Mrudula and Joshua’s paper measuring the incidence and fitness effects of antagonistically pleiotropic mutations is now out in Evolution!
As they improve at performing one function, organisms often get worse at another function. Such a negative relationship between two functions (or traits) is called a tradeoff, and is a central idea in evolutionary biology. Tradeoffs may constrain adaptation, and underlie many important evolutionary processes such as the evolution of organisms’ life history strategies, diversification and speciation. One way in which tradeoffs can arise is via mutations that are antagonistically pleiotropic. These mutations increase fitness in one environment, while simultaneously decreasing fitness in another. Antagonistic pleiotropy (AP) could therefore explain tradeoffs if such mutations were frequent and had large fitness effects. However, the frequency and fitness effects of these mutations remains poorly studied.
We measured the frequency and fitness effects of AP mutations across 11 different carbon sources in a large set of random single mutations in Escherichia coli. Our results suggest that overall AP is very rare, and that AP-mediated tradeoffs are unlikely to constrain adaptation very often. Thus, while there is no denying that tradeoffs are abundant in nature, it is unlikely that they are caused by single antagonistically pleiotropic mutations. Rather, accumulation of multiple mutations in genes that are not under very strong selection may degrade other functions, presenting as a tradeoff.