Butterfly and moth genomes mostly unchanged despite 250 million years of evolution

Researchers at the Wellcome-Saenger Institute and their colleagues at the University of Edinburgh analyzed and compared more than 200 high-quality chromosome-level genomes in butterflies and moths to better understand their evolutionary history.

They further revealed rare groups of species that break these genetic rules and undergo genetic rearrangements, including chromosome fusion — where two chromosomes join — and fission — where one chromosome splits.

The results were published today (February 21). Nature Ecology and Evolution, highlighted the tight constraints governing genome evolution in these ecologically important insects. They also offer insight into the factors that have enabled selected species to defy these rules of evolution. These insights can inform and enhance conservation efforts by guiding targeted strategies, monitoring ecosystem health, adapting to climate change, and incorporating genetic information into broader conservation initiatives.

This work is part of the Darwin Tree of Life project.¹which aims to sequence all 70,000 species in the UK and Ireland, and collaborates with the larger Earth Biogenome Project to sequence all 1.6 million named species on Earth.².

The study raises broader questions about how chromosomal changes shape biodiversity over time. Researchers will continue focused efforts to sequence all 11,000 European butterfly and insect species as part of the newly launched Project Psyche.³.

Butterflies and moths – collectively known as Lepidoptera – represent 10 percent of all described animal species and are very important pollinators and herbivores in many ecosystems.

In this new study, Wellcome-Singer Institute researchers and their colleagues set out to understand the processes driving the evolution of the chromosomes of this highly diverse group.

They identified 32 ancestral chromosome building blocks, named “marine elements” after the 17th-century entomologist Maria Sibylla Marian, that since their last common ancestor 250 million years ago, most butterflies and are maintained across insect species.

Except for an ancient fusion event between the two chromosomes that led to the 31 chromosomes seen in most species today.⁴, the chromosomes of most extant species correspond directly to these ancestral merian elements. The team found that not only were the chromosomes incredibly stable, but so was the order of genes within them.

The team found some species with minor changes, mainly involving fusions of short autosomes⁵ and sex chromosomes. This highlights the role of chromosome length as a driver of evolutionary change.

However, researchers discovered a rare subset of species such as blue butterflies — Lysandra — and a group consisting of cabbage white butterflies — Perez – which has denied these constraints of genome structure. These groups underwent extensive chromosomal rearrangements, including chromosome breakage, and large-scale rearrangements by fission and fusion.

This work adds to the understanding of the factors that lead to genetic diversity within these insects. It can guide conservation and conservation efforts for the unique challenges associated with climate change and for specific species facing climate change.

Charlotte Wright, first author of the study at the Wellcome Sanger Institute, said: “The chromosomes of most butterflies and moths living today can be directly traced back to 32 ancestral marine elements that existed 250 million years ago. Surprisingly, even though species are diversifying widely, their chromosomes are remarkably intact. This challenges the idea that stable chromosomes can limit species diversity. In fact, this trait builds diversity. “There may be a basis for this. We hope to find clues in those rare groups that have avoided these rules.”

Professor Mark Blaxter, senior author of the study and head of the Tree of Life Program at the Wellcome Sanger Institute, said: “Studies like this, which allow us to understand these evolutionary processes, are only possible with measures like Darwin’s tree. Life project that produces high-quality, publicly available genome assemblies. We are expanding these efforts in Project Psyche, which aims to map all 11,000 butterfly and insect species in Europe with colleagues across the continent. As important pollinators, herbivores, and food sources for diverse ecosystems, as well as powerful indicators of ecosystem health, Project Psyche’s deeper understanding of butterfly and insect biology on adaptation and hypothesis for biodiversity conservation. It will inform future studies.”

Notice:

1. The work is part of the Darwin Tree of Life project which aims to sequence the genomes of 70,000 species of eukaryotic organisms in the UK and Ireland. It is the collaboration between biodiversity, genomics and analysis partners that is changing the way we approach biology, conservation and biotechnology.
2. The Earth Biogenome Project is a global network of initiatives and institutions with the goal of eventually sequencing all 1.6 million named species on the planet, in order to find solutions for biodiversity conservation.
3. Project Psyche will sequence the genomes of all 11,000 European lepidopteran species, helping to drive conservation, conservation and innovation.
4. This occurred at the evolutionary branch that resulted in the Ditrysia, the most diverse group of Lepidoptera, containing 98 percent of all described species of butterflies and moths.
5. Autosomes are asexual chromosomes that contain genetic information that affects traits such as color and arm pattern, which are different from those that determine the insect’s sex.