Male birds display remarkable variation in plumage coloration, and females assess these differences when selecting mates. The rationale for such mate choice is that ornamentation is correlated with genetic quality so that, by choosing colorful males, females obtain good genes for their offspring. Genes contributing to greater disease resistance are quintessential in the natural world because pathogens greatly affect their hosts' reproduction and survival. As a result, "resistance" genes have often been assumed to be the good genes associated with bright coloration. The hypothesis of plumage coloration signaling good genes will be tested first by determining which genes are switched on or off when House Finches are infected with the bacterial pathogen, Mycoplasma gallicepticum. Gene expression will be determined using tools called microarrays that can accurately quantify the increase or decrease in expression of thousands of genes simultaneously. Gene expression patterns will be compared between brightly colored and drably colored male House finches. If the Good Genes Hypothesis is correct, brighter males should show different gene expression profiles than drabber ones. Furthermore, the turning on of specific genes known to play a role in disease resistance will help determine whether plumage coloration is associated with specific good genes. This research is important because it improves understanding of the evolutionary processes that lead to the evolution of disease resistance. Understanding all facets of disease resistance is crucial for predicting and responding to the threats of emerging infectious diseases in wildlife, domestic animals, and humans.
One of the most enigmatic ideas in evolutionary biology is that females gain good genes for offspring through the choice of highly ornamented males as mates. For 25 years, this hypothesis has defied attempts by biologists to test it, primarily because we did not know enough about the genetics of disease resistance. New breakthroughs in genomics now provide opportunities to directly test the good genes model of sexual selection. We undertook such a test focusing on the beautiful red feather coloration of one of the most familiar backyard birds in the U.S., the House Finch (Carpodacus mexicanus). Male House Finches have variable yellow to red feather coloration that is a primary criterion used by females to choose mates. Ornamental plumage coloration has been shown to reflect the health of the male, so this was a good place to look for good genes the might link ornamentation and disease resistance. We conducted the study by subjecting House Finches of different coloration to Mycoplasma infection. We looked at the patterns of expressed genes and found that the activation of certain genes was related to better resistance to the disease. These findings are an important first step in understanding the role of ornaments in signaling disease resistance and potentially of female mate choice selecting for healthier males.