Is there convergence in the molecular pathways underlying the repeated evolution of sociality in African cichlids?

Despite wide variation in the complexity of social interactions across taxa, the basic behavioural components of sociality appear to be modulated by conserved hormone pathways. Specifically, the nonapeptide hormones oxytocin and vasopressin and their receptors have been implicated in regulating diverse social behaviours across vertebrates. Here, we took advantage of the repeated evolution of cooperative breeding in African cichlids to investigate whether there are consistent brain gene expression patterns of isotocin and arginine vasotocin (teleost homologues of oxytocin and vasopressin), as well as their receptors, between four closely related pairs of social (cooperative) and non-social (non-cooperative) species. We first found that the coding sequences for the five genes studied were highly conserved across the eight species. This is the first study to examine the expression of both isotocin receptors, and so we performed a phylogenetic analysis that suggests these two isotocin receptors are paralogues that arose during the teleost genome duplication. When we then examined brain gene expression patterns relative to social system, we found that there were whole-brain gene expression differences between the social and non-social species in many of the species pairs. However, these relationships varied in both the direction and magnitude among the four species pairs. In conclusion, our results suggest high sequence conservation and species-specific gene expression patterns relative to social behaviour for these candidate hormone pathways in the cichlid fishes.