Unusual Pattern of Nucleotide Sequence Variation at the OS-E and OS-F Genomic Regions of Drosophila simulans

摘要

Nucleotide variation at the genomic region encompassing the odorant-binding protein genes OS-Enand OS-F (OS region) was surveyed in two populations of Drosophila simulans, one from Europe and thenother from Africa. We found that the European population shows an atypical and large haplotype structure,nwhich extends throughout the u00025-kb surveyed genomic region. This structure is depicted by twonmajor haplotype groups segregating at intermediate frequency in the sample, one haplogroup with nearlynno variation, and the other at levels more typical for this species. This pattern of variation was incompatiblenwith neutral predictions for a population at a stationary equilibrium. Nevertheless, neutralityntests contrasting polymorphism and divergence data fail to detect any departure from the standardnneutral model in this species, whereas they confirm the non-neutral behavior previously observed at thenOS-E gene in D. melanogaster. Although positive Darwinian selection may have been responsible for thenobserved unusual nucleotide variation structure, coalescent simulation results do not allow rejectingnthe hypothesis that the pattern was generated by a recent bottleneck in the history of European populationsnof D. simulans.