A novel Hox gene promoter fuels the evolution of adaptive phenotypic plasticity

Adaptive phenotypic plasticity allows organisms to display distinct phenotypes in response to variable environments, but little is known about the genomic changes that promote the evolution of plasticity on a macroevolutionary scale. Combining spatial transcriptomics, comparative genomics, and genome editing, we show that temperature-mediated plasticity in the size of eyespot wing patterns in satyrid butterflies, a derived seasonal adaptation evolved ∼80 million years ago in this subfamily, is associated with the taxon-specific evolution of a novel promoter in the Hox gene Antennapedia ( Antp ). The promoter activates Antp expression specifically in satyrid eyespot center cells, sensitizes these cells to environmental temperatures, and plays a critical role in regulating satyrid eyespot size plasticity. Our study demonstrates that a taxon-specific cis-regulatory innovation in an ancestral developmental gene fueled the evolution of adaptive phenotypic plasticity across a clade of animals.