Figure 2. Phylogenetic analysis of Grl, GR and OR genes.

Maximum likelihood tree showing the relationships between select arthropod GRs/ORs, C. elegans GURs and all Grls (except the short sequence fragments predicted in P. miniata and A. millepora), colour-coded as in Fig. 1a. Drosophila Rhodopsins are included as an outgroup; although it remains unclear whether these two different families of heptahelical membrane proteins share a common ancestor, they clearly belong to a separate clade. For clarity, branches for large clades of D. melanogaster GRs/ORs or D. pulex GRs have been collapsed. The scale bar represents the number of amino acid substitutions per site.