Social stimulation,nuptial colouration,androgens and immunocompetence in a sexual dimorphic cichlid fish |
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Authors: | Peter D Dijkstra Renske Hekman Rüdiger W Schulz Ton G G Groothuis |
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Institution: | (1) Research Group Behavioural Biology, University of Groningen, P.O. Box 14, 9750 AA Haren, The Netherlands;(2) Research Group Endocrinology, Science Faculty, University of Utrecht, P.O. Box 80058, 3508 TB Utrecht, The Netherlands;(3) Research Group Animal Behaviour, University of Groningen, P.O. Box 14, 9750 AA Haren, The Netherlands |
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Abstract: | The nature of the costs maintaining honesty of sexual signalling in inter- and intrasexual interactions remains a contentious
issue. For carotenoid-based colour ornaments, it has been hypothesized that the honesty of the signal is enforced when carotenoid
allocation to colour expression is traded off against carotenoid availability for immunocompetence. In addition, honesty is
enforced if androgens required for colour expression are immunosuppressive. We tested whether there is a trade-off between
colour expression and immunocompetence in a lek-breeding haplochromine cichlid fish, Pundamilia nyererei, from Lake Victoria with a carotenoid-based nuptial dress. First, we showed that expression of red nuptial colouration and
social rank in a group were positively correlated. We then successfully manipulated the level of colour advertisement by socially
stimulating individually housed males with a rival male: Stimulated males developed larger areas of red nuptial colouration
and had higher levels of circulating 11-ketotestosterone (11-KT) than non-stimulated males. We subsequently tested the humoral
immune response to a novel antigen (sheep red blood cells). There was no overall significant effect of social stimulation
on antibody production, but in the stimulated males, the degree of red colouration and the antibody response were negatively
correlated. This significant interaction between colour and treatment thus shows that the negative correlation between colouration
and antibody production is dependent on the (manipulated) social environment. This study provides correlational and experimental
evidence for a trade-off between expression of a sexual trait and one component of immune function in fish. We found no evidence
for a direct effect of 11-KT on antibody production, and we discuss alternative mechanisms that could mediate the trade-off. |
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Keywords: | Immunocompetence Sexual selection Male– male competition Cichlid fish Lake Victoria |
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