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