INBREEDING DEPRESSION, GENETIC LOAD, AND THE EVOLUTION OF OUTCROSSING RATES IN A MULTILOCUS SYSTEM WITH NO LINKAGE

Area of Science:

• Population genetics
• Evolutionary biology
• Quantitative genetics

Background:

• Mutation-selection balance can lead to inbreeding depression in partially self-fertilizing populations.
• Understanding the interplay between selfing rates, inbreeding depression, and selection is crucial for evolutionary dynamics.

Purpose of the Study:

• To investigate zygote fitness, inbreeding depression magnitude, and the evolution of selfing rates under varying inbreeding levels.
• To examine the selective pressures on modifiers of the outcrossing rate in partially self-fertilizing populations.

Main Methods:

• Deterministic modeling of multilocus systems.
• Analysis of mutation-selection balance with unlinked loci and multiplicative fitness interactions.
• Simulation of populations with varying degrees of self-fertilization.

Main Results:

• Biologically plausible parameters can result in substantial inbreeding depression in moderately selfing populations, especially with recessive mutations and weak selection.
• Modifier alleles that decrease selfing rates can be favored under these conditions.
• In highly inbred populations, inbreeding depression is reduced, and selection may favor increased selfing, particularly when deleterious alleles have a strong selective disadvantage.

Conclusions:

• The level of inbreeding significantly influences the evolution of selfing rates and the magnitude of inbreeding depression.
• Weak selection generally favors the maintenance of outcrossing, while strong selection can promote selfing even with high inbreeding depression.
• Evolutionary trajectories are sensitive to allele dominance, selection strength, and population inbreeding levels.