Parasite infection, but not immune response, influences paternity in western bluebirds

Anne C. Jacobs, Jeanne M. Fair, Marlene Zuk

Research output: Contribution to journalArticlepeer-review

6 Scopus citations


Parasites can impose heavy costs on their hosts, and females may benefit from selecting mates that are parasite resistant and/or have a stronger immune response. Trade-offs between immune response and sexual signaling have been proposed as a mechanism to ensure signal honesty. Much of the work on sexual signaling and immune response does not consider parasites directly and thus cannot confirm whether a stronger immune response necessarily results in lower parasite burdens. Also, immunity is costly, and these costs can lower the overall fitness of individuals with too strong of an immune response. Males with immune responses of intermediate strength are therefore expected to be preferred by females and have the highest reproductive success. We tested whether immune response and blood parasite loads relate to sexual signaling and mating preferences in western bluebirds (Sialia mexicana). Immunity did not predict male reproductive success when considering either within- or extra-pair offspring, although a stronger immune response was correlated with lower parasite loads. However, uninfected males were more likely to sire extra-pair offspring than males infected with avian malaria. Thus, females were more likely to mate with uninfected males but not necessarily males with a stronger immune response. Our results may indicate that females select parasite-resistant males as mates to gain resistance genes for their offspring or that infected males are less likely to pursue extra-pair copulations.

Original languageEnglish (US)
Pages (from-to)193-203
Number of pages11
JournalBehavioral Ecology and Sociobiology
Issue number2
StatePublished - Oct 30 2015

Bibliographical note

Funding Information:
We are grateful to K. Burnett, C. Hathcock, D. Keller, L. Maestas, R. Robinson, L. Reader, and C. Lemanski for assistance in the field. We thank B. Faircloth, J. Burnette, L. Enders, L. Nunney, and A. Cortez for invaluable advice and assistance regarding the molecular analyses. We thank Y. Shou, K. McCabe, E. Hong-Geller, and the Bradbury lab for assistance with the immune assays and M. Venesky for help with the statistical analyses. This project was funded by the University of California, Riverside and Los Alamos National Security, LLC, operator of the Los Alamos National Laboratory under contract no. DE-AC52-06NA25396 with the US Department of Energy. Additional funding for molecular work was provided by a Sigma Xi Grant-in-Aid-of-Research, a Ralph Schreiber Memorial Award from the Los Angeles Audubon’s Society, and a National Science Foundation Doctoral Dissertation Improvement Grant awarded to ACJ.

Publisher Copyright:
© 2014 Springer-Verlag Berlin Heidelberg.


  • Avian malaria
  • Extra-pair paternity
  • Immunity
  • Mate choice
  • Sialia mexicana


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