show Abstracthide AbstractTo investigate the influence of migration load on the evolution of distribution range, we performed field and laboratory observations as well as population transcriptomics for the common river snail, Semisulcospira reiniana. This species meets the conditions that migration from source populations can prevent local adaptation in a sink population because they inhabit the broader range of environments including river rapid and estuaries within a single river and they are predicted to have lower spontaneous (upward) locomotion activity.