Lookalike butterflies use hidden cues to identify each other

In the dense forests of Central and South America, a strange thing happens. Hundreds of butterfly species – most of them nearly identical in appearance – flutter through the trees, each warning predators that they’re toxic through shared colors and patterns.

But if the butterflies all look the same, how do they find the right partner to mate with? New research reveals that these butterflies can smell each other.

Even among species that look nearly identical, each one produces a unique scent. This tiny chemical difference is how they tell each other apart.

Genetics of glasswing butterflies

The research was conducted by an international team of scientists led by the Wellcome Sanger Institute.

The team sequenced the genomes of dozens of glasswing butterfly species – specifically focusing on two groups known for rapidly forming new species.

Glasswing butterflies are not rare. There are more than 400 species across Central and South America, and many live in the same areas.

These butterflies are often used in conservation as “indicator species” because their presence reflects the health of the broader insect ecosystem.

Lookalike butterflies have a strategy

What makes things tricky is that all glasswing butterflies look strikingly alike – and this similarity is no accident. It’s a defense strategy that warns predators they’re poisonous.

But while this mimicry helps protect them, it poses a serious challenge for scientists trying to identify or monitor them in the wild.

To solve this, the research team mapped the genetics of the butterflies. In doing so, they discovered six subspecies were actually distinct enough to count as separate species.

The experts also produced ten high-quality reference genomes now freely available to the research community.

Scent matters for glasswing butterflies

One major discovery: even butterflies that look the same can still recognize their own species through pheromones – chemicals they release to communicate through smell.

This matters a lot for mating. Because many of these butterflies have gone through a process called rapid radiation – where lots of new species evolve in a short period – they’re often closely related.

Visually, the butterflies are often indistinguishable. But smelling different? That’s a game-changer.

“Having the reference genomes for the two groups of glasswing butterflies, Mechanitis and Melinaea, allowed us to take a closer look at how they have adapted to life in such close proximity to their relatives,” said study senior author Dr. Caroline Bacquet.

“These butterflies share the responsibility of warding off predators by displaying similar color patterns, and by producing different pheromones they can successfully find mates and reproduce.”

“Now that we have clarity on glasswing butterfly species, we can look for specific markings or differences between them, giving new ways to track them during fieldwork.”

Butterflies that evolve quickly

The team also uncovered something surprising in the butterflies’ DNA. Most butterflies have 31 chromosomes, but in glasswing species, that number varied from 13 to 28.

The genes were mostly the same, but they were rearranged in different ways – a phenomenon called chromosomal rearrangement. These rearrangements aren’t just quirky genetic facts. They affect reproduction.

When butterflies with mismatched chromosome arrangements try to reproduce, their offspring are sterile. That means mating with the wrong species is a dead end. So, the butterflies have evolved to rely on pheromones as a way to ensure they choose the right partner.

Scientists think this high level of chromosomal rearrangement might be a key reason why these butterflies evolve into new species so quickly.

Protecting lookalike butterflies

Once a population’s chromosome count shifts, it effectively becomes its own species, better able to adapt to local environments or food sources.

“Glasswing butterflies are an incredibly adaptive group of insects that have been valuable in ecology research for around 150 years,” said Dr. Eva van der Heijden, first author of the study.

“However, until now, there was no genetic resource that allowed us to robustly identify different species, and it is difficult to monitor and track something that you can’t identify easily.”

“With this new genetically informed evolutionary tree, and multiple new reference genomes, we hope that it will be possible to advance biodiversity and conservation research around the world, and help protect the butterflies and other insects that are crucial to many of Earth’s ecosystems.”

Understanding how new species evolve

Understanding how these lookalike butterflies evolved – and continue to evolve – could help scientists tackle broader questions.

Why do some insects branch into many species while others don’t? How do environmental pressures drive rapid adaptation? And can this knowledge help us in agriculture or pest control?

Dr. Joana Meier, senior author at the Wellcome Sanger Institute, warned that we are in the middle of an extinction crisis and understanding how new species evolve, and evolve quickly in some cases, is important for preserving species.

“Comparing butterflies that rapidly form new species to others that do not could benchmark how common this is in insects and highlight the factors involved,” said Dr. Meier.

“This, in turn, could identify any species that require closer conservation and possibly identify genes that are important in the adaptation process and might have uses in agriculture, medicine, or bioengineering.

“This research would not have been possible without global collaboration. We have one planet, and we must work together to understand and protect it.”

The full study was published in the journal Proceedings of the National Academy of Sciences.

—–

Like what you read? Subscribe to our newsletter for engaging articles, exclusive content, and the latest updates. 

Check us out on EarthSnap, a free app brought to you by Eric Ralls and Earth.com.

—–