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American Association for the Advancement of Science

Stick bugs show that some evolution is predictable

A stick insect resting upon one of its host plant species.
[Image courtesy of Moritz Muschick]

If we could go back to the beginning of life on Earth—or rewind "the tape of life," as scientists say—would plants and animals evolve exactly the same way they did? Or would it have all gone differently? It's a question that researchers have been trying to answer for a long time.

Now, researchers studying stick insects in California have discovered that at least certain aspects of evolution related to the creation of new species can be predicted and repeated. Victor Soria-Carrasco and his colleagues knew that the stick insect, Timema cristinae, had evolved into two ecotypes, or variations of the same species that were adapted for two different plants. So, the researchers sequenced the genomes of these two different ecotypes to find the genetic differences between them.

They identified regions of the insects' genomes that were becoming more and more different over time, suggesting that the insects were splitting into two different species. But, they say that those genetic changes were due to their locations, rather than the different plants they were living on.

When the researchers transplanted the stick insects from one plant to another, they found evidence that the two ecotypes were becoming more similar in certain ways after just one generation on their new plants. These findings suggest that natural selection can cause two different ecotypes to develop similar traits by making similar genetic changes on their genomes. So, according to the researchers, two very similar species might be able to evolve separately if they were placed under similar environmental pressures.