The most extensive analysis of its kind reveals how butterfly and moth chromosomes have remained largely unchanged since their last common ancestor over 250 million years ago. This stability exists despite the incredible diversity seen today in wing patterns, sizes, and caterpillar forms across over 160,000 species globally. They further uncovered rare groups of species that broke these genetic norms and underwent genetic rearrangements, including chromosome fusions -- where two chromosomes merge -- and fissions -- where a chromosome splits.

The study raises broader questions about how chromosomal changes shape biodiversity over time. The researchers will continue focused efforts to sequence all 11,000 European butterfly and moth species as part of the newly launched Project Psyche3. They identified 32 ancestral chromosome building blocks. With the exception of a single ancient fusion event between two chromosomes that led to the 31 chromosomes seen in most species today4, chromosomes of most current species directly correspond to these ancestral Merian elements. The team found not only were chromosomes incredibly stable, but the order of genes within them was too.

The work increases understanding of factors that lead to genetic diversity within these insects. This can guide efforts to protect and preserve specific species facing unique challenges and environmental changes tied to climate change. It is striking that despite species diversifying extensively, their chromosomes have remained remarkably intact. This challenges the idea that stable chromosomes may limit species diversification. Indeed, this feature might be a base for building diversity. They hope to find clues in rare groups that have evaded these rules.