Comparing evolutionary rates between trees, clades, & traits

1. The tempo of evolutionary change through time is among the most heavily studied dimensions of macroevolution using phylogenies. 2. Here, we present a simple, likelihood-based method for comparing the rate of phenotypic evolution for continuous characters between trees. Our method is derived from a previous approach published by Brian O’Meara and colleagues in 2006. 3. We examine the statistical performance of the method and find that it suffers from the typical downward bias expected for maximum likelihood estimates of the variance, but only for very small trees. We find that evolutionary rates are estimated with minimal bias for trees of even relatively modest size. 4. We also find that type I error rates based on a likelihood-ratio test are minimally elevated above the nominal level, even for small phylogenies. The type I error rate can be reduced to a level at or below its nominal value by substituting a test-statistic distribution obtained via simulation under the null hypothesis...