# The fate of a mutation in a fluctuating environment

## TL;DR

This paper explores how changing environments affect the survival of new genetic mutations, showing that environmental variability can override average selection pressures.

## Contribution

The study reveals that environmental fluctuations can reduce selection efficiency and alter mutation fixation probabilities beyond time-averaged effects.

## Key findings

- Environmental variability can make selection ineffective at distinguishing beneficial from deleterious mutations.
- Temporal fluctuations often have a greater impact on mutation fixation than average selection pressures.
- Mutations with average deleterious effects can fix more often than neutral or beneficial ones in fluctuating environments.

## Abstract

Natural environments are never truly constant, but the evolutionary implications of temporally varying selection pressures remain poorly understood. Here we investigate how the fate of a new mutation in a variable environment depends on the dynamics of environmental fluctuations and on the selective pressures in each condition. We find that even when a mutation experiences many environmental epochs before fixing or going extinct, its fate is not necessarily determined by its time-averaged selective effect. Instead, environmental variability reduces the efficiency of selection across a broad parameter regime, rendering selection unable to distinguish between mutations that are substantially beneficial and substantially deleterious on average. Temporal fluctuations can also dramatically increase fixation probabilities, often making the details of these fluctuations more important than the average selection pressures acting on each new mutation. For example, mutations that result in a tradeoff between conditions but are strongly deleterious on average can nevertheless be more likely to fix than mutations that are always neutral or beneficial. These effects can have important implications for patterns of molecular evolution in variable environments, and they suggest that it may often be difficult for populations to maintain specialist traits, even when their loss leads to a decline in time-averaged fitness.