Evolution Selects for Evolvability: Adaptation in Changing Environments

Evolution doesn't operate with a goal in mind, but it does seem to select for evolvability. Scientists have discovered that organisms that have a greater capacity to evolve are likely to fare better in rapidly changing environments, which suggests that evolution may favor characteristics that increase a species' ability to evolve.

In order to take a closer look at evolution, the researchers examined the Lyme disease bacteria, Borrelia burgdorferi. For pathogens to survive over the long-term, they have to possess an ability to rapidly adapt and evolve. This allows them to stay one step ahead of their hosts' immune systems and makes them the perfect subject to look at for this particular study.

B. burgdorferi possesses one protein that is essential for establishing a long-term infection of a mammalian host: VIsE. In the Lyme bacteria's genome, this gene is preceded by "cassettes" which are normally not expressed, or made into individual proteins, but can recombine with the gene to alter the expressed protein and thus present a novel challenge to a host's immune defenses.

Earlier studies have actually suggested that selection may directly favor the capacity to evolve. Yet they weren't able to rule out that evolvability had arisen for other reasons. In the Lyme disease system, the researchers examined the diversity in the unexpressed cassettes, which would not have been the object of direct selection because they would have no known function on their own; they simply exist as a way of increasing potential diversity, and thus evolvability.

"Organisms with greater diversity among the cassettes will have a selective advantage as they will be more antigenically evolvable, or better able to repeatedly generate novel antigens, and thus be more likely to persist within hosts," wrote the researchers in a news release.

The findings reveal a little bit more about evolution. More specifically, they show that evolvability is a favored trait. This, in turn, could tell us a little bit more about the past history of evolution and why various species arose.

"It would be incredibly difficult to demonstrate this for free-living eukaryotic organisms, like humans," said Dustin Brisson, one of the researchers, in a news release. "But we can now say that evolvability can be the object of selection in the face of environmental pressure."

The findings are published in the journal PLOS Pathogens.