Study of Butterfly Wings Offers Proof of Evolution’s Unpredictability

A species of Heliconius, or longwing, butterfly. (Hans Hillewaert via Wikipedia)

(CN) – Heliconius butterflies develop nearly identical wing and color patterns whether they’re in Peru or Costa Rica, and a team of scientists have discovered the reason why.

Heliconius butterflies refer to a group of unrelated butterfly species that have been looked to for decades for lessons in evolution. They are affectionately called longwings, or passion vine butterflies due to the caterpillars’ exclusive taste for passion vine plants. Their bright, colorful wings have splashes of red, orange, yellow, or blue on a black base. Along with the adults’ slow-moving pace, they are very conspicuous in the light of day – but their flashy colors warn bird predators of their protective toxins that make them taste unpleasant.

The males will also don flashy colors to signal females of the same species that they are looking for a mate.

Researchers at the Smithsonian Tropical Research Institute (STRI) in Panama set out to uncover the mystery of how these two factors produce similar wing patterns in groups of butterflies residing in the mountain valleys and foothills of the Andes.

“Our team is the first to report that although evolution of similar color patterns in Heliconius may be driven by similar forces – like predators avoiding a particular kind of butterfly – the pathway to that outcome is not predictable,” said Carolina Concha, lead author of the paper and a post-doctoral fellow at STRI. “This really surprised us because it reveals the importance of history and chance in shaping the genetic pathways leading to butterfly wing-pattern mimicry.”

In their study published Thursday in the journal Current Biology, Concha and her team of 24 other authors from STRI looked for answers in the butterflies’ genes. To achieve this, they removed a single gene called WntA in 12 different species as well as their variants to decipher whether a pair of butterflies with the same wing patterns were using the same genetic pathways to design their wings. Much to the surprise of these scientists, they were not.

“Imagine two teams given the same Lego blocks are asked to build the same device,” said Arnaud Martin, co-author and head of the Butterfly Evo-Devo Lab at George Washington University. “Each team goes about the task in a different way, but in the end, the result is the same. Butterflies face much more serious challenges: they build structures made of wing scales that are essential to their survival and ability to reproduce.”

Butterfly mimicry has baffled scientists for years, and they have lacked the necessary technology to analyze a specific gene. But over the past five years with CRISPR/Cas 9 gene editing, scientists have had more luck studying the genetic codes of organisms.

The technology allowed the team to remove the major patterning gene WntA, resulting in a new pattern displayed on the wings. This occurs because in the absence of this gene, the microscopic structure and color of the scales that compose the butterfly’s wing is altered.

The evidence procured from this study left the researchers with even more questions. Moving forward, the team is curious as to how the gene WntA interacts with other genes to display the colors red or black. The most pressing question on their minds, however, is how the WntA gene is controlled.

“We learned that while a developmental gene (WntA) can have a broad role in the evolution of most butterfly wing color patterns, its precise use to color a butterfly’s wing is not completely predictable,” said Riccardo Papa, co-author and professor at the University of Puerto Rico. “Distinct species with identical wing-color patterns, such as co-mimetic butterflies, can evolve using different molecular strategies. Imagine the same notes played on different instruments!”

Owen McMillan, staff scientist and head of the ecological genomics lab at STRI, offered a hopeful call to action.

“The Smithsonian labs in Gamboa are certainly one of the best places in the world to understand how butterflies evolve, and we hope that inspired researchers will join us here as we continue to ask questions about these incredibly beautiful creatures,” McMillan said.

The Smithsonian Tropical Research Institute, headquartered in Panama City, Panama, is a unit of the Smithsonian Institution. The institute furthers the understanding of tropical biodiversity and its importance to human welfare, trains students to conduct research in the tropics and promotes conservation by increasing public awareness of the beauty and importance of tropical ecosystems.

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