Experimentally elevated testosterone levels enhance courtship behaviour and territoriality but depress acquired immune response in Red Bishops Euplectes orix
Article first published online: 2 NOV 2010
© 2010 The Authors. Journal compilation © 2010 British Ornithologists’ Union
Volume 153, Issue 1, pages 46–58, January 2011
How to Cite
EDLER, R., GOYMANN, W., SCHWABL, I. and FRIEDL, T. W. P. (2011), Experimentally elevated testosterone levels enhance courtship behaviour and territoriality but depress acquired immune response in Red Bishops Euplectes orix. Ibis, 153: 46–58. doi: 10.1111/j.1474-919X.2010.01075.x
- Issue published online: 6 DEC 2010
- Article first published online: 2 NOV 2010
- Received 25 August 2010; revision accepted 5 October 2010. Associate Editor: Suhel Quader.
- acquired immune response;
- heterophil/lymphocyte ratio;
- immunocompetence handicap hypothesis;
- polygynous weaverbird;
- repeated PHA-test;
- territorial behaviour
The immunocompetence handicap hypothesis (ICHH) posits that the hormone testosterone mediates a trade-off between investment in reproduction and immunological condition. In this study, we tested the ICHH in the Red Bishop Euplectes orix, a polygynous weaverbird. Males of this strongly sexually dimorphic species show an elaborate courtship display to attract females and compete aggressively with other males for nesting sites in breeding colonies. We experimentally elevated testosterone levels in breeding male Red Bishops kept in an aviary with a subcutaneous implantation of testosterone-releasing pellets. We then compared behaviour, development of territory size and immunological condition (as assessed through a white blood cell count) of the experimental group with a control group treated with placebos. In addition, we measured the primary and secondary response to phytohaemagglutinin (PHA) to investigate the effect of testosterone on both innate and acquired immunity. Males with elevated levels of testosterone enlarged their territories and conducted more courtship behaviour, while showing a decrease in health, expressed by an increased heterophil/lymphocyte ratio compared with the control group. Males of the control group showed an increase of the secondary response to PHA, as expected under the assumption that repeated exposure to an antigen enhanced the immune response due to acquired immunity. However, males with experimentally increased testosterone levels did not show such an enhanced immune response in the secondary PHA test (although sample size and power of the statistical tests were low), indicating that testosterone treatment might directly or indirectly suppress some component of the acquired immune response.