By any other name, the Anopheles gambiae mosquito would still bear—with its tiny buzzing wing beats—the deadly threat of malaria, which can be passed to humans in a single blood-sucking bite. But what if this species were to split in twain?
Two new studies, published online October 21 in Science, have found evidence that A. gambiae, which is one of the major carriers of the malaria parasite in sub-Saharan Africa, is evolving in two directions. The species has long been known to consist of several different subtypes of closely related mosquitoes. After careful genetic analysis, it appears that the Mopti (M) and Savanna (S) varieties of this insect might be on a path to become distinct species.
The two types are physically and developmentally "indistinguishable"—they have been observed "even flying in the same mating swarms," noted the researchers of one study. Only genetic differences reveal a difference between them.
"We can see that mosquitoes are evolving more quickly than we thought," Mara Lawniczak, of the Division of Cell and Molecular Biology at the Imperial College London and co-author of the first study, said in a prepared statement. She and her colleagues studied the genomes of the two varieties and detected more genetic differences between the two strains than would have been expected given their frequent geographical overlap.
The second group of researchers compared key genetic differences between these two A. gambiae types (in addition to the Bamako strain, which falls into the S subtype). Their study found that, based on genetic sites that seemed to have changed the most, the mosquitoes might be diverging in part due to habitat differences.
"It's important to identify and monitor these hidden genetic changes in mosquitoes if we are to succeed in bringing malaria under control by targeting mosquitoes," Lawniczak said. Some 247 million people were infected with malaria as of 2008, according to the World Health Organization, and it is implicated in about one million deaths each year.
"Unfortunately, strategies that might work against one strain of mosquito might not be effective against the other," Lawniczak said. Nevertheless, a more refined picture of mosquito genetic makeup—and mutation—could lead to more targeted intervention in the future.
"Our studies help us to understand the makeup of the mosquitoes that transmit malaria," George Christophides, also of Imperial College London and co-author of the first study, said in a prepared statement. And that, in turn, they hope will help them "find new ways of preventing them from infecting people."
Image of two types of Anopheles gamiae mosquito courtesy of Jim Gathany/CDC