Atala butterflies have retained ancient wing patterns

A growing collection of research suggests that the unique wing patterns found among thousands of butterfly species are all tied to an ancient set of simple ingredients. The latest of these studies, led by the Florida Museum of Natural History, was focused on the rare Atala butterfly.

“Evolution does not just mean change,” said study lead author Andrei Sourakov. “When it stumbles upon successful designs, they stick around, sometimes for hundreds of millions of years.”

In particular, Sourakov set out to test a theory from the 1920s called the nymphalid groundplan, which proposes that butterfly wing patterns are organized around distinct, concentrically arranged bands.

“Rather than a unified composition, butterfly wings are more like a collage created by wing-pattern elements belonging to different symmetry systems,” said Sourakov.

While this basic blueprint has been confirmed in several decades of research, the studies were primarily focused on butterfly species of the Nymphalidae family.

Nymphalids diverged from their closest relatives, the lycaenids, around 90 million years ago. Now, Sourakov wanted to investigate whether lycaenids have maintained the ancient pattern of wing symmetry found in nymphalids. 

“The idea that the nymphalid ground plan applies to the lycaenids, which diverged from nymphalids when the dinosaurs were still around, is a big assumption to make,” explained Sourakov.

The Atala butterfly was chosen for the study for its unique history and its striking color patterns. The Atala is one of the only toxic species in the lycaenid family, and this toxicity is signaled by its bright red abdomen. On the Atala’s bottom wings, two spots of the same red color stand out against black scales and blue spots.

In the early 1900s, Atala butterflies nearly disappeared from their native range in Florida when their host plant was overharvested. Today, the plants and butterflies have been restored. For the study, Sourakov used a colony of Atala butterflies that is preserved at the Florida Museum’s McGuire Center.

Based on an interesting method used in previous studies, Sourakov exposed pupating insects to a blood thinner called heparin. This technique has been found to alter the wings of adult butterflies.

“Wing-pattern elements belonging to the same symmetry systems should react in similar ways to the same treatment,” said Sourakov. “By tweaking the expression of the underlying genes, such experiments allow us to understand the amazing variation that is found in butterflies and help us pinpoint the exact source of that variation.”

The experiment revealed that Atala and nymphalid butterflies shared similar responses to heparin. Depending on the concentration of heparin used, the adult wing spots either expanded, contracted, or faded entirely. 

“Remarkably, there seems to be many similarities between Atala’s wing pattern and the nymphalid ground plan,” said Sourakov. “Future studies will be necessary for determining whether the same genes control the banding patterns and colors of Atala and other lycaenids compared to other butterfly families, but I hope these results have laid the groundwork for further inquiry.”

The study is published in the journal Tropical Lepidoptera Research. 

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By Chrissy Sexton, Earth.com Staff Writer