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The role of testosterone in bib size determination in the male house sparrow Passer domesticus, is age dependent

journal contribution
posted on 01.05.2012, 00:00 authored by M Roberts, Kate BuchananKate Buchanan, A Goldsmith, M Evans
Secondary sexual signals are thought to indicate individual quality. In order to understand the evolutionary pressures that give rise to such traits it is important to understand the physiological mechanisms underlying their production. The black bib of the house sparrow Passer domesticus is known to function as a badge of social status in males. Past studies have found that the size of the bib in older males is determined, at least partly, by the androgen testosterone. The immunocompetence handicap hypothesis suggests that testosterone has a key role in maintaining honest signalling – it is both involved in the development or expression of sexual signals and is immunosuppressive. In this paper we test experimentally two hypo theses relating to bib size development, whether 1) testosterone is only immunosuppressive in conditions where the natural feedback loop from the testes has been removed, and 2) testosterone is, in addition to influencing the bib size of older males, responsible for the size of the bib in juvenile sparrows. In the first experiment we found that exogenous testosterone administered to intact males during the winter (when LH and FSH levels are very low and were not artificially increased by castration) caused significant immunosuppression, albeit in interaction with the stress hormone corticosterone. Second, we found that exogenous testosterone administration in castrated fledgling male house sparrows had no effect on subsequent post-juvenile moult bib size relative to controls. Our results suggest that in some circumstances testosterone can be immunosuppressive, but that its role in bib size determination is age-dependent.

History

Journal

Journal of avian biology

Volume

43

Issue

3

Pagination

264 - 272

Publisher

Wiley - Blackwell Publishing

Location

Malden, Mass.

ISSN

0908-8857

eISSN

1600-048X

Language

eng

Publication classification

C1 Refereed article in a scholarly journal

Copyright notice

2012, The Authors. Journal of Avian Biology. 2012 Nordic Society Oikos