When a species lives in two distinct types of habitats, individuals with traits better suited to each habitat will thrive and reproduce, naturally selecting descendants with those traits. But what about mobile aquatic species that live across a broad range of temperatures and latitudes? New research from Cornell University and the University of Connecticut finds that chromosomal inversions—which occur when a chunk of chromosome containing tens to thousands of genes breaks off, flips and reattaches—help these species maintain genetic differences adapted to various regions, even when they interbreed.