• adaptation;
  • convergence;
  • Gasterostidae;
  • evolution;
  • fish;
  • genetics

The nine-spined stickleback (Pungitius pungitius) is emerging as a model for evolutionary biology, genetic, and behavioral research in the wake of its better-known relative, the three-spined stickleback (Gasterosteus aculeatus). This interest has been fed by its fascinating biological features, such as the repeated evolution of similar phenotypes in isolated pond populations. A large body of recent research has uncovered the finding that pond nine-spined sticklebacks have evolved numerous morphological, life history, neuroanatomical, and behavioral adaptations—possibly in response to reduced threat of fish predation—which differentiate them from their marine conspecifics. These features, together with insights from recent population genetic studies, suggest that this species provides an interesting model for studies aiming to understand—and differentiate between—genetic convergence and parallelism as underlying mechanism(s) of evolution of similar phenotypes in multiple independent sites. This review provides a synopsis of and reflections on the insights borne out of recent studies of nine-spined sticklebacks—the little sister of ecology's “new supermodel.”