Evolutionary Pathways for the Generation of New Self-Incompatibility Haplotypes in a Nonself-Recognition System

Area of Science:

• Evolutionary biology
• Population genetics
• Plant reproductive biology

Background:

• Self-incompatibility (SI) prevents self-fertilization in plants, but the maintenance of its high diversity remains a puzzle.
• SI systems are broadly classified into self-recognition (SR) and nonself-recognition (NSR) types, with less research on NSR diversification pathways.
• Understanding haplotype evolution in NSR systems is crucial for comprehending plant reproductive diversity.

Purpose of the Study:

• To investigate the evolutionary pathways and conditions for novel S-haplotype evolution in gametophytic nonself-recognition (NSR) SI systems.
• To explore how factors like inbreeding depression, self-pollination, and mutation order influence diversification.
• To compare theoretical predictions with outcomes from stochastic simulations in finite populations.

Main Methods:

• Utilized a deterministic population genetic model to analyze S-haplotype evolution.
• Employed stochastic simulations to account for finite population sizes and random effects.
• Examined diversification through different mutation orders of female (SRNase) and male (SLF) components.

Main Results:

• Diversification is possible analytically under high inbreeding depression and self-pollination, particularly with lower haplotype numbers.
• Stochastic simulations reveal broader conditions for diversification in finite populations.
• The number of observed haplotypes was often less than naturally occurring levels, and haplotype lifespan depended on completeness.

Conclusions:

• The study provides insights into the evolution and maintenance of haplotype diversity in NSR SI systems, common in flowering plants.
• Diversification can occur via pathways maintaining SI or through self-compatible intermediates.
• Model limitations highlight the complexity of achieving natural levels of haplotype diversity in SI systems.