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Behavioral Ecology and Sociobiology

, Volume 47, Issue 4, pp 230–242 | Cite as

Ectoparasites of house sparrows (Passer domesticus): an experimental test of the immunocompetence handicap hypothesis and a new model

  • A. Poiani
  • A. R. Goldsmith
  • M. R. Evans
Original Article

Abstract 

Conspicuous secondary sexual traits may have evolved as handicap-revealing signals or as badges of status. We present results of an experiment using males of the sexually dimorphic house sparrow (Passer domesticus), that support the idea that the male-specific bib can be both a handicap-revealing signal and a reliable badge indicating the physical condition of the bird. In a test of the immunocompetence handicap hypothesis, wild-caught adult male house sparrows were studied in captivity. Birds implanted with elevated doses of testosterone were more dominant, had higher circulating levels of both testosterone and corticosterone and they also harboured relatively larger ectoparasite loads. Higher parasite loads were also associated with individuals showing lower immunocompetence and larger changes in bib size. A new model for immunocompetence effects in sexual selection is introduced, integrating actions that the hypothalamopituitary axis exerts on gonads, adrenals and the thyroid gland. The ”integrated immunocompetence model” synthesizes both the ”handicap” (i.e. survival-decreasing) and ”badge of status” (i.e. survival- enhancing) models for evolution of secondary sexual traits.

Key words Ectoparasites House sparrows Sexual selection Immunocompetence Steroid hormones 

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Copyright information

© Springer-Verlag Berlin Heidelberg 2000

Authors and Affiliations

  • A. Poiani
    • 1
  • A. R. Goldsmith
    • 2
  • M. R. Evans
    • 3
  1. 1.Department of Zoology, University of Melbourne, Parkville, Victoria 3052, Australia e-mail: a.poiani@zoology.unimelb.edu.au Fax: +61-3-93447909AU
  2. 2.School of Biological Sciences, University of Bristol, BS8 1UG, UKGB
  3. 3.Department of Biological and Molecular Sciences, University of Stirling, FK9 4LA, UKGB

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