Species-specific patterns of nonapeptide brain gene expression relative to pair-bonding behaviour in grouping and non-grouping cichlids

Comparative studies have revealed that vasopressin-oxytocin pathways are associated with both pair bonding and grouping behaviour. However, the relationship between pair bonding and grouping behaviourremains unclear.In this study,our aim was to identify whether two species that differ in grouping behaviourdisplay a corresponding difference in their pair bonds, and in the underlying vasopressin-oxytocinhormonal pathways. Using two species of cichlid fishes, the highly social Neolamprologuspulcher and the non-social Telmatochromis temporalis, we measuredproximity of pairs during pair bond formation, and then measured social behaviors (proximity, aggression, submission,affiliation)and brain gene expression of isotocin and arginine vasotocin (the teleost homologues of oxytocin and vasopressin, respectively), as well as their receptors, after a temporary separation and subsequent reunion of the bonded pairs. Pairs of the social species spent more time in close proximity relative to the non-social species. Rates of aggression increased in both species following the separation and reunion treatment, relative to controls that were not separated.Overall, whole brain expression of isotocin was higher in the social species relative to the non-social species, and correlated with proximity, submission, and affiliation, but only in the social species. Our results suggest that both a social and a non-social cichlid species have similar behavioural responses to a temporary separation from a mate, and we found no differencein the brain gene expression of measured hormones and receptors based on our separation-reunion treatment. However, our results highlight the importance of isotocin in mediating submissive and affiliativebehaviourin cichlid fishes, and demonstrate thatisotocinhas species-specific correlations with socially relevantbehaviours.