Evolution is Surprisingly Predictable: Specialization isn't so Special
Different species can have surprising and unusual adaptations; but in the end, evolution and the resulting species diversity is surprisingly predictable. Now, a new study proves it. Scientists used separate populations of E. coli to show that evolution may not be as unique as we might expect.
Published in the journal PLOS Biology, researchers watched separate populations of the bacteria evolve in different environments over more than 1000 generations. Conducted by Matthew Herron and Michael Doebeli, the experiment involved three different populations total.
At the start of the experiment, the two researchers saw that each of the populations mainly consisted of generalists that competed for two different sources of dietary carbon (glucose and acetate). After 1200 generations of the bacteria, though, the bacteria evolved into two coexisting types of "species," each of them specializing and adapting to eat only one of the carbon sources.
In order to slow down and examine this evolution, researchers froze populations of the bacteria at 16 different points and then sequenced the genomes. Recent advances in sequencing technology allowed the scientists to sequence large numbers of whole bacterial genomes.
They found that, surprisingly, there were quite a few similarities in the evolution. In all three populations, a core set of genes were causing the two different phenotypes that they saw. In fact, in a few cases the researchers witnessed the same exact genetic change. Their research showed evidence that there was predictability in evolutionary diversity. Seeing the same exact changes in different populations showed that, surprisingly, selection can be deterministic.
So why is this the case? The scientists believed that a particular form of selection, known as negative frequency dependence, played an important role when it comes to evolution--at least in the E. Coli. The idea is that when there are limited resources available, a species that specializes in an alternative resource will have an advantage; for example, the bacteria each specialized in consuming a particular food source.
While interesting, there still need to be more experiments conducted to see if this theory holds true on a larger scale. Fortunately, the two researchers are looking forward to further testing. They hope that similar experiments in larger organisms will soon be possible. Until then it seems that, at least for the bacteria, evolution isn't as unpredictable as we once thought.