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- Owen-Ashley, N T, et al.
(författare)
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Androgens and the immunocompetence handicap hypothesis: Unraveling direct and indirect pathways of immunosuppression in song sparrows
- 2004
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Ingår i: American Naturalist. - 0003-0147. ; 164:4, s. 490-505
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Forskningsöversikt (refereegranskat)abstract
- The immunocompetence handicap hypothesis proposes that testosterone (T)-dependent sexual signals are honest indicators of male health or genetic quality because only high-quality males are able to withstand the obligate effects of T-induced immunosuppression. In birds, the basic assumption that T suppresses immune function is equivocal, and the physiological mechanisms underlying T-induced immunosuppression remain to be investigated. We explored the proximate pathways of T-induced immunosuppression in song sparrows (Melospiza melodia) by treating captive nonbreeding males with different androgens and measuring several components of acquired immune function. Males implanted with T suppressed cell-mediated and humoral immune responses compared to males implanted with 5proportional to-dihydrotestosterone (DHT), dehydroepiandrosterone, or control ( empty) implants. Furthermore, T treatment increased plasma levels of corticosterone and decreased body mass and fat stores in relation to other treatments. The failure of DHT to depress immune function suggests that T-induced immunosuppression does not occur through a direct pathway because both T and DHT bind to androgen receptors on target cells. Instead, we outline indirect pathways that are likely responsible for suppression of the avian immune system that include stress-induced immunosuppression, aromatization to estrogen, and alterations in energy allocation that constrain expenditures toward immune system activation.
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| 3. |
- Westneat, D F, et al.
(författare)
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Tests of association between the humoral immune response of red-winged blackbirds (Agelaius phoeniceus) and male plumage, testosterone, or reproductive success
- 2003
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Ingår i: Behavioral Ecology and Sociobiology. - : Springer Science and Business Media LLC. - 1432-0762 .- 0340-5443. ; 53:5, s. 315-323
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Tidskriftsartikel (refereegranskat)abstract
- We explored the potential relationships between male traits, reproductive success, testosterone levels in the breeding season, and Immoral immunocompetence in male red-winged blackbirds (Agelaius phoeniceus). Males responded to a single injection of diphtheriatetanus vaccine by producing antibodies to both antigens. The primary responses to each antigen were positively correlated with each other, but the relationship was clearly non-linear. No male responded strongly to diphtheria without also responding strongly to tetanus, but many males had strong responses to tetanus and weak responses to diphtheria. Response to tetanus was positively associated with hormone levels, whereas the relationship between testosterone and the response to diphtheria was weakly and nonsignificantly negative. We found no convincing relationships between immune responses and male morphological traits (epaulet size, body blackness, and body size), male success in male-male competition (territory size and tenure), or male reproductive success (number of mates, average clutch size, proportion of offspring sired, or proportion of young fledged). These results do not support testosterone acting as a constraint on immunity. Testosterone could be mediating a condition-dependent trade-off between sexual ornaments and the immune system, but the evidence for this was weak, as neither any male sexual trait nor any measure of performance was associated with immune responses. We could not eliminate the possibility that male sexual traits advertise other aspects of immunity that are not dependent upon condition or hormones.
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