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), however, has never been assessed systematically. METHODS: We tested this hypothesis using phylogenetic and karyotypic information from 235 plant genera (mostly angiosperms). We fi rst 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 that incorporates anagenetic transitions over one with only cladogenetic transitions. Furthermore, the Bayesian analysis supported a preponderance of cladogenetic change in four genera but did not support a preponderance of anagenetic change in any genus. CONCLUSIONS: Overall, these phylogenetic analyses provide the fi rst broad confi rmation that polyploidization is temporally associated with speciation events, suggesting that it is indeed a major speciation mechanism in plants, at least in some genera.
Bibliographical noteFunding Information:
We thank Sean W. Graham and Michael S. Barker for helpful discussions and for their insightful comments on an early working draft of this manuscript. We are also grateful to two anonymous reviewers for helpful suggestions and to Lior Glick for helping to obtain genus diversity counts from The Plant List database. Finally, we thank Compute Canada, Fusion Genomics Corp., and UBC Zoology Computing Unit for providing access to computational resources that facilitated this research. Th is study was supported by the Israel Science Foundation (1265/12) to I.M., by the United States–Israel Binational Science Foundation (2013286) to I.M. and E.E.G., by the Natural Sciences and Engineering Research Council of Canada to S.P.O., and by the Canadian Institutes of Health Research Doctoral Research Award to S.H.Z.
© 2016 Botanical Society of America.