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Quantitative Genetics in Red Squirrels:mechanisms of adaptation
• Basics• Red squirrel examples
– Parturition date– Growth rate
• Genomics and the future
Andrew McAdamUniversity of California, Santa Cruz
Quantitative Genetics
Examines the genetics of continuously varying (quantitative) traits
Understanding the genetic basis to quantitative traits allows us to predict future evolutionary responses to selection
Growth rate (g/day)
# o
bse
rva
tion
s
0
50
100
150
200
250
300
350
400
450
500
550
600
650
700
750
<= 0 (0,.5] (.5,1] (1,1.5] (1.5,2] (2,2.5] (2.5,3] (3,3.5] (3.5,4] > 4
Traditional Quantitative Genetics estimates sources of trait variation by examining the phenotypic resemblance among known relatives.
R = h2 S
J. Merilä
R. Rothman
Schroeder
1. Sources of variation• Heritability• Maternal effects
2. Selection
3. Response to selection
Quantitative Genetics in Red Squirrels
Sp
ruce
Co
nes
1988 1990 1992 1994 1996 1998 20000
50
100
150
200
250
300
350
Parturition Date
1975 1980 1985 1990 1995 2000
Ave
rage
spr
ing
tem
pera
ture
(o C
)
0
2
4
6
8
10
12
Increase in Temperature Increase in Food Abundance
Year of birth
89 90 91 92 93 94 95 96 97 98
Mea
n nu
mbe
r of
spr
uce
cone
s av
aila
ble
durin
g a
fem
ale'
s re
prod
uctiv
e lif
etim
e
20
40
60
80
100
120
140
160
180
Parturition Date - Heritability
h2 = 0.16 ± 0.03
Matrilineal Pedigree (1989-2001)1059 breeding events
568 females5 generations
Paternity and Maternal Effects??
- Réale et al., 2003, Evolution
S = - 8.96 ± 2.56 Parturition Date (s.d. units)
Lif
etim
e fi
tnes
s re
sid
ual
s
-2 -1 0 1 2 3-2
02
4
Parturition Date - Selection
Fitness: total number of offspring produced in lifetime.
Considered females dead prior to 2000 (n=303)
- Réale et al., 2003, Evolution
Response to Selection (R)
R = h2 S Predicted R = - 1.4 days/gen.Observed R = - 6.0 days/gen.
Generation
1 2 3 4E
stim
ated
bre
edin
g va
lue
(day
s)-3.5
-3.0
-2.5
-2.0
-1.5
-1.0
-0.5
0.0
0.5
133 98 105 38
Plasticity = - 23.1 days/cone index- Réale et al., 2003, Proc. Roy. Soc. L., B
log LYC
0.0 0.5 1.0 1.5 2.0 2.5 3.0
Age
Cor
rect
ed P
artu
ritio
n D
ate
90
100
110
120
130
140
150
160
(1991-2001)n = 11 years
Parturition Date Questions
1. Does food supplementation result in the plastic advancement in breeding?
2. Are there differences in the heritability of parturition date between the experimental and control populations?
3. Does selection on parturition date differ between experimental and control populations?
4. Do these differences in selection result in experimental evolution of earlier breeding?
• Widespread
• Strong in mammals
• Predicted to have important effects on evolutionary dynamics…if heritable
Maternal Effects
Occur when the phenotype of a mother causes phenotypic effects in her offspring
www.sbgmath.com
~25 Days~25 Days
Nestling Growth Rate
(g/day)
Cross-Foster
Percentage of variation in growth in body mass
GeneticMaternalG x EError
10%
8181%%
99%%
h2 = 0.09 ± 0.04
Maternal Growth Rate
Offspring Growth Rate
MaternalEffects
Litter SizeParturition Date
h2 = 0.09
Maternal Growth Rate
Offspring Growth Rate
MaternalEffects
h2 = 0.09
h2t = 0.31
++
- McAdam et al., 2002, Evolution
Food Effects on Growth
log Cones in Previous Year
0.0 0.5 1.0 1.5 2.0 2.5
Ave
rag
e G
row
th R
ate
(g/
da
y)
1.2
1.4
1.6
1.8
2.0
2.2
1999 2000 Food
Gro
wth
ra
te (
g/d
ay)
1.5
1.6
1.7
1.8
1.9
2.0
2.1
Cross-fostered
n =
32
n =
176
n =
72
1989 - 2001
Slope = 0.23 g/day/log conest-1
n = 13 years
Maternal
cov(dir,mat)1999 0.0432000 0.079Food - 0.005
Co
eff
icie
nt
of
Va
ria
tio
n
0.00
0.05
0.10
0.15
0.20
0.25
DirectGenetic
1999 2000 Food
h2t = 0.52*(h2 = 0.10)*
h2t = 0.70
(h2 = 0.12)
h2t = 0.57
(h2 = 0.57)
- McAdam & Boutin, 2003, J. Evol. Biol.
Lin
ear
sele
ctio
n g
rad
ien
ts (
β')
- 0.4
0.0
0.4
0.8
1.2
1.6
1990 1992 1994 1996 1998 2000 All years
*
*
*
*
*
Viability Selection on Growth
- McAdam & Boutin 2003, Evolution
Fitness: survival to potential breeding age
Other variables in model: Litter size, parturition date, sex, year
No spatial variation in selection
Components of Selection
Birth
Emergence
Recruitment
Breeding
Spring temperature (-)
Previous year’s cones (+)
CorrectedGrowth (t)
CorrectedGrowth (t+1)
Selection
Maternal Effectsh2
Response
Maternal Effects and the Response to Selection
1989 1991 1993 1995 1997 1999
Res
po
nse
(g
/day
)
-0.3
-0.2
-0.1
0.0
0.1
0.2
0.3
0.4
0.5
Year
*
* *
1. Observed response greater than predicted by h2
2. Response not independent of selection in the previous generation
- McAdam & Boutin 2003, Proc. Roy. Soc. L., B
Growth Rate Questions
1. Does food supplementation increase nestling growth rates?
2. Does food supplementation eliminate maternal effects?
3. Does selection on growth rates differ between experimental and control populations?
4. Do these differences in selection result in experimental evolution of earlier breeding?
5. Do maternal effects contribute to evolution in the control population but not the food supplemented one?
Genetic Mechanisms of Adaptation
It has recently become possible to use genetic markers to determine regions of the genome (loci?) that contribute to quantitative variation.
Quantitative Trait Loci (QTL’s)
QTL’s can be mapped for natural populations with extensive pedigrees and many molecular markers
Genetics of Speciation in Sticklebacks
- Peichel et al., 2001, Nature
Ecological and Evolutionary Functional Genomics (EEFG)
Genes Genotype Phenotype Phenotype’
Evolution
Genom
ics
Q. Gen
etics
Develo
pmen
t
Selecti
on
Genes Genotype Phenotype Phenotype’
Evolution