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Members of social groups must defend their shared territory against both predators and competitors. However, individuals differ widely in their contributions to territorial defence. Assessing the variation in response to territorial intrusions provides insight into both the benefits and costs of group living for different group members. In this study, we assessed the response of wild Neolamprologus savoryi to experimentally staged territorial intrusions. Neolamprologus savoryi is an understudied cooperatively breeding cichlid fish endemic to Lake Tanganyika, East Africa. We found that dominant male and dominant female N. savoryi were both highly aggressive towards heterospecific predators and towards same-sex conspecific rivals. Both dominant males and females were less aggressive towards opposite-sex conspecific opponents, with the relative reduction in aggression being most pronounced in males …