Molecular evidence of incipient speciation within Anopheles gambiae s.s. in West Africa

We karyotyped and identified by polymerase chain reaction restriction fragm ent length polymorphism (PCR-RFLP) analysis Anopheles gambiae s.s. samples collected in several African countries. The data show the existence of two non-panmictic molecular forms, named S and M, whose distribution extended f rom forest to savannahs, Mosquitoes of the S and M forms are homosequential standard for chromosome-2 inversions in forest areas. In dry savannahs, S is characterized mainly by inversion polymorphisms typical of Savanna and B amako chromosomal forms, while M shows chromosome-2 arrangements typical of Mopti and/or Savanna and/or Bissau, depending on its geographical origin. Chromosome-2 inversions therefore seem to be involved in ecotypic adaptatio n rather than in mate-recognition systems. Strong support for the reproduct ive isolation of S and M in Ivory Coast comes from the observation that the kdr allele is found at high frequencies in S specimens and not at all in c hromosomal identical M specimens. However, the kdr allele does not segregat e with molecular forms in Benin.