Through a glass darkly? Divergent reactions of eight Lake Tanganyika cichlid species towards their mirror image in their natural environment

Josi, Dario and Frommen, Joachim G (2021) Through a glass darkly? Divergent reactions of eight Lake Tanganyika cichlid species towards their mirror image in their natural environment. Ethology, 127 (10). pp. 925-933. ISSN 0179-1613

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Abstract

Behavioural reactions towards a mirror image are frequently used to measure individual aggression in a standardized way, especially in fishes. However, this approach was criticized recently on several grounds. One point of concern is that mirror tests are often conducted under highly artificial laboratory settings, while there exists a lack of knowledge of how individuals will react towards their reflection in the wild. We measured the responses of eight sympatric lamprologine cichlid species towards their mirror images in their natural environment in Lake Tanganyika. All species reacted by showing aggression towards their mirror image. The occurrence of overt and restrained aggression varied between species, reflecting species-specific aggressive behaviours. The finding that larger species showed a higher amount of overt attacks further supports this interpretation. A commonality across all species was that aggression escalated over time, resembling behavioural patterns during prolonged aggressive encounters between life opponents with similar resource holding potential. These results shed light on the behaviour of closely related fish species towards their mirror image under natural conditions and contribute knowledge to the ongoing discussion on the suitability of mirror tests when measuring aggression.