Software for generating directional phylogenetic independent contrasts for traits evolving under a Brownian motion model with directional tendency.
Methods used here are described in a 2015 paper.
Standard independent contrasts assume that a trait evolves by accumulating increments from a zero-centred distribution with fixed variance. As a result, the deviation in trait value along a branch of a phylogeny is normally distributed with mean zero and variance proportional to branch length t. When a directional tendency is present (i.e. the generating distribution has a nonzero mean), the deviation in trait value is normally distributed with mean tM where M is directional tendency per unit time. In this situation, we have to use a different formulation of independent contrasts to estimate M and generate the contrasts themselves taking into account the extra variance in the trait introduced by the directional drift. The program below takes as input a bifurcating phylogeny and a set of trait values, and outputs the inferred value of M and the contrasts.