Butterfly genome has barely changed after 250 million years of evolution

Scientists have provided an unprecedented glimpse into the evolutionary history of butterflies and moths. Having lived on Earth for over 250 million years, the genome of butterfly and moth species remains relatively unchanged.

Researchers from the Wellcome Sanger Institute, in collaboration with the University of Edinburgh, analyzing over 200 high-quality, chromosome-level genomes. They discovered that the chromosomal makeup of these insects has seen little change during their time on our planet.

250 million years of Lepidoptera evolution

Despite the remarkable diversity observed in the more than 160,000 species worldwide — from the myriad of wing patterns to the various caterpillar forms — the fundamental genetic structures of these creatures have remained largely the same since their last common ancestor.

Collectively known as Lepidoptera, which account for 10% of all described animal species, butterfly and moth species have retained 32 ancestral chromosome blocks in their genomes.

These are referred to in scientific circles as “Merian elements,” named in honor of Maria Sibylla Merian, a pioneering entomologist of the 17th century.

Merian elements have remained intact across the vast majority of species, with most species today exhibiting chromosomes that directly correlate to these ancient structures, save for a singular ancient fusion event.

Genome exceptions in butterfly evolution

The study also identifies rare instances of genetic rearrangement within certain species, such as chromosome fusions and fissions.

These occurrences highlight the remarkable stability of Lepidoptera genomes alongside occasional deviations that have led to significant genetic diversity.

Specifically, species like the blue butterflies (Lysandra) and those in the group containing the cabbage white butterflies (Pieris) have shown extensive chromosomal reshuffling, defying the norm and offering insights into the genetic flexibility and diversity within this group.

From ancestral elements to modern diversity

Charlotte Wright, the first author of the study from the Wellcome Sanger Institute, emphasized the significance of the findings.

“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. It is striking that despite species diversifying extensively, their chromosomes have remained remarkably intact,” Wright explained.

“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.”

Project Psyche: Future of butterfly genome research

Professor Mark Blaxter, senior author and Head of the Tree of Life programme at the Wellcome Sanger Institute, highlighted the importance of such studies for understanding evolutionary processes and their implications for conservation.

“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. 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,” Blaxter added.

“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.”

This research is part of the Darwin Tree of Life Project, which aims to sequence all 70,000 species in Britain and Ireland, and contributes to the global effort of the Earth BioGenome Project to sequence all 1.6 million named species on Earth.

Beyond the cocoon: What butterflies and moths teach us

In summary, this intriguing study reaffirms the incredible genetic stability of butterflies and moths over hundreds of millions of years, while highlighting the exceptions that have fueled their astonishing diversity.

By tracing the chromosomes of these species back to their ancient Merian elements, researchers have challenged previous notions about genetic stability limiting diversification.

Instead, they’ve unveiled a complex picture where stability serves as a foundation upon which rare genetic rearrangements contribute to evolutionary novelty. This research underscores the critical importance of genetic studies in informing conservation strategies.

Differences between butterfly and moth genomes

As discussed above, butterflies and moths, both belonging to the order Lepidoptera, share many similarities in their genomes, but there are several key differences that distinguish them.

Understanding these differences helps in identifying and appreciating the diversity within this fascinating group of insects.

Time of activity and antennae

Butterflies are primarily diurnal, meaning they are active during the day. Moths, on the other hand, are mostly nocturnal or crepuscular, being active at night or during twilight, although there are exceptions.

One of the most noticeable differences is in their antennae. Butterflies have slender antennae with club-shaped tips, while moths have a variety of antennae shapes, but they are often feathery or filamentous without the clubbed end.

Resting posture, cocoon and chrysalis

When at rest, butterflies typically fold their wings vertically above their bodies. Moths usually rest with their wings spread out flat or slightly tented over their bodies, although there are variations.

Moths often create cocoons from silk they produce, which envelops them during their pupal stage. Butterflies, in contrast, undergo metamorphosis within a chrysalis, which is a hard case formed without silk.

Shape, size and coloration

Moths tend to have a thicker, hairier body compared to butterflies, which are generally slender and smoother. This is not a universal rule but a general observation across many species.

Butterflies usually have bright, vibrant colors which are visible when their wings are open. Moths are typically more muted in color, with browns, grays, and whites being common, which aids in camouflage during their nocturnal activities, though there are colorful exceptions.

Pupal stage and flight patterns

Many moths pupate in the ground or in hidden locations, such as under leaves or in crevices. Butterflies often form their chrysalides in more exposed locations, such as on the branches of trees or under leaves, suspended in the air.

Butterfly flight tends to be more graceful and often appears as fluttering. Moth flight can seem more erratic or direct, depending on the species.

These differences, while helpful for distinguishing between butterflies and moths, come with many exceptions due to the vast diversity within the Lepidoptera order.

Some moth species exhibit characteristics more typical of butterflies, and vice versa, demonstrating the evolutionary complexity and variety within this group of insects.

As we move forward, leveraging the insights of the butterfly and moth genomes will be key to preserving the rich biodiversity of our planet, showcasing how understanding the past can illuminate the path to protecting the future.

The full study was published in the journal Nature Ecology & Evolution.

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