While we often imagine the formation of new species as the division of an ancestral species into at least two new species, an international consortium involving researchers from CNRS has just demonstrated the formation of a new species through a hybridization process.
The study, published in the journal
Nature, reveals that the Amazonian butterfly
Heliconius elevatus arose from the crossbreeding between the species
Heliconius pardalinus and
Heliconius elevatus 200,000 years ago.
Figure: Heliconius elevatus (top), an Amazonian butterfly species resulting from the crossbreeding between Heliconius pardalinus (bottom left) and Heliconius melpomene (bottom right).
Credits: Kanchon Dasmahapatra (H. elevatus) and Michel Cast (pardalinus and melpomene)
We often perceive the tree of life as a structure where branches, representing ancestral species, split over time, giving rise to new species. This model corresponds, for instance, to the establishment of a geographical barrier that physically separates populations of the same species, which then evolve independently until they are no longer inter-fertile, or to the action of ecological barriers, also leading to divergence between populations until fully-fledged species form.
A new study conducted by an international consortium and published in the journal
Nature shows that the tree of life does not always conform to this picture. Indeed, the branches of the tree of life are intertwined, as the formation of new species sometimes results from the crossbreeding between two species. This consortium demonstrated that an Amazonian butterfly species,
Heliconius elevatus, emerged from the crossbreeding of two other species,
Heliconius pardalinus and
Heliconius melpomene, around 200,000 years ago.
These three species still coexist today in the Amazon. Following over 10 years of research, combining genetic studies, captive crossbreeding, and measurements of traits related to survival or reproduction, the team established that
H. elevatus is genetically closer to
H. pardalinus than to
H. melpomene, but it is
H. melpomene that transmitted the traits causing its separation from
H. pardalinus (see Figure).
Among the traits inherited from
H. melpomene are the colorful wing patterns, which play a crucial role in mate selection during reproduction, as well as sexual pheromones, oviposition preference on the host plant of the caterpillars, wing shape, and even flying style. Together, these traits isolate the hybrid lineage from the two parental species by limiting genetic exchange, particularly with the closest species (
H. pardalinus), even though they are inter-fertile in captivity.
This mode of species formation, known as hybrid speciation, is considered very rare in the animal kingdom. However, this rarity may be due to the difficulty in formally demonstrating hybrid speciation: it requires showing that a species resulted from the crossbreeding between two other species and that the crossbreeding, via the resulting characteristics, is responsible for the reproductive isolation of the hybrid lineage from the parental species.
With the development of high-throughput DNA sequencing techniques, discovering gene exchanges between closely related but distinct species is becoming increasingly common. It is therefore possible that, in some cases, these gene exchanges, occurring during a rare hybridization event, may have sparked the formation of a new species. The significance of hybrid speciation in the diversification of life remains to be documented.
Reference:
Rosser, N., Seixas, F., Queste, L. M., Cama, B., Mori-Pezo, R., Kryvokhyzha, D., Nelson, M., Waite-Hudson, R., Goringe, M., Costa, M., Élias, M., Figueiredo, C. M. É., Freitas, A. V. L., Joron, M., Kozak, K. M., Lamas, G., Martins, A. R. P., McMillan, W. O., Ready, J. S.,... Dasmahapatra, K. K.
Hybrid speciation driven by multilocus introgression of ecological traits.
Nature, published on April 17, 2024.