Malaria mosquitoes’ DNA shows evolving species

Two strains of Anopheles gambiae, a type of mosquito responsible for the majority of malaria transmission in Africa, have evolved such substantial genetic differences that they are becoming different species.

Over 200 million people globally are infected with malaria, according to the World Health Organization, and the majority of these people are in Africa. Malaria kills one child every 30 seconds.

Two Very Different Strains

This international research effort looks at two mosquito strains, known as M and S, which are physically identical but have genetic differences that seem to be prompting them to become different species. This indicates that efforts to control mosquito populations may be effective against one strain of mosquito but not the other. According to these new findings, when researchers are developing new ways of controlling malarial mosquitoes – for example by creating new insecticides or trying to interfere with their ability to reproduce – they now need to make sure that they are effective in both strains.

The authors also suggest that mosquitoes are evolving more quickly than previously thought, implying that researchers need to continue to monitor the genetic makeup of the different strains very closely, in order to watch for changes that might enable the mosquitoes to evade control measures in the future.

"From our new studies, we can see that mosquitoes are evolving more quickly than we thought and that unfortunately, strategies that might work against one strain of mosquito might not be effective against another. 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,” says Imperial College London’s Dr. Mara Lawniczak, a lead researcher involved in the work.

The researchers reached their conclusions after carrying out the most detailed analysis so far of the genomes of the M and S strains of Anopheles gambiae mosquito, over two studies. One study, which sequenced the genomes of both strains, revealed that M and S are genetically very different and that these genetic differences are scattered around the entire genome. Previous studies had only detected a few ‘hot spots’ of divergence between the genomes of the two strains. The work suggests that many of the genetic regions that differ between the M and S genomes are likely to affect mosquito development, feeding behavior and reproduction.

Whole Genome Sequencing

“Sequencing the whole genomes of both mosquito strains was a key step in demonstrating how these seemingly identical insects still had these important differences in their DNA,” says author Dr. Sandra Clifton, former Assistant Director of Genomics at The Genome Institute.

A second study showed that the mosquito strains appear to be evolving differently, probably in response to factors in their specific environments – for example, different larval habitats or different pathogens and predators. This study was the first to carry out such detailed genetic analysis of an invertebrate, using a high-density genotyping array.

The researchers will further explore which variations in mosquito genes affect their propensity to become infected with malaria and other pathogens.

The studies were collaborations between researchers at Washington University’s Genome Institute, Imperial College London, the University of Notre Dame, the J. Craig Venter Institute and the Broad Institute. Funding for the projects was provided by the National Human Genome Research Institute, the National Institutes of Health, the Biotechnology and Biological Sciences Research Council and the Burroughs Wellcome Fund.