Malarial mosquitoes are evolving into new species, say Imperial researchers

Studies show that two strains of malarial mosquito have substanial genetic differences - <em>News release</em>

Imperial College London News Release

Under strict embargo for
14.00 Eastern Time / 19.00 London Time
Thursday 21 October 2010

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, according to researchers behind two new studies published today in the journal Science.

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

Today's 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 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.

Dr George Christophides, one of the lead researchers behind today's work 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 array.

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 pathogens.

Both of the studies published today were collaborations between researchers at Imperial and international colleagues, involving researchers from institutions including the University of Notre Dame, the J. C. 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.

-ends-

For further information please contact:

Laura Gallagher
Research Media Relations Manager
Imperial College London
e-mail: l.gallagher@imperial.ac.uk
Telephone: +44 (0)207 594 8432 or ext. 48432
Out of hours duty Press Officer: +44 (0)7803 886 248

Notes to editors:

1. Study details

a) "Widespread divergence between incipient Anopheles gambiae species revealed by whole genome sequences" Science, 21 October 2010

Lead authors: Mara Lawniczak, Imperial College London and S. Emrich, University of Notre Dame (for full list of authors please see paper)

b) "Complex gene flow boundaries among sympatric Anopheles vector mosquito populations revealed by genome-wide SNP genotyping" Science, 21 October 2010

Lead authors: Mara Lawniczak, Imperial College London and D.E. Neafsey, Broad Institute (for full list of authors please see paper)

2. About Imperial College London

Consistently rated amongst the world's best universities, Imperial College London is a science-based institution with a reputation for exc ellence in teaching and research that attracts 14,000 students and 6,000 staff of the highest international quality. Innovative research at the College explores the interface between science, medicine, engineering and business, delivering practical solutions that improve quality of life and the environment - underpinned by a dynamic enterprise culture.

Since its foundation in 1907, Imperial's contributions to society have included the discovery of penicillin, the development of holography and the foundations of fibre optics. This commitment to the application of research for the benefit of all continues today, with current focuses including interdisciplinary collaborations to improve global health, tackle climate change, develop sustainable sources of energy and address security challenges.

In 2007, Imperial College London and Imperial College Healthcare NHS Trust formed the UK's first Academic Health Science Centre. This unique partnership aims to improve the quality of life of patients and populations by taking new discoveries and translating them into new therapies as quickly as possible. www.imperial.ac.uk