A new butterfly species was created by two species hybridising 200,000 years ago

The Amazonian butterfly Heliconius elevatus is the result of a cross between two other species, H. pardalinus and H. melpomene. Heliconius elevatus is genetically closer to H. pardalinus, but it was H. melpomene that transmitted the traits responsible for its divergence from H. pardalinus, including colour pattern, wing shape, host plant preference, sex pheromones and mate choice.This mode of new species formation, in which hybridization plays a crucial role in setting up reproductive barriers, is known as hybrid speciation.

The discovery, by an international team led by scientists at the University of York and Harvard University, demonstrates how the formation of new species can be more complex than previously imagined. Scientist of the LIB contributed to the study.

“This study addressed so many different layers on the speciation process, with enphasis in introgression of ecological traits, and could only be accomplished with the collaborative work of an international team and Dr. Neil Rosser´s (Harvard University) determination and hard work”, emphasiszes Dr. Karina Lucas Silva-Brandão, Curator of Lepidoptera, at the LIB, who contributed with Brazilian samples of Heliconius butterflies and has been collaborating on several evolutionary studies with these butterflies.

Species are often thought of as the tips, or leaves in a ‘tree of life’. In this model, new species are produced by the tips splitting to form new species over thousands to millions of years. Scientists now understand that the branches in the tree of life are tangled, with genes being transferred from one species to another by occasional interbreeding. This can theoretically result in the formation of a new species; a process known as hybrid speciation.

However, proving hybrid speciation is possible in animals is a difficult task, as scientists need to demonstrate that breeding between two species actually triggered the formation of an entirely new species that is genetically distinct from both parents. The team of scientists, which includes researchers from a number of South American countries, have now found an example of a hybrid species among the brightly coloured Heliconius butterflies of the Amazon.

In a decade-long study, the researchers accumulated genetic and ecological evidence demonstrating that almost 200,000 years ago, the ancestor of today’s Heliconius melpomene and Heliconius pardalinus contributed parts of their genomes to produce a distinct third species, Heliconius elevatus, and that all three species now co-exist in the Amazon rainforest.

Professor Kanchon Dasmahapatra, from the University of York’s Department of Biology, and senior author of the study said: “Hybrid speciation may not be that uncommon, but convincing examples of animal hybrid species are really difficult to come by.  In the few examples that exist, either the supposed hybrid species have only existed for a few generations and may be short-lived entities, or the hybrid species does not live alongside its parental species, making it difficult to know whether it is actually a new species.”

Lead author Dr Neil Rosser, postdoctoral researcher at the University of York and now at Harvard University, spent several years in the Amazon crossing the species involved to uncover the genetic basis of multiple traits that are important for maintaining a species’ distinctiveness. These traits included colour pattern, wing shape, host plant preference, sex pheromones, mate choice and flight. He said: “Remarkably, we found that in the butterfly Heliconius elevatus, the parts of the genome controlling these important traits tended to coincide with regions of the genome derived from Heliconius melpomene. This finding is key to demonstrating that Heliconius elevatus is a hybrid species as it strongly suggests that hybridisation led to the butterfly having different traits to those of its parent and which prevent it from breeding with them.”

Professor Dasmahapatra added: “With species’ distributions changing rapidly due to human actions and climate change, opportunities for hybridisation or mixing between species are likely to increase, which has important implications. This increased mixing will likely cause more genes to move among species, in some cases leading to species being swamped by other species’ genes, and in other cases possibly to the formation of new hybrid species in the future.”

Original paper

Rosser, N., Seixas, F., Queste, L.M. et al. Hybrid speciation driven by multilocus introgression of ecological traits. Nature (2024). https://doi.org/10.1038/s41586-024-07263-w