Fig. 2. Gene tree of Nav1.4a with the estimated number of non-synonymous/synonymous substitutions for each branch. Red branches indicate lineages in which Nav1.4a is known to be lost from muscle (the dotted line in E. electricus indicates that its loss is likely but not yet tested), and the blue branch indicates that Nav1.4a expression is not lost from muscle. Note the much longer branch lengths of the electric fish lineages from which Nav1.4a was lost from muscle and the high ratio of non-synonymous to synonymous substitutions in these branches indicative of elevated rates of evolutionary change. Reproduced with permission (Zakon et al., 2006).