Experimental demonstration of a parasite-induced immune response in wild birds: Darwin's finches and introduced nest flies
Article first published online: 26 JUN 2013
© 2013 The Authors. Ecology and Evolution published by John Wiley & Sons Ltd.
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Ecology and Evolution
Volume 3, Issue 8, pages 2514–2523, August 2013
How to Cite
Ecology and Evolution 2013; 3(8): 2514–2523
- Issue published online: 12 AUG 2013
- Article first published online: 26 JUN 2013
- Manuscript Accepted: 22 MAY 2013
- Manuscript Revised: 10 MAY 2013
- Manuscript Received: 21 FEB 2013
- National Science Foundation. Grant Number: DEB-0816877
- National Institutes of Health-Postdoctoral Fellowship. Grant Number: K12-GM000708
- Sigma Xi Grants-in-aid of Research
- National Science Foundation Research Coordination Network in Ecoimmunology grant
- University of Utah Undergraduate Bioscience Research Program
- Undergraduate Research Opportunities Program
- Geospiza fortis ;
- invasive species;
- Philornis downsi
Ecological immunology aims to explain variation among hosts in the strength and efficacy of immunological defenses. However, a shortcoming has been the failure to link host immune responses to actual parasites under natural conditions. Here, we present one of the first experimental demonstrations of a parasite-induced immune response in a wild bird population. The recently introduced ectoparasitic nest fly Philornis downsi severely impacts the fitness of Darwin's finches and other land birds in the Galápagos Islands. An earlier study showed that female medium ground finches (Geospiza fortis) had P. downsi-binding antibodies correlating with presumed variation in fly exposure over time. In the current study, we experimentally manipulated fly abundance to test whether the fly does, in fact, cause changes in antibody levels. We manipulated P. downsi abundance in nests and quantified P. downsi-binding antibody levels of medium ground finch mothers, fathers, and nestlings. We also quantified host behaviors, such as preening, which can integrate with antibody-mediated defenses against ectoparasites. Philornis downsi-binding antibody levels were significantly higher among mothers at parasitized nests, compared to mothers at (fumigated) nonparasitized nests. Mothers with higher antibody levels tended to have fewer parasites in their nests, suggesting that antibodies play a role in defense against parasites. Mothers showed no behavioral changes that would enhance the effectiveness of the immune response. Neither adult males, nor nestlings, had P. downsi-induced immunological or behavioral responses that would enhance defense against flies. None of the parasitized nests fledged any offspring, despite the immune response by mothers. Thus, this study shows that, while the immune response of mothers appeared to be defensive, it was not sufficient to rescue current reproductive fitness. This study further shows the importance of testing the fitness consequences of immune defenses, rather than assuming that such responses increase host fitness.