Androgen control of immunocompetence in the male house finch,Carpodacus mexicanusMüller

Pierre Deviche,Luis Cortez

doi:10.1242/jeb.01531

Abstract

The immunocompetence handicap (ICH) hypothesis predicts that elevated levels of the gonadal androgen testosterone (T) entail obligatory costs, such as immunosuppression, but evidence supporting this immunosuppressive influence is equivocal. To investigate this question, adult males house finches, Carpodacus mexicanus, were exposed to short days and chronically treated with T-filled (T males; N=10) or empty (C males; N=10) Silastic capsules. Testosterone administration increased plasma T levels and the size of the cloacal protuberance, an androgen-dependent secondary sexual characteristic. To study humoral immunity, finches received injections of sheep red blood cells (SRBC) and we measured circulating concentrations of antibodies to these cells with a hemagglutination test. All males produced antibodies following four SRBC injections at weekly intervals. Antibody titers in T and C males did not differ 5 days after the fourth injection, but were 59% lower in T than C males 2 weeks later. To study cell-mediated immunity, we measured the local inflammatory response to an injection of phytohemaglutinin (PHA). This response in T and C males was similar 1 day after PHA injection, but was 58% less in T than C males 2 days following the injection. Thus, T and C males mounted similar humoral and cell-mediated immune responses, but T treatment compromised maintenance of these responses. The results, demonstrating immunosuppressive effects of elevated T, are consistent with the ICH hypothesis.

Highlights

Behavioral ecologists, sociobiologists and physiologists are seeking to understand how reproductive hormones affect sexual secondary characteristics, the immune system and male quality (Sheldon and Verhulst, 1996)
Ten males (T males) received two subcutaneous Tfilled Silastic capsules prepared as described in Dloniak and Deviche (2001) and 10 males (C males) received two identical, but empty capsules
We defined the day that capsules were administered as Day 0 (D0) and all data are reported with reference to this date (Table·1)

Summary

Introduction

Behavioral ecologists, sociobiologists and physiologists are seeking to understand how reproductive hormones affect sexual secondary characteristics, the immune system and male quality (Sheldon and Verhulst, 1996). According to one hypothesis [immunocompetence handicap (ICH) hypothesis: Folstad and Karter, 1992] sexually selected male characteristics reliably indicate male quality. Elevated circulating concentrations of the testicular androgen, testosterone (T), promote the development and maintenance of these characteristics, and suppress certain physiological parameters and, in particular, may be immunosuppressive. All males of a population may potentially respond to elevated T levels by developing sexually selected characteristics. ‘low status’ males, instead of jeopardizing their immune responses, may maintain lower plasma testosterone and less developed sexual ornaments than ‘high status’ males, resulting in less success in mate choice

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Discussion

Conclusion