How should we measure population-level inbreeding depression? Impacts of standing genetic associations between selfing rate and deleterious mutations

TL;DR

The paper explores how inbreeding depression and selfing rates are genetically linked and how this affects population evolution.

Contribution

It introduces new metrics for measuring population-level inbreeding depression based on selfing rate and offspring fitness correlations.

Findings

The association between selfing rate and inbreeding depression shifts from positive to negative as mutation selection strength increases.

Standing genetic associations between selfing rate and fitness alleles influence the evolution of population selfing rates.

New metrics for population-level inbreeding depression are proposed using correlation coefficients between selfing rates and offspring fitness.

Abstract

Inbreeding depression (ID) is a major selective force during mating system evolution primarily contributed by highly to partially recessive deleterious mutations. Theories suggest that transient genetic association with fitness alleles can be important in affecting the evolution of alleles that modify the selfing rate during its sweep. Nevertheless, empirical tests often focus on the pre-existing genetic association between selfing rate and ID maintained under mutation–selection balance. Therefore, how this standing genetic association is affected by key factors and its impacts on the evolution of selfing remain unclear. I show that as the selection coefficient of deleterious mutations increases, the association between selfing rate and ID declines from positive to negative. These results predict that association between selfing and ID tends to be negative in populations with low selfing rates, while positive in highly selfing populations. Using population genetic and quantitative genetic models, I show that standing genetic associations between selfing rate and fitness alleles can significantly impact the evolution of the mean selfing rate of a population. I present better metrics of population-level ID, which can be calculated based on the correlation coefficient between individual selfing rate and the fitness of selfed and outcrossed offspring.

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