Butterflies are uniquely stunning examples of the diversity of patterns and colors organisms can develop in nature. Many species evolve to display these numerous patterns in response to pressures from their environment. Well-camouflaged wings are more likely to go unnoticed by predators, and similarly, non-toxic butterflies with patterns that mimic poisonous species are less likely to be eaten. Thus, individuals with such advantageous physical characteristics can pass on their genetic makeup to subsequent generations, furthering the species’ adaptation to its environment. A long-standing question in evolutionary biology follows: how did all these pattern phenotypes come about, i.e. what genetic changes have led to such variation?

In 2016, scientists had concluded that a gene called cortex was responsible for butterfly wing pigmentation, but a new study has revealed that this is not the case. In a population of mutant butterflies with depigmented yellowish-white wings, scientists found that part of a new gene, termed ivory, had been deleted. To verify whether ivory was actually responsible for the unexpected trait, they decided on a common experimental approach in biology: ‘break’ the gene and see what happens. These days, that’s done using a gene-editing technology called  CRISPR, which specifically targets and removes desired sections of DNA in a genome. Researchers deleted just the first portion of  ivory in five species of butterflies. Resulting individuals showed a striking loss of dark pigment across all areas of the wing, with scales transitioning from black or brown to the eponymous ivory yellow-white color. When authors instead deleted  cortex for comparison in one species, they found no change in pigmentation at all.

Because of its unusual status as a gene that doesn’t code for the production of cellular proteins, ivory had continuously gone unnoticed by previous genome analysis methods, which often exclude such elements based on historical precedent. In reconsidering this bias, this study made great progress towards understanding the sometimes unorthodox ways genetic information can be converted into physical characteristics, while also shedding light on these novel genetic elements’ potential to be powerful evolutionary influencers. 

This research was led by Luca Livraghi, a postdoctoral researcher at George Washington University, working in friendly collaboration with researchers at Duke, Cornell, and the University of Singapore.

Managing Correspondent: Maati McKinney

Press Article: Surprise RNAs solve mystery of how butterfly wings get their colorful patterns (Science)

Original Journal Article: A long non-coding RNA at the cortex locus controls adaptive colouration in butterflies (bioRxiv)

Image Credit:Pixabay/miniformat65