Visual threat signals influence social interactions in a cooperatively breeding fish

Many animals use visual signals to indicate their aggressive intentions. While much research has focused on these signals as predictors of an individual's behavioural motivations, how these social signals are perceived by others and whether social rank influences the response to these signals remain poorly understood. Using the cooperatively breeding cichlid, Neolamprologus pulcher, we investigated how visual signals influence social interactions. To do so, we conducted two experiments in which we manipulated the intensity of facial bars – which are used as a visual threat signal in this species – and assessed how these manipulations influenced social interactions. In experiment 1, we found that N. pulcher displayed less submission towards conspecifics with reduced facial bars compared to conspecifics with enhanced bars, but they did not exhibit an affiliative preference towards either stimuli. In experiment 2, we found that dominant males and large helpers, but not dominant females, performed more aggression towards a conspecific territory intruder with reduced facial bars. Large helpers seemed particularly sensitive to facial bar intensity, performing ∼4× as much aggression towards intruders with reduced facial bars compared to controls; an increase greater than that of dominants of either sex. Thus, taken together our results show that N. pulcher use facial bar intensity as a measure of the threat imposed by a conspecific, and helpers display high rates of territory defence towards conspecific territory intruders that are likely perceived as less threatening. Visual signals are clearly considered during social interactions, and the responses to such signals can be influenced by one's own social rank.