Joint effects of natural selection and recombination on gene flow between Drosophila ananassae populations

We estimated DNA sequence variation in a 5.7-kb fragment of the furrowed (f w) gene region within and between four populations of Drosophila ananassae; Sw is located in a chromosomal region of very low recombination. We analyz ed gene flow between these four populations along a latitudinal transect on the Indian subcontinent: two populations from southern, subtropical areas (Hyderabad, India, and Sri Lanka) and two from more temperate zones in the north (Nepal and Burma). Furthermore, ave compared the pattern of different iation at fw with published data from Om(1D), a gene located in a region of normal recombination. While differentiation at Om(1D) shows an isolation-b y-distance effect, at fw the pattern of differentiation is quite different such that the frequencies of single nucleotide polymorphisms are homogenize d over extended geographic regions (i.e., among the two populations of the northern species range from Burma and Nepal as well as among the two southe rn populations from India and Sri Lanka), but strongly differentiated betwe en the northern and southern populations. To examine these differences in t he patterns of Variation and differentiation between the Om(1D) and fw gene regions, we determine the critical Values of our previously proposed test of the background selection hypothesis (henceforth called F-ST test). Using these results, we show that the pattern of differentiation at fw may be in consistent with the background selection model. The data depart from this m odel in a direction that is compatible with the occurrence of recent select ive sweeps in the northern as well as southern populations.