Continuously fluctuating selection reveals fine granularity of adaptation

Area of Science:

• Evolutionary Biology
• Population Genetics
• Ecology

Background:

• Natural habitats frequently present temporally fluctuating environmental conditions.
• Understanding how populations adapt to these dynamic conditions using standing genetic variation is crucial but remains largely unknown.

Purpose of the Study:

• To investigate the adaptive tracking of fluctuating selection pressures by natural populations.
• To analyze shifts in standing genetic variation over multiple generations in response to environmental changes.

Main Methods:

• Generated genome-wide allele frequency data every 1-2 generations for a diverse Drosophila melanogaster population over approximately 12 generations.
• Utilized replicated field mesocosms to simulate natural habitat conditions from late June to mid-December.
• Compared allele frequency changes with an independent dataset from the same experimental system.

Main Results:

• Observed extremely rapid and parallel changes in genomic variation across replicates, underpinning adaptation during population expansion, peak density, and collapse.
• Documented repeated fluctuations in the dominant direction of selection, even within ecological phases.
• Demonstrated that targets of selection are predictable across years.

Conclusions:

• Standing genetic variation has fitness relevance that may be obscured by static sampling or low-resolution time-series data.
• Fine-scaled, temporally fluctuating selection likely maintains functional genetic variation in natural populations.
• Fluctuating selection acts as a stochastic force impacting genome-wide diversity at linked neutral sites, similar to genetic draft.