Molecular dating of Winteraceae reveals a complex biogeographical history involving both ancient Gondwanan vicariance and long-distance dispersal

Abstract

Aim: Our aim was to implement a molecular dating analysis and assess divergence times among taxa of Winteraceae. This enabled us to test hypotheses of vicariance versus long-distance dispersal to explain intercontinental disjunctions in the family. Location: Madagascar, Australia (including Lord Howe Island), New Zealand, New Caledonia and South America. Methods: We sampled all Australian species and subspecies of Winteraceae. We also included the monotypic 'Takhtajania perrieri' and at least two species of each genus from New Zealand, New Caledonia and South America. Three sets of sequences were combined into one data matrix, including two internal transcribed spacer (ITS) data sets and a trnL-F data set. Both ITS data sets included all genera of Winteraceae, and the paralogous genes identified in 'Zygogynum' s.l. in a previous study were sequenced and aligned in separate ITS data sets. A Bayesian molecular phylogenetic tree of extant Winteraceae was used as a backbone constraint in PAUP to establish the placement of fossils. Bayesian analyses were performed using BEAST, implementing fossil priors to fit lognormal distributions, to test a maximum-parsimony phylogeny and assess divergence times. Results: Interspecific relationships generally agreed with previous analyses. In particular, 'Bubbia comptonii' was found to be sister to the rest of the 'Bubbia/Zygogynum' clade, but our analysis has uniquely found sister clades within this group: one from New Caledonia, and one from Australia including Lord Howe Island. The phylogeny yields an age of 91.2 Ma with a 95% confidence interval of 118-67 Ma for crown-group Winteraceae. Main conclusions: The estimated age of 'Takhtajania' is consistent with its origin in Madagascar as a result of Gondwanan vicariance - the only angiosperm for which this has been demonstrated with confidence. Differentiation of the rest of this ancient clade is a complicated story of vicariance as a result of the rifting, submergence and exhumation of continents and of long-distance dispersal and extinctions.