Genetic & environmental contributions to a divergent plumage trait in barn swallows
Joanna Hubbard, Amanda Hund, Tomas Albrecht, & Rebecca Safran
University of Colorado BoulderEcology & Evolutionary BiologyPhoto: Matt Wilkins
Hill 1992
Brawner et al 2000Geographic
Location
Hill 1993
Genetic variation in biosynthetic
pathway
McGraw 2003
♀
♂♂
Rosenblum et al 2005Nachman et al 2003
Theron et al 2001
Melanin-Based Color
Barn Swallow Species Complex
Tetrahedral Color Space
Stoddard & Prum. 2008. Am Nat
Cou
nt
North America Czech Republic
• Nestling color is predictive of adult color
• Mechanism to maintain color throughout lifetime– Genotype or Developmental Plasticity?
Hubbard et al in review
Site ANest 1
Site BNest 1
Reciprocal exchange
Cross-Foster Nestlings
Decouple genetic and environmental
influences
Nests paired by:- Hatch date- Brood size (± 1)
Swapped 90 nests(45 nest pairs)
56 control nests
After Predation and Mortality:
431 Offspring(211 WPY, 189 EPY,
31?)
Site ANest 1
Site BNest 1
Summer 2012: CO Summer 2013: CZ
Swapped 60 nests(30 nest pairs)
11 control nests
After Predation and Mortality:
283 Offspring(227 WPY, 47 EPY, 9
P)
Multivariate Animal Model
Random effects• Pedigree• Nest Origin • Nest Reared
Phenotypic Variation
Genetic Variation
Environmental Variation
UnmeasuredVariation
Early Environmen
t
Rearing Environmen
t
Response Variables• Theta• Phi• r Achieved• Brightness
(95% Bayesian Credible Interval – BCI)
Theta Phi r Achieved Brightness
Heritability0.163 0.161 0.165 0.172
(0.132 - 0.205)
(0.133 - 0.205)
(0.132 - 0.206)
(0.136 - 0.210)
Early Environment
0.373 0.352 0.328 0.356(0.281 - 0.421)
(0.281 - 0.427)
(0.282 - 0.426)
(0.271 - 0.418)
Rearing Environment
0.359 0.35 0.347 0.347(0.274 - 0.416)
(0.269 - 0.413)
(0.273 - 0.417)
(0.266 - 0.410)
Heritability0.149 0.153 0.149 0.161
(0.112 - 0.195)
(0.111 - 0.197)
(0.107 - 0.198)
(0.115 - 0.207)
Early Environment
0.354 0.367 0.352 0.318(0.262 - 0.461) (0.262 - 0.46) (0.255 -
0.459)(0.248 - 0.449)
Rearing Environment
0.361 0.383 0.359 0.364
(0.27 - 0.463) (0.267 - 0.464)
(0.263 - 0.471)
(0.266 - 0.467)
EnvironmentalContext
e2 ≅ 0.32 - 38Selection
h2 ≅ 0.15 - 17
Population 1 Population 2
h2 is not directly comparable
VA1/VP1 ≅ VA2/VP2
Phenotypic Variation
Genetic Variation
Environmental Variation
Phenotypic Variation
Genetic Variation
Environmental Variation
Compare genetic variance-covariance matrices
The G-Matrix
Trait 1 Breeding Value
Trait
2 B
reedin
g V
alu
e
Trait 1 Breeding ValueTr
ait
2 B
reedin
g V
alu
e
Breeding Value: how an individual’s genotype shifts it away from the mean phenotype
Comparative Quantitative Genetics
CO1,1 CO2,1 ... CO1,n
... ... ... ...
COm,1 COm,2 ... COm,n
CZ1,1 CZ2,1 ... CZ1,n
... ... ... ...
CZm,1 CZm,2 ... CZBm,n
alp
ha
E1 E1
ObservedRandomized
NoDivergence Divergence
Aguirre et al Heredity 2014
G-Matrix Comparison
Lower BCI Upper BCI
Observed 3.9 x 10-5 2.67 x 10-
4
Randomized 0 8 x 10-6
Brightness contributes to this difference more so
than other color metrics
Phenotypic Variation
Environmental Variation
Genetic Variation
Divergence in covariance structure
?
Selection
A1A2
A3 A6
A5A7
A9A6 A3
A8
Conclusions• Melanin-based color variation is affected
by environmental variation with low heritability
• Divergent selection on plumage brightness will increase phenotypic differences
• Divergent selection may have led to current phenotypic differences
Photo: Matt Wilkins
Future Directions
• Identify pigmentation genes that associate with color variation within and across populations
• Include additional subspecies and incorporate comparative phylogenetic methods
• Identify specific environmental factors that influence coloration
Collaborators:
• Adela Petrželková
• Romana Michálková
• Martina Soudková
• Olda Tomášek
• Natália Prekopová
• Lucie Jančíková
Funding:• EBIO department• CU Graduate School• Animal Behavior Society• American Ornithologists’
Union• American Museum of Natural
History• Colorado Field Ornithologists
• Max Joseph• Matt Wilkins• Liz Scordato• David Zonana• Iris Levin• Undergraduate Assistants• Site Owners
Acknowledgments