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Long-Term Maintenance of Complex Chromosomal Inversion Polymorphism in Drosophila mediopunctata.

Fabiana Uno1, Felipe Bastos Rocha2, Louis Bernard Klaczko3

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Natural selection maintains stable chromosomal inversions in Drosophila populations over 30 years. Overdominance and epistatic selection are key to this complex polymorphism

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Area of Science:

  • Evolutionary biology
  • Population genetics
  • Genomics

Background:

  • Natural selection influences gene combinations and recombination rates via epistasis.
  • Understanding these dynamics in natural populations is challenging.
  • Complex polymorphisms involving chromosomal inversions are crucial for evolutionary studies.

Purpose of the Study:

  • Investigate the long-term stability of linked chromosomal inversions in *Drosophila mediopunctata*.
  • Examine the roles of recombination suppression, epistasis, and overdominance in maintaining polymorphism.
  • Clarify the evolutionary dynamics of inversion systems in natural populations.

Main Methods:

  • Long-term population monitoring over 30 years.
  • Analysis of linkage disequilibrium (LD) and seasonal allele frequency cycles.
  • Computer simulations incorporating selection coefficients and overdominance.

Main Results:

  • Observed stable linkage disequilibrium (LD) between inversions, defying predicted decay.
  • Identified consistent seasonal patterns of heterozygote excess and homozygote deficiency.
  • Moderate selection coefficients maintain LD but lead to unstable equilibria.
  • Simulations show overdominance stabilizes the system for long-term persistence.

Conclusions:

  • A balance of LD, recombination, and selection, particularly overdominance, maintains complex inversion polymorphism.
  • Epistatic interactions and selective pressures significantly shape evolutionary trajectories.
  • This study provides insights into the evolutionary mechanisms governing inversion systems in natural populations.