Open AccessThe Origin of Additive Genetic Variance Driven by Positive Selection
Author(s) -
Li Liu,
Yayu Wang,
Di Zhang,
Zhuoxin Chen,
Xiaoshu Chen,
Zhijian Su,
Xionglei He
Publication year - 2020
Publication title -
molecular biology and evolution
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 6.637
H-Index - 218
eISSN - 1537-1719
pISSN - 0737-4038
DOI - 10.1093/molbev/msaa085
Subject(s) - biology , natural selection , heritability , selection (genetic algorithm) , evolutionary biology , epistasis , population , divergence (linguistics) , genetic correlation , variance (accounting) , genetic variation , genetics , gene , linguistics , philosophy , demography , accounting , artificial intelligence , sociology , computer science , business
Fisher’s fundamental theorem of natural selection predicts no additive variance of fitness in a natural population. Consistently, studies in a variety of wild populations show virtually no narrow-sense heritability ( h 2 ) for traits important to fitness. However, counterexamples are occasionally reported, calling for a deeper understanding on the evolution of additive variance. In this study, we propose adaptive divergence followed by population admixture as a source of the additive genetic variance of evolutionarily important traits. We experimentally tested the hypothesis by examining a panel of ∼1,000 yeast segregants produced by a hybrid of two yeast strains that experienced adaptive divergence. We measured >400 yeast cell morphological traits and found a strong positive correlation between h 2 and evolutionary importance. Because adaptive divergence followed by population admixture could happen constantly, particularly in species with wide geographic distribution and strong migratory capacity (e.g., humans), the finding reconciles the observation of abundant additive variances in evolutionarily important traits with Fisher’s fundamental theorem of natural selection. Importantly, the revealed role of positive selection in promoting rather than depleting additive variance suggests a simple explanation for why additive genetic variance can be dominant in a population despite the ubiquitous between-gene epistasis observed in functional assays.