How did leaf-like Kallima butterflies get so good at camouflage?

Kallima butterflies are experts at disguise. When open, their wings feature bright oranges, blues and blacks – but when closed, they look like dead leaves.

The mimicry has made butterflies in the genus (also called oak leaf butterflies) a sterling example of natural selection. Now, researchers have found the gene responsible for their camouflage – shedding more light on how they evolved.

“Butterfly wings have relatively simple structures, but this simple structure is responsible for some very complex functions: locomotion, thermoregulation, mate preference, and predator avoidance,” says Professor Wei Zhang, a butterfly researcher at Peking University, China, and senior author on a paper describing the research, published in Cell.

“Because these wings are structurally simple but functionally complex, I think butterfly wings are the ideal system to address multiple evolutionary questions,” she says.

The researchers sequenced genomes – the entire DNA sequence – from 36 butterflies in the genus Kallima, representing over half a dozen species and subspecies.

For comparison, they sequenced genomes from 105 other butterfly samples, all from the Nymphalidae family.

They found one gene – called cortex – which seems to be responsible for the leaf patterns on Kallima wings.

“This leaf wing polymorphism has been maintained in multiple Kallima species, but different species may have different phenotype frequencies,” says Zhang. (A phenotype is an observable characteristic, for example size or colour.)

“I think this is due to the proliferation of specific plants in particular habitats, so the butterflies will gain more protective benefits by having different frequencies of wing phenotypes.”

They also found that Kallima butterflies were much more genetically diverse in the eastern Himalayas. This suggests that they dispersed from there to their other current habitats, in East and Southeast Asia.

“We generally focus on biodiversity at a macroevolutionary level,” says Zhang. “But we seldom have cases that illustrate in detail how species’ diversity and genetic diversity originated in such a diversity hotspot.”

Next, the researchers are keen to see how the butterflies’ wing patterns are linked to local plant life.

“We would like to understand how these genes facilitate, and originated, such beautiful diversifying wing patterns,” says Zhang.