Adding time-calibrated branch lengths to the Asteraceae supertree

Abstract

Abstract New inference techniques, such as supertrees, have improved the construction of large phylogenies, helping to reveal the tree of life. In addition, these large phylogenies have enhanced the study of other evolutionary questions, such as whether traits have evolved in a neutral or adaptive way, or what factors have influenced diversification. However, supertrees usually lack branch lengths, which are necessary for all these issues to be investigated. Here, divergence times within the largest family of flowering plants, namely the Asteraceae, are reviewed to estimate time-calibrated branch lengths in the supertree of this lineage. An inconsistency between estimated dates of basal branching events and the earliest asteraceous fossil pollen record was detected. In addition, the impact of different methods of branch length assignment on the total number of transitions between states in the reconstruction of sexual system evolution in Asteraceae was investigated. At least for this dataset, different branch length assignation approaches influenced maximum likelihood (ML) reconstructions only and not Bayesian ones. Therefore, the selection of different branch length information is not arbitrary and should be carefully assessed, at least when ML approaches are being used. The reviewed divergence times and the estimated time-calibrated branch lengths provide a useful tool for future phylogenetic comparative and macroevolutionary studies of Asteraceae.