1. 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
2. Mating System
• Who is your sexual partner?
• For animals
▫ Monogamy
▫ Polygamy
• For plants
▫ Outcrossing
▫ Selfing
Vector-mediated pollination
Autogamous, no vector necessary
3. Mating System Evolution
• Relative to their outcrossing progenitors or
relatives, selfingtaxa often exhibit
▫ Reduced corolla size
▫ Lower pollen: ovule
▫ Shorter anther-stigma distance (herkogamy)
▫ Closer dehiscence and receptivity (dichogamy)
▫ Faster development rates
▫ Earlier flowering
4. Clarkia ssp
• Selfing evolved numerous times
• Outcrossing-selfing diploid sister pairs
• Flowers large, numerous and easily manipulated
• Maintain many of the trait divergence patterns
5. Phenotypic differences (greenhouse)
Life history Morphology
• C. exilisflowers earlier than C.
unguiculata
• C. exilis is protogynous; C.
unguiculata is protandrous
• (Dudley et al 2007)
• C. exilissmaller at senescence
• C. exilishas less pollen/flower
• C. exilisproduces more ovules/ovary
• (Mazer et al 2009)
• C. exilissmaller anther-stigma distance
C. exilis C. unguiculata
6. 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
7.
8. 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)
Transpiration
(μmolH2Om-2
leafareasec-1)
C. unguiculataEarly transpiration
10. 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
Flowerandfruitproduction
(Log10xi+1)
Main stem height (cm) Senescent plant stem mass (g)
12. 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
15. Direct selection, early sampling period
C.exilisfrequencyC.unguciulatafrequency
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
16. Direct selection, late sampling period
C.exilisfrequencyC.unguciulatafrequency
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
17. 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
Editor's Notes
Really talking about the union of gametesAnd generallizing into 2 distinct poles: outcrossing (pollen from one individual transferred to another distinct individual) to selfing (pollen transferred onto receptive stigma on the same flower (plant))
General patterns of trait divergence btw outcrossers and selfersOrnduff 1969, Dudley et al. 2007, Guerrant et al. 1989, Snell and Aarson 2005, Runions and Geber 2000, Mazer et al. 2010)
Clarkia, native Californian annual is ideal
In 2008, we further examined phenotypic mean differences between the 2 sister species by examining another type of trait, physiological traits
Early in the season we found that photosynthesis and WUE was higher in exilis relative to unguiculataLate in the season, we also measure these same physiological traits, but we also were interested in how far along a plant wasFigure 2. Phenotypic frequency distributions of temperature- and node-adjusted physiological traits (photosynthesis, transpiration, instantaneous water use efficiency) recorded during vegetative (Early) and flowering (Late) phases in several populations of C. exilis(A) and C. unguiculata(B). The maturity index, a measure of an individual’s size-adjusted flower and fruit production, was recorded only during the flowering phase.Mixed-model ANCOVA showed no population effectsANCOVAPhotosynthesis Species F=10.8, P=0.0011Trans allP>0.2WUE Species x sampling period F=8.3, P=0.0042
By that I mean, we were interested in how relatively reproductive mature a plant was in a particular population
Figure 2. Phenotypic frequency distributions of temperature- and node-adjusted physiological traits (photosynthesis, transpiration, instantaneous water use efficiency) recorded during vegetative (Early) and flowering (Late) phases in several populations of C. exilis(A) and C. unguiculata(B). The maturity index, a measure of an individual’s size-adjusted flower and fruit production, was recorded only during the flowering phase.
Lande and Arnold 1983Multiple regressions used to estimate selection gradients2 general models due to colinearity between photosynthesis (A) and transpiration (E) with instantaneous water use efficiency (WUE)Relative fitness (w) and standardized physiological traits and MI (z) were calculated for each conspecific population separately
Lande and Arnold 1983Multiple regressions used to estimate selection gradients2 general models due to colinearity between photosynthesis (A) and transpiration (E) with instantaneous water use efficiency (WUE)Relative fitness (w) and standardized physiological traits and MI (z) were calculated for each conspecific population separately
Early in the season we found that photosynthesis and WUE was higher in exilis relative to unguiculataLate in the season, we also measure these same physiological traits, but we also were interested in how far along a plant wasFigure 2. Phenotypic frequency distributions of temperature- and node-adjusted physiological traits (photosynthesis, transpiration, instantaneous water use efficiency) recorded during vegetative (Early) and flowering (Late) phases in several populations of C. exilis(A) and C. unguiculata(B). The maturity index, a measure of an individual’s size-adjusted flower and fruit production, was recorded only during the flowering phase.Mixed-model ANCOVA showed no population effectsANCOVAPhotosynthesis Species F=10.8, P=0.0011Trans allP>0.2WUE Species x sampling period F=8.3, P=0.0042
Figure 2. Phenotypic frequency distributions of temperature- and node-adjusted physiological traits (photosynthesis, transpiration, instantaneous water use efficiency) recorded during vegetative (Early) and flowering (Late) phases in several populations of C. exilis(A) and C. unguiculata(B). The maturity index, a measure of an individual’s size-adjusted flower and fruit production, was recorded only during the flowering phase.
