title: The "far-west" of Anopheles gambiae molecular forms.
abstract: The main Afrotropical malaria vector, Anopheles gambiae sensu stricto, is undergoing a process of sympatric ecological diversification leading to at least two incipient species (the M and S molecular forms) showing heterogeneous levels of divergence across the genome. The physically unlinked centromeric regions on all three chromosomes of these closely related taxa contain fixed nucleotide differences which have been found in nearly complete linkage disequilibrium in geographic areas of no or low M-S hybridization. Assays diagnostic for SNP and structural differences between M and S forms in the three centromeric regions were applied in samples from the western extreme of their range of sympatry, the only area where high frequencies of putative M/S hybrids have been reported. The results reveal a level of admixture not observed in the rest of the range. In particular, we found: i) heterozygous genotypes at each marker, although at frequencies lower than expected under panmixia; ii) virtually all possible genotypic combinations between markers on different chromosomes, although genetic association was nevertheless detected; iii) discordant M and S genotypes at two X-linked markers near the centromere, suggestive of introgression and inter-locus recombination. These results could be indicative either of a secondary contact zone between M and S, or of the maintenance of ancestral polymorphisms. This issue and the perspectives opened by these results in the study of the M and S incipient speciation process are discussed.
authors.affiliation: Istituto Pasteur-Fondazione Cenci-Bolognetti, Dipartimento di Sanità Pubblica e Malattie Infettive, Università di Roma Sapienza, Rome, Italy.
authors.forename: Beniamino
authors.initials: B
authors.lastname: Caputo
authors.forename: Federica
authors.initials: F
authors.lastname: Santolamazza
authors.forename: José L
authors.initials: JL
authors.lastname: Vicente
authors.forename: Davis C
authors.initials: DC
authors.lastname: Nwakanma
authors.forename: Musa
authors.initials: M
authors.lastname: Jawara
authors.forename: Katinka
authors.initials: K
authors.lastname: Palsson
authors.forename: Thomas
authors.initials: T
authors.lastname: Jaenson
authors.forename: Bradley J
authors.initials: BJ
authors.lastname: White
authors.forename: Emiliano
authors.initials: E
authors.lastname: Mancini
authors.forename: Vincenzo
authors.initials: V
authors.lastname: Petrarca
authors.forename: David J
authors.initials: DJ
authors.lastname: Conway
authors.forename: Nora J
authors.initials: NJ
authors.lastname: Besansky
authors.forename: João
authors.initials: J
authors.lastname: Pinto
authors.forename: Alessandra
authors.initials: A
authors.lastname: della Torre
mesh_terms: D000818:Animals; D000852:Anopheles / Q000166:cytology / Q000235:genetics*; D002503:Centromere / Q000235:genetics; D005260:Female; D005819:Genetic Markers / Q000235:genetics; D049810:Genetic Speciation; D060005:Genotyping Techniques; D006824:Hybridization, Genetic; D061350:Sympatry / Q000235:genetics*; D014960:X Chromosome / Q000235:genetics
chemical_list: D005819:Genetic Markers