Social partner cooperativeness influences brainoxytocintranscription in Trinidadian guppies (Poecilia reticulata)

For non-kin cooperation to be maintained, individuals need to respond adaptively to the cooperative behaviour of their social partners. Currently, however, little is known about the biological responses of individuals to experiencing cooperation. Here, we quantify the neuroregulatory response of Trinidadian guppies (Poecilia reticulata) experiencing cooperation or defection by examining the transcriptional response of theoxytocingene (oxt; also known asisotocin), which has been implicated in cooperative decision-making. We exposed wild-caught females to social environments where partners either cooperated or defected during predator inspection, or to a control (non-predator inspection) context, and quantified the relative transcription of theoxtgene. We tested an experimental group, originating from a site where individuals are under high predation threat and have previous experience of large aquatic predators (HP), and a control group, where individuals are under low predation threat and naïve to large aquatic predators (LP). In HP, but not LP, fish brain mid-sectionoxtrelative transcription varied depending on social partner behaviour. HP fish experiencing cooperation during predator inspection had loweroxttranscription than those experiencing defection. This effect was not present in the control population or in the control context, where the behaviour of social partners did not affectoxttranscription. Our findings provide insight into the neuromodulation underpinning behavioural responses to social experiences, and ultimately to the proximate mechanisms underlying social decision-making.