When genetic distance matters: Measuring genetic differentiation at microsatellite loci in whole-genome scans of recent and incipient mosquito species

Genetic distance measurements are an important tool to differentiate field populations of disease vectors such as the mosquito vectors of malaria. Her e, we have measured the genetic differentiation between Anopheles arabiensi s and Anopheles gambiae, as well as between proposed emerging species of th e latter taxon, in whole genome scans by using 23-25 microsatellite loci. I n doing so, we have reviewed and evaluated the advantages and disadvantages of standard parameters of genetic distance, F-ST, R-ST, (delta mu)(2), and D. Further, we have introduced new parameters, D ' and D-K, which have wel l defined statistical significance tests and complement the standard parame ters to advantage. D ' is a modification of D, whereas DK is a measure of c ovariance based on Pearson's correlation coefficient. We find that A. gambi ae and A. arabiensis are closely related at most autosomal loci but appear to be distantly related on the basis of X-linked chromosomal loci within th e chromosomal Xag inversion. The M and S molecular forms of A. gambiae are practically indistinguishable but differ significantly at two microsatellit e loci from the proximal region of the X, outside the Xag inversion. At one of these loci, both M and S molecular forms differ significantly from A. a rabiensis, but remarkably, at the other locus,A. arabiensis is indistinguis hable from the M molecular form of A. gambiae. These data support the recen t proposal of genetically differentiated M and S molecular forms of A. gamb iae.