‘Nature, red in tooth and claw’

by jelleprins

Scientists reveal driving force behind evolution

[Via Eureka! Science News]

The team observed viruses as they evolved over hundreds of generations to infect bacteria. They found that when the bacteria could evolve defences, the viruses evolved at a quicker rate and generated greater diversity, compared to situations where the bacteria were unable to adapt to the viral infection. The study shows, for the first time, that the American evolutionary biologist Leigh Van Valen was correct in his ‘Red Queen Hypothesis’. The theory, first put forward in the 1970s, was named after a passage in Lewis Carroll’s Through the Looking Glass in which the Red Queen tells Alice, ‘It takes all the running you can do to keep in the same place’. This suggested that species were in a constant race for survival and have to continue to evolve new ways of defending themselves throughout time.

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I hate interesting press releases that contain no link to the paper itself. Luckily, the lab’s website is totally up to date (a short search revealed thanks to Google) and not only had the paper listed but also a link.

Antagonistic coevolution accelerates molecular evolution is a great title. What they showed is that organisms do not evolve simply due to environmental conditions (i.e. climate), but also are under tremendous pressure from every other organism in the same environment. Whether it is infectious organisms, predators or simply those that want to eat the same foods, the species that have the greatest chance for survival are those that have the greatest diversity, allowing them to respond to all the different pressure of natural selection.

The greatest diversity occurs when the organism is under direct pressure by other organisms. Without this selective pressure, overall diversity is greatly reduced, decreasing the ability of the population to respond to changes.

Thus, in this very specific experimental set up, when only the virus could evolve, its genetic responses were less robust than when the bacteria could also evolve. Then the virus had to keep finding new ways around the protection that the bacteria kept coming up with – the Red Queen’s Race. In order to just keep surviving, the population had to constantly change.

This constant struggle to overcome bacterial changes actually resulted in a viral population that was able to get around many different barriers the bacteria could erect.

Sequencing the viral DNA at different points revealed that these changes were actually selective in nature and not simply some sort of demographic or global change. such as more rapid generation time or higher mutation rates.

Under these conditions, the viral population developed much larger genetic diversity. They evolved at twice the rate as those that did not have to respond to changes in the bacteria. And the genes in the virus that showed the greatest diversity were those involved with infecting the bacteria.

Importantly, the paper showed that this diversity produced by the coevolution of viruses and bacteria allowed the resulting viral populations to infect a wide range of bacterial mutants. No matter what barriers the bacteria erected, there were always some number of viruses in the population that could still infect.

In contrast, the viruses that simply evolved by themselves were totally unable to infect any of the bacterial mutants.

Thus, having to fight with a metaphorical tooth and claw, actually made the viral populations more fit and more able to survive whatever the bacteria could come up with.

This is a nice real world example of something that had been postulated several decades ago. It should also have some impact on our use of anti-viral medications or antibiotics.

Not only could we be selecting for organisms that can get around some of the barriers we erect, we are possibly creating populations that can get around all the barriers we could erect.

Anyone who thinks a single anti-disease approach will always work is looking at the world too simplistically. We will always be fighting. If we ever have to stop, it would make us actually less able to deal with new infectious agents,

The fight is what makes us better.