Species Tree Topology Impacts the Inference of Ancient Whole-Genome Duplications Across the Angiosperm Phylogeny

Abstract

Premise: The history of angiosperms is marked by repeated rounds of ancient whole-genome duplications (WGDs). Here we use state of the art methods to provide an up-to-date view of the distribution of WGDs in the history of angiosperms that considers both the uncertainty introduced by inference methods and alternative phylogenetic hypotheses. Methods: Transcriptomic and genomic data were used to infer and place WGDs across two hypothesized angiosperm phylogenies. Initial WGD hypotheses were made using rate corrections to the distribution of synonymous divergences (Ks) of paralogs and orthologs. WGD hypotheses were tested using syntenic inferences and Bayesian models of duplicate gene gain and loss across the phylogeny. Key results: The number of ancient WGDs in the history of angiosperms (~170) is largely similar across different inference methods, but there is often variation in the precise placement of WGDs on the phylogeny. Ks based methods often yield alternative hypothesized WGD placements largely due to variation in substitution rates among lineages. Phylogenetic models of duplicate gene gain and loss are more robust to topological variation, allowing for post hoc testing of WGD hypotheses. However, errors in species tree inference can still produce spurious WGD hypotheses regardless of method used. Conclusions: Here we show that different WGD inference methods largely agree on an average of 3.5 WGD in the history of angiosperm species. However, the precise placement of WGDs on the phylogeny is subject to the inference method and tree topology. As researchers continue to test hypotheses regarding the impacts ancient WGDs have on angiosperm evolution, it is important to consider the uncertainty of the phylogeny as well as WGD inference methods.