A long non-coding RNA at thecortexlocus controls adaptive colouration in butterflies

Abstract

AbstractEvolutionary variation in the wing pigmentation of butterflies and moths offers striking examples of adaptation by crypsis and mimicry. Thecortexlocus has been independently mapped as the locus controlling colour polymorphisms in 14 lepidopteran species, suggesting 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 novel long non-coding RNA (lncRNA) which we nameivory, transcribed from thecortexlocus, in modulating colour patterning in butterflies. Strikingly,ivoryexpression 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 thativorymutagenesis yields transformations of dark pigmented scales into white or light-coloured scales. Genotyping ofVanessa carduigermline mutants associates these phenotypes to small on-target deletions at the conserved first exon ofivory. In contrast,cortexgermline mutant butterflies with confirmed null alleles lack any wing phenotype, and exclude a colour patterning role for this adjacent gene. Overall, these results show that a lncRNA acts as a master switch of colour pattern specification, and played key roles in the adaptive diversification of colour patterns in butterflies.Significance statementDeciphering the genetic underpinnings of adaptive variation is fundamental for a comprehensive understanding of evolutionary processes. Long non-coding RNAs (lncRNAs) represent an emerging category of genetic modulators within the genome, yet they have been overlooked as a source of phenotypic diversity. In this study, we unveil the pivotal role of a lncRNA in orchestrating colour transitions between dark and light patterns during butterfly wing development. Remarkably, this lncRNA gene is nested within thecortexlocus, a genetic region known to control multiple cases of adaptive variation in butterflies and moths, including iconic examples of natural selection. These findings highlight the significant influence of lncRNAs in developmental regulation, and also underscore their potential as key genetic players in the evolutionary process itself.