title: Evaluating the Impact of Genomic Data and Priors on Bayesian Estimates of the Angiosperm Evolutionary Timescale.
abstract: The evolutionary timescale of angiosperms has long been a key question in biology. Molecular estimates of this timescale have shown considerable variation, being influenced by differences in taxon sampling, gene sampling, fossil calibrations, evolutionary models, and choices of priors. Here, we analyze a data set comprising 76 protein-coding genes from the chloroplast genomes of 195 taxa spanning 86 families, including novel genome sequences for 11 taxa, to evaluate the impact of models, priors, and gene sampling on Bayesian estimates of the angiosperm evolutionary timescale. Using a Bayesian relaxed molecular-clock method, with a core set of 35 minimum and two maximum fossil constraints, we estimated that crown angiosperms arose 221 (251-192) Ma during the Triassic. Based on a range of additional sensitivity and subsampling analyses, we found that our date estimates were generally robust to large changes in the parameters of the birth-death tree prior and of the model of rate variation across branches. We found an exception to this when we implemented fossil calibrations in the form of highly informative gamma priors rather than as uniform priors on node ages. Under all other calibration schemes, including trials of seven maximum age constraints, we consistently found that the earliest divergences of angiosperm clades substantially predate the oldest fossils that can be assigned unequivocally to their crown group. Overall, our results and experiments with genome-scale data suggest that reliable estimates of the angiosperm crown age will require increased taxon sampling, significant methodological changes, and new information from the fossil record. [Angiospermae, chloroplast, genome, molecular dating, Triassic.].
authors.affiliation: School of Life and Environmental Sciences, Edgeworth David Building A11, University of Sydney, Sydney, New South Wales 2006, Australia.
authors.forename: Charles S P
authors.initials: CSP
authors.lastname: Foster
authors.affiliation: Laboratoire écologie, Systématique, évolution, Université Paris-Sud, CNRS UMR 8079, bat. 360, Orsay 91405, France.
authors.forename: Hervê
authors.initials: H
authors.lastname: Sauquet
authors.affiliation: National Herbarium of New South Wales, Royal Botanic Gardens & Domain Trust, Mrs Macquaries Road, Sydney, New South Wales 2000, Australia.
authors.forename: Marlien
authors.initials: M
authors.lastname: van der Merwe
authors.affiliation: National Herbarium of New South Wales, Royal Botanic Gardens & Domain Trust, Mrs Macquaries Road, Sydney, New South Wales 2000, Australia.
authors.forename: Hannah
authors.initials: H
authors.lastname: McPherson
authors.affiliation: National Herbarium of New South Wales, Royal Botanic Gardens & Domain Trust, Mrs Macquaries Road, Sydney, New South Wales 2000, Australia.
authors.forename: Maurizio
authors.initials: M
authors.lastname: Rossetto
authors.affiliation: School of Life and Environmental Sciences, Edgeworth David Building A11, University of Sydney, Sydney, New South Wales 2006, Australia.
authors.forename: Simon Y W
authors.initials: SYW
authors.lastname: Ho
mesh_terms: D001499:Bayes Theorem; D005075:Biological Evolution; D019143:Evolution, Molecular; D005580:Fossils; D018745:Genome, Plant / Q000235:genetics*; D019684:Magnoliopsida / Q000145:classification* / Q000235:genetics*; D010802:Phylogeny; D013995:Time