Battistuzzi, F. U. | bioRxiv Science

bioRxiv2018

Using taxon resampling to identify species with contrasting phylogenetic signals: an empirical example in Terrabacteria

MotivationThe promise of higher phylogenetic stability through increasing dataset size within Tree of Life (TOL) reconstructions has not been fulfilled, especially for deep nodes. Among the many causes proposed are changes in species composition (taxon sampling) that could influence phylogenetic accuracy of the methods by altering the relative weight of the evolutionary histories of each individual species. This effect would be stronger in clades that are represented by few lineages, which is common in many Prokaryote phyla. Indeed, phyla with fewer taxa showed the most discordance among recent TOL studies. Thus, we implemented an approach to systematically test how the number of taxa and the identity of those taxa among a larger dataset affected the accuracy of phylogenetic reconstruction.\n\nResultsWe utilized an empirical dataset of 766 fully-sequenced proteomes for phyla within Terrabacteria as a reference for subsampled datasets that differed in both number of species and composition of species. After evaluating the backbone of trees produced as well as the internal nodes, we found that trees with fewer species were more dissimilar to the tree produced from the full dataset. Further, we found that even within scenarios consisting of the same number of taxa, the species used strongly affected phylogenetic stability. These results hold even when the tree is composed by many phyla and only one of them is being altered. Thus, the effect of taxon sampling in one group does not seem to be buffered by the presence of many other clades, making this issue relevant even to very large datasets. Our results suggest that a systematic evaluation of phylogenetic stability through taxon resampling is advisable even for very large datasets.\n\nContactbattistu@oakland.edu\n\nSupplementary informationSupplementary text and figures are available on the journals website.

bioinformatics↗

bioRxiv2017

RelTime relaxes the strict molecular clock throughout the phylogeny

The RelTime method estimates divergence times when evolutionary rates vary among lineages. Theoretical analyses show that RelTime relaxes the strict molecular clock throughout a molecular phylogeny, and it performs well in the analysis of empirical and computer simulated datasets in which evolutionary rates are variable. Lozano-Fernandez et al. (2017) found that the application of RelTime to one metazoan dataset (Erwin et al. 2011) produced equal rates for several ancient lineages, which led them to speculate that RelTime imposes a strict molecular clock for deep animal divergences. RelTime does not impose a strict molecular clock. The pattern observed by Lozano-Fernandez et al. (2017) was a result of the use of an option to assign the same rate to lineages in RelTime when the rates are not statistically significantly different. The median rate difference was 5% for many deep metazoan lineages for Erwin et al. (2011) dataset, so the rate equality was not rejected. In fact, RelTime analysis with and without the option to test rate differences produced very similar time estimates. We found that the Bayesian time estimates vary widely depending on the root priors assigned, and that the use of less restrictive priors produce Bayesian divergence times that are concordant with those from RelTime for Erwin et al. (2011) dataset. Therefore, it is prudent to discuss Bayesian estimates obtained under a range of priors in any discourse about molecular dating, including method comparisons.

evolutionary biology↗