Environment changes epistasis to alter trade-offs along alternative evolutionary paths.

Area of Science:

• Evolutionary biology
• Genetics

Background:

• Mutation fitness effects are influenced by genetic background (epistasis) and external environment.
• Few studies integrate both epistasis and environmental factors, especially for coevolved mutations.

Purpose of the Study:

• To investigate the combined effects of genetic background and environmental context on the fitness of coevolved mutations.
• To understand how these interactions shape evolutionary trajectories and trade-offs.

Main Methods:

• Examined interactions among five coevolved mutations.
• Assessed fitness effects across eight diverse environments.

Main Results:

• Mutations were generally beneficial but exhibited significant fitness variation across environments and genetic backgrounds.
• Specific, environment-dependent interactions were common, leading to context-specific costs or benefits.
• Diminishing returns epistasis was observed, where fitness gains decreased with increasing genotype fitness.

Conclusions:

• Mutation effects are highly contingent on the specific combination of genetic and external environments.
• Evolutionary paths and resulting trade-offs are dependent on the historical sequence of mutations and environmental exposures.
• A genotype's current fitness correlates with its future adaptive potential.