Malaria mosquitoes rapidly evolving into new species
22 Oct 2010
Genetic analysis of the two strains of mosquito responsible
for the majority of malaria transmission in Africa has found that they
have evolved such substantial genetic differences that they are becoming
The research, co-led by scientists from Imperial College London,
looked 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
such 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 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.
Professor George Christophides, one of the lead researchers
behind today's work and from the Division of Cell and Molecular
Biology at Imperial College London, said: "Malaria is a deadly
disease that affects millions of people across the world and amongst
children in Africa, it causes one in every five deaths.
"We know that the best way to reduce the number of people who
contract malaria is to control the mosquitoes that carry the
disease. Our studies help us to understand the makeup of the
mosquitoes that transmit malaria, so that we can find new ways of
preventing them from infecting people."
Dr Mara Lawniczak, another lead researcher from the Division of
Cell and Molecular Biology at Imperial College London, added: "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."
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 behaviour, 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 analyse 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
As a next step in their research, the Imperial 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
1. M Lawniczak, S Emrich et al. Widespread divergence
between incipient Anopheles gambiae species revealed by whole genome
sequences. Science, 21 October 2010.
2. M Lawniczak, DE Neafsey et al. Complex gene
flow boundaries among sympatric Anopheles vector mosquito
populations revealed by genome-wide SNP genotyping. Science,
21 October 2010.
Both of the studies, published in the journal
Science, were collaborations between researchers at Imperial
and international colleagues, involving researchers from
institutions including the University of Notre Dame, the JC Venter
Institute, Washington University and the Broad Institute. Funding
for the projects was provided by the National Human Genome Research
Institute, the National Institutes of Health, the BBSRC, and the
Burroughs Wellcome Fund.