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Death to all males
A bizarre bug has developed some extraordinary powers, writes Roger Highfield from London.
Imagine an infection that murders males, triggers virgin births and turns boys into girls. Feminist fantasy? Misandrist propaganda? Science Fiction? No. This is science fact.
Welcome to the bizarre world of Wolbachia, the gender bender, widowmaker and slayer of males, a bacterium which is of fascination, even obsession, to scientists because of the insights it provides into sex, parasitism and disease.
The creature was found lurking in the reproductive tissues of a mosquito in 1924. In the past few years it has emerged that the bug exerts extraordinary influence in nature by its ability to warp the sex ratio.
Wolbachia toy with the sex lives of an estimated 20 per cent of all insect species, from wasps and butterflies to ladybirds. The bugs also hang out in crustacea, such as woodlice, and in nematodes, a class of primitive worms that infects many organisms such as insects, plants and people.
In the past few weeks, European scientists decided that Wolbachia is important enough to justify an effort to unravel the genetic code of several strains, after the first international conference dedicated to the strange creature was held in Crete. "They are phenomenal," said Dr Mike Majerus of Cambridge University, one of the delegates. "They are being taken extremely seriously in a wide range of fields."
Wolbachia can decide who its host mates with. Infected males can make females sterile (leaving partners infected with the same Wolbachia alone). The bugs can eliminate the need for males by triggering virgin births. They can turn genetic males into females. Indeed, they are so influential that it has been suspected they help shape the development of new species.
Dr Majerus, working with Dr Francis Jiggins and Dr Greg Hurst at the University of Cambridge, was the first to document the male-murdering tendencies of Wolbachia. "A female produces both male and female embryos but the bacterium kills all the male ones," said Dr Majerus. "Their daughters eat their dead sons, so you have fratricidal cannibalism."
Wolbachia survives and spreads because it benefits the female population. In response, infected species alter their behaviour. In studies of African butterflies, Dr Majerus and Dr Jiggins observed that females can no longer afford to be choosy after Wolbachia has decimated the local supply of potential mates: they form swarms or "leks" with the sole intention of luring the few males that are left. In females, this behaviour is almost unheard of - it is the males that usually hang about in packs looking for action.
Wolbachia's anti-male tendencies stem from where it likes to live - in the cytoplasm, the jelly inside a cell. While eggs are big, and contain a cytoplasm, sperm do not. Thus, Wolbachia is maternally inherited. That is why Wolbachia loves females and hates males to the point where it has developed various strategies to eliminate them.
They can disturb the careful choreography that brings together the sperm's chromosomes with the egg's during fertilisation. Through so called "cytoplasmic incompatibility", they ensure that infected males and uninfected females have no offspring. They can "feminise" an embryonic wood louse that is genetically male by disrupting masculinising hormones.
Such unbridled feminism is performed by so called "ultraselfish" Wolbachia which aid their own transmission by harming some of their hosts, the poor males, while helping others, the lucky females. But there are other types of Wolbachia that are benign.
Something along these lines may even live in us. Wolbachia is a member of a family called the Rickettsiaceae, one that probably includes the ultimate beneficial infection: its small members are related to mitochondria, the subcompartments of our cells that act as batteries.
Although it cannot be proved, it is thought that mitochondria - which have their own genetic code - may be the simplified descendants of something like Wolbachia that infected the cells of one of our ancestors hundreds of millions of years ago.
Fortunately, male-killing Wolbachia do not infect humans. Or at least Dr Majerus does not think so, after playing with them for a decade. But Wolbachia do infect some of the organisms that infect us, notably parasitic nematode worms, and this recognition has offered new avenues to defeat a debilitating disease that afflicts more than 17 million people, mainly in sub-Saharan Africa.
Onchocerciasis, better known as river blindness, is caused by a worm called Onchocerca volvulus. The parasite is spread by blackflies which breed in rivers and deposit the larvae of the O. volvulus worm into any person they bite. Infection results in severe itching, disfiguring lesions, and eye damage that can lead to blindness.
At present, there is no safe drug that can be used to fully treat river blindness. But scientists from Germany and Cameroon, working with Professor Sandy Trees of Liverpool University, have discovered for the first time that killing Wolbachia packed in the worm tissues leads to the death of the worm. Rather than being a parasite, the bugs are "beneficial endosymbionts". "It appears that these bacteria are essential to the worm and the worm is essential to them," said Professor Trees.
In a paper published in the Royal Society's Proceedings: Biological Sciences, Professor Trees and his colleagues found that the most closely related parasite to the O. volvulus worm eventually died after the bacteria living in it were wiped out by ordinary antibiotic treatments of tetracycline over long periods.
While the successful worm-killing therapy in this paper was observed in cows, Professor Trees believes that similar antibiotic treatments could be just as effective in eliminating the infection in people. "This is an important step in finding a cheap and safe way of curing the infection," he said.
In elephantiasis, a nematode disease prevalent in Africa, Asia and the Pacific, treatment with drugs which are active against the worms can provoke life threatening side-effects so that they are dangerous to use. It is thought these effects may be due to a sudden release of Wolbachia from dead worms. Now the work on river blindness suggests it may be possible to slowly get rid of the bacteria by antibiotic treatment without causing harm to the patient.
While conventional antibiotic treatments last a few days, the worms are killed by courses spread over several months. Human trials are now planned by the World Health Organisation in Ghana, revealing how an apparently arcane scientific fascination, in this case with Wolbachia the widowmaker, can have an impact on the lives of ordinary people.
The Daily Telegraph
Posted to slurp bandwidth and contest those blistering bandwidth users who insist on being moreish & boreish, just like nematode noodles soup - bland and primeordial sludgeish.
Regards from the bog Down Under
-- Pieter (email@example.com), July 06, 2000
Rather than being a parasite, the bugs are "beneficial endosymbionts".
Anybody else think immediately of Judzia DAX?
Pieter this is really fascinating stuff. Thank you.
-- Bingo1 (firstname.lastname@example.org), July 06, 2000.
An obvious Creationist plot to stop evolution.
Will follow this closely and report back.
-- Carlos (email@example.com), July 06, 2000.
"Comment: Posted to slurp bandwidth and contest those blistering bandwidth users who insist on being moreish & boreish, just like nematode noodles soup - bland and primeordial sludgeish."
This was the most interesting thing I read on this forum today, Pieter. Please post more to slurp bandwith. Reproduction [to ME] is a fascinating topic. I suppose it has something to do with the female calling the shots, eh? Think about it. The female praying mantis bites off the head of the mating male. The black widow spider kills the mating male. The Wolbachia goes even beyond those examples. Ah...the matriarchy of it all. [grin] I've said it before, but I'll say it again: Human males lost their evolutionary advantage with successful cloning, not to mention the precursing sperm banks. Could it be that this is what was meant by the "meek will inherit the earth?"
-- Anita (Anita_S3@hotmail.com), July 06, 2000.
-- Lars (firstname.lastname@example.org), July 06, 2000.
Excellant Pieter. Good work.
Anita, hey, calm it down, now. There is still room for both genders, and for heterosexual females-IT-still feels good.
-- FutureShock (email@example.com), July 06, 2000.