Butterflies Reveal Evolution of a New Species May Not be so Difficult

What do butterflies tell us about evolution? It turns out that they can reveal quite a bit about the process. By studying the full genome sequences of 32 Heliconius butterflies, scientists have found that the evolution of new species might not be as hard as it seems, even when diverging populations remain in contact and continue to produce offspring.

"The butterflies have performed a beautiful natural experiment for us that lets us address important questions about evolution," said Marcus Kronforst, one of the researchers, in a news release. "Even as biologists, we often think of the origin of new species as a moment in time when a new species splits from an old one, and this type of thinking is reflected in the evolutionary 'trees,' or phylogenies that we draw. In reality, evolution is a long-term process thatp lays out in stages, and speciation is no different."

In order to learn more about the process of evolution, the researchers compared closely-related, interbreeding species of butterflies. They found that the initial divergence between butterfly populations is restricted to a small fraction of the genome. In the case of the butterflies, the key genes are those involved in wing patterning, which is important for mating behavior and predator avoidance.

"We find that only a small fraction of the genome is markedly different between closely related species, but then much more of the gnome--more than you'd expect--shows similar differences between more distantly related species," said Kronforst in a news release. "That indicates that the genetic changes that are important for causing speciation are tightly clustered early in speciation, but not so later on in the process; the overall pattern of genome divergence starts slow and then skyrockets."

In fact, the process is a bit like a tug-of-war between natural selection and gene flow. In the case of the butterflies, the result has been a rapid divergence of species, driven by a combination of new mutations and borrowed genes. The butterfly genomes also show that the same spots in the genome have been important in multiple speciation events.

"Beyond butterflies, it is possible that this type of speciation, in which natural selection for ecology causes the origin of new species, has been important for the evolution of other organisms," said Kronforst in a news release.

The findings reveal a little bit more about the process of evolution. More specifically, it shows how related species can quickly diverge into many different ones. This is important for understanding the history of how various species emerged in the past.

The findings are published in the journal Cell Reports.