title: Recent speciation of Capsella rubella from Capsella grandiflora, associated with loss of self-incompatibility and an extreme bottleneck.
abstract: Flowering plants often prevent selfing through mechanisms of self-incompatibility (S.I.). The loss of S.I. has occurred many times independently, because it provides short-term advantages in situations where pollinators or mates are rare. The genus Capsella, which is closely related to Arabidopsis, contains a pair of closely related diploid species, the self-incompatible Capsella grandiflora and the self-compatible Capsella rubella. To elucidate the transition to selfing and its relationship to speciation of C. rubella, we have made use of comparative sequence information. Our analyses indicate that C. rubella separated from C. grandiflora recently ( approximately 30,000-50,000 years ago) and that breakdown of S.I. occurred at approximately the same time. Contrasting the nucleotide diversity patterns of the 2 species, we found that C. rubella has only 1 or 2 alleles at most loci, suggesting that it originated through an extreme population bottleneck. Our data are consistent with diploid speciation by a single, selfing individual, most likely living in Greece. The new species subsequently colonized the Mediterranean by Northern and Southern routes, at a time that also saw the spread of agriculture. The presence of phenotypic diversity within modern C. rubella suggests that this species will be an interesting model to understand divergence and adaptation, starting from very limited standing genetic variation.
authors.affiliation: Department of Molecular Biology, Max Planck Institute for Developmental Biology, 72076 Tübingen, Germany.
authors.forename: Ya-Long
authors.initials: YL
authors.lastname: Guo
authors.forename: Jesper S
authors.initials: JS
authors.lastname: Bechsgaard
authors.forename: Tanja
authors.initials: T
authors.lastname: Slotte
authors.forename: Barbara
authors.initials: B
authors.lastname: Neuffer
authors.forename: Martin
authors.initials: M
authors.lastname: Lascoux
authors.forename: Detlef
authors.initials: D
authors.lastname: Weigel
authors.forename: Mikkel H
authors.initials: MH
authors.lastname: Schierup
mesh_terms: D029687:Capsella / Q000145:classification* / Q000235:genetics; D004463:Ecology; D017343:Genes, Plant; D049810:Genetic Speciation; D005843:Geography; D006115:Greece; D019083:Mediterranean Region; D008969:Molecular Sequence Data; D010802:Phylogeny