WHAT: Researchers funded by the National Institutes of Health have found that the major malaria-transmitting mosquito species, Anopheles gambiae, is evolving into two separate species with different traits, a development that could both complicate malaria control efforts and potentially require new disease prevention methods. Their findings were published in back-to-back articles in the October 22 issue of the journal Science.

A. gambiae is the most common vector of human malaria in sub-Saharan Africa, where rates of the disease are highest. The researchers compared the genomes of two emerging species, dubbed M and S. Given that M and S appear to be physically indistinguishable and interbreed often, they were unexpectedly different at the DNA level. They also were found to behave differently and thrive in different habitats. For example, in the absence of predators, S mosquitoes outcompeted M mosquitoes, but the outcome was reversed when predators were present.

As these two emerging species of mosquito evolve to develop new traits and behaviors, changes in disease transmission could result, the authors say. This could complicate malaria control efforts, which currently are based on the mosquitoes' patterns of behavior and vulnerability to insecticides.

Future research will further investigate these emerging species, exploring how they compete with one another in various habitats and the molecular basis of their evolution. The results will be used to refine existing malaria interventions and inform the development of new disease prevention strategies.