The butterfly effect

Tiny changes can make a large difference in the way the world develops. This is known in chaos theory as the “butterfly effect,” a concept that may be easy to understand when it comes to how human behaviors — whether a gesture, a decision, or a habit — can affect other people. But it’s more difficult to grasp on the deeper biological level of cells, proteins, and genes that help individuals within the same animal family — such as different species of butterflies — to differentiate from each other when it comes time to find a mate.

In humanity’s quest to better understand nature, scientists have worked to measure and control genomics to isolate and identify the way genes influence the evolution of various species. The smallest of units — such as genes — are invisible to the human eye, but they can set the course of existence for living things and how individuals within a species relate to each other.

An image of an orange sulphur butterfly with UV photography overlays, revealing bright iridescence in UV colors. Courtesy of Vincent Ficarrotta/The George Washington University.

A group of researchers at The George Washington University (GW) recently set out to establish how creatures — when set apart only by visual cues such as patterns and coloration — recognize their own kind. Using the CRISPR genome-editing technique, the researchers switched off a gene in the wings of two North American butterfly species to switch on their latent ultraviolet iridescence — putting on a lovely light show while helping to explain the evolutionary process by which such species become distinct from one another and are able to breed accordingly.

The researchers looked at the characteristics of the orange sulphur butterfly and the clouded sulphur butterfly. The wings of the male orange sulphur reflect UV light. The wings of the female orange sulphur and the male and female clouded sulphur do not. The team scanned the butterflies’ genomes and found a single dissimilar sex chromosome. Using a high-powered electron microscope, the researchers targeted the chromosome’s “bric-a-brac” gene, which, when expressed, gives rise to the pigmentation of the individual microscopic scales comprising a butterfly’s wings.

When the team switched off the gene that affects the coloration of the wings of the noniridescent butterflies, the nanoscale structure of the scales changed and so did the butterflies’ appearance.

“As evolutionary biologists, we’re interested in identifying and understanding the genes that drive physical differences between species,” said Arnaud Martin, an assistant professor of biology and lead author on the paper detailing the research. “Here, we showed how a single gene determines whether UV coloration is switched on or off in two separate butterfly species. Because the geographic ranges of these two species overlap today, that visual distinction is all the more important when it comes time to find a mate.”

“The CRISPR experiments returned impressive and very shiny results,” said Vincent Ficarrotta, a doctoral student in Martin’s lab and co-first author of the paper. “Upon breaking the [bric-a-brac] gene, I raised butterflies that were now covered in unique patterns of iridescent UV.”

“Our next steps in the research will include looking more closely at how these scales develop their interesting structure and how these scales occur in many species, among a few other ideas,” Ficarrotta said. “We all have different interests in butterfly coloration, so that’s how we will split the experiments.”