Evolutionary stalling and a limit on the power of natural selection to improve a cellular module

Abstract

Significance Cellular modules, such as the translation machinery (TM), are key units of adaptive evolution because fitness depends on their performance. In rapidly evolving populations, natural selection may not be able to improve all modules simultaneously because adaptive mutations in different modules compete against each other. We hypothesize that adaptation in some modules would stall, despite the availability of beneficial mutations. We empirically demonstrate such evolutionary stalling in the TM module in experimental populations of Escherichia coli . Natural selection initially improved the TM, but its focus shifted away to other cellular modules before TM’s performance was fully restored. This work shows that rapid shifts in the focus of selection can slow down the improvement of individual cellular components in nature.