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. SafranDepartment 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 10 - 12 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 = 0.038
A B
Heritability of
Coloration
A. y = 0.366x + 19, F1,317 = 18.49, p < 0.001, r2 = 0.055
B. Genetic: y = 0.043x + 30, F1,70 = 0.07, p = 0.788, r2 = 0.001Social: y = 0.139x + 26, F1,227 = 2.05, p = 0.154, r2 = 0.009
2008
2009
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 1 Bird 2 Relation
A1 A2 Full
:
A3 A4 Full
B1 A1Same Dad
:
B1 A4Same Dad
B1 B2Same Mom
B1 B3Same Mom
B2 B3 Full
C1 A1 Unrelated
:
C1 B3 Unrelated
Nest A
Nest C
Nest B
Site 1
1 1
1
22
2
33
3
4
4
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) = 1.2646, p = 0.286
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 WuenschMarch 5, 2011 3:42 pm
7 lbs. 2 oz. 19 in
