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Male ornament size in a passerine predicts the inhibitory effect of testosterone on macrophage phagocytosis
Author(s) -
Gil Diego,
Culver Renée
Publication year - 2011
Publication title -
functional ecology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.272
H-Index - 154
eISSN - 1365-2435
pISSN - 0269-8463
DOI - 10.1111/j.1365-2435.2011.01878.x
Subject(s) - phagocytosis , biology , testosterone (patch) , macrophage , immune system , basal (medicine) , passerine , endocrinology , medicine , in vitro , immunology , zoology , biochemistry , insulin
Summary 1. The immunocompetence handicap hypothesis (ICHH) proposes that androgen‐induced immunosuppression is the mechanism that restricts the expression of exaggerated male ornaments to superior males. Numerous tests of this hypothesis have been conducted on the humoral and cell‐mediated components of immunity, with mixed results. Surprisingly, no study so far has addressed whether macrophage phagocytosis, a basic immune function, plays a role in the ICHH. 2. We tested whether the ornament size of male spotless starlings ( Sturnus unicolor ) is a predictor of in vitro macrophage phagocytosis. We found that a moderate physiological concentration of testosterone (T) induced strong phagocytic inhibition. We found no relationship between ornament size and phagocytic activity in basal conditions. 3. Basal phagocytosis was not significantly predicted by ornament size or original testosterone levels. Contrary to expectations, phagocytosis under a moderate T concentration was negatively related to ornament size. Furthermore, a nonsignificant trend for original T concentration to negatively affect T‐medium phagocytosis was also found. 4. Our results provide support to the ICCH and suggest that males with exaggerated ornaments and high T concentrations may counteract the inhibitory action of testosterone by some compensatory mechanism. Possible candidates include the presence of immunoenhancing substances, such as melatonin or antioxidants, or differential receptor activity. These mechanisms should be evaluated when testing the reliability of the ICCH in wild populations.