Selection on X-linked genes during speciation in the Drosophila athabasca complex

Area of Science:

• Population genetics
• Molecular evolution
• Drosophila genomics

Background:

• Drosophila athabasca exhibits distinct semispecies with varying genetic divergence.
• Previous studies examined variation at the period locus, necessitating further investigation across multiple genes.

Purpose of the Study:

• To survey genetic variation at five loci in Drosophila athabasca.
• To compare differentiation patterns between X-linked and autosomal genes.
• To test the neutral model of molecular evolution against observed genetic divergence.

Main Methods:

• Restriction site survey of five genetic loci (period, no-on-transient-A, E74A, Xdh, Adh, RC98).
• Application of a modified HKA (Haldane-Kimura-Aquadro) test using fixed differences and Fst.
• Computer simulations to explore evolutionary scenarios.

Main Results:

• X-linked loci (period, no-on-transient-A, E74A) show significantly greater differentiation among semispecies than autosomal loci (Xdh, Adh, RC98).
• The observed pattern of differentiation is inconsistent with a neutral model of molecular evolution.
• Selective sweeps on the X-chromosome are proposed as the best explanation for the data.

Conclusions:

• Natural selection, specifically X-linked selective sweeps, likely played a significant role in shaping genetic divergence in Drosophila athabasca semispecies.
• This finding suggests that X-linked traits, such as mating song differences, may have been targets of selection.
• The study provides evidence against a purely neutral evolutionary process for these genes.