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Physiological performance and mating system in Clarkia (Onagraceae): does phenotypic selection predict divergence
Leah S Dudley1, Alisa A Hove, Susan J Mazer
1Department of Ecology, Evolution and Marine Biology, University of California, Santa Barbara, California 93106, USA. dudley@lifesci.ucsb.edu
American Journal of Botany
|March 8, 2012
Summary
Natural selection favors higher photosynthetic rates in Clarkia exilis, a self-fertilizing species, aligning with its higher photosynthetic rates compared to Clarkia unguiculata. However, selection on other traits like water use efficiency was less consistent.
Area of Science:
- Plant evolutionary biology
- Ecology
- Plant physiology
Background:
- Self-fertilization often co-evolves with other traits.
- Clarkia exilis (self-fertile) and Clarkia unguiculata (outcrossing) differ in photosynthetic rates and water use efficiency (WUE(i)).
Purpose of the Study:
- Investigate the strength and direction of natural selection on photosynthetic rates and water use efficiency (WUE(i)) in Clarkia exilis and Clarkia unguiculata.
- Determine if selection explains phenotypic differences between these sister taxa.
Main Methods:
- Measured gas exchange rates (photosynthesis, transpiration, WUE(i)) in nine populations during vegetative growth and flowering.
- Conducted selection gradient analyses and estimated selection differentials to assess selection.
- Evaluated selection consistency across seasons and pooled populations.
Main Results:
- Selection on photosynthetic rates was stronger and more consistent in C. exilis, favoring higher rates, which aligns with observed phenotypic differences.
- Selection on transpiration and WUE(i) was less consistent with phenotypic differences between the taxa.
- Flowering time selection patterns also showed inconsistencies with phenotypic divergence.
Conclusions:
- Natural selection can drive phenotypic divergence between sister taxa, particularly for photosynthetic rates in Clarkia.
- Selection on other traits, such as water use efficiency and flowering time, did not consistently explain the observed phenotypic differences.
- Some instances of selection were equivocal or did not predict the realized phenotypic divergence.
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