A sex-specific regulator expands the embryonic ocular field to generate a novel visual system

The study used single-cell transcriptomics, chromatin accessibility profiling, and functional genetics in mayflies to trace the developmental origin of TurbEyes, an extra visual system unique to males. They show that this novelty develops through deployment of an ancestral retinal determination program, which is activated ectopically via a sex-specific regulator that expands the ocular field during embryogenesis. This provides a concrete example of how developmental programs are repurposed to generate evolutionary novelties, with implications for understanding the genetic basis of morphological innovation. Future work will likely identify the specific sex-specific regulator and its downstream targets.