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Beyond Fixation: Persistent Genetic Variation Under Intense Selection.

Kenneth R Arnold1, Zachary S Greenspan2, Ryan D Robinson1

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Summary
This summary is machine-generated.

Genetic variation persists under strong selection, revealed by experimental evolution in fruit flies. This genetic diversity allows rapid adaptation when selection pressures reverse, suggesting balancing selection plays a key role.

Keywords:
Antagonistic pleiotropyBalancing selectionDrosophila melanogasterEvolutionary reversibilityExperimental evolutionLife-history evolutionPolygenic adaptationStanding genetic variation

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Area of Science:

  • Evolutionary Genetics
  • Population Genetics
  • Experimental Evolution

Background:

  • Maintaining genetic variation under sustained selection is a key evolutionary genetics question.
  • Adaptation often involves polygenic shifts from standing variation, not just hard sweeps.
  • Existing models don't fully explain persistent genetic variation after long-term directional selection.

Purpose of the Study:

  • To investigate if balancing selection maintains genetic variation under strong life-history selection in *Drosophila melanogaster*.
  • To assess the role of genetic variation in evolutionary reversibility.
  • To test if standing variation is depleted by intense directional selection.

Main Methods:

  • Long-term experimental evolution of *Drosophila melanogaster* populations under directional selection for reproduction timing.
  • Reciprocal shifts in selection regimes (early vs. delayed reproduction) to test evolutionary reversibility.
  • Deep sequencing to detect ultra-rare alleles and assess genome-wide heterozygosity changes.

Main Results:

  • Populations rapidly converged phenotypically after reciprocal selection shifts, showing coordinated polygenic responses.
  • Relaxing early-life selection led to a significant rebound in genome-wide heterozygosity.
  • Ultra-rare alleles, undetectable with standard sequencing, were found at supposedly fixed sites, indicating persistent low-frequency variation.

Conclusions:

  • Substantial genetic variation can persist under intense directional selection and be rapidly redeployed upon selection reversal.
  • Results support the hypothesis that widespread balancing selection actively maintains genetic variation.
  • Persistent genetic variation enhances evolutionary adaptability and reversibility.