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

Abstract

SUMMARY 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.

Food restriction negatively affects multiple levels of the reproductive axis in male house finches, Haemorhous mexicanus

“…In contrast to testicular size, cloacal protuberance growth in finches was not affected by food availability. Cloacal protuberance size usually varies in parallel with testis size (Perfito et al, 2005;Small et al, 2008) and both are influenced by circulating testosterone levels (Deviche and Cortez, 2005). Although food-restricted finches had lower plasma testosterone than ad libitum-fed finches, it appears that the precise relationship between plasma testosterone and cloacal protuberance growth is somewhat dissociated, an observation that is not without precedent (Wingfield et al, 2012).…”

“…A validated (Deviche and Cortez, 2005) commercial enzyme-linked immunoassay (Enzo Life Sciences, Farmingdale, NY, USA) was used to measure plasma testosterone. Instructions outlined by the manufacturer were followed.…”

Energetic cost of communication

“…In addition, SMRs of every male B. gauderio we tested exceeded those of every female, despite the presumed trade-off (Fig.6). Androgens increase signal power in B. gauderio (Allee et al, 2009), and also reduce immunocompetence in a variety of vertebrates (Cutolo et al, 2002;Deviche and Cortez, 2005). Thus, males with the strongest signals could be obtaining the energy needed to boost signal power by reallocating energy away from immune function or other 'discretionary' functions (Wedekind and Folstad, 1994).…”

The effects of testosterone on immune function in quail selected for divergent plasma corticosterone response

“…There is good evidence of the immunosuppressive nature of T in laboratory mammals (Grossman, 1985), and several manipulative avian studies have found a deleterious effect of elevated T on humoral immunity (Duffy et al, 2000;Peters, 2000;Casto et al, 2001;Buchanan et al, 2003;Owen-Ashley et al, 2004;Deviche and Cortez, 2005), as well as on cell-mediated immunity (Duffy et al, 2000;Casto et al, 2001;Owen-Ashley et al, 2004;Deviche and Cortez, 2005;Boughton et al, 2007;Fargallo et al, 2007). However, other studies have found no such effect on either humoral (Hasselquist et al, 1999;Roberts et al, 2007a) or cellmediated immunity (Buchanan et al, 2003;Greenman et al, 2005;Roberts et al, 2007a).…”