From neurons to novelty: Circuit mechanisms shaping courtship evolution.

The vast diversity of animal behaviors has long inspired ethologists and neuroscientists, but circuit mechanisms driving this variation remain elusive. Recent advances in genetic tools and comparative approaches have enabled unprecedented insights into how neural circuits evolve to produce behavioral novelty. Here we focus on the discoveries emerging from the study of courtship behaviors, which are particularly well poised to capitalize on these advances. Comparative studies of sensory and motor circuits have begun to demonstrate that evolution can act through diverse mechanisms. The modular organization of courtship-controlling circuits emerges as a key feature facilitating rapid evolutionary innovation while maintaining essential functions. Changes in the neuronal composition of circuits, by both cellular and subcellular mechanisms, represent common mechanisms. Organisms may even carry vestigial circuits with the latent potential to be repurposed for new behavioral paradigms. We highlight how understanding the 'extended nervous system' of a species has begun to provide these critical insights into courtship evolution and offers fertile ground for future discoveries. As comparative approaches expand beyond model organisms, evolutionary neuroscience is on the cusp of revealing the principles governing behavioral diversity in nature.