P1.122 Jan. 4 Environmental and genetic effects on structural coloration in nestling bluebirds SIEFFERMAN, L.M.*; MCGLOTHLIN, J.W.; HILL, G.E.; Indiana University email@example.com
Sexually selected traits are expected to exhibit genetic variation and to be honest indicators of individual quality. Eastern bluebirds (Sialia sialis) have brilliant, structural blue-ultraviolet coloration that has been shown to be sexually selected. We used field experiments to estimate the additive genetic and environmental influences on the coloration of feathers grown by eastern bluebird nestlings. Our experiments took advantage of the growth of UV-blue wing feathers in nestlings that are retained as part of the first nuptial plumage. In the first experiment, we cross-fostered nestlings to create enlarged and reduced broods with the purpose of manipulating parental feeding rates and measured the effect on nestling growth and plumage coloration. Brood size influenced feeding rates to offspring and offspring coloration but the effect varied with season. Nestlings reared in reduced broods were fed more often, weighed more, and displayed brighter structural plumage compared to nestlings reared in enlarged broods. Moreover, nestlings that hatched later in the season displayed brighter overall plumage and greater UV chroma. In a second field experiment, we cross-fostered offspring to compare morphology and coloration of siblings reared in different nests. Restricted maximum-likelihood method revealed that growth parameters and plumage brightness were significantly heritable. Moreover growth parameters, and the brightness and UV chroma of plumage coloration exhibited variation due to natal environment. These data indicate that variation in structural plumage coloration is influenced both by genetic and environmental processes.