Hybrid origins and homoploid reticulate evolution within Heliosperma (Sileneae, Caryophyllaceae)--a multigene phylogenetic approach with relative dating.

We used four potentially unlinked nuclear DNA regions from the gene family encoding the second largest subunit of the RNA polymerases, as well as the psbE-petG spacer and the rps16 intron from the chloroplast genome, to evaluate the origin of and relationships within Heliosperma (Sileneae, Caryophyllaceae). Relative dates of divergence times are used to discriminate between hybridization and gene duplication/loss as alternative explanations for topological conflicts between gene trees. The observed incongruent relationships among the three major lineages of Heliosperma are better explained by homoploid hybridization than by gene duplication/losses because species branching events exceed gene coalescence times under biologically reasonable population sizes and generation times, making lineage sorting an unlikely explanation. The origin of Heliosperma is complex and the gene trees likely reflect both reticulate evolution and sorting events. At least two lineages have been involved in the origin of Heliosperma, one most closely related to the ancestor of Viscaria and Atocion and the other to Eudianthe and/or Petrocoptis.