Quantitatively determined self-incompatibility : 3. Genetical variability in Borago officinalis.

Area of Science:

• Population genetics
• Plant reproductive biology
• Molecular evolution

Background:

• Self-incompatibility (SI) systems are crucial for maintaining genetic diversity in flowering plants.
• Quantitative genetic models are used to predict the evolutionary dynamics of complex traits like SI.
• Previous studies suggest SI systems can promote higher genetic variability compared to random mating.

Purpose of the Study:

• To investigate the theoretical capacity of multilocus, quantitative self-incompatibility systems to maintain genetic variability in small populations.
• To compare the predicted variability maintenance with empirical data from a specific plant species.

Main Methods:

• Computer simulations were employed to model a hypothetical multilocus, quantitatively determined self-incompatibility system (both gametophytic and sporophytic).
• Population genetic models were used to assess variability levels under SI versus panmixia (random mating).
• Empirical data from studies of over 20 isozyme loci in borage were analyzed.

Main Results:

• Simulation results indicate that both gametophytic and sporophytic quantitative SI systems should maintain higher genetic variability in small populations than panmixia.
• Empirical studies of borage revealed a striking lack of genetic variability across more than 20 isozyme loci.
• A significant discrepancy exists between theoretical predictions and observed genetic diversity in borage.

Conclusions:

• Multilocus, quantitative self-incompatibility systems theoretically possess a strong capacity for preserving genetic diversity, particularly in small populations.
• The observed near-absence of genetic variability in borage challenges the direct applicability or specific genetic architecture of its SI system in relation to theoretical models.
• Further research is needed to reconcile the theoretical potential of SI systems with empirical observations of low genetic diversity in certain species.