M. Aguade, N. Miyashita, and C. Langley. Genetics, 122 (3):
607-615(July 1989)"In particular, the low genetic diversity seen in regions of low recombination in Drosophila and other organisms (Aguade et al. 1989; Aquadro et al. 1994) must be due to some kind of selection.".
R. Wang, J. Wakeley, and J. Hey. Genetics, 147 (3):
1091-1106(1997)In three species of Drosophila, looks at three different nuclear loci (two of which is on the X chromosome) and finds evidence of recent gene flow in one, but not in the other two. Cites mtDNA and allozyme studies as well, with differing conclusions..