Heritability of a sexually selected melanin-based trait in North American Barn Swallows, Hirundo rustica ertythrogatser Joanna K. Hubbard, Brittany R. Jenkins, and Rebecca J. Safran Department of Ecology and Evolutionary Biology University of Colorado, Boulder

Melanin-based Coloration

Genetic Control of Coloration Evolutionary response to selection requires an underlying genetic basis to the trait Identified several genes that are associated with melanin-based color polymorphisms MC1R, Agouti, Tyrosinase, etc. Strength of genetic control for continuous color variation remains unknown

Barn Swallows and Color Safran & McGraw 2004; Safran et al, 2005

Barn Swallows Form social bonds at the beginning of the breeding season High rates of extra-pair paternity Most nests consist of nestlings of mixed paternity

Hypotheses

Field Work Monitored nests during 2008 and 2009 breeding seasons Banded, bled, and took plumage samples from day old nestlings

Color Descriptors Average Brightness Amount of light reflected off the feather surface Hue Wavelength at steepest slope Chroma Proportion of light reflected within a given color range

Molecular Analyses Determined parentage using 7 microsatellite markers Determined nestling sex based on chromo- helicase-DNA-binding genes (CHD-W and CHD-Z) No difference between male and female nestling coloration

Nestling and Adult Color Correlation between nestling plumage color and adult plumage color: A. rho = 0.52, n = 21, p = 0.018; B. rho = 0.46, n = 21, p = AB

Heritability of Coloration A.y = 0.366x + 19, F 1,317 = 18.49, p < 0.001, r 2 = B.Genetic: y = 0.043x + 30, F 1,70 = 0.07, p = 0.788, r 2 = Social: y = 0.139x + 26, F 1,227 = 2.05, p = 0.154, r 2 = 0.009

Color Comparisons Created pairs of individuals based on relationship One individual could be represented in all 4 relationship categories Calculated the magnitude of the difference in average brightness for each pair For each individual, averaged the pair- wise differences within each category For some individuals, there was only one difference per category

Example Bird 1Bird 2Relation A1A2Full : A3A4Full B1A1Same Dad : B1A4Same Dad B1B2Same Mom B1B3Same Mom B2B3Full C1A1Unrelated : C1B3Unrelated Nest A Nest C Nest B Site Extra-pair young from A male

Nestling Color Differences Linear Mixed Model Fixed effect: relationship Random effects: Year (2008 and 2009) Site (n = 26) n = 130 per category F (3, 491) = , p = a

Conclusions Relatedness appears to play an important role in determining nestling color Within-pair young show a moderately high heritability for plumage brightness Related nestlings are no more similar in coloration than unrelated nestlings Environmental influence on color Extra-pair young color not predicted by genetic or social parents

Future Directions In 2010, we experimentally increased brood size in a subset of nests Compare unrelated siblings raised in the same nest to unrelated siblings raised in different nests Compare full-siblings raised in different nests to full-siblings raised in the same nest Tease apart effects of environment and genetics

Acknowledgments Lab and Field Work: Conner Fitzhugh Andrew Flynn Lori Fraser Eric Lord Julie Marling Alex Oesterle Rachel Wildrick Matt Wilkins Photos: Matt Wilkins Funding: American Ornithologists Union Animal Behavior Society CU EBIO Department CU Graduate School Thanks!

Beckett Avery Wuensch March 5, :42 pm 7 lbs. 2 oz. 19 in