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Androgens and the immunocompetence handicap hypothesis: Unraveling direct and indirect pathways of immunosuppression in song sparrows

Author:
  • N T Owen-Ashley
  • Dennis Hasselquist
  • J C Wingfield
Publishing year: 2004
Language: English
Pages: 490-505
Publication/Series: American Naturalist
Volume: 164
Issue: 4
Document type: Journal article review
Publisher: University of Chicago Press

Abstract english

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.

Keywords

  • Biological Sciences
  • immunosuppression
  • song sparrow
  • testosterone
  • corticosterone
  • androgens
  • immunocompetence

Other

Published
  • Molecular Ecology and Evolution Lab
  • ISSN: 0003-0147
Dennis Hasselquist
E-mail: dennis [dot] hasselquist [at] biol [dot] lu [dot] se

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