A chemical produced by the male genitals of this tropical butterfly is so repulsive that scientists refer to it as an “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 signaling, in which perfume is used for communication. In this case, the chemical, called ocimen, “acts as an anti-aphrodisiac pheromone, transferred from males to females during mating to repel further courtship from subsequent males,” the authors write in their paper.
Fascinatingly, some plants also produce ocimen, but use it for another purpose. The new research highlights a unique case of convergent evolution. In addition to identifying the genes in 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 ocimen from plants (experiments performed in 2007 he showed that females covered with ocimen were approached less frequently by males than those covered by a control substance). As new research shows, however, these butterflies can make this chemical on their own.
Members of Heliconius melpomene they have an extraordinarily long lifens for butterflies, which live about six months as opposed to the usual month. I live in Central and South America and features a wide range of wing color patterns, depending on their geographical location. These butterflies are toxic, therefore the patterns act as a warning to future predators. These patterns also play a role in sexual selection, as butterflies of this species choose pairs that resemble themselves.
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“Although the patterns have attracted the most attention, it has long been noticed that the smell of these butterflies,” explained Kathy Darragh, main author of the new paper, in an e-mail. “We now know that this scent is involved in protecting partners, acting as an anti-aphrodisiac to repel other men’s future mating attempts.” Darragh he did this research while doing his PhD at Cambridge University.
Humans are very visual creatures, but many animals depend on the chemical signalas the main form of communication. Orchids, for example, imitate the scent of female insects to attract males for pollination. The anti-aphrodisiac has 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. Darragh, now with UC Davis, wanted to investigate how chemical signals can play a role in butterfly communication.
“An interesting aspect of this, which has been at the heart of the current study, is how butterflies can produce these chemicals that they use as a sign.ling, ”she said. In other words, what genes do butterflies have that allow them to produce these compounds? And are the same genes used to produce these compounds in plants? ”
Indeed, ocimen is also produced by tropical plants to attract butterflies for pollination (more about this apparent contradiction in just a little). This is an example of convergent evolution, in which two independent species evolve a similar trait. However, what is unique about this finding is that plants and insects use this chemical for different purposes (although still for chemical signaling) and plants and insects use different genetic mechanisms to produce it. In the new work, the researchers identified a new gene in Heliconius melpomene responsible for ocimen, which is not related to the genes described above in plants with the same function.
“Ocimen production has evolved independently through different genes in plants and butterflies, demonstrating how different molecular mechanisms may underlie the production of a specific chemical compound,” he said. Darragh. “The independent evolution of the same trait, in this case the production of pheromones, several times, provides an excellent system to help us understand the evolution.”
The fact that plants use ocimen to attract insects, but this butterfly uses it as a repellent, is a strange observation. The authors do not fully understand why, but I 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 a factor of attraction when it comes from a plant but as an anti-aphrodisiac when it comes from another butterfly. “The smell itself does not vary,” Darragh said, “but the context and therefore the way the signal is interpreted, yes.”
All of this is good and good, but if a man successfully mates with a female, why should he care about other suitors? The answer is that the woman Heliconius melpomene store semen for months, during which time he patiently fertilizes his eggs. Subsequent mating episodes would introduce new sperm. This has led to observed competition from man to man and to this bizarre arms race involving stinking genitals.
This becomes even stranger, as it creates scenarios in which eager females would very much like to connect, but males have nothing to do with them. Think of it as an insectoid version of sexual frustration.
At the same time, however, Darragh believes it can actually work to the benefit of women. “Anti-aphrodisiacs can also act as honest signals of receptivity, reducing harassment by men, while women are not receptive to subsequent mating,” she said. This is beneficial for both men and women, as “men do not waste time courting unresponsive females, and women can reduce harassment by men.”
I feel like there’s an important lesson here for us humans, but I can’t really put my finger on it.