Vomeronasal Receptors in Vertebrates and the Evolution of Pheromone Detection

Pheromones were identified as chemical signals used for intraspecific communication in insects (e.g., sexual attraction) in the 1950s. However, only almost 40 years later the vomeronasal receptors type-1 (V1R) and type-2 (V2R) were identified, usually associated with the presence of a vomeronasal organ (VNO). VRs are widespread in amphibians, reptiles, and mammals, but birds lost the VNO. Similarly, fishes lack VRs and a VNO but can still detect pheromones, instead using the olfactory receptors related to class A and class C G protein-coupled receptors. Here, we review recent evidence on VR repertoire contraction/expansion in vertebrates. We assess the association between VNO development and VR repertoire size. Phylogenetic relationships and selective pressures illuminate the dynamic evolutionary history of the VRs in vertebrates.