Effects of coccidial and mycoplasmal infections on carotenoid-based plumage pigmentation in male House Finches

Carotenoid pigments produce the ornamental red, orange, and yellow integume ntary coloration of many species of animals. Among individuals of a populat ion, the hue and saturation of carotenoid-based ornaments can be extremely variable, and studies of fish and birds have shown that females generally p refer males that display the most saturated and reddest coloration. Consequ ently, there has been a great deal of interest in determining the proximate factors that affect individual expression of carotenoid-based pigmentation . Parasites might affect production of ornamental coloration, and the Hamil ton-Zuk hypothesis proposes that parasitized males will show decreased expr ession of the secondary sexual traits preferred by females. We found that c aptive male House Finches (Carpodacus mexicanus) experimentally infected wi th Isospora spp. (coccidians) and / or Mycoplasma gallisepticum produced ca rotenoid-based plumage coloration that was significantly less red and less saturated than that of noninfected males. These observations validate a nec essary condition of the Hamilton-Zuk hypothesis, but heritable resistance t o the pathogens we examined remains to be demonstrated.