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bioRxiv · 10.1101/2025.11.17.688329

Mean fitness is maximized in small populations under stabilizing selection on highly polygenic traits

Ragsdale, A. P.
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Abstract

Stabilizing selection commonly acts on complex traits that affect individual fitness. Here, we relate mean fitness under stabilizing selection to population size and trait architecture, using a simple application of theoretical predictions for the distribution of phenotypic values in a single-trait Gaussian stabilizing selection model. We show that mean fitness is maximized by a finite (often small) population size when the total diploid mutation rate U across trait-affecting loci is reasonably large. Namely, this occurs when U > {sigma}2/(4(VS+VE)), where {sigma}2 is the variance of the distribution of effect sizes of new mutations, VS determines the strength of stabilizing selection, and VE is the environmental variance. We validate these predictions using individual-based simulations and briefly discuss their implications for interpreting genetic load and adaptability in small populations.

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Ragsdale, A. P.. 2025-11-19. Mean fitness is maximized in small populations under stabilizing selection on highly polygenic traits. https://doi.org/10.1101/2025.11.17.688329

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