Atlas Blue Butterfly Breaks World Record for Chromosomes
The tiny Atlas blue butterfly, Polyommatus atlantica, has been genetically confirmed to carry the highest number of chromosomes among multicellular animals. Researchers report an astonishing 229 pairs of chromosomes, far surpassing the chromosome counts of many of its close relatives, which often have about 23 or 24 pairs. This discovery marks a milestone in comparative genomics and reshapes ideas about how chromosome number and structure influence evolution.
Scientists from the Wellcome Sanger Institute and the Institute of Evolutionary Biology led the genomic analysis, revealing that these chromosomes were primarily broken up over time rather than simply duplicated. The study opens a window into the forces that shape genome organization, offering a potential blueprint for understanding how extreme chromosome counts arise and persist in nature.
The first genomic study of Polyommatus atlantica was published in Current Biology, laying the groundwork for exploring the evolutionary reasons behind this unusual chromosome count. A key achievement of the project is the creation of a gold-standard reference genome for the Atlas blue butterfly, enabling researchers to compare its genome with those of related species. By providing a high-quality reference, scientists can examine how chromosomes rearrange, fuse, or split and how such changes relate to speciation, adaptation, and biodiversity.
Why This Discovery Matters for Evolution and Biology
Chromosome architecture is a fundamental aspect of biology. In humans and many other animals, chromosome counts are relatively stable, but in some lineages they can diverge dramatically. Observing how the Atlas blue butterfly maintains 229 chromosome pairs raises important questions about genome flexibility, gene regulation, and the mechanisms that prevent detrimental chaos when chromosomes split or rearrange.
Moreover, researchers note that chromosomal changes can be observed in human cancer cells, indirectly linking this butterfly’s genome biology to broader domains of biomedicine. Understanding how chromosomes reorganize in a natural genome can illuminate how similar processes operate in disease, potentially guiding cancer research and the study of genome instability across species.
From Genome to Speciation: Implications for Biodiversity
The Atlas blue butterfly belongs to a rapidly evolving group of species that have diversified in relatively short evolutionary timescales. The extreme chromosome count may influence how these organisms form new species and adapt to their alpine environments in the mountain ranges of Morocco and northeast Algeria. The newly available reference genome enables comparative analyses with other butterflies, helping scientists discern which genes and regulatory elements are conserved, which are lost, and how large-scale chromosomal rearrangements contribute to phenotypic diversity.
Future Directions and Open Questions
The researchers emphasize that many questions remain. How does chromosome splitting affect genetic diversity and genome stability? Which genes are preserved or repositioned, and what are the functional consequences for development, reproduction, and adaptation? Further comparisons across the butterfly family will help reveal whether similar chromosomal histories exist in related species and how such rearrangements influence ecological niches and evolutionary trajectories.
A senior author at the Wellcome Sanger Institute, Professor Mark Blaxter, underscored the broader significance: “Genomes hold the key to how a creature comes and might to go in the future. To be able to tell the story of our planet, we must have the story of each species and see where they overlap and interact with each other and to better understand this process in the Atlas blue butterfly.”
