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Developmental selection within the angiosperm style: using gamete DNA to visualize interspecific pollen competition
J H Williams1, W E Friedman, M L Arnold
1Department of Genetics, University of Georgia, Athens, GA 30602-7223, USA. williams@dogwood.botany.uga.edu
Summary
Flowering plants can control fertilization after pollination. Birch species prevent hybridization by inhibiting foreign pollen tube growth, ensuring over 98% of offspring are from compatible pollen.
Area of Science:
- Plant reproductive biology
- Evolutionary botany
- Population genetics
Background:
- Flowering plants often lack control over pollen deposited on stigmas.
- Postpollination, prefertilization processes are crucial for mate choice and reproductive isolation.
- Mechanistic evidence for mate choice in plants is limited.
Purpose of the Study:
- Investigate postpollination, prefertilization mechanisms of reproductive isolation in naturally hybridizing birch species (Betula).
- Determine the role of pollen tube growth and development in species recognition and hybridization barriers.
Main Methods:
- Utilized a 3-fold difference in ploidy level between two Betula species to track pollen paternity.
- Performed conspecific, heterospecific, and mixed-species pollinations.
- Analyzed pollen tube growth dynamics and developmental fate within female reproductive tissues.
Main Results:
- Conspecific pollen sired over 98% of seedlings in mixed-species pollinations.
- Reproductive isolation was not due to embryo abortion.
- Strong postpollination barriers included pollen tube incompatibility, slower growth, and delayed generative cell division.
Conclusions:
- Early postpollination, prefertilization interactions mediate reproductive isolation in Betula.
- Favorable male-female interactions, not male-male antagonism, drive conspecific fertilization precedence.
- These mechanisms significantly impact hybridization dynamics and population genetics in natural settings.