Fig. 3.

Positive selection in the olfactory receptors gene family. Phylogenetic tree of manually annotated protein-coding sequences of olfactory receptors genes, including 291 genes from Pogonomyrmex barbatus in blue, 320 genes from Linepithema humile in green, and 262 genes from Nasonia vitripennis in black. The topology of the tree depicts the assemblage of 16 subtrees where positive selection was tested using the branch-site test of Codeml (Materials and Methods). Tested branches are depicted in gray if there was no evidence for positive selection and in red if there was significant evidence for positive selection at 10% FDR. Untested branches are depicted in black. Scale bar indicates the number of amino acid substitutions per site.