Two new graphical methods for mapping trait evolution on phylogenies

Abstract

Modern phylogenetic comparative biology uses data from the relationships between species (phylogeny) combined with comparative information for phenotypic traits to draw model?based statistical inferences about the evolutionary past. Recent years have seen phylogeny methods for evolutionary inference become central in the study of organic evolution. Here, I present two different graphical methods for visualizing phenotypic evolution on the tree. Method 1 is a new approach for plotting the posterior density of stochastically mapped character histories for a binary (two?state) phenotypic trait on a phylogeny. Method 2 is a closely related technique that uses ancestral character estimation to visualize historical character states for a continuous trait along the branches of a tree. One shortcoming of Method 2 is that by mapping the point estimates of ancestral states along the branches of the tree, we have effectively ignored the uncertainty associated with ancestral character estimation of continuous traits. To alleviate this issue, I propose a new method for visualizing ancestral state uncertainty using a type of projection of the tree into morphospace called a ‘traitgram.’ All of these approaches should prove useful in summarizing complex comparative inferences about ancestral character reconstruction. They are implemented in the freely available and open?source R phylogenetics package ‘phytools.’