Butterfly Species Sprays Mate With Anti-Aphrodisiac to Ward Off Competition

The anti-aphrodisiac the male Heliconius melponene sprays the female butterfly with after mating smells like flowers.

The Heliconius cydno butterfly (left) and the Heliconius melpomene (right) are photographed mating in captivity. (Credit: Luca Livraghi)

(CN) — The evolution of certain traits and behaviors throughout wildlife typically stems from the natural interplay between plants and animals. Butterflies, however, evolved a pheromone entirely independent of its presence in the plants the insects feed on, according to a study released Tuesday.

In the animal kingdom, insects and plants use self-produced chemicals — often built from the same compounds — to communicate and compel certain behaviors. 

Orchids, for example, produce a scent mimicking the aura of female insects in order to attract male pollinators. The scent which aids in attracting pollinators, (E)-beta-ocimene — a 10-carbon chemical compound, or terpene — is produced by many plants.

While a variety of fungi and microorganisms also produce terpenes through biosynthesis, only a few insect species including the tropical butterfly Heliconius melponene have been shown to create their own chemical compounds.

The male Heliconius melponene produces ocimene in its sex glands and passes it onto females during mating. Once attached to the female, the chemical acts as an anti-aphrodisiac, signaling to other potential mates that the female is unavailable.

University of California at Davis researcher Kathy Darragh and colleagues set out to research how the Heliconius melponene creates the pheromone and examine the ways in which insects and plants converge on the evolutionary timeline of its production.

The team began by closely examining the butterfly’s genome and the regions of genetic code associated with ocimene production, according to the University of Cambridge-based study.

Researchers analyzed genes that were stimulated by receptors and then inserted them into the bacterium E. coli to further understand the gene’s function.

The process identified two novel terpene synthase enzymes, including one that produced ocimene, that were unrelated to compounds found in other plants and animals.

The case is the first instance of ocimene synthase identified in any animal and shows the development of a gene family from an ancestral gene, according to the study published Tuesday in the open-access journal PLOS Biology.

Researchers concluded the Heliconius melponene produced the pheromone in an independent evolutionary process.

Darragh said in a statement released with the study she and her colleagues were excited to analyze the evolution of butterflies’ genes and traits.

“The results of our study indicate that the existence of (E)-beta-ocimene in these butterflies is due to an independent and convergent evolutionary event, unrelated to the existence of the same compound found in many of the plants these butterflies feed on,” Darragh said. “The same gene is responsible for the divergence between two closely related species in their anti-aphrodisiac pheromone signaling, a key aspect of their mating ecology.”

Researchers plan to study the genetics of a related butterfly species called Heliconius cydno, which doesn’t produce ocimene, Darragh said. 

“In Heliconius butterflies, there are other closely related species pairs which differ in their production of ocimene,” Darragh said. “We hope to study these other pairs to see whether changes in ocimene production is associated with similar types of genetic changes as found in our current study.”

Researchers did not immediately respond to a request for further comment on the study.

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