It’s not often that scientists see the stage in which a species begins to evolve, changing certain traits to better fit into its environment. But Heliconius cydno alithea butterflies of Ecuador are providing this unique opportunity as some of their ranks begin to change their coloration, which may preclude a split into a whole new species.

The butterflies are breaking up into two distinct groups, with different coloration and mate preferences. Some are white, mimicking the coloration of another species in the area, Heliconius sapho.

Others are yellow, mimicking the species Heliconius eleuchia. Each displays a tendency to mate with butterflies of the same color – but white and yellow varieties differ only at the color-determining gene.

"Our paper provides a unique glimpse into the earliest stage of ecological speciation, where natural selection to fit the environment causes the same trait in the same population to be pushed in two different directions," says researcher Marcus Kronforst of Harvard University, whose study was published this week in the journal Science.

"If this trait is also involved in reproduction, this process can have a side effect of causing the divergent subpopulations to no longer interbreed. This appears to be the process that is just beginning among Heliconius butterflies in Ecuador."

Kronforst is hopeful that this research will help shed light on the still-mysterious process of evolution.

"Subsequent work could elucidate exactly how changes in individual genes can, over long periods of time, lead to novel species."