Continuously fluctuating selection reveals extreme granularity and parallelism of adaptive tracking

Area of Science:

• Evolutionary biology
• Population genetics

Background:

• Natural habitats feature temporally fluctuating environmental conditions.
• Understanding adaptive tracking of fluctuating selection pressures via standing genetic variation is crucial.

Approach:

• Generated high-frequency, genome-wide allele frequency data from Drosophila melanogaster populations in replicated field mesocosms over ~12 generations.
• Analyzed adaptation during population expansion, peak density, and collapse phases.
• Compared allele frequency changes with an independent dataset from the same experimental system.

Key Points:

• Rapid, parallel genomic variation changes underpinned adaptation across replicates.
• Dominant selection direction fluctuated repeatedly, even within ecological phases.
• Targets of selection are predictable across years.

Conclusions:

• Fitness-relevance of standing variation is revealed, potentially masked by static sampling or insufficient time-series data.
• Fine-scaled, temporally fluctuating selection may maintain functional genetic variation in natural populations.
• Fluctuating selection acts as a stochastic force affecting genome-wide standing genetic variation.