LAUSR

Untangling the genetics of plasticity The common buckeye butterfly, Junonia coenia, exhibits plastic coloration; it has two color morphs, light tan and dark red, that depend on day length and temperature. By selecting for more and less color plasticity, van der Burg et al. generated butterfly lines that were used to map the genetic variants that underlie differential coloration. Genome-wide analysis and RNA sequencing identified the genes most likely to be associated with the differences in color plasticity. Inactivation of genes with CRISPR–Cas9 identified three genes that affected the red phenotype, and other techniques identified cis-regulatory, noncoding genomic variants that were correlated with coloration. From these results, the authors were able to model how genetically encoded plasticity and assimilation of the plastic trait likely evolved. Science, this issue p. 721 A genomic examination characterizes the genetic mechanisms underlying a seasonal butterfly wing color. Developmental plasticity allows genomes to encode multiple distinct phenotypes that can be differentially manifested in response to environmental cues. Alternative plastic phenotypes can be selected through a process called genetic assimilation, although the mechanisms are still poorly understood. We assimilated a seasonal wing color phenotype in a naturally plastic population of butterflies (Junonia coenia) and characterized three responsible genes. Endocrine assays and chromatin accessibility and conformation analyses showed that the transition of wing coloration from an environmentally determined trait to a predominantly genetic trait occurred through selection for regulatory alleles of downstream wing-patterning genes. This mode of genetic evolution is likely favored by selection because it allows tissue- and trait-specific tuning of reaction norms without affecting core cue detection or transduction mechanisms.