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Local population structure and sex ratio: evolution in gynodioecious plants
1Department of Biology, Vanderbilt University, Nashville, Tennessee 37235, USA.
The American Naturalist
|September 25, 2008
Summary
Population structure significantly impacts the evolution of plant sex expression. Local sex ratio variations can maintain genetic diversity for cytoplasmic male sterility (CMS) in gynodioecious plants, influencing female and hermaphrodite fitness.
Area of Science:
- Evolutionary Biology
- Population Genetics
- Plant Reproduction
Background:
- Theoretical studies have explored population structure's evolutionary influence.
- Few empirical examples link specific traits to local population structure.
- Gynodioecious plants exhibit variation in sex expression (females and hermaphrodites).
Purpose of the Study:
- To model how local population structure affects sex expression in gynodioecious plants.
- To investigate the fitness consequences of local sex ratio variation on females and hermaphrodites.
- To understand the maintenance of genetic polymorphisms under population structure.
Main Methods:
- Developed a theoretical model for sex expression in gynodioecious plants.
- Incorporated local sex ratio as a determinant of female and hermaphrodite fitness.
- Analyzed the evolutionary dynamics of cytoplasmic male sterility (CMS) alleles.
- Introduced nuclear restorer alleles to examine joint dynamics.
Main Results:
- Among-deme variance in local sex ratio can maintain cytoplasmic male sterility (CMS) allele polymorphism without nuclear restorer alleles.
- Sex ratio variance reduces female fitness when pollen availability is limited.
- Sex ratio variance increases hermaphrodite fitness from a maternal gene perspective.
- When nuclear restorer alleles are present, CMS alleles can fix, and female frequency depends on restorer allele frequency and population structure.
Conclusions:
- Population structure significantly alters the fitness and evolutionary trajectories of frequency-dependent traits like sex expression.
- Local sex ratio dynamics are crucial for maintaining genetic variation in traits influenced by cytoplasmic inheritance.
- The interplay between population structure, sex ratio, and genetic systems (cytoplasmic and nuclear) shapes evolutionary outcomes.
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