Digest: Phenotypic plasticity and the genomic signature of novel castes: insights from soldier evolution in Cephalotes.

Phenotypic plasticity can alter evolutionary dynamics, but its genomic consequences remain contested. Barkdull & Moreau (2025) combine comparative genomics and developmental transcriptomics in Cephalotes turtle ants to show that the repeated evolution of a soldier morph produces an asymmetric genomic signature: protein-coding genes experience genome-wide relaxed selection and reduced positive selection, whereas conserved noncoding regulatory elements show increased purifying constraint. Worker morph plasticity is driven mainly by co-option of ancient genes and by integration of insulin, imaginal-disc, and Hippo signaling.