Intrinsic adaptive value and early fate of gene duplication revealed by a bottom-up approach

Abstract

Gene duplication is a major source of functional innovations and genome complexity, albeit this evolutionary process requires the preservation of duplicates in the genomes for long time. However, the population genetic mechanisms governing this preservation, especially in the critical very initial phase, have remained largely unknown. Here, we demonstrate that gene duplication confers per se a weak selective advantage in scenarios of fitness trade-offs. Through a precise quantitative description of a model system, we show that a second gene copy enhances the information transfer from the environmental signal to the phenotypic response by reducing gene expression inaccuracies derived from pervasive molecular noise and suboptimal gene regulation. We then reveal that such a phenotypic accuracy yields a selective advantage in the order of 0.1% on average, which would allow the positive selection of gene duplication in populations with moderate or large sizes. This advantage is greater at higher noise levels and intermediate concentrations of the environmental molecule, when fitness trade-offs become more evident. Moreover, we show that the genome rearrangement rates greatly condition the eventual fixation of duplicated genes, either by natural selection or by random genetic drift. Overall, our theoretical results highlight an original adaptive value for cells carrying new-born duplicates, broadly analyze the selective conditions that determine their early fates in different organisms, and reconcile population genetics with evolution by gene duplication.