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Everywhere we look in the natural world, there is evidence of natural selection: the resin armor of a lodgepole pine cone evolved to defend itself against seed-hungry birds and squirrels, or a giraffe’s long neck was evolutionarily favored to reach high vegetation that the competition cannot touch. Natural selection is known to shape the way animals, plants and other organisms evolve and adapt. But does natural selection also affect an organism’s own ability to evolve? And if so, to what extent?
The group under strong selection won the “evolution race”
A new study, published in Science, suggests some surprising answers to this question. A team of researchers led by Andreas Wagner of the University of Zurich (UZH) and the Santa Fe Institute subjected populations of a yellow fluorescent protein from a marine invertebrate transferred to E. coli enterobacteria to strong and weak selection pressure to find which improves evolution more effectively. The evolutionary goal of the experiment was to make the protein populations evolve from yellow to green fluorescence. The results showed that the highly selected group won the “race to evolution”, because those populations underwent mutations that made them more robust and therefore more able to evolve.
“To our knowledge, this is the first experimental evidence that selection can drive the ability to adapt in a Darwinian sense and increase evolvability itself,” says Wagner. “There are still people who wonder if evolution is real. But let’s not just look at fossils for which we have historical documentation. We observe the evolution directly in the laboratory. “
Strong selection increases robustness
Until now it has been widely assumed in the field of evolutionary biology that weak selection provided an advantage to an organism’s ability to evolve. But now the research team was able to show that proteins under strong selection accumulated mutations that increased their robustness to a greater extent than those under weak selection. Indeed, increased robustness of proteins is a key requirement for evolutionary success.
“This discovery was a real surprise because it showed that selection for fitness does not conflict with selection for robustness, which contrasts with previous work,” says first author Jia Zheng of UZH. “While most mutations encountered by proteins impair their stability or ability to assume their correct spatial shape, mutations that enhance robustness actually mitigate such deleterious effects. Robust proteins have a better chance of functioning and thus evolving new traits. “
There is no need for controversy
Wagner hopes the findings will help resolve the long-standing controversy over whether the very evolution of an organism can evolve. “Until now, some scientists thought that natural selection on evolvability doesn’t have to be very straightforward – it has to be overridden by selection on fitness,” he says. “But now we have an example where they both go hand in hand. In other words: there is no need for this controversy. “
Literature:
Jia Zheng, Ning Guo, Andreas Wagner. Selection enhances protein evolution by increasing mutational robustness and foldability. Science. Doi: 10.1126 / science.abb5962
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