Phylogenetic evidence for cladogenetic polyploidization in land plants

Premise of the study: Polyploidization is a common and recurring phenomenon in plants and is often thought to be a mechanism of \"instant speciation.\" Whether polyploidization is associated with the formation of new species (\"cladogenesis\") or simply occurs over time within a lineage (\"anagenesis\") has never, however, been assessed systematically. Methods: Here, we tested this hypothesis using phylogenetic and karyotypic information from 235 plant genera (mostly angiosperms). We first constructed a large database of combined sequence and chromosome number data sets using an automated procedure. We then applied likelihood models (ClaSSE) that estimate the degree of synchronization between polyploidization and speciation events in maximum likelihood and Bayesian frameworks. Key results: Our maximum likelihood analysis indicated that 35 genera supported a model that includes cladogenetic transitions over a model with only anagenetic transitions, whereas three genera supported a model tha...