dudley sse2011

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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. Mazer Dept. of Ecology, Evolution and Marine Biology University of California, Santa Barbara 20 June 2011; Evolution 2011; Norman, Oklahoma

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Page 1: Dudley sse2011

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

Page 2: Dudley sse2011

Mating System

• Who is your sexual partner?

• For animals▫ Monogamy▫ Polygamy

• For plants▫ Outcrossing▫ Selfing

Vector-mediated pollination

Autogamous, no vector necessary

Page 3: Dudley sse2011

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

Page 4: Dudley sse2011

Clarkia ssp

•Selfing evolved numerous times•Outcrossing-selfing diploid sister pairs•Flowers large, numerous and easily

manipulated•Maintain many of the trait divergence

patterns

Page 5: Dudley sse2011

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

Page 6: Dudley sse2011

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

Page 7: Dudley sse2011
Page 8: Dudley sse2011

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

mol

H2O

m-2

leaf

are

a s

ec-

1) C. unguiculata Early transpiration

Page 9: Dudley sse2011

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

Page 10: Dudley sse2011

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)

Page 11: Dudley sse2011

Phenotypic means, Maturity index

LS

M M

atu

rity

in

dex

C. exilis C. unguiculata

SpeciesP<0.000

1

Page 12: Dudley sse2011

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

Page 13: Dudley sse2011

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

Page 14: Dudley sse2011

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

Page 15: Dudley sse2011

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

Page 16: Dudley sse2011

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

Page 17: Dudley sse2011

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