Across the rainforests of Central and South America, dozens of butterfly species wear nearly identical wing patterns. Some are toxic; others are bluffing. The mimicry is so precise that even trained entomologists sometimes need DNA to tell them apart. Now, a study published in PLOS Biology in April 2026 reveals that this copycat trick has been running on the same two genes, ivory and optix, for roughly 120 million years. More striking still, the researchers pinpointed the regulatory “switches” near those genes that control the mimicry, stretches of noncoding DNA that evolution has flipped again and again across lineages separated by tens of millions of years of independent history.
“What surprised us most was the sheer predictability,” said the study’s senior author in a press statement distributed alongside the paper. “Evolution keeps returning to the same small region of the genome, toggling the same switches, even in lineages that have been on their own for over a hundred million years.”
The finding challenges a common assumption about evolution: that adaptation is driven by an essentially limitless pool of random mutations. Instead, natural selection appears to keep returning to the same small genetic toolkit, dialing the same knobs to produce convergent results.
The same switches, across distant lineages
The research team ran genome-wide association analyses across multiple neotropical butterfly lineages that split from one another up to roughly 30 million years ago. In every group, the strongest links between genotype and convergent color-pattern variation landed in shared noncoding regions near ivory and optix. These are not mutations in the protein-coding sequences of the genes themselves. They sit in stretches of DNA that govern when, where, and how intensely the genes are expressed, functioning as volume knobs for wing pigmentation.
The gene optix already had a well-established reputation in mimicry research. Earlier work on Heliconius butterflies showed it was a major locus for wing-pattern differences, with most variation mapping to regulatory segments rather than coding changes. What the new study adds is a second gene, ivory, working alongside optix through the same regulatory architecture. And the pattern holds not just across butterfly families but also in a day-flying moth whose lineage split from butterflies an estimated 120 million years ago.
A genetic clamp in a moth
In that moth, the researchers found something additional: a chromosomal inversion, a large-scale rearrangement in which a segment of a chromosome is flipped end to end. Inversions act like genetic clamps. Once a favorable combination of gene variants is captured inside a flipped segment, recombination can no longer easily break it apart. The result is a “supergene,” a block of linked alleles inherited as a unit that can encode a complex trait like a complete mimicry pattern.
The concept is not new. A 2017 study in Nature Communications documented how inversions preserve complex mimicry phenotypes in swallowtail butterflies. But finding a similar supergene-like architecture in a moth lineage separated from butterflies by 120 million years of evolution strengthens the case that this genetic toolkit is deeply conserved, not a one-off invention of any single group.
“The moth result was the clincher for us,” one of the study’s co-authors noted in the same press release. “It told us this is not just a butterfly story. The same regulatory logic has been sitting in the genome since before butterflies and moths went their separate ways.”
The team deposited raw sequencing data in public repositories synchronized among GenBank, the European Nucleotide Archive, and DDBJ as part of the international nucleotide sequence collaboration. Independent researchers can retrieve the underlying reads and attempt to reproduce the findings, consistent with the open-data standards of PLOS Biology.
What the study cannot yet prove
Strong statistical associations are not the same as a proven causal chain. Functional experiments, such as using CRISPR to edit specific regulatory elements and then measuring the effect on wing patterns, would be needed to confirm that flipping these switches is both necessary and sufficient for mimicry shifts. The PLOS Biology paper does not report such experiments, so the causal role of each individual regulatory change remains provisional.
Details of the moth inversion are also thin. The study identifies its presence and shows that it tracks with mimicry forms, but the precise breakpoints, the full set of genes captured within it, and the selective pressures maintaining it have not been fully characterized. Whether the moth inversion behaves like a true supergene or merely resembles one in broad outline is an open question that will require fine-scale mapping and population-genetic analysis.
Then there is ivory itself. While optix has been studied intensively for more than a decade, ivory’s contribution to mimicry coloration is far less documented outside this new paper. How ivory interacts with optix at the molecular level, whether the two genes share upstream regulators, and whether ivory plays a comparable role in Lepidoptera outside the neotropics are all questions that future work will need to address. It is also unclear whether ivory has functions beyond pigmentation that might constrain how its regulatory regions can evolve.
Finally, the 120-million-year time frame deserves a caveat. That number reflects the estimated divergence between the butterfly and moth lineages examined, not a continuous fossil-calibrated record of mimicry. The data show that similar regulatory architectures exist today in distantly related groups. They do not, by themselves, reveal when mimicry first arose in each lineage or how often it may have been lost and regained.
Why a constrained toolkit matters beyond butterflies
If two genes and their nearby regulatory DNA have been recycled across 120 million years of independent evolution, the menu of genetic options available to natural selection may be far more limited than textbook accounts of random mutation suggest. For species facing rapid environmental change, that constraint cuts both ways.
On one hand, having a small, well-tuned set of switches for traits like coloration could allow fast adaptive responses when predators, habitats, or climate shift. On the other, if key regulatory regions are reused repeatedly, they may become evolutionary bottlenecks. Damage those switches, and an entire class of adaptive responses could disappear.
The supporting evidence from earlier, independent lines of research adds weight. The Heliconius studies and the swallowtail supergene work were conducted by different teams, in different years, using different methods, and they all converge on the same conclusion: optix and chromosomal rearrangements are recurring players in Lepidoptera mimicry. The 2026 study extends that framework by adding ivory and by reaching across the butterfly-moth divide.
For now, the evidence supports a cautious but striking conclusion. Ivory and optix appear to operate through deeply conserved regulatory neighborhoods that evolution has tapped again and again to build mimicry. The discovery of a supergene-like inversion in a distantly related moth hints that complex trait architectures can persist across vast spans of time. Yet without functional experiments and broader taxonomic sampling, the full extent of this predictability remains to be tested. As more genomes are sequenced and more regulatory landscapes mapped, biologists will learn whether the same switches keep turning up, or whether entirely new ones are waiting in the wings.
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*This article was researched with the help of AI, with human editors creating the final content.
