Structural color in Junonia butterflies evolves by tuning scale lamina thickness.

In diverse organisms, nanostructures that coherently scatter light create structural color, but how such structures are built remains mysterious. We investigate the evolution and genetic regulation of butterfly scale laminae, which are simple photonic nanostructures. In a lineage of buckeye butterflies artificially selected for blue wing color, we found that thickened laminae caused a color shift from brown to blue. Deletion of the patterning gene also altered color via lamina thickening, revealing shared regulation of pigments and lamina thickness. Finally, we show how lamina thickness variation contributes to the color diversity that distinguishes sexes and species throughout the genus . Thus, quantitatively tuning one dimension of scale architecture facilitates both the microevolution and macroevolution of a broad spectrum of hues. Because the lamina is an intrinsic component of typical butterfly scales, our findings suggest that tuning lamina thickness is an available mechanism to create structural color across the Lepidoptera.

Thayer RC ，Allen FI ，Patel NH 《eLife》

Cortex cis-regulatory switches establish scale colour identity and pattern diversity in Heliconius.

In butterflies, wing colour pattern diversity and scale types are controlled by a few genes of large effect that regulate colour pattern switches between morphs and species across a large mimetic radiation. One of these genes, , has been repeatedly associated with colour pattern evolution in butterflies. Here we carried out CRISPR knockouts in multiple species and show that is a major determinant of scale cell identity. Chromatin accessibility profiling and introgression scans identified -regulatory regions associated with discrete phenotypic switches. CRISPR perturbation of these regions in black hindwing genotypes recreated a yellow bar, revealing their spatially limited activity. In the lineage, the candidate CRE from yellow-barred phenotype morphs is interrupted by a transposable element, suggesting that -regulatory structural variation underlies these mimetic adaptations. Our work shows that functionally controls scale colour fate and that its -regulatory regions control a phenotypic switch in a modular and pattern-specific fashion.

Livraghi L ，Hanly JJ ，Van Bellghem SM ，Montejo-Kovacevich G ，van der Heijden ES ，Loh LS ，Ren A ，Warren IA ，Lewis JJ ，Concha C ，Hebberecht L ，Wright CJ ，Walker JM ，Foley J ，Goldberg ZH ，Arenas-Castro H ，Salazar C ，Perry MW ，Papa R ，Martin A ，McMillan WO ，Jiggins CD ... -  《eLife》

Single master regulatory gene coordinates the evolution and development of butterfly color and iridescence.

The gene has been implicated in butterfly wing pattern adaptation by genetic association, mapping, and expression studies. The actual developmental function of this gene has remained unclear, however. Here we used CRISPR/Cas9 genome editing to show that plays a fundamental role in nymphalid butterfly wing pattern development, where it is required for determination of all chromatic coloration. knockouts in four species show complete replacement of color pigments with melanins, with corresponding changes in pigment-related gene expression, resulting in black and gray butterflies. We also show that simultaneously acts as a switch gene for blue structural iridescence in some butterflies, demonstrating simple regulatory coordination of structural and pigmentary coloration. Remarkably, these knockouts phenocopy the recurring "black and blue" wing pattern archetype that has arisen on many independent occasions in butterflies. Here we demonstrate a simple genetic basis for structural coloration, and show that plays a deeply conserved role in butterfly wing pattern development.

Zhang L ，Mazo-Vargas A ，Reed RD 《-》

Artificial selection for structural color on butterfly wings and comparison with natural evolution.

Brilliant animal colors often are produced from light interacting with intricate nano-morphologies present in biological materials such as butterfly wing scales. Surveys across widely divergent butterfly species have identified multiple mechanisms of structural color production; however, little is known about how these colors evolved. Here, we examine how closely related species and populations of Bicyclus butterflies have evolved violet structural color from brown-pigmented ancestors with UV structural color. We used artificial selection on a laboratory model butterfly, B. anynana, to evolve violet scales from UV brown scales and compared the mechanism of violet color production with that of two other Bicyclus species, Bicyclus sambulos and Bicyclus medontias, which have evolved violet/blue scales independently via natural selection. The UV reflectance peak of B. anynana brown scales shifted to violet over six generations of artificial selection (i.e., in less than 1 y) as the result of an increase in the thickness of the lower lamina in ground scales. Similar scale structures and the same mechanism for producing violet/blue structural colors were found in the other Bicyclus species. This work shows that populations harbor large amounts of standing genetic variation that can lead to rapid evolution of scales' structural color via slight modifications to the scales' physical dimensions.

Wasik BR ，Liew SF ，Lilien DA ，Dinwiddie AJ ，Noh H ，Cao H ，Monteiro A ... -  《-》

Longwing (Heliconius) butterflies combine a restricted set of pigmentary and structural coloration mechanisms.

Longwing butterflies, Heliconius sp., also called heliconians, are striking examples of diversity and mimicry in butterflies. Heliconians feature strongly colored patterns on their wings, arising from wing scales colored by pigments and/or nanostructures, which serve as an aposematic signal. Here, we investigate the coloration mechanisms among several species of Heliconius by applying scanning electron microscopy, (micro)spectrophotometry, and imaging scatterometry. We identify seven kinds of colored scales within Heliconius whose coloration is derived from pigments, nanostructures or both. In yellow-, orange- and red-colored wing patches, both cover and ground scales contain wavelength-selective absorbing pigments, 3-OH-kynurenine, xanthommatin and/or dihydroxanthommatin. In blue wing patches, the cover scales are blue either due to interference of light in the thin-film lower lamina (e.g., H. doris) or in the multilayered lamellae in the scale ridges (so-called ridge reflectors, e.g., H. sara and H. erato); the underlying ground scales are black. In the white wing patches, both cover and ground scales are blue due to their thin-film lower lamina, but because they are stacked upon each other and at the wing substrate, a faint bluish to white color results. Lastly, green wing patches (H. doris) have cover scales with blue-reflecting thin films and short-wavelength absorbing 3-OH-kynurenine, together causing a green color. The pigmentary and structural traits are discussed in relation to their phylogenetic distribution and the evolution of vision in this highly interesting clade of butterflies.

Wilts BD ，Vey AJM ，Briscoe AD ，Stavenga DG ... -  《BMC EVOLUTIONARY BIOLOGY》