New form of survival of the fittest

Scientists have discovered a new form of survival of the fittest.

Writing in Science, University of Rochester researcher John Jaenike and his colleagues have found a fly species that have evolved to fend off a parasitic worm, using a bacterium as a weapon.

The team have been studying a fly species called Drosophila neotestacea, which frequently falls prey to a parasitic worm (a nematode species called Howardula) that renders female flies infertile.

But, the researchers have found, flies carrying a bacterium known as Spiroplasma are protected from the parasite. Moreover, in 1980, when samples were first collected, fewer than 10% of this fly species in the US were carrying this bacterium. In 2008 that number had grown to 80%.

Incredibly, this paper shows that evolution can move in mysterious ways; rather than the flies having to alter their own genes to fight off a threat, they're effectively borrowing someone else's, by co-opting the bacteria, which presumably olblige their new host by producing factors that suppress the parasite and ensure that the fly remains fertile.

The benefit to the Spiroplasma bacteria is that when the flies reproduce, they also pass this on to their offspring too. Significantly, the scientists also point out that, apart from being academically very interesting, the results may also have therapeutic potential for humans.

A number of common clinical conditions, including elephantiasis and river blindness, are caused by nematode parasites, suggesting that understanding how the Spiroplasma bacteria suppress the fly parasite might offer fresh therapeutic possibilities for humans.