Amberleigh E. Henschen, Linda A. Whittingham and Peter O. Dunn
Department of Biological Sciences, UW-Milwaukee, hensche9@uwm.edu, pdunn@uwm.edu, whitting@uwm.edu
Elaborate ornaments are hypothesized to honestly signal individual quality, including the ability of an individual to combat parasitic infection. Although there have been many studies of this hypothesis, the results of these studies have been mixed. One explanation for these varying results is that measures of ornaments and parasitic infection intensity are typically obtained only once for each individual. Therefore, correlations between ornamentation and parasitic infection intensity do not consider within-individual relationships, which may differ from between-individual relationships. We examined the relationship between ornaments and intensity of infection by haemosporidian parasites within individuals (using data from two breeding seasons) in the common yellowthroat, Geothlypis trichas. Male common yellowthroats have two ornaments, a melanin-based (black) mask and a carotenoid-based (yellow) bib, and in our study population females prefer to mate with males that have larger black masks. In addition, mask size is positively correlated with antibody production, body condition, survival, resistance to oxidative stress, and immune gene variation (major histocompatibility complex, MHC). Of the males analyzed over two years, 89.3% were infected with haemosporidian parasites during at least one breeding season. Interestingly, we found a positive within-individual relationship between mask size and infection intensity, but no relationship across individuals. This result is potentially explained by the high costs of immune response, which may outweigh the benefits of parasite clearance. Ph.D. research, Dr. Linda Whittingham, Major Advisor.