Red Queen drives evolution

25 February 2010

What drives evolution? Is it steered by changes in the physical environment or is it the interactions that occur between species that are responsible?

It's a question that has plagued biologists ever since Darwin first proposed his theory of natural selection in 'On the Origin of Species', and now researchers part-funded by the Wellcome Trust may have found some clues - from the bacterial kingdom and the viruses that infect them.

When pairs of species have opposing needs - for instance a host and its virus parasite - they can become locked in an arms race, where an adaptation that improves the chances of one's survival is necessarily detrimental to the other. The other has to evolve a counter-attack just to keep up. And so forms the basis of the 'Red Queen Hypothesis', named after Lewis Carroll's character from 'Through the Looking-glass' who explains to Alice: "here, it takes all the running you can do, to keep in the same place."

This week in the journal 'Nature', a team led by Michael Brockhurst and Steve Paterson from the University of Liverpool provide the first experimental evidence that the Red Queen Hypothesis holds true. Using viruses known as phages that replicate by infecting and killing bacteria, they were able to observe hundreds of generations of evolution in action.

"We found that when left to their own devices, the bacteria evolved to resist the virus which in turn evolved to infect the resistant bacteria, and so on, exactly as the Red Queen Hypothesis predicts," Dr Paterson explained.

The team then switched off evolution on one side, by holding the bacteria in a constant state and providing a fixed target for the virus, to see whether this would affect how fast the virus evolved.

When the bacteria were unable to adapt themselves, the rate of virus evolution slowed down to almost half that seen when the two species were allowed to evolve in tandem. What's more, the team found there was much less genetic variation in the resulting virus populations than those that co-evolved with the bacteria under Red Queen evolution.

"Together, our findings suggest that it is the interactions between species that are the main drivers of evolution. And by causing rapid divergence, they could even lead to speciation itself," said Dr Brockhurst.

Image: Red Queen. Credit: Stephen - Cat Herder on Flickr

Reference

Paterson S et al. Antagonistic coevolution accelerates molecular evolution. Nature 2010 [Epub ahead of print].