000818:Animals; D001499:Bayes Theorem; D018509:DNA, Helminth / Q000235:genetics; D051456:Gene Flow; D014644:Genetic Variation; D005828:Genetics, Population; D005838:Genotype; D015810:Linkage Disequilibrium; D018895:Microsatellite Repeats; D015999:Multivariate Analysis; D009348:Nematoda / Q000235:genetics* / Q000502:physiology; D010802:Phylogeny; D012098:Reproduction / Q000235:genetics; D017422:Sequence Analysis, DNA
chemical_list: D018509:DNA, Helminth