dudley sse2011
TRANSCRIPT
From elegant to slender, does phenotypic selection on leaf physiological traits predict the divergence between Clarkia sister species, C. unguiculata and C. exilis?
Dr. Leah S. Dudley*, Alisa A. Hove, and Dr. Susan J. MazerDept. of Ecology, Evolution and Marine BiologyUniversity of California, Santa Barbara20 June 2011; Evolution 2011; Norman, Oklahoma
Mating System
• Who is your sexual partner?
• For animals▫ Monogamy▫ Polygamy
• For plants▫ Outcrossing▫ Selfing
Vector-mediated pollination
Autogamous, no vector necessary
Mating System Evolution
•Relative to their outcrossing progenitors or relatives, selfing taxa often exhibit▫Reduced corolla size ▫Lower pollen: ovule▫Shorter anther-stigma distance
(herkogamy)▫Closer dehiscence and receptivity
(dichogamy) ▫Faster development rates▫Earlier flowering
Clarkia ssp
•Selfing evolved numerous times•Outcrossing-selfing diploid sister pairs•Flowers large, numerous and easily
manipulated•Maintain many of the trait divergence
patterns
Phenotypic differences (greenhouse)
Life history Morphology
• C. exilis flowers earlier than C. unguiculata
• C. exilis is protogynous; C. unguiculata is protandrous
• (Dudley et al 2007)
• C. exilis smaller at senescence• C. exilis has less pollen/flower• C. exilis produces more
ovules/ovary• (Mazer et al 2009)
• C. exilis smaller anther-stigma distanceC.
exilisC. unguiculata
Physiological traits
• Instantaneous gas-exchange▫Photosynthetic rate (A)▫Transpiration rate (E)▫Water use efficiency (WUE)
•Twice during the growing season in 2008▫Early, Vegetative▫Late, Reproductive
•Several populations per species (n=24-56 plants/pop)
▫Sierra Nevada▫Lake Isabella and vicinity
Colleague A. Hove warming up LiCor 6400
Accounting for microclimatic variation• Linear regression for each population• Leaf position within the plant• Air temperature at time of measurement
Node number Air temperature (°C)
Tra
nsp
irati
on
(μ
mol
H2O
m-2
leaf
are
a s
ec-
1) C. unguiculata Early transpiration
Phenotypic means
LSM
Pho
tosy
nthe
sis
LSM
Tra
nspi
ratio
n
LSM
Inst
anta
neou
s w
ater
use
effi
cien
cy
Also see Mazer et al 2010
SpeciesP=0.001
1
Early Late
Early Late
ns
Species x Period
P=0.0042a
b
ab
ab
C. exilisC. unguiculata
Maturity index (Mi)•Late season only•Relative measure of reproductive maturity•Total flower and fruit production•Statistically control for plant size
▫Plant height at time of gas-exchange sampling▫Above ground stem biomass at senescence
Flo
wer
an
d f
ruit
p
rod
uct
ion
(L
og
10 x
i+1
)
Main stem height (cm) Senescent plant stem mass (g)
Phenotypic means, Maturity index
LS
M M
atu
rity
in
dex
C. exilis C. unguiculata
SpeciesP<0.000
1
Natural selection
•Goal: to detect evidence that natural selection may contribute to or reinforce the observed phenotypic divergence between sister species.
•Prediction: Direction or strength of natural selection should be consistent with the directon of phenotypic divergence between sister taxa
Models•Relative fitness
▫w=xi (x -1)
•Standardized trait value▫z=(xi - x)(SDx)-1
• wearly=βAzA+βEzE+βAE(zA*zE)+βAAz2A+βEEz2
E+ε
• wearly=βWuezWue+βWueWuez2Wue+ε
• wlate=βAzA+βEzE+βMizMi+βAE(zA*zE)+βAMi(zA*zMi)+βEMi(zE*zMi)+βAAz2A+βEEz2
E+βMiMiz2Mi+ε
• wlate=βWuezWue+βMizMi+βWueMi(zWue*zMi)+βWueWuez2Wue+βMiMiz2
Mi+ε
Models• Relative fitness
▫ w=xi (x -1)
• Standardized trait value▫ z=(xi - x)(SDx)-1
• wearly=βAzA+βEzE+ε
• wearly=βWuezWue+ε
• wlate=βAzA+βEzE+βMizMi+ε
• wlate=βWuezWue+βMizMi+ε
• Direct selection, linear slope estimates▫ βA, βE, βMi, βWue
Direct selection, early sampling period
C. e
xilis
freq
uenc
yC.
ung
uciu
lata
freq
uenc
y
Photosynthesis Transpiration Instantaneous water use efficiency
Granite Willow Springs Woody RoadJack and Stage Live Oak Stark Creek
Cow FlatPopulations:
C. exilis > C. unguiculata
C. exilis > C. unguiculata
Direct selection, late sampling period
C. e
xilis
freq
uenc
yC.
ung
uciu
lata
freq
uenc
y
Photosynthesis Transpiration Instantaneous water use efficiency
Granite Willow Springs Woody RoadJack and Stage Live Oak Stark Creek
Cow FlatPopulations:
C. exilis > C. unguiculata C. exilis > C. unguiculata
Also see Mazer et al 2010
Maturity index
Conclusions
•Photosynthesis is the trait under the most consistent direct selection (positive)
•Selection on WUEi is in the direction expected▫C. exilis < C. unguiculata▫Direct selection favors low WUE
•Selection on the maturity index opposes the phenotypic mean differences▫C. exilis >C. unguiculata▫Selection favors low MI in C. exilis