The major malaria-transmitting mosquito species in Africa is evolving into two different species, each able to better exploit differing habitats.

That could mean the need for new efforts to prevent and control malaria, a disease that kills an estimated one million children under the age of 5 a year in Africa – one every 30 seconds.

Writing in this week's edition of the journal Science, researchers present two papers looking at Anopheles gambiae, the mosquito that is the most common carrier of malaria in sub-Saharan Africa.

What they found was that the mosquitoes are diverging into two different incipient species, which are called M and S forms. Though physically indistinguishable and able to interbreed, their DNA is becoming more and more different. The two proto-species behave differently and thrive in different habitats.

The mosquito is very adaptive, living happily in coastal rain forests to dry savannas. It's able to do that because its chromosomes carry a lot of variation, says Nora Besansky, a professor of biology at Notre Dame University in South Bend, Indiana and an author on both of the papers.

The proto-species M is typically found in association with more permanent bodies of water, often connected to human agricultural activities such as irrigated rice fields. It faces lots of predators but a longer-lived aquatic habitat. These can be found in dry parts of Africa even during the dry season, making M a new invader into areas that previously hadn't seen as much mosquito activity, at least during the dry season.

"What that means in terms of disease transmission is that malaria is found in drier places and drier seasons that it normally would," says Besansky.

The S type, on the other hand, is adapted to small, short-lived bits of water. On a dirt road full of ruts, the rainy season can bring innumerable puddles and S readily breeds there.

The advantages for S is that there are few predators in those environments. The disadvantages are that the puddles don't last long. Unfortunately, "it's adapted to breed very fast and get out of the puddle before it dries up," says Besansky.

These proto-species are physically indistinguishable and can still interbreed but are becoming more distinct.

The discovery that the one species is beginning to differentiate highlights the need for more research into this ancient and still-deadly human scourge, says Besansky.

"We need to understand the genetics of these mosquitoes, we're still incredibly ignorant."

On a positive note, the sequencing of the mosquito genomes gives "a blueprint to what makes them different, hopefully guiding us to a better understanding of their unique behaviors and physiologies, from which we can design novel and specific malaria interventions," she says.

By Elizabeth Weise