Caught in the Act of Evolution: California Stick Insect Evolves in a Similar Fashion

A certain insect in California has been caught in the act of evolving into two separate species. Scientists have taken a closer look at the genome of a Southern California stick bug and have found a bit more about the process of evolution.

"Speciation is the evolutionary process that gives rise to new species, and it occurs when barriers prevent two groups of populations from exchanging genes," said Scott Egan, one of the researchers, in a news release. "One way to study how speciation occurs is to look for examples where partial reproductive barriers exist but where genes are still exchanged."

Fortunately, there are a few examples out there, and the stick insect Timema cristinae is one of them. This insect is closely related to "walking sticks," which are plant-eating insects that look like twigs. Instead of looking like a stick, though, Timema's shape and color allows it to blend into specific plants in California and northern Mexico.

One specific species, T. cristinae, can be found in two distinct variety. One feeds on the thin, needle-like leaves of a shrub; it has a distinct white stripe on its back to serve as camouflage. The other variety has no stripe and instead feeds on a different plant with wide, green leaves; having a stripe would make it stand out.

"Populations of T. cristinae on the two host plants have evolved many differences in their physical form while still exchanging genes," said Egan in a news release. "These same populations have also evolved barriers to gene flow. We call this process 'speciation with gene flow,' and evolutionary biologists have long wondered if the genetic basis for this process is highly repeatable and if the genes involved are spread out across the whole genome or in a few discrete regions."

The researchers conducted genome and ecological tests on these populations of insects. More specifically, they examined which genes were differentiated between populations adapted to different host plants.

So what did the researchers find? It turns out that there were regions of the genome that exhibited significant differences between populations from both of the different plants, regardless of where the individuals were collected. This suggests that evolution was occurring in the same repeatable fashion at each location.

The findings reveal for the first time that genomes of species may evolve in a similar, repeatable fashion. This, in turn, paves the way for future evolutionary studies and reveals exactly how the process of evolution may occur.

The findings are published in the journal Science.