Question: How heritable is a sexually-selected plumage color trait? Background: To see an evolutionary response to selection, a trait must be heritable so that phenotypes (and their underlying genotypes) that confer a fitness advantage are passed on to the next generation at a higher frequency than those with lower fitness. Sexually selected traits are often also condition dependent to maintain the honesty of signals. Thus, to understand the evolutionary dynamics of a sexually selected trait, it is essential to quantify the contribution of genetic and environmental variation to phenotypic variation in a population. Study System: In North American barn Swallows (Hirundo rustica erythrogaster) the sexually dimorphic ventral melanin- based (McGraw et al. 2005) plumage color is the target of selection (Safran et al. 2005). Within individuals, nestling plumage color is predictive of adult color and can thus be used as a proxy for the sexually- selected adult color trait. THE ROLE OF GENETIC AND ENVIRONMENTAL CONTROL IN A MELANIN-BASED PLUMAGE TRAIT Joanna K. Hubbard, Amanda K. Hund, Brittany R. Jenkins, & Rebecca J. Safran Ecology and Evolutionary Biology, University of Colorado, Boulder, CO USA INTRODUCTIONNATURAL EXPERIMENT X-FOSTERING EXPERIMENT Photo: Matt Wilkins ACKNOWLEDGMENTS This work was supported by NSF, American Ornithologists Union, Animal Behavior Society, CU EBIO Department, CU Graduate School, CU BURST and UROP programs. Special thanks to Safran Lab members, private landowners, and many field assistants Scenario: On average, 40% of nestlings in a given year are extra-pair offspring. Methods: Estimate heritability: Compare color of nestlings to genetic parents. Compare color among nestlings of differing relatedness. Results: Conclusions: Heritability estimates suggest genetic variation affects plumage color Effect of shared environment suggests environmental variation is also important. To fully understand how these two sources of variation affect color, must isolate genetics from environment. Nest A Full siblings Nest B Full and maternal half siblings Nest C Full and maternal half siblings Sired by male A paternal half siblings Purpose: With a cross-fostering design, we are able to compare color between full siblings that are reared in the same and different environments, as well as unrelated individuals reared in the same and different environment. This will allow us to isolate the effect of shared environment from the effect of shared genetics. Furthermore, this experiment will provide a more accurate estimate for the heritability of ventral plumage color in North American barn swallows. Methods: Paired nests: Same hatch date Same brood size (± 1 nestling) Different sites Reciprocally exchange two nestlings on day 2 (hatch day = day 0). Hypotheses: 2012 Data Collection: 35 cross-fostered nests 32 control nests 10 cross-fostered nests with parasite treatment* 13 control nests with parasite treatment* *see Amanda Hund’s poster at session II  Full Sibs – Same Nest  Full Sibs – Diff Nests  Unrelated – Same Nest  Unrelated – Diff Nests h 2 =0.36±0.36; n=125h 2 =0.27±0.33; n=125h 2 =0.46±0.35; n=125 Figure 2. Weighted parent-offspring regressions of mean within-pair young brightness and a) mid-parent breast brightness (b = 0.358, F 1 and 123 = 9.462, p = 0.003, R 2 = 0.064), b) maternal breast brightness (b = 0.133, F 1 and 123 = 0.020, p = 0.112, R 2 = 0.012), and c) paternal breast brightness (b = 0.232, F 1 and 123 = 0.049, p = 0.013, R 2 = 0.041). h 2 =0.84±0.29; n=107h 2 =1.96±0.74; n=52h 2 =1.19±1.18; n=31 Figure 3. Correlations between a) full siblings (r = 0.42, n = 107, p << 0.001, b) maternal half siblings (r = 0.49, n = 52, p = ), and c) paternal half siblings (r = 0.30, n = 31, p = 0.104). Figure 1. Distributions of brightness for a) juvenile color of returning nestlings, b) adult breast color of returning nestlings, d) juvenile color of 2010 nestlings, e) adult breast color of 2010 adults. c) Shows the within-individual relationship between nestling or juvenile plumage brightness and adult breast brightness in a bird’s first breeding season, and f) shows the within-individual relationship between an adults’ coloration in the first year it is detected and the following year.