Unusual pattern of nucleotide sequence variation at the OS-E and OS-F genomic region of Drosophila simulans
Alejandro Sánchez-Gracia 1 and Julio Rozas 1*
1 Universitat de Barcelona
* To whom correspondence should be addressed. E-mail: jrozas{at}ub.edu.
Submitted on November 8, 2006
Revised on December 13, 2006
Accepted on 1 February 2007
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Abstract |
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Nucleotide variation at the genomic region encompassing the odorant-binding protein genes OS-E and OS-F (OS-region) was surveyed in two populations of Drosophila simulans, one from Europe and the other from Africa. We found that the European population shows an atypical and large haplotype structure, which extends throughout the ~5kb surveyed genomic region. This structure is depicted by two major haplotype groups segregating at intermediate frequency in the sample, one haplogroup with nearly no variation, and the other at levels more typical for this species. This pattern of variation was incompatible with neutral predictions for a population at a stationary equilibrium. Nevertheless, neutrality tests contrasting polymorphism and divergence data fail to detect any departure from the standard neutral model in this species, whereas they confirm the non-neutral behavior previously observed at the OS-E gene in D. melanogaster. Although positive Darwinian selection may have been responsible for the observed unusual nucleotide variation structure, coalescent simulations results do not allow rejecting the hypothesis that the pattern was generated by a recent bottleneck in the history of European populations of D. simulans.
Key Words:
DNA polymorphism, Haplotype structure, Natural selection, Odorant-binding proteins, Population bottleneck
