Distribution of genetic variation among chromosomal forms of Anopheles gambiae s.s.:: introgressive hybridization, adaptive inversions, or recent reproductive isolation?

A series of four papers in this issue explores the reproductive status of the five chromosomal forms of An. gambiae ss. using molecular techniques to examine the variation among twelve different genes located throughout the An. gambiae s.s. genome. Results of these and previous studies are consistent with a hypothesis of at least partial barriers to gene flow between some chromosomal forms in the Ivory Coast and other West African countries to the north and west, but introgression between S and M types in Benin and countries to the east. Collectively, these studies indicate the need for a broader geographical sampling of An. gambiae s.s., increased research on mechanisms of prezygotic reproductive isolation and field-based studies of survival and fecundity in hybrids to test for postzygotic reproductive isolation.