Inbreeding load in finite populations from dominant and overdominant mutations

Area of Science:

• Evolutionary genetics
• Population genetics

Background:

• Inbreeding depression arises from the expression of deleterious alleles in homozygous individuals.
• This inbreeding load (B) can stem from recessive mutations (dominance model) or heterozygote advantage (overdominance model).
• Previous research primarily focused on the dominance model in finite populations and overdominance in infinite populations.

Purpose of the Study:

• To investigate the combined effects of dominant and overdominant mutations on inbreeding load.
• To analyze these effects in both self-fertilizing and bottlenecked panmictic populations using computer simulations.

Main Methods:

• Computer simulations were employed to model populations.
• The simulations examined the impact of both dominant and pure overdominant mutations.
• Scenarios included self-fertilizing populations and panmictic populations experiencing bottlenecks.

Main Results:

• Genetic drift significantly reduces overdominant inbreeding load, even with symmetrical overdominance and small-effect mutations.
• In bottlenecked populations, distinguishing the reduction of inbreeding load from dominance versus overdominance loci is challenging.
• Purging of dominant loci slows inbreeding depression and allows partial fitness recovery, whereas overdominant loci lead to monotonic fitness decline.

Conclusions:

• Genetic drift plays a crucial role in modulating inbreeding load, particularly for overdominant mutations.
• The dynamics of inbreeding depression differ significantly between dominant and overdominant loci under population bottlenecks.
• Understanding these distinct mechanisms is vital for predicting population viability under inbreeding stress.