Mutation potentiates migration swamping in polygenic local adaptation

Area of Science:

• Evolutionary genetics
• Population genetics
• Quantitative genetics

Background:

• Local adaptation can arise from divergence at few or many genetic loci.
• Migration rates influence the genetic architecture of adaptation, with low migration favoring divergence.
• Previous simulations indicated that high mutation rates can destabilize adaptation architecture.

Purpose of the Study:

• To analytically investigate how population size, selection strength, and mutation parameters affect the transition to transient genetic architectures.
• To develop a mathematical theory predicting the threshold mutation rate for this transition.

Main Methods:

• Developed an analytical two-population model.
• Employed diffusion approximation to derive a mathematical theory.
• Validated theoretical predictions against individual-based simulations across diverse parameter spaces.

Main Results:

• The threshold mutation rate for the transition to transient adaptation architecture is primarily determined by the average effect size of mutations.
• Selection strength has a weaker influence, and population size has a marginal effect on this threshold.
• A trait-wide mutation rate between 10^-3 and 10^-2 often triggers the transition, relevant for complex traits.

Conclusions:

• The stability of genetic architecture in many local adaptation examples suggests relatively low per-trait mutation rates.
• The developed diffusion approximation model accurately predicts the transition threshold across a broad parameter range.
• Understanding mutation rate dynamics is crucial for predicting the evolutionary trajectories of locally adapted traits.