The evolution of courtship and exaggerated secondary sexual characters is one of the favourite puzzles in behavioural ecology. Such traits may result either from a co-evolutionary arms race between a heritable trait in one sex and a heritable preference for it in the other (Fisher’s runaway selection process), or they may serve as a costly and hence honest indicator of the fitness of the signal bearer (‘Good genes’ attributes). Exaggerated characters are not confined to bodily ornaments, however. In many species they are 'constructed' by purposive behaviours, resulting in extended phenotypes with a signalling function. Extended phenotype signals have many advantages over bodily ornaments, such as persistence without the signaller, integration of diverse information, and the potential to separate environmental quality effects from 'good genes' attributes.
Several mouth-brooding cichlids in Lake Tanganyika and Lake Malawi build conspicuous sand craters that attract females ready to spawn. Males of Cyathopharynx furcifer, for example, invest enormous amounts of time and energy in the creation and maintenance of these structures that merely serve for spawning; eggs, larvae and fry are tended in the female's mouth. In the field and under controlled laboratory conditions we can manipulate male bodily and crater qualities independently from each other and measure female preference in simultaneous, interactive choice tests. Remarkably, female choice depends strongly on male building behaviour and much less on the resulting crater characteristics itself. Apart from crater building, males display also a number of other signals serving to attract mates, including temporary, gaudy colour patterns, elongated fins with bright tassels, and exaggerated courtship behaviours. This allows us to study the function of multiple mating signals, including bodily ornaments and extended phenotypes, and female control of pre- and postmating sexual selection.
Large males of the shell-brooding cichlid Lamprologus callipterus collect empty snail shells to attract females for spawing. Nests may contain several hundred shells, many of which are not suitable for spawning and brood care. This suggests that the males' shell collection may serve as extended phenotype signal.
Principal investigator: Michael Taborsky
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Mitchell, J.S., Wirtz Ocana, S. & Taborsky, M. (2014: Male and female shell-brooding cichlids prefer different shell characteristics. Anim. Behav. 98:131-137 [PDF]
Haesler M.P., Lindeyer C.M., Otti O., Bonfils D., Heg D. & Taborsky M. (2011): Female mouthbrooders in control of pre- and postmating sexual selection. Behav. Ecol. 22:1033-1041 [PDF]
Schaedelin F.C. & Taborsky M. (2010): Female choice of a non-bodily ornament: an experimental study of cichlid sand craters in Cyathopharynx furcifer. Behav. Ecol. Sociobiol. 64:1437-1447 [PDF]
Schaedelin F.C. & Taborsky M. (2009): Extended phenotypes as signals. Biological Reviews 84:293–313 [PDF]