London School of Hygiene & Tropical Medicine

There have been concerns in the scientific community that Anopheles gambiae mosquitoes, which are responsible for most cases of malaria in Africa, are splitting into two completely new species. However, a team of researchers led by Professor David Conway at the London School of Hygiene & Tropical Medicine, have found that the different molecular types of Anopheles gambiae have actually been interbreeding with one another resulting in a more complex range of forms.

These hybrids may have implications for insecticide resistance and malaria parasite infectivity. The study documents substantial amounts of hybridisation in a large area spanning four countries in sub-Saharan western Africa.

“Our research shows that Anopheles gambiae mosquitoes, which are responsible for most cases of malaria in Africa, are more genetically complex than we thought due to interbreeding,” said senior author Professor Conway, who carried out the work with the Medical Research Council Unit in The Gambia. “Mosquitoes are very good at evolving quickly and this information will help us use existing control methods appropriately and consider possible new tools that will further malaria control efforts in Africa.”

The scientists collected mosquitoes from houses located within 100 kilometres of the Atlantic coast in Senegal, Gambia, Guinea Bissau, and Republic of Guinea. They characterised the mosquitoes’ DNA to identify the proportions of each major type, “M”, “S”, and hybrid “M/S” forms. Pools of each of the forms of mosquitoes from representative sites were analysed for genome-wide genetic profiles revealing that the genomes, which are known to be different between the forms, are not different in these areas.  That is, the genetic variation that exists is shared between the forms, as if they were a single species.

Commenting on the implications of the new findings, Dr Jo Lines, Reader in Vector Biology and Malaria Control at the School, said: “The biggest practical implication of the study is for insecticide resistance. However, the findings do not necessarily imply that resistance overall will arrive more quickly. We will still be using the same weapons to control these mosquitoes and we won't be tailoring our control measures as a result of this new finding.”

Publication

• Davis C. Nwakanma, Daniel E. Neafsey, Musa Jawara, Majidah Adiamoh, Emily Lund, Amabelia Rodrigues, Kovana M. Loua, Lassana Konate, Ngayo Sy, Ibrahima Dia, T. Samson Awolola, Marc A. T. Muskavitchand and David J. Conway. Breakdown in the Process of Incipient Speciation in Anopheles gambiae. Genetics. doi: 10.1534/genetics.112.148718