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Reproductive mode and population genetic structure of the cereal aphid Sitobion avenae studied using phenotypic and microsatellite markers

Authors


  • This study results from a collaboration among three groups who focused their research on the evolution and population genetics of parthenogenetic invertebrates. This article is the main body of the postdoctorate thesis of Sigrid Baumann who, directed by J.-C. Simon and C.-A. Dedryver, performed the microsatellite analysis on French Sitobion avenae. Paul Sunnucks is working on the population genetics of Sitobion species and first developed microsatellites in this genus. Paul Hebert has extensive experience on breeding system evolution in cyclic parthenogens and has, for several years, been engaged in a fruitful collaboration with J.-C. Simon on aphids.

Dr Jean-Christophe Simon Fax: +33 (0) 29-928-5150; E-mail: jcsimon@rennes.inra.fr

Abstract

As French populations of the aphid Sitobion avenae exhibit a range of reproductive modes, this species provides a good opportunity for studying the evolution of breeding system variation. The present analysis combined ecological and genetic investigations into the spatial distribution of variation in reproductive mode. Reproductive mode was characterized in 277 lineages of S. avenae from France, and these aphids were scored for five microsatellite loci. The analyses revealed strong geographical partitioning of breeding systems, with obligate asexuals mostly restricted to the south of France, while lineages producing sexual forms were more common in the north. Contrary to what might be anticipated for organisms with frequent parthenogenesis, there was substantial genic and genotypic diversity, even in the obligately asexual lineages. More than 120 different genotypes were detected among the 277 aphid lineages, with an average of 5.9 alleles per locus (range four to 16) and heterozygosity of 56.7%. As with previous studies of allozyme variation in aphids, most loci showed heterozygote deficits, and disequilibrium was common among allelic variants at different loci, even after removal of replicate copies of genotypes that might have been derived through clonal reproduction. Our results suggest that selection is important in structuring reproductive systems and genetic variation in French S. avenae. Canonical correspondence analysis was employed to examine the associations between genotypic and phenotypic variables, enabling the identification of alleles correlated with life-history traits.

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