Interplay between extreme drift and selection intensities favors the fixation of beneficial mutations in selfing maize populations

Author:

Desbiez-Piat Arnaud1,Le Rouzic Arnaud2ORCID,Tenaillon Maud I1ORCID,Dillmann Christine1ORCID

Affiliation:

1. Université Paris-Saclay, INRAE, CNRS, AgroParisTech, GQE—Le Moulon, 91190 Gif-sur-Yvette, France

2. Université Paris-Saclay, CNRS, IRD, UMR Évolution, Génomes, Comportement et Écologie, 91120 Gif-sur-Yvette, France

Abstract

Abstract Population and quantitative genetic models provide useful approximations to predict long-term selection responses sustaining phenotypic shifts, and underlying multilocus adaptive dynamics. Valid across a broad range of parameters, their use for understanding the adaptive dynamics of small selfing populations undergoing strong selection intensity (thereafter High Drift-High selection regime, HDHS) remains to be explored. Saclay Divergent Selection Experiments (DSEs) on maize flowering time provide an interesting example of populations evolving under HDHS, with significant selection responses over 20 generations in two directions. We combined experimental data from Saclay DSEs, forward individual-based simulations, and theoretical predictions to dissect the evolutionary mechanisms at play in the observed selection responses. We asked two main questions: How do mutations arise, spread, and reach fixation in populations evolving under HDHS? How does the interplay between drift and selection influence observed phenotypic shifts? We showed that the long-lasting response to selection in small populations is due to the rapid fixation of mutations occurring during the generations of selection. Among fixed mutations, we also found a clear signal of enrichment for beneficial mutations revealing a limited cost of selection. Both environmental stochasticity and variation in selection coefficients likely contributed to exacerbate mutational effects, thereby facilitating selection grasp and fixation of small-effect mutations. Together our results highlight that despite a small number of polymorphic loci expected under HDHS, adaptive variation is continuously fueled by a vast mutational target. We discuss our results in the context of breeding and long-term survival of small selfing populations.

Funder

French National Research Agency

Saclay Plant Sciences-SPS

Institut Diversité, Ecolgie et Evolution du Vivant

French ministry of Research

Publisher

Oxford University Press (OUP)

Subject

Genetics

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