The Thereus butterflies are hard to identify due to their similar colours and patterns. © The Trustees of the Natural History Museum, London
By James Ashworth
Butterflies are some of the world’s most distinctive insects – but it can be surprisingly hard to tell them apart.
Some species copy each other’s appearance, while others haven’t been seen alive in over a century. Now, following advances in DNA sequencing, scientists are finally separating more of these hidden species.
Around the world, scientists are on an epic quest to find the world’s missing butterflies before it’s too late.
Rather than travelling to distant and remote jungles, many scientists are turning to museum collections. These vast archives hold millions of specimens gathered over centuries, forming a treasure trove more mysterious than any unexplored forest.
As butterflies are notorious mimics of each other, there has been confusion about their identities for hundreds of years. It means the butterfly family tree has ended up as a tangled thicket, with many species yet to be spotted.
Hopefully, it’s a problem that butterfly researchers won’t have to face for too much longer. A new museum research project, known as AMISTAD, is combining ancient DNA, modern computing technology and traditional techniques to find out which species stand up to scrutiny.
The first phase of results is now in, with five former Thereus butterflies from South America revealed as 16 different species. Doing so has taken the work of an international team of researchers, led by world expert Christophe Faynel.
“Thanks to the collaborative work of researchers on specimens from several museums and private collections, the pieces of the puzzle are coming together to solve the taxonomy of this complex group of species,” Christophe says. “Our efforts have clarified long-confused species and revealed a richer biodiversity than anyone expected.”
“We live in an age of museums,” adds Dr Blanca Huertas, our Principal Curator of butterflies and co-lead of AMISTAD. “Museums contain a huge library of old specimens, and this project will help to index that library so that anyone can check their work against it.”
“By resolving the taxonomy of these butterflies, we’re showing the hidden diversity of the world out there. That’s vital as habitats are being damaged or destroyed, and hopefully helps to protect not just individual species, but wider ecosystems. This is just the start of our work and, as the diversity in tropical ecosystems is vast, there’s still so much left to do.”
The findings of the study were published in the journal Zootaxa.
For over 150 years, the only record of Thereus tiasa were illustrations from its original description (right). A replacement type specimen (left) has now been chosen to help scientists recognise the species. © The Trustees of the Natural History Museum, London
To work out which species are which, scientists often return to the type specimens of animals and plants. These are the individuals that were originally used to describe a species and are attached to its name.
Most type specimens are found in museums, and the butterfly and moth collection we look after is particularly comprehensive. Out of the 180,000 or so species of moths and butterflies described to date, our collections contain more than 125,000 type specimens collected over the past 400 years. This allows researchers to resolve all kinds of scientific puzzles.
One such mystery surrounded the type specimen of the butterfly Thereus tiasa. Richard O’Brien, a curatorial assistant for AMISTAD, says that the type specimen of this species went missing more than 150 years ago.
“These butterflies were first described by William Hewitson, a passionate artist and naturalist who assembled a large and important collection of beetles and butterflies,” explains Richard. “Using a combination of documents, artworks and specimens, we’re now able to firmly identify T. tiasa for the first time in more than a century.”
“We had to designate a replacement type for the species in the end, but there’s good evidence that it may actually be the original specimen.”
Differences in certain wing scales of male Thereus butterflies has allowed scientists to tell the species apart. © Zootaxa
With one historic mystery solved, the team took a closer look at the rest of the Thereus genena species group. This was understood to contain five species and four synonyms – former species that were later revealed to be the same as an existing one.
Butterfly species have historically been described based on features such as their wing colour patterns. But that doesn’t work very well for these butterflies. This is because most of the males are bright blue and very similar looking, while females are often indistinguishable shades of brown.
To tell them apart, the researchers had to turn to other parts of their anatomy, such as the structure of their wings and sex organs. The genitals of butterflies are often unique to prevent different species breeding together, providing one line of evidence for the scientists. Structures in the wings provided another.
“One key way we’ve identified new species is through their androconia – specialised male scales that produce pheromones to attract females,” Richard reveals. “They appear as dark patches on the wings and are unique to each species.”
While this was enough to identify some species, others needed DNA evidence to distinguish them. The team examined a specific genome sequence known as the DNA barcode to help split species apart.
The AMISTAD project continues to examine butterfly specimens and name new species. © The Trustees of the Natural History Museum, London
Between genetic and morphological evidence, the team reinstated two synonyms as full species and identified nine more that were previously unknown.
Some of the new species, such as T. cacao, were named after the areas where the specimens were originally found. Others, such as T. ramirezi, were named after local scientists who have worked on these insects. T. confusus, meanwhile, reflects the puzzle the team faced in identifying all these different butterflies.
As the project continues, there’ll be more new butterfly species to uncover. Butterflies are indicators of how healthy an ecosystem is, and so studying them can uncover the true conservation state of the tropics.
“We’ve been working on this project for the last few years, but there’s so much more we need to do,” says Blanca. “We’re not even sure if some of these species are still alive in the wild, or if the forests they were caught in many years ago still exist.”
“Unfortunately, funding for taxonomy is very limited and genomic testing for historic specimens is expensive. We’ve got this far on the generosity of donors from the Fåhraeus Biodiversity Institute, but, if we want to make real progress through the backlog of unidentified species, then we’ll need much more in the long term.”
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