Kin recognition and the 'armpit' effect: Evidence of self-referent phenotype matching

In species with multiple paternity or maternity, animals may best assess their relatedness to unfamiliar conspeci¢cs by comparing their own phenotype(s) with those of unidenti¢ed individuals. Yet whether animals can recognize kin through self-matching is controversial. Because golden hamsters (Mesocricetus auratus) mate multiply and can produce multiply sired litters, they were tested for their ability to use self-matching for kin recognition. Hamsters that were reared only with non-kin since birth responded di¡erentially to odours of unfamiliar relatives and non-relatives. Postnatal association with kin was not necessary for this discrimination. Prenatal learning was unlikely because of delayed production and perception of social odours. To our knowledge, this is the ¢rst demonstration that a vertebrate can use its own phenotype for kin-recognition purposes without prior experience with kin. By using itself as a referent, rather than its siblings or parents, a golden hamster may be better able to direct nepotism towards the most appropriate individuals. Kin discrimination via self-inspection may be especially important in nepotistic contexts (to identify most closely related conspeci¢cs), whereas inclusion of the phenotypes of close kin as referents may be favoured in mate-choice contexts (to identify all related indi-viduals)