Effects of Early-Life Social Status on Vasopressin Signaling in A. burtoni

The neuropeptide vasopressin (AVP) is associated with a variety of social behaviors in vertebrates, including aggression. In fish, AVP is found in the preoptic area of the hypothalamus (POA). AVP’s relationship with aggression is variable, but previous research shows that AVP is correlated with adult male aggression. AVP’s enmeshment with aggression suggests a possible effect of AVP on juvenile dominance, but this effect is not well-understood. In this study, the link between juvenile social status, aggression, and AVP expression in the POA is investigated. A. burtoni were used in this study as fish that readily form size-based status relationships as juveniles. Juveniles were paired, habituated in order to form a dominance hierarchy based on size, and then small fish were isolated. Small fish were either placed back in their home tank, or introduced to a new tank with an unfamiliar large fish. Agonistic behaviors between fish pairs were quantified. Brains were collected 1 hour after reintroduction of small fish, and an RNAscope in situ hybridization assay was performed in order to map AVP mRNA expression. Results showed that large fish exhibited more aggressive behaviors than did small fish, affirming a size-based dominance hierarchy, but there was no significant effect of treatment on behavior. AVP expression was treatment-dependent: stable groups had higher AVP levels than did switch groups, but expression was not significantly impacted by social status. These results may contradict research that supports AVP’s association with aggression, but underlies the importance of the relationship between AVP and juvenile A. burtoni.