Neighbor-joining trees of intact vomeronasal receptors from vertebrates. (A) The V1R tree. (B) The V2R tree. The trees were reconstructed with protein Poisson distances and the scale bars show 0.1 amino acid substitutions per site. The open arrow in the V2R tree indicates the root of the tree, which is determined using vertebrate T1R taste receptors as an outgroup. Bootstrap percentages for some major groups are presented. Vomeronasal receptors from the mammals, frog, and fishes are shown by orange, green, and blue symbols, respectively. The numbers of amino acid sites used for the two trees are 138 and 246, respectively, after the removal of alignment gaps.