The effect of a reduction in population size on mean fitness and inbreeding depression

Bottlenecks in small, randomly mating populations founded from mutation–selection–drift equilibrium predict an initial mean-fitness drop followed by recovery only when selection outweighs drift and mutations are sufficiently recessive.

• Why it matters: The work addresses limited theory on how population bottlenecks jointly shape mean fitness and inbreeding depression, including whether purging can reverse early declines.
• What they did: The authors build a theoretical framework for small populations after sudden size reduction, combining simulations with approximate analytical results to track mean fitness and inbreeding depression dynamics.
• The result: They derive an approximate expression for the time to mean-fitness recovery, while showing that weakly deleterious mutations yield fitness and inbreeding-depression changes similar to those expected from neutral-allele homozygosity over short timescales.

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