This stability exists despite the incredible diversity seen today in wing patterns, sizes, and caterpillar forms across over 160,000 species globally, according to a new paper published in the journal Nature Ecology and Evolution.
Butterflies and moths (order Lepidoptera) represent 10% of all described animal species and are hugely important pollinators and herbivores in many ecosystems.
In a new study, Wellcome Sanger Institute’s Professor Mark Blaxter and his colleagues set out to understand the processes that drive the evolution of chromosomes of this highly diverse group.
They analyzed and compared over 200 high-quality chromosome-level genomes of butterflies and moths.
They identified 32 ancestral chromosome building blocks, named Merian elements after the pioneering 17th century entomologist Maria Sibylla Merian, that have stayed intact across most butterfly and moth species since their last common ancestor over 250 million years ago.
With the exception of a single ancient fusion event between two chromosomes that led to the 31 chromosomes seen in most species today, chromosomes of most current species directly correspond to these ancestral Merian elements.
The researchers found not only were chromosomes incredibly stable, but the order of genes within them was too.
They found some species with minor changes, mainly involving fusions of small autosomes and the sex chromosome. This highlights the role of chromosome length as a driver of evolutionary change.
However, the scientists uncovered a rare subset of species such as the blue butterflies (Lysandra) and the group containing cabbage white butterflies (Pieris) that have defied these genome structure constraints.
These groups underwent extensive chromosome reshuffling, including breakage of chromosomes, and large scale reshuffling through fission and fusion.
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.
“The chromosomes of most butterflies and moths living today can be traced directly back to the 32 ancestral Merian elements that were present 250 million years ago,” said Dr. Charlotte Wright, a researcher at the Wellcome Sanger Institute.
“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. We hope to find clues in rare groups that have evaded these rules.”
“Studies like this, which allow us to delve into these evolutionary processes, are only possible with initiatives like the Darwin Tree of Life project generating high-quality, publicly available genome assemblies,” Professor Blaxter said.
“We are amplifying these efforts in Project Psyche, aiming to sequence all 11,000 butterfly and moth species in Europe with collaborators across the continent.”
“As vital pollinators, herbivores, and food sources of various ecosystems, as well as powerful indicators of ecosystem health, a deeper understanding of butterfly and moth biology through Project Psyche will inform future studies on adaptation and speciation for biodiversity conservation.”
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C.J. Wright et al. Comparative genomics reveals the dynamics of chromosome evolution in Lepidoptera. Nat Ecol Evol, published online February 21, 2024; doi: 10.1038/s41559-024-02329-4