Are two South-Western Atlantic wrasses involved in a case of social mimicry?

We investigated whether two South-Western Atlantic wrasses [Halichoeres penrosei (models) and Thalassoma noronhanum (mimics)] were involved in social mimicry. In mixed shoals, we recorded species-specific abundances and lengths, and qualitatively assessed these fishe’s behaviour. In all aggregations, mimics were fewer than models but of comparable body size. Furthermore, mimics faithfully followed model’s behaviour. As mimicry should provide benefits, we measured the flight initiation distance (FID) of mimics to an approaching predator. FID was negatively correlated with group size, suggesting that larger shoals were perceived as safer. These results suggest that social mimicry between these species takes place, and provide antipredation benefits.