Explaining social learning of food preferences without aversions: an evolutionary simulation model of Norway rats

Norway rats (Rattus norvegicus) transmit preferences for novel foods social ly by smelling each other's breath. However, rats fail to learn aversions, acquiring a preference even if the rat whose breath they smell has been poi soned. Rats can distinguish between sick and healthy conspecifics and socia l learning of both preferences and aversions is present in other species-he nce it is unclear why rats cannot learn aversions socially. We constructed an evolutionary simulation in which a population of rats foraged from a cen tral location, exploiting food sites that could contain edible or toxic foo dstuffs. We examined the relationship between toxin lethality and selection for individual versus social learning and discrimination between sick and healthy conspecifics in order to allow learning of both preferences and ave rsions. At low lethality levels individual learning was selected for and at intermediate levels we found social learning of both preferences and avers ions. Finally, given high lethality levels the simulated rats would employ social learning but failed to learn aversions, matching the behaviour of re al rats. We argue that Norway rats do not learn aversions socially because their environment may contain only highly lethal toxins which make interact ion with a sick conspecific an extremely rare event.