Selective sweep near the In (2L)t inversion breakpoint in an African population of Drosophila melanogaster

Chromosomal inversions largely inhibit recombination and may be associated with selective forces, such as hitch-hiking effects: the effect of positive selection on linked loci. A West African population of Drosophila melanoga ster showed a high frequency (0.61) of the In(2L)t inversion. Departure fro m neutrality statistically associated with the inversion polymorphism was p reviously recorded at Su(H). a locus distant from the proximal breakpoint o f the inversion. These results were consistent with hitch-hiking effects wi th recombination. The present sequence polymorphism survey involves a 1 kb fragment of the Vha68-1 locus located closer to the proximal breakpoint of the inversion. It shows a significant deficit of polymorphism with respect to divergence when compared with other loci studied in the same population, thus suggesting selective effects. Only 11 polymorphic sites are present i n a sample of 20 chromosomes and these sites present a significant excess o f rare-frequency variants. The major haplotype shows an unexpectedly high f requency. Our estimate of the background selection effect is not sufficient to account for the observed reduction of polymorphism. Intraspecific varia tion is structured between inverted and standard chromosomes: there are no shared polymorphisms but also no fixed differences between them. This patte rn, together with that found on other loci previously studied near this inv ersion breakpoint, suggests hitch-hiking effects enhanced by the inversion.