Use of short tandem repeats for the analysis of genetic variability in sympatric populations of Anopheles gambiae and Anopheles arabiensis.

Anopheles gambiae and An. arabiensis were analysed at 30 short tandem repeat (STR) loci originally developed for use in An. gambiae. All specimens were collected from the same village in Kilifi district, coastal Kenya. All 30 loci were amplified in the An. gambiae specimens, whereas 25 out of 30 loci (83.3%) were successfully amplified in the An. arabiensis specimens. Both species had similar levels of polymorphism for the loci that were amplified (93.3% for An. gambiae and 92% for An. arabiensis). Median FST and RST values between the two species were 0.249 and 0.197, respectively, corresponding to Nm values of 0.75 and 0.51, respectively, and suggesting limited interchange of genes between these species. These, together with the relatively high Nei unbiased genetic distance (0.202) between the two sibling species, are consistent with the occurrence of sympatric species with limited gene flow. FST/RST values for individual loci varied greatly (FST range 0.00-0.87; RST range 0.00-0.73), indicating that the loci differ in their ability to measure levels of differentiation between these two species. Location of loci within paracentric inversions seems to be an important factor affecting levels of differentiation measured by the different loci.