Dudley sse2011
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This document summarizes a study that investigated phenotypic differences in physiological traits between the sister species Clarkia unguiculata and Clarkia exilis. The study found that C. exilis had higher photosynthetic rates, earlier flowering, smaller size, and produced more ovules than C. unguiculata. Models of natural selection showed consistent direct selection favoring higher photosynthesis in both species, as well as selection for lower water use efficiency in C. exilis, matching phenotypic differences. However, selection on a maturity index opposed phenotypic differences between the species.
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Dudley sse2011
- 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
- 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
- 9. Phenotypic means LSMPhotosynthesisLSMTranspiration LSMInstantaneouswateruseefficiency Also see Mazer et al 2010 Species P=0.0011 Early Late Early Late ns Species x Period P=0.0042 a b ab ab C. exilis C. unguiculata
- 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)
- 11. Phenotypic means, Maturity index LSMMaturityindex C. exilis C. unguiculata Species P<0.0001
- 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
- 13. Models • Relative fitness ▫ w=xi (x-1) • Standardized trait value ▫ z=(xi - x)(SDx)-1 • wearly=βAzA+βEzE+βAE(zA*zE)+βAAz2 A+βEEz2 E+ε • wearly=βWuezWue+βWueWuez2 Wue+ε • wlate=βAzA+βEzE+βMizMi+βAE(zA*zE)+βAMi(zA*zMi)+βEMi(zE*zMi)+βAAz2 A+βEEz2 E+βMiMiz2 Mi+ε • wlate=βWuezWue+βMizMi+βWueMi(zWue*zMi)+βWueWuez2 Wue+βMiMiz2 Mi+ε
- 14. 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
- 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.