Phylogenetic tree of vomeronasal 2 receptors. (A) The tree was calculated using the neighbour-joining method with 1000 bootstrap replicas and contained CaSRs and V2Rs from X. tropicalis (green branch), pufferfish (blue branch), human (red branch) and mice (purple branch). The GPRC6A genes were used as an outgroup. (B) Magnification of the marked clade (yellow solid circle) in A. Only one CaSR and one family C V2R were found in X. tropicalis according to the phylogenetic tree.