Condition and androgen levels: are condition-dependent and testosterone-mediated traits two sides of the same coin?

Abstract

The immunocompetence handicap hypothesis posits that androgen-mediated signals honestly indicate the responsiveness of the immune system because of the immunosuppressive effect of androgens. How- ever, androgen levels may also be related to nutritional status, and differences in body condition could be a more parsimonious explanation for variation in the expression of the signal. We maintained captive male red-legged partridges, Alectoris rufa, under regulated food shortage until they reached 85% of their initial body mass. Controls were provided with food ad libitum. After food shortage, experimental birds had lower androgen and higher corticosterone levels than controls. The condition dependence in andro- gen levels suggests that androgen-mediated signals could be indicating general nutritional state rather than immune function specifically. We propose that androgen-dependent signals may act as indicators of body condition or indicators of immune system quality, depending on the nutritional status of the individual.