Princess of Burundi

A ‘princess’ (N. pulcher) in an aquarium. Photo credit: Susan Rothenberger.

War and peace in the 'princess of Burundi'

A new study published in The American Naturalist by Dr Rick Bruintjes and colleagues finds that conflict with outsiders promotes affiliation between group members in the ‘princess of Burundi’, an East-African fish. Surprisingly, territorial intrusions by neighbours elicited a stronger reaction than those by strangers.

Despite strong theoretical predictions, evidence for a link between out-group conflict and subsequent within-group behavioural interactions is rare in non-human animals. Dr Bruintjes, University of Exeter, explains: “Increases in post-conflict affiliation might be important in reducing stress, enhancing cohesion among group members and simultaneously signalling group unity to neighbours.”

The ‘princess of Burundi’ (Neolamprologus pulcher) is a highly social group-living cichlid fish that lives in Lake Tanganyika, Africa. Groups typically consist of a dominant breeding pair and up to 15 subordinates. All group members frequently show affiliate behaviour (consisting of soft body touches, parallel swimming and following) with others in the group. Additionally, all group members help in tasks such as brood care, territory maintenance and territory defence. When individuals from other groups intrude, resident fish fiercely defend their home to ensure a safe place to breed, hide and their keep their dominance rank in the group. Apparently, intrusions by neighbours cause greater post-conflict affiliative response than intrusions by non-neighbours.

Co-author Dr Andy Radford, University of Bristol, says “Although we as humans might feel more comfortable with neighbours rather than strangers visiting our homes, neighbours represent the greater threat to dominance rank and breeding success in our study fish species”. Consequently, the stronger within-group bonding in the aftermath of neighbour intrusions makes sense.

The results show the importance of considering post-conflict behaviour for our understanding of cooperation among group members and the evolution of social structure and behaviour. Moreover, they demonstrate that it is not just in humans that warfare plays a crucial role in the selection for cooperation and group cohesion.

Date: 11 December 2015

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