Geographic variation in intron I sequence of the voltage-gated sodium channel gene within and among species of the Anopheles gambiae complex.

The sequence analysis of the Intron I of the voltage-gated sodium channel gene in Anopheles gambiae sensu stricto samples from ten West-African Countries showed the existence of twelve Intron I haplotypes, six in the Mand six S-populations. Two haplotypes occurred in very high frequencies over the entire geographic area studied and are separated by a single mutational step, which distinguish two main clusters corresponding to the S and M molecular forms. The third most common haplotype was found in M specimens from several geographical areas, while the other nine haplotypes are geographical variants of either the S- or the M-form, mostly linked to single localities. The single nucleotide mutation defining the two most common haplotypes represents the first marker found in an intronic DNA region that consistently correlates over a wide geographical range with the rDNA markers used to define A. gambiae molecular forms; this provides further support to the existence of barriers to gene flow between them. As a follow-up of these results and to test the level of differentiation between the taxa of the A. gambiae complex, we extended the sequence analysis of Intron I both to samples of molecular forms from a wider geographical range (from West to East Africa and Madagascar), and to other species (A. arabiensis, A. melas and A. quadriannulatus). The results, allowed to place the evolution of this intronic sequence in a phylogeographic context. (ACMCIP abstract)