Mosquitoes can’t spot a spermless mate

by administrator on August 8, 2011

A female mosquito cannot tell if the male that she has mated with is fertile or 'spermless' and unable to fertilise her eggs, according to a new study from scientists at Imperial College London.

The research, published today in the journal Proceedings of the National Academy of Sciences, could help scientists in their mission to prevent the spread of malaria by interfering with the mosquitoes' ability to reproduce.

Malaria is a debilitating disease that affects more than 300 million people every year, and kills nearly 800,000 annually. In Africa, a child dies of malaria about every 45 seconds. Public health experts are working towards the eradication of malaria, but there is a recognised need for better and lower cost tools to achieve the eradication goal. The new study focuses on Anopheles gambiae, the species of mosquito primarily responsible for the transmission of malaria in Africa.

Today's results lend support to the idea that in the future it will be possible to control the size of the malaria-carrying mosquito population by introducing a genetic change that makes the males sterile. Such a method would rely on females mating unknowingly with such modified males and failing to produce any offspring. Although researchers are currently working on this solution, nothing has yet been trialled.

This study was carried out thanks to funding by the Medical Research Council in the UK and the European Community FP7 Collaborative Project grant called Malbecblok.

Lead author of the study, Dr Flaminia Catteruccia from the Department of Life Sciences at Imperial College London, said: "In the fight against malaria, many hope that the ability to genetically control the mosquito vector will one day be an key part of our armoury. In order for these currently theoretical control strategies to work, we need to make sure that the insects continue to mate as normal, unaware that we have interfered with their sexual mechanisms. This study strongly suggests that they cannot tell the difference between a fertile and a spermless mate."

Co-author Professor Charles Godfray, from the University of Oxford Department of Zoology, said: "This is an exciting time with modern genetics providing a series of new ideas about how to control the major insect vectors of human disease, including the mosquito Anopheles gambiae - perhaps the single most dangerous insect species for mankind. A number of these techniques involve disrupting natural mating patterns and to get these to work a really good understanding of mosquito mating and reproduction is essential."

After mating for the first and only time in her life, the female mosquito undergoes certain physiological changes, then eats a blood meal and lays a batch of eggs. In the new experiments, the researchers observed that this behaviour was the same regardless of whether or not the mating encounter had produced fertilised eggs that could hatch into mosquito larvae.

The scientists were also surprised to discover that after mating with a spermless male, the female made no attempt to find a supplementary mate, effectively missing out on the opportunity to reproduce and pass on her genes. They expected to find that the species had evolved a mechanism so that females could avoid or bypass sterile males. For example, female fruit flies can mate with more than one male, helping to ensure their eggs are fertilised.

The scientists produced 100 spermless males for the study by injecting ordinary mosquito eggs with a protein that disrupted the development of their testes and prevented them from producing sperm in adulthood. Importantly, this did not interfere with any other sexual function or behaviours in either the female or the male.

They reached their conclusions after isolating mating mosquito couples in the laboratory and closely observing their behaviour and physiology during key stages of reproduction. They tested for the following characteristics in non-fertile mating couples: the males produced functioning seminal fluid, that brought about the same physiological changes in the females; the female laid the same number eggs in the absence of sperm; and the females abstained from sex following their first intercourse, as they do after mating with a fertile male.

For further information please contact:

Simon Levey
Research Media Officer
Imperial College London
Email: s.levey@imperial.ac.uk
Tel: +44(0)20 7594 6702
Out of hours duty press officer: +44(0)7803 886 248

Notes to editors:

1. Journal reference: Thailayil J, Magnusson K, Godfray HCJ, Crisanti A, and Catteruccia F, "Spermless males elicit large-scale female responses to mating in the malaria mosquito Anopheles gambiae" http://www.pnas.org/cgi/doi/10.1073/pnas.1104738108

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 excellence 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.

Website: www.imperial.ac.uk
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Podcast: www.imperial.ac.uk/media/podcasts

3. About Medical Research Council

For almost 100 years the Medical Research Council has improved the health of people in the UK and around the world by supporting the highest quality science. The MRC invests in world-class scientists. It has produced 29 Nobel Prize winners and sustains a flourishing environment for internationally recognised research. The MRC focuses on making an impact and provides the financial muscle and scientific expertise behind medical breakthroughs, including one of the first antibiotics penicillin, the structure of DNA and the lethal link between smoking and cancer. Today MRC funded scientists tackle research into the major health challenges of the 21st century. http://www.mrc.ac.uk

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