Relaxed phylogenetics and dating with
These huge datasets pose computational challenges, but typically generate trees that are fully resolved (entirely bifurcating, i.e.dichotomous) and well-supported (most branches having maximum possible statistical significance).We find no significant rate autocorrelation among branches in three large datasets, suggesting that autocorrelated models are not necessarily suitable for these data.In addition, we place these datasets on the continuum of clocklikeness between a strict molecular clock and the alternative unrooted extreme.This study illustrates the potential of including pollen-based calibrations in molecular studies of divergence times.► Most robust and well sampled Myrtaceae phylogeny to date (106 taxa, 80 genera).► Twenty-six fossil pollen parsimoniously tested to select those appropriate as calibrations.Mena I, Nelson MI, Quezada-Monroy F, Dutta J, Cortes-Fernández R, Lara-Puente JH, Castro-Peralta F, Cunha LF, Trovão NS, Lozano-Dubernard B, Rambaut A, van Bakel H & García-Sastre A (2016) e Life 5, e16777.
Estimates of rate variation among lineages were affected by the choice of calibrations, suggesting that the use of multiple calibrations can improve estimates of rate heterogeneity among lineages.
However, the pollen record can also inform age calibrations if fossils matching extant pollen groups are found.
Recent work has shown that pollen of the myrtle family, Myrtaceae, can be classified into a number of morphological groups that are synapomorphic with molecular groups.
By assembling a data matrix of pollen morphological characters from extant and fossil Myrtaceae, we were able to measure the fit of 26 pollen fossils to a molecular phylogenetic tree using parsimony optimisation of characters.
We identified eight fossils as appropriate for calibration based on the most parsimonious placements of these fossils on the tree.We describe how it can be used to estimate phylogenies and divergence times in the face of uncertainty in evolutionary rates and calibration times.