Structural color in Junonia butterflies evolves by tuning scale lamina thickness, bioRxiv, 2019-03-22

AbstractStructural color is a pervasive natural phenomenon, caused by photonic nanostructures that refract light. Diverse organisms employ structural color to mediate ecological interactions and create specific optical effects such as iridescence. Despite its importance for living systems, the developmental, genetic, and evolutionary processes that generate structural color largely remain mysterious. Here, we focus on simple photonic structures, thin film reflectors, in the lower lamina of Junonia butterfly scales. We present multiple lines of evidence that the thickness of the lamina quantitatively controls lamina color, which is an important determinant of overall wing color, even when pigments are also present. First, in a lineage of buckeye butterflies artificially selected for blue wing color for 12 generations, a thicker lamina resulted in a color shift from brown to blue. A similar lamina thickness increase explains the appearance of blue scales in butterflies with mutations in the optix wing patterning gene. Finally, lamina thickness variation underlies the color diversity that distinguishes seasonal variants, sexes, and species throughout the genus Junonia. Thus, quantitatively tuning a single dimension of the existing scale architecture allows butterflies to evolve a broad spectrum of hues over both microevolutionary and macroevolutionary time frames. Because the lower lamina is an intrinsic component of typical butterfly scales, our findings imply that lamina structural color influences wing color in most butterflies.Significance StatementStructural colors, which result from photonic nanostructures that refract light and can create iridescence, are an important tool for many organisms. We use thin films, which are morphologically simple nanostructures that generate structural color in the lower lamina of butterfly scales, to dissect how photonic structures evolve. By combining interspecies comparisons with two different experimental approaches—artificial selection on wing color, and genetically engineered mutation of the optix wing patterning gene—we demonstrate that lamina thickness controls the wavelength (hue) of the structural color. These lamina structural colors are ubiquitous in the genus Junonia, and determine wing color along with pigments. Our results suggest that lamina structural colors probably exist in most butterflies, and that tuning lamina thickness facilitates wing color evolution.

biorxiv evolutionary-biology 0-100-users 2019

Frequent birth of de novo genes in the compact yeast genome, bioRxiv, 2019-03-13

AbstractEvidence has accumulated that some genes originate directly from previously non-genic sequences, or de novo, rather than by the duplication or fusion of existing genes. However, how de novo genes emerge and eventually become functional is largely unknown. Here we perform the first study on de novo genes that uses transcriptomics data from eleven different yeast species, all grown identically in both rich media and in oxidative stress conditions. The genomes of these species are densely-packed with functional elements, leaving little room for the co-option of genomic sequences into new transcribed loci. Despite this, we find that at least 213 transcripts (~5%) have arisen de novo in the past 20 million years of evolution of baker’s yeast-or approximately 10 new transcripts every million years. Nearly half of the total newly expressed sequences are generated from regions in which both DNA strands are used as templates for transcription, explaining the apparent contradiction between the limited ‘empty’ genomic space and high rate of de novo gene birth. In addition, we find that 40% of these de novo transcripts are actively translated and that at least a fraction of the encoded proteins are likely to be under purifying selection. This study shows that even in very highly compact genomes, de novo transcripts are continuously generated and can give rise to new functional protein-coding genes.

biorxiv evolutionary-biology 0-100-users 2019

Frequent birth ofde novogenes in the compact yeast genome, bioRxiv, 2019-03-13

AbstractEvidence has accumulated that some genes originate directly from previously non-genic sequences, orde novo, rather than by the duplication or fusion of existing genes. However, howde novogenes emerge and eventually become functional is largely unknown. Here we perform the first study onde novogenes that uses transcriptomics data from eleven different yeast species, all grown identically in both rich media and in oxidative stress conditions. The genomes of these species are densely-packed with functional elements, leaving little room for the co-option of genomic sequences into new transcribed loci. Despite this, we find that at least 213 transcripts (~5%) have arisende novoin the past 20 million years of evolution of baker’s yeast-or approximately 10 new transcripts every million years. Nearly half of the total newly expressed sequences are generated from regions in which both DNA strands are used as templates for transcription, explaining the apparent contradiction between the limited ‘empty’ genomic space and high rate ofde novogene birth. In addition, we find that 40% of thesede novotranscripts are actively translated and that at least a fraction of the encoded proteins are likely to be under purifying selection. This study shows that even in very highly compact genomes,de novotranscripts are continuously generated and can give rise to new functional protein-coding genes.

biorxiv evolutionary-biology 0-100-users 2019

 

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