Scientists have sequenced the genome of the Atlas blue butterfly for the first time and confirmed it holds the highest chromosome number among multicellular animals.
The butterfly lives in the mountain ranges of Morocco and northeast Algeria. It carries 229 pairs of chromosomes, while close relatives such as the Common blue butterfly have only 24.
Researchers at the Wellcome Sanger Institute and the Institute of Evolutionary Biology in Barcelona found that the butterfly’s extreme chromosome count came from splitting rather than duplication.
Over about three million years, the chromosomes broke at sites where DNA was loosely packed. The sex chromosomes stayed intact, but the rest fractured into smaller pieces.
Dr Charlotte Wright, first author at the Wellcome Sanger Institute, said the team deliberately chose to study the species. “When we set out to start to understand evolution in butterflies, we knew we had to sequence the most extreme, and somewhat mysterious, Atlas blue butterfly,” she said.
Wright credited earlier fieldwork for making sequencing possible.
She added, “Being able to see, in detail, how the Atlas blue butterfly chromosomes have been split over time in specific places, we can start to investigate what benefits this might have, how it impacts their ability to adapt to their environment, and whether there are any lessons we can learn from their DNA that might aid conservation in the future.”
Implications for evolution and health
Chromosome changes like these may help species form and adapt. The Atlas blue butterfly belongs to a group that produced many related species in a short period of time.
Splitting chromosomes could increase genetic diversity by allowing more frequent reshuffling of DNA, though it may also create risks because of added complexity.
Atlas blue butterfly.
Credit – Dr Roger Vila/The Institute of Evolutionary Biology
Dr Roger Vila, senior author at the Institute of Evolutionary Biology, said, “Breaking down chromosomes has been seen in other species of butterflies, but not on this level, suggesting that there are important reasons for this process which we can now start to explore.”
He said studying whether these changes affect butterfly behaviour could explain how new species appear.
The findings may also have medical value. Chromosome rearrangements occur in human cancers, where DNA segments break and reorganize.
Scientists may find ways to slow or stop the process by comparing butterflies with cancer cells.
Professor Mark Blaxter, senior author at the Wellcome Sanger Institute, explained why such research matters. “Genomes hold the key to how a creature came to be, but also, where it might go in the future,” he said.
He pointed out that lessons from one species can inform conservation and health research.
Conservation pressures grow
Although the Atlas blue butterfly has survived for millions of years with its fractured genome, its future is now uncertain.
Habitat loss from the destruction of cedar forests, overgrazing, and climate change threatens its survival. Sequencing its genome provides a critical reference for conservationists to study how it might respond to warming conditions.
Researchers say this high-quality reference genome will help uncover how butterflies evolve and adapt. It may also guide efforts to develop crops that are better able to withstand environmental stress.
The Atlas blue butterfly may be small and elusive, but its genetic story is vast.
With 229 chromosome pairs, it sets a world record and opens new paths to understanding evolution, survival, and health.
The study is published in the journal Current Biology.