Expression of arginine vasotocin in distinct preoptic regions is associated with dominant and subordinate behaviour in an African cichlid fish.

Neuropeptides have widespread modulatory effects on behaviour and physiology and are associated with phenotypic transitions in a variety of animals. Arginine vasotocin (AVT) is implicated in mediating alternative male phenotypes in teleost fish, but the direction of the association differs among species, with either higher or lower AVT related to more territorial behaviour in different fishes. To clarify the complex relationship between AVT and alternative phenotype, we evaluated AVT expression in an African cichlid in which social status is associated with divergent behaviour and physiology. We compared AVT mRNA expression between territorial and non-territorial (NT) males in both whole brains and microdissected anterior preoptic areas using transcription profiling, and in individual preoptic nuclei using in situ hybridization. These complementary methods revealed that in the posterior preoptic area (gigantocellular nucleus), territorial males exhibit higher levels of AVT expression than NT males. Conversely, in the anterior preoptic area (parvocellular nucleus), AVT expression is lower in territorial males than NT males. We further correlated AVT expression with behavioural and physiological characteristics of social status to gain insight into the divergent functions of individual AVT nuclei. Overall, our findings highlight a complex association between AVT and social behaviour.