Do feather-degrading bacteria affect sexually selected plumage color?
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Models of parasite-mediated sexual selection propose that males with more elaborate sexual traits will have fewer parasites. These models have generally been tested using metazoan or protozoan parasites of the blood, gut, or integument. Fewer studies have examined sexual ornaments in relation to bacterial infections. While most surface bacteria are harmless or beneficial, feather-degrading bacteria may have detrimental effects. In this study, we examined the relationships between overall bacterial load, feather-degrading bacterial load, and sexually selected carotenoid-based plumage color in a wild population of house finches (Carpodacus mexicanus). We found that males with the redder plumage preferred by females had similar overall bacterial loads, but lower feather-degrading bacterial loads, than males with less red plumage. These data suggest that plumage color can signal abundance of feather-degrading bacteria to potential mates. It remains unclear whether feather-degrading bacteria directly or indirectly affect plumage color, but the observed correlations suggest that feather-degrading bacteria may play some role in sexual selection.
KeywordsCarotenoids Preen oil House finch
We would like to thank Kimberly L. Mills for help in the lab, and Lisa Snowberg for help in the field. This manuscript was greatly improved by the comments of three anonymous referees, Anne M. Estes and the members of the Hill lab group: Michelle L. Beck, Stéphanie Doucet, Kristy L. Farmer, Daniel P. Mennill, Kristen Navara, Paul M. Nolan, and Lynn M. Siefferman. This work was supported in part by NSF grants DEB007804 and IBN9722971 and was performed in accordance with the laws of the USA.
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