Malaria mosquitoes evolve into new species -- Researchers PDF Print E-mail
Tuesday, 26 October 2010 14:04

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

China's Xinhua news agency citing the international research effort, co-led by scientists from Imperial College London, looks at two strains of the Anopheles gambiae mosquito, the type of mosquito primarily responsible for transmitting malaria in sub-Saharan Africa.

These strains, known as M and S, are physically identical.

However, the new research shows that their genetic differences are so substantial that they appear to be becoming different species, so efforts to control mosquito populations may be effective against one strain of mosquito but not the other.

The scientists argue that when the 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 need to make sure that they are effective in both strains.

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

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.

The first 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 suggested that many of the genetic regions that differ between the M and S genomes are likely to affect mosquito development, feeding behavior, and reproduction.

In the second study, the researchers looked at many individual mosquitoes from the M and S strains, as well as a strain called Bamako, and compared 400,000 different points in their genomes where genetic variations had been identified, to analyze how these mosquitoes are evolving.

This showed that the 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.

As a next step in their research, the researchers are now carrying out genome-wide association studies of mosquitoes, using the specially designed genotyping chip that they designed for their second study, to explore which variations in mosquito genes affect their propensity to become infected with malaria and other pathogens.

The two new studies will be published on Friday in US Journal Science.

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.