Sexual ornamentation, androgens and papillomatosis in male roach (Rutilus rutilus)

According to the immunocompetence handicap hypothesis, males with attractive sexual ornamentation are more handicapped than their less ornamented rivals because of the immunosuppressive androgens required for the production of secondary sexual characters. Here we studied the predictions of the hypothesis in a wild cyprinid fish, the roach (Rutilus rutilus). We assayed (1) sexual ornamentation (breeding tubercles), (2) circulating androgens (11-ketotestosterone and testosterone) and (3) epidermal papilloma disease of male roach at spawning. We found that elaborated sexual ornaments were associated with high circulating concentrations of testosterone and 11-ketotestosterone. Furthermore, papillomatosis was associated with high concentrations of testosterone and elaborated sexual ornaments. The results were consistent with the predictions of the immunocompetence handicap hypothesis. It had previously been shown in the present study system that breeding tubercles of males signal resistance against a predominant parasite, as predicted by the Hamilton and Zuk hypothesis. The present results suggest that male roach with high concentrations of circulating androgens express strongly secondary sexual characters, but may be at a high risk of papillomatosis. In the present system, we propose that papilloma disease, which occurs during spawning, may contribute to the honesty of the signal of sexual ornamentation in roach.