Kin recognition in guppies uses self-referencing on olfactory cues

Kin recognition plays an important role in social evolution, but the proximate mechanisms by which individuals recognize kin remain poorly understood. In many species, individuals form a kin template that they compare against the phenotype of the conspecific to assess phenotypic similarity (and by association, relatedness). Individuals may form a kin template through self-inspection (i.e. self-referencing) and/or by observing their rearing associates (i.e. family-referencing). However, despite much interest, few empirical studies have successfully disentangled self- and family-referencing. Here, we use a novel set of breeding crosses in the Trinidadian guppy (Poecilia reticulata) to definitively disentangle referencing systems by manipulating exposure to kin from conception onwards. We show that guppies discriminate among their full- and maternal half-siblings, which can only be explained by self-referencing. Additional behavioral experiments revealed no evidence that guppies incorporate the phenotypes of their broodmates or mother into the kin template. Finally, by manipulating the format of our behavioral tests, we show that olfactory communication is both necessary and sufficient for kin discrimination. These results demonstrate that individuals recognize kin by comparing the olfactory phenotypes of conspecifics against their own. This study resolves key questions about the proximate mechanisms underpinning kin recognition, with implications for the ontogeny and evolution of social behavior.