A long noncoding RNA at the <i>cortex</i> locus controls adaptive coloration in butterflies.

Abstract

Evolutionary variation in the wing pigmentation of butterflies and moths offers striking examples of adaptation by crypsis and mimicry. The <i>cortex</i> locus has been independently mapped as the locus controlling color polymorphisms in 15 lepidopteran species, suggesting that it acts as a genomic hotspot for the diversification of wing patterns, but functional validation through protein-coding knockouts has proven difficult to obtain. Our study unveils the role of a long noncoding RNA (lncRNA) which we name <i>ivory</i>, transcribed from the <i>cortex</i> locus, in modulating color patterning in butterflies. Strikingly, <i>ivory</i> expression prefigures most melanic patterns during pupal development, suggesting an early developmental role in specifying scale identity. To test this, we generated CRISPR mosaic knock-outs in five nymphalid butterfly species and show that <i>ivory</i> mutagenesis yields transformations of dark pigmented scales into white or light-colored scales. Genotyping of <i>Vanessa cardui</i> germline mutants associates these phenotypes to small on-target deletions at the conserved first exon of <i>ivory</i>. In contrast, <i>cortex</i> germline mutant butterflies with confirmed null alleles lack any wing phenotype and exclude a color patterning role for this adjacent gene. Overall, these results show that a lncRNA gene acts as a master switch of color pattern specification and played key roles in the adaptive diversification of wing patterns in butterflies.