BUTLER, MA*; KING, AA; University of Tennessee; University of Michigan: OUCH! an improved method for phylogenetic tests of adaptive evolution

The comparative method is a central tool for investigating the adaptive significance of traits. Using interspecific data, biologists seek to identify and study the factors which have been important in producing the diversity of life that we see today. The use of phylogenies to rigorously investigate character evolution has become standard practice in modern evolutionary biology. However, all existing “phylogenetic comparative” methods share the significant shortcoming that they use a completely neutral model of evolution. That is, they fail to account for natural selection, despite the fact that it is the central feature of interest. Using the Ornstein-Uhlenbeck model, we have been able to simultaneously account for genetic drift, common ancestry, and natural selection under multiple adaptive regimes. The truly novel feature of this approach is the modelling of multiple evolutionary optima or �adaptive regimes�, which can be �painted� on the phylogeny to represent alternative evolutionary hypotheses (models). We can then use model selection techniques to identify the best supported models. By explicitly modeling the causal factors of interest, scientists will be abe to identify which aspects of the evolutionary process are most important, describe the relative stengths and directions of these forces, and understand how they have influenced the tempo and mode of evolution. We will illustrate use of the software and the method using new empirical examples.