a1 Université des Sciences et Technologies de Lille 1, Laboratoire de génétique et évolution des populations végétales, CNRS UMR 8016, 59655 Villeneuve d'Ascq, France
Hitch-hiking to a site under balancing selection is expected to produce a local increase in nucleotide polymorphism and a decrease in population differentiation compared with the background genomic level, but empirical evidence supporting these predictions is scarce. We surveyed molecular diversity at four genes flanking the region controlling self-incompatibility (the S-locus) in samples from six populations of the herbaceous plant Arabidopsis halleri, and compared their polymorphism with sequences from five control genes unlinked to the S-locus. As a preliminary verification, the S-locus flanking genes were shown to co-segregate with SRK, the gene involved in the self-incompatibility reaction at the pistil level. In agreement with theory, our results demonstrated a significant peak of nucleotide diversity around the S-locus as well as a significant decrease in population genetic structure in the S-locus region compared with both control genes and a set of seven unlinked microsatellite markers. This is consistent with the theoretical expectation that balancing selection is increasing the effective migration rate in subdivided populations. Although only four S-locus flanking genes were investigated, our results suggest that these two signatures of the hitch-hiking effect are localized in a very narrow genomic region.
(Received September 08 2007)
(Revised October 15 2007)
c1 Corresponding author. Laboratoire GEPV, UMR CNRS 8016, Bat. SN2, Université des Sciences et Technologies de Lille 1, 59655 Villeneuve d'Ascq, France. Telephone: +33 3 20 43 67 53. Fax: +33 3 20 43 69 79. e-mail: email@example.com