A chemical produced by the male genitals of this tropical butterfly is so repulsive that scientists refer to it as “anti-aphrodisiac.”
New research published today in PLOS Biology describes the genetic foundations of a chemical compound produced by men Heliconius melpomene butterflies. It is a striking example of chemical signage, in which smell is used for communication. In this case, the chemical, called ocimene, “acts as an anti-aphrodisiac pheromone, transferred from males to females during mating to repel more courtship from later males,” the authors write in their article.
Fascinatingly, some plants also produce ocimene, but use it for a different purpose. The new research reveals a unique case of convergent evolution. In addition to identifying the genes of Heliconius melpomene responsible for the production of the chemical, is the first time that scientists document the production of this chemical, a terpene, in an animal.
Consequently, new research dispels the previous belief that Heliconius melpomene ocimene from plants (experiments performed in 2007 he showed that females covered with oxymene were approached less frequently by males than those covered with a control substance). As new research shows, however, these butterflies can make this product on their own.
Members of Heliconius melpomene have an extraordinarily long lifens for butterflies, which live about six months compared to the usual one month. They live in Central and South America and feature a wide range of wing color patterns, depending on its geographical location. These butterflies are toxic, so the patterns act as a warning to potential predators. These patterns also play a role in sexual selection, as butterflies of this species choose pairs that resemble themselves.
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“While patterns have attracted more attention, it has also been observed for a long time that these butterflies smell,” explained Kathy Darragh, main author of the new paper, in an email. “We now know that this odor is related to the protection of the mate, which acts as an anti-aphrodisiac to repel future mating attempts by other males.” Darragh he carried out this research while doing his doctorate at Cambridge University.
Humans are very visual creatures, but many animals depend on the chemical signalas the main form of communication. Orchids, for example, imitator the aroma of female insects to attract males for pollination. Anti-aphrodisiacs have also been documented in other insects, including burying beetles and plant insects.
Butterflies, with their striking colors and patterns, clearly use visual cues to communicate, but that doesn’t mean they don’t use chemicals either. Darragh, now with UC Davis, wanted to investigate how chemical signals can play a role in butterfly communication.
“An interesting aspect of this, which was the focus of the current study, is how butterflies can make these chemicals that they use to sign“In other words, what genes do butterflies have that allow them to make these compounds? And are they the same genes that are used to make these compounds in plants?”
In fact, ocimene is also produced by tropical plants to attract butterflies for pollination (more on this apparent contradiction in a bit). This is an example of convergent evolution, in which two independent species develop a similar trait. What is unique about this finding, however, is that plants and insects use this chemical for different purposes (though still for chemical signaling), and plants and insects use different genetic mechanisms to produce it. In the new article, researchers identified a new gene in Heliconius melpomene responsible for the ocimen, which is unrelated to anything previously described in plants with the same function.
“Ocymene production has evolved independently through different genes in plants and butterflies, demonstrating how different molecular mechanisms can underpin the production of a specific chemical compound,” he said. Darragh. “Independent evolution of the same trait, in this case the production of pheromones, several times, provides a great system to help us understand evolution.”
That plants use ocimene to attract insects, but this butterfly uses it as a repellent, is a strange observation. The authors don’t quite understand why, but they think it may have something to do with how visual and olfactory information work together. In other words, context matters; a butterfly interprets the chemical as attractive when it comes from a plant but as an anti-aphrodisiac when it comes from another butterfly. Darragh said that “the perfume itself does not vary,” but so does the context and therefore how the signal is interpreted. “
All of this is fine, but if a male successfully mates with a female, why should he care about other suitors? The answer is that woman Heliconius melpomene store sperm for months, during this time patiently fertilize the eggs. Subsequent mating episodes would introduce new sperm. This has led to the observed competition between men and to this bizarre arms race involving stinky geniuses.
This becomes even stranger as it creates scenarios in which eager females would love to connect, but males don’t want to have anything to do with them. Think of it as an insectoid version of sexual frustration.
At the same time, however, Darragh believes it can actually benefit women. “Anti-aphrodisiacs can also act as honest signals of receptivity, reducing harassment by males, while females are not receptive to mating,” he said. This is beneficial for both men and women, as “males do not waste time courting non-receptive women and females can reduce harassment by men.”
I think there’s an important lesson for humans here, but I can’t put my finger on it.