Different categories of genes experience different levels of functional divergence.

<p>Proportion (FD) is the proportion of tested branches with at least one functionally divergent site across all gene trees in a particular functional category. Categories are labeled according to the COG ontology system <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0035659#pone.0035659-Tatusov1" target="_blank">[38]</a>, <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0035659#pone.0035659-Tatusov2" target="_blank">[73]</a>. Eighteen of the nineteen categories fall into two groups: significantly enriched or impoverished. Most information processing genes (K, J, L, A) fall into the latter group, while metabolic functions (E,F,G,H,P,Q) and genes involved in defense (V) or found on the cell surface (M) are enriched for radical change. Description of COG tags can be found in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0035659#pone.0035659.s006" target="_blank">Table S5</a>.</p>