system mediated relatively stereotyped innate responses to pheromones, However, this has given way to a more complex picture in which both the main olfactory and vomeronasal sys- tems can mediate sterotyped responses to chemosignals, and the responses via both systems can be influenced by learning. The two systems have interrelated functions often providing complemen- ary information about the same stimulus source. For instance, both the main and vomeronasal systems can mediate an avoid- ance response and freezing behaviour in mice. Predators produce involatile urinary chemosignals belonging to the major urinary protein (MUP) family, which stimulate the V2r receptor class of vomeronasal receptor to elicit freezing and avoidance behaviour in mice (Papes et al., 2010). Different predators produce different MUP variants in their urine potentially enabling mice to discriminate chemosignals from different species of predator (Ben-Shaul et al.. 2010)