Age and infection history are revealed by different ornaments in a warbler
Female preference for older or more disease-resistant males are both possible outcomes of parasite-mediated sexual selection, but the extent to which infection alters the development of ornaments to yield signals of male age and health has rarely been explored. In a longitudinal study of 61 male common yellowthroats (Geothlypis trichas), age-related increases in the size of the melanin-based mask and carotenoid-based bib were not correlated among young males, likely owing to differences in how blood parasites affect ornament development. Infection with trypanosomes and hemosporidians in a male’s first breeding season was associated with slower growth of the mask; uninfected males attained large masks in their second breeding season, while infected males attained large masks in their third breeding season. In contrast, the bib size of males increased every year regardless of infection. As a consequence, different populations of males are identified by the largest ornaments—older males in the case of bib and a combination of older males and young, uninfected males in the case of mask. Although mask is thus the more informative trait with respect to male health, females prefer large bibs in our population. If infection is opportunistic, young, uninfected males may not possess good genes for parasite resistance but simply good luck, and it may benefit females to prefer older males who are more likely to have withstood prior episodes of selection. A “pure” signal of age may be a more reliable signal of resistance to parasites than an ornament whose expression is modulated by infection.
KeywordsHamilton–Zuk Parasites Good genes Sexual selection Signaling
We thank Rebecca Schneider, Megan Garfinkel, Stephanie Wein, Joel Amidon, Kate Littrell, Ben Yamane, Lindsey Duval, and Evan Krasner for assistance in all aspects of the field work and two anonymous referees for helpful comments on an earlier version of the manuscript.
Author contribution statement
CFG and CCT both conducted field and laboratory work and conceived the analysis. CFG wrote the manuscript, with substantial input provided by CCT.
This study was funded by Skidmore College, with additional support provided to CCT by grants from the Rosemary Grant Fund, the Francine A. Bradley Award, and the National Science Foundation (DDIG, no. 1209464).
Compliance with ethical standards
Conflict of interest
The authors declare that they have no conflict of interest.
All applicable institutional and/or national guidelines for the care and use of animals were followed.
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