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London School of Hygiene & Tropical Medicine Malaria Centre

Malaria research in parasite biology

Minimal genomic differentiation between putative incipient species of Anopheles gambiae with extensive interbreeding at ecologically diverse sites in West Africa.

LSHTM investigators:
David Conway
External collaborators:
Davis Nwakanma, Musa Jawara, Samson Awolola & Majidah Adiamoh (Medical Research Council, The Gambia); Lassana Konate, Ngayo Sy & Ibrahima Dia (Cheikh Anta Diop University, Service de Lutte Antiparasitaire and Pasteur Institute, Senegal); Amabelia Rodrigues (Bandim Health Project, Guinea Bissau); Kovana Marcel Loua (National Institute of Public Health, Guinea); Daniel Neafsey, Emily Lund & Marc Muskavitch (Harvard University, USA)
Funding body:
Medical Research Council, UK, Foundation for the National Institutes of Health/Gates Grand Challenges in Global Health.

M and S molecular forms of the major African malaria vector Anopheles gambiae sensu stricto (s.s.) are widely considered as incipient species with strong reproductive isolation, with M/S hybrids rarely seen except in a few sites in the extreme west of Africa.

We undertook new surveys of 12 sites in four contiguous countries in this region, with a total of 3499 An. gambiae s.s. identified and genotyped. High frequencies of M/S hybrid forms were seen at each site, ranging from 5% to 42%, and there was a large spectrum of inbreeding coefficient values from 0.11 to 0.76 (spanning most of the range expected between the alternative extremes of panmixia and assortative mating). At a site in The Gambia sampled each month for 2 years, M/S hybrid forms were seen throughout, and a genome-wide scan with an Affymetrix 400,000 single nucleotide polymorphism (SNP) microarray showed marked differentiation between M and S forms only in the pericentromeric region of the X chromosome that contains the molecular form-specific marker locus. Such minimal inter-form genomic differentiation was also seen in such a scan of two other populations, in Senegal and Guinea Bissau. These results clearly indicate that M and S forms are not strongly isolated in this part of Africa.