Natural selection favours those with a greater capacity to generate genetic variation.
Some gamblers succeed by spiriting cards up their sleeves, giving them a wider range of hands to play. So do some bacteria, whose great capacity for genetic variability helps them evolve and adapt to rapidly changing environments.
Now research on Borrelia burgdorferi, the bacterium that causes Lyme disease, shows that the capacity to evolve can itself be the target of natural selection. The results were published today in PLoS Pathogens1.
“There are other data that suggest that there could be selection on evolvability, but this is the first example where there really aren’t any other confounding answers for the data,” says lead author Dustin Brisson, an evolutionary biologist at the University of Pennsylvania in Philadelphia.
B. burgfdorferi can cause a chronic infection even if its animal host mounts a strong immune response — evading those defences by tweaking the shape and expression of its main surface antigen, VIsE. A series of unexpressed genetic sequences organized into ‘cassettes’ recombine with the VIsE gene, changing the resulting protein such that it escapes detection by the host’s immune system.
“They make a clever case that the variation in these cassettes tells you something about evolvability and the results back up the idea,” says Tim Cooper, an evolutionary biologist at the University of Houston in Texas.
Continue reading the story in Nature.
Image by Lamiot via Wikimedia Commons.
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