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

AbstractWe karyotyped and identified by polymerase chain reaction restriction fragment 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 from 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 Bamako 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 adaptation rather than in mate‐recognition systems. Strong support for the reproductive 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 chromosomal identical M specimens. However, the kdr allele does not segregate with molecular forms in Benin.