Territorial aggression reduces vigilance but increases aggression towards predators in a cooperatively breeding fish

In many species, aggressive individuals outcompete their less aggressive conspecifics for resources such as food and access to mates. Nevertheless, variation in aggression is maintained in populations, but the underlying mechanisms are not well understood. Here we tested the hypothesis that aggressive behaviours compromise the antipredator behaviour of prey, which would link aggressive behaviours to a cost of predation. We presented computer-animated images of predators to the cooperatively breeding cichlid fish Neolamprologus pulcher either during territorial contests with a group of territory intruders or when the test fish were alone. We investigated their response latencies and the behaviour directed towards predator images. We found that test fish responded to the predator images significantly later during territorial contests than when they were alone. Moreover, during territorial contests, response latencies of test fish increased with increasing levels of aggression towards conspecifics. Test fish also responded more aggressively to the predator images during territorial contests than when they were alone. During territorial contests, fish that responded later to the predator images were more aggressive towards these images. Our findings suggest that territorial contests compromised the ability of prey to respond quickly to predators. However, we propose that increased aggression towards predators might increase survival chances of prey during predator encounters in nature, and it may thus compensate for costs incurred by delayed predator responses during territorial contests. To test this hypothesis experiments under natural predation regimes that examine the relationship between predation risk, territorial and antipredator aggression are required. •Aggression during territorial contest affects antipredator behaviour in a cichlid.•Territorial aggression was negatively correlated with vigilance.•However, fish were also more aggressive towards predators during contests.•Increased aggression towards predators may be an alternative antipredator strategy.•Despite reduced vigilance, aggression may thus not lead to increased predation risk.