Developmental evolution in fast-forward: insect male genital diversification

Insect male genitalia are among the fastest evolving structures of animals. Studying these changes among closely related species represents a powerful approach to dissect developmental processes and genetic mechanisms underlying phenotypic diversification and the underlying evolutionary drivers. Here, we review recent breakthroughs in understanding the developmental and genetic bases of the evolution of genital organs among Drosophila species and other insects. This work has helped reveal how tissue and organ size evolve and understand the appearance of morphological novelties, and how these phenotypic changes are generated through altering gene expression and redeployment of gene regulatory networks. Future studies of genital evolution in Drosophila and a wider range of insects hold great promise to help understand the specification, differentiation, and diversification of organs more generally.