Plumage color as a composite trait: Developmental and functional integration of sexual ornamentation

Most studies of condition-dependent sexual ornaments have treated such orna ments as single traits. However, sexual ornaments are often composites of s everal components, each produced by partially independent developmental pat hways. Depending on environmental and individual condition, components of t hese ornaments may reflect different behavioral or physiological properties of an individual. One of the best-known, condition-dependent ornaments is carotenoid-based plumage coloration, which has at least four distinct compo nents: pigment elaboration, patch area, pigment symmetry, and patch area sy mmetry. Here we examined fitness consequences of variation in individual co mponents of carotenoid ornamentation in male house finches (Carpodacus mexi canus). Over 5 yr and several selection episodes, we studied variation in t he plumage components in a large sample (n = 498) of males from a Montana p opulation. The ornament components were partially independent of each other and had distinct fitness consequences. Selection for higher fecundity favo red an increase in redness of coloration and a decrease in pigment asymmetr y and patch area asymmetry but did not act on patch area itself. In contras t, viability selection favored larger and more symmetrical ornamental patch es but did not act on pigment elaboration. Developmental and functional int errelationships among individual components of ornamentation strongly diffe red between house finch populations. Distinct patterns of selection on indi vidual components of condition-dependent ornaments, combined with partially independent development of components, should favor the evolution of compo site sexual traits whose components reliably reflect condition across a wid e array of environments.