Mating craters of Cyathopharynx furcifer (Cichlidae) are individually specific, extended phenotypes

Sexually selected traits have been intensively studied in the recent past, but there is comparatively little information about the signalling value of the extended phenotype, despite its unique potential in mate choice and intersexual competition. Individuals manipulating their environment to create a nonbodily ornament may reveal their immediate quality more reliably than by using conventional signals. Nonbodily ornaments may also integrate a bearer's behaviour over a recent interval, which would save the potential receiver repeated or prolonged sampling of the signaller's behaviour. We investigated factors involved in the production of a nonbodily ornament and assessed its potential as a signal in the reproductive context. The crater-building behaviour of the Lake Tanganyika cichlid Cyathopharynx furcifer was observed and manipulated in the field and laboratory. Craters were maintained for prolonged periods, and crater size correlated with male body size, building behaviour and crater location in the lek. Larger craters had a higher ‘neatness index’, and this index correlated negatively with a male condition factor. Behaviour of cichlids after a storm and our manipulations of crater size showed that crater size is a repeatable, individual character; destroyed craters were rebuilt to their original sizes roughly within 1 day and both, experimentally enlarged and diminished craters were immediately reconstructed to their original sizes. We conclude that mating craters are an individually characteristic, extended phenotype of the building males and potentially a suitable signal for conspecifics, providing information about the owner's size, capability and condition.